U.S. patent application number 12/876067 was filed with the patent office on 2011-03-10 for acoustic resonance device.
This patent application is currently assigned to Yamaha Corporation. Invention is credited to Keiichi Fukatsu, Shinichi Kato, Yasutaka Nakamura, Hiroshi Nakashima, Rento Tanase, Atsushi Yoshida.
Application Number | 20110056763 12/876067 |
Document ID | / |
Family ID | 43646820 |
Filed Date | 2011-03-10 |
United States Patent
Application |
20110056763 |
Kind Code |
A1 |
Tanase; Rento ; et
al. |
March 10, 2011 |
ACOUSTIC RESONANCE DEVICE
Abstract
An acoustic resonance device is installed in a compartment of a
vehicle so as to reduce a low-frequency sound pressure (or noise)
dependent upon a natural vibration. Specifically, an acoustic
resonance device is a panel/diaphragm resonator, a resonance pipe,
or a Helmholtz resonator, the inner space of which communicates
with the compartment via an opening. The acoustic resonance device
is positioned in proximity to an antinode of sound pressure owing
to a natural vibration occurring in a driver/passenger space inside
the compartment. Alternatively, the acoustic resonance device
increases a particle velocity at a specific natural frequency or
decreases sound pressure at an excitation frequency which occurs
due to an external condition of the vehicle. The acoustic resonance
device can be installed in a roof, a seat, a pillar supporting the
roof, or a door of a vehicle.
Inventors: |
Tanase; Rento; (Iwata-shi,
JP) ; Nakashima; Hiroshi; (Hamamatsu-Shi, JP)
; Nakamura; Yasutaka; (Hamamatsu-Shi, JP) ;
Fukatsu; Keiichi; (Hamamatsu-Shi, JP) ; Yoshida;
Atsushi; (Hamamatsu-Shi, JP) ; Kato; Shinichi;
(Hamamatsu-Shi, JP) |
Assignee: |
Yamaha Corporation
Hamamatsu-Shi
JP
|
Family ID: |
43646820 |
Appl. No.: |
12/876067 |
Filed: |
September 3, 2010 |
Current U.S.
Class: |
181/295 |
Current CPC
Class: |
B60R 13/0815
20130101 |
Class at
Publication: |
181/295 |
International
Class: |
E04B 1/82 20060101
E04B001/82 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 7, 2009 |
JP |
2009-206496 |
Claims
1. An acoustic resonance device comprising at least one resonator
which has an inner space and an opening, wherein the inner space of
the resonator communicates with a compartment of a vehicle via the
opening, and wherein the resonator reduces sound pressure at a
specific natural frequency corresponding to an antinode of a
natural vibration emerging in a driver/passenger space inside the
compartment of the vehicle.
2. The acoustic resonance device according to claim 1, wherein the
resonator is positioned to reduce sound pressure at the specific
natural frequency corresponding to the antinode of the natural
vibration whose position is closest to the driver/passenger space
among a plurality of antinodes of the natural frequency occurring
in the compartment of the vehicle.
3. An acoustic resonance device comprising at least one resonator
which has an inner space and an opening, wherein the inner space of
the resonator communicates with a compartment of a vehicle via the
opening, and wherein the resonator increases a particle velocity at
a specific natural frequency corresponding to an antinode of a
natural vibration emerging in a driver/passenger space inside the
compartment of the vehicle.
4. The acoustic resonance device according to claim 1, wherein the
resonator reduces sound pressure at an excitation frequency, which
occurs due to an external condition of the vehicle and which
differs from the specific natural frequency, by way of
resonance.
5. The acoustic resonance device according to claim 3, wherein the
resonator reduces sound pressure at an excitation frequency which
occurs due to an external condition of the vehicle and which
differs from the specific natural frequency.
6. The acoustic resonance device according to claim 4, wherein the
natural vibration is a primary mode of vibration spreading sound
pressure in a width direction of the vehicle.
7. The acoustic resonance device according to claim 5, wherein the
natural vibration is a primary mode of vibration spreading sound
pressure in a width direction of the vehicle.
8. The acoustic resonance device according to claim 4, wherein the
natural vibration is a secondary mode of vibration spreading sound
pressure in a forward-backward direction of the vehicle.
9. The acoustic resonance device according to claim 5, wherein the
natural vibration is a secondary mode of vibration spreading sound
pressure in a forward-backward direction of the vehicle.
10. The acoustic resonance device according to claim 4, wherein at
least one seat is facilitated in the driver/passenger space so that
the resonator is installed in the seat.
11. The acoustic resonance device according to claim 5, wherein at
least one seat is facilitated in the driver/passenger space so that
the resonator is installed in the seat.
12. The acoustic resonance device according to claim 4, wherein the
resonator is installed in a roof of the vehicle.
13. The acoustic resonance device according to claim 5, wherein the
resonator is installed in a roof of the vehicle.
14. The acoustic resonance device according to claim 4, wherein the
resonator is installed in a pillar supporting a roof of the
vehicle.
15. The acoustic resonance device according to claim 5, wherein the
resonator is installed in a pillar supporting a roof of the
vehicle.
16. The acoustic resonance device according to claim 4, wherein the
resonator is installed in a door of the vehicle.
17. The acoustic resonance device according to claim 5, wherein the
resonator is installed in a door of the vehicle.
18. The acoustic resonance device according to claim 1, wherein the
opening of the resonator is directed towards the outside of the
vehicle.
19. The acoustic resonance device according to claim 3, wherein the
opening of the resonator is directed towards the outside of the
vehicle.
20. The acoustic resonance device according to claim 1, wherein the
resonator is attached to a roof of the vehicle and positioned
opposite to the internal space of the compartment so as to
communicate with an outside air of the vehicle, and wherein the
opening of the resonator is directed in proximate to a hole which
runs through the roof of the vehicle and which communicates with
the internal space of the compartment.
21. The acoustic resonance device according to claim 3, wherein the
resonator is attached to a roof of the vehicle and positioned
opposite to the internal space of the compartment so as to
communicate with an outside air of the vehicle, and wherein the
opening of the resonator is directed in proximate to a hole which
runs through the roof of the vehicle and which communicates with
the internal space of the compartment.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to acoustic resonance devices
which reduce sounds/noises in cabins/compartments of vehicles.
[0003] The present application claims priority on Japanese Patent
Application No. 2009-206496, the content of which is incorporated
herein by reference.
[0004] 2. Description of the Related Art
[0005] Conventionally, various technologies have been developed to
improve quietness/noiselessness in cabins/compartments of vehicles
by use of sound-absorbing materials. Patent Document 1 discloses a
sound-absorbing material (e.g. a felt material) attached to a duct
inside a dash panel in a cabin of a vehicle. Patent Document 2
discloses a panel/diaphragm sound-absorbing structure in which a
panel/diaphragm vibrator and a rear cavity (or an air space in the
rear of the vibrator) cooperate together to absorb sound.
[0006] Even when the technology of Patent Document 1 adopts the
sound-absorbing structure of Patent Document 2, it is difficult to
sufficiently reduce low-frequency sound owing to engine sound of a
vehicle and frictional noise (which occurs due to friction between
tires and roads while a vehicle is running). The technology of
Patent Document 1 is unable to demonstrate a high sound-absorbing
effect at positions of seats at which a driver and/or passengers
may actually hear sound/noise inside a vehicle.
[0007] Patent Document 1: Japanese Patent Application Publication
No. 2001-97020
[0008] Patent Document 2: Japanese Patent Application Publication
No. 2006-11412
SUMMARY OF THE INVENTION
[0009] It is an object of the present invention to provide an
acoustic resonance device which reduces low-frequency sound so as
to demonstrate a sound-absorbing effect at positions of seats at
which a driver and/or passengers actually hear sound/noise inside a
vehicle.
[0010] An acoustic resonance device according to the present
invention is installed in a compartment of a vehicle and
constituted of at least one resonator having an inner space and an
opening. The resonator is arranged in the compartment of a vehicle
such that the inner space communicates with the compartment via the
opening. The resonator reduces sound pressure at a specific natural
frequency corresponding to an antinode of a natural vibration
emerging in a driver/passenger space inside the compartment of a
vehicle.
[0011] Preferably, the resonator is positioned to reduce sound
pressure at an antinode of natural vibration whose position is
closest to the driver/passenger space among a plurality of
antinodes of natural frequency occurring in the compartment of a
vehicle.
[0012] In addition, the resonator increases a particle velocity at
a specific natural frequency corresponding to an antinode of
natural vibration emerging in the driver/passenger space inside the
compartment of a vehicle.
[0013] Furthermore, the resonator reduces sound pressure at an
excitation frequency which occurs due to an external condition of
the vehicle and which differs from the specific natural
frequency.
[0014] In the above, the natural vibration is a primary mode of
vibration spreading sound pressure in the width direction of a
vehicle. Alternatively, the natural vibration is a secondary mode
of vibration spreading sound pressure in the forward-backward
direction of a vehicle.
[0015] The resonator can be installed in a seat in connection with
the driver/passenger space in the compartment of a vehicle. The
resonator can be installed in a roof of a vehicle. The resonator
can be installed in a pillar supporting the roof of a vehicle. The
resonator can be installed in a door of a vehicle.
[0016] Generally speaking, a low-frequency sound which a
driver/passenger may distinctively sense as noise has a strong
dependency on a natural vibration occurring in the compartment of a
vehicle. Considering a natural vibration which occurs in a height
equivalent to the position of a driver/passenger's head on a front
seat, the wavelength is approximately twice the width of a vehicle
so that sound pressure spreads in the width direction of a vehicle.
Antinodes of sound pressure owing to this natural vibration emerge
in proximity to side windows fixed above front doors of a vehicle.
For this reason, an acoustic resonance device is positioned to
reduce sound pressure or to increase particle velocity at an
antinode of sound pressure which is closest to the driver/passenger
space among a plurality of antinodes of sound pressure owing to a
natural vibration, thus achieving mode suppression. That is, the
present invention is able to reduce a low-frequency sound pressure
and to thereby improve a noise reduction effect at a
driver/passenger's position at which a driver/passenger actually
suffers from noise.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] These and other objects, aspects, and embodiments of the
present invention will be described in more detail with reference
to the following drawings.
[0018] FIG. 1 is a perspective view showing the exterior appearance
of a vehicle equipped with an acoustic resonance device according
to a first embodiment of the present invention.
[0019] FIG. 2 is a side view partly in section showing a
compartment and its related mechanical parts in the vehicle.
[0020] FIG. 3 is a perspective view showing the exterior appearance
of a panel/diaphragm resonator serving as the acoustic resonance
device of the first embodiment.
[0021] FIG. 4 is a cross-sectional view taken along line II-II in
FIG. 3.
[0022] FIG. 5A is a perspective view of the rear sides of front
seats in a diagonal direction inside the compartment of the
vehicle.
[0023] FIG. 5B is a graph showing natural vibration in which sound
pressure is spread in a width direction of the compartment.
[0024] FIG. 6 diagrammatically shows the details of measurement
testing regarding a two-dimensional mode of vibration.
[0025] FIG. 7 is a graph showing the result of the measurement
testing representing sound pressure at each evaluation
position.
[0026] FIG. 8 is a perspective exploded view of the vehicle whose
roof is equipped with panel/diaphragm resonators.
[0027] FIG. 9 is a perspective view showing the rear sides of front
seats in a diagonal direction inside the compartment of the vehicle
equipped with panel/diaphragm resonators.
[0028] FIG. 10 is a cross-sectional view taken along line VIII-VIII
in FIG. 2, showing the constitution of a roof equipped with
panel/diaphragm resonators.
[0029] FIG. 11 is a cross-sectional view of a center pillar which
is cut in a plane perpendicular to its longitudinal direction.
[0030] FIG. 12A is a lateral sectional view taken along line A-A on
a front seat in FIG. 9.
[0031] FIG. 12B is a vertical sectional view taken along line B-B
on the front seat in FIG. 9.
[0032] FIG. 13 is a vertical sectional view of a front door which
is cut in a plane perpendicular to the width direction of the
vehicle.
[0033] FIG. 14A is a front view of a resonance pipe unit
constituted of plural resonance pipes attenuating sound
pressure.
[0034] FIG. 14B is across-sectional view illustrating the internal
structure of two adjacent resonance pipes which are combined
together to cause coupled oscillation therebetween.
[0035] FIG. 15 is a perspective exploded view of the vehicle whose
roof is equipped with resonance pipe units.
[0036] FIG. 16 is a perspective view of the rear sides of front
seats in a diagonal direction inside the compartment of the vehicle
equipped with resonance pipe units.
[0037] FIG. 17 is across-sectional view taken along line VIII-VIII
in FIG. 2, showing the constitution of a roof equipped with
resonance pipe units.
[0038] FIG. 18 is a cross-sectional view of the front pillar taken
along line D-D in FIG. 16, illustrating installation of the
resonance pipe unit.
[0039] FIG. 19 is a perspective view partly in section, showing the
front door equipped with the resonance pipe unit.
[0040] FIG. 20A is a perspective view showing a Helmholtz resonator
serving as an acoustic resonance device according to a third
embodiment of the present invention.
[0041] FIG. 20B is a cross-sectional view of the Helmholtz
resonator constituted of a body and a tubular portion.
[0042] FIG. 21 is a cross-sectional view taken along line VIII-VIII
in FIG. 2, showing the constitution of a roof equipped with
Helmholtz resonators in addition to panel/diaphragm resonators.
[0043] FIG. 22 is a graph showing frequency characteristics on
sound pressure, indicating a noise reduction effect owing to
resonators in terms of A-characteristic sound pressure.
[0044] FIG. 23A is a cross-sectional view of a tubular portion
according to a second variation in the Helmholtz resonator.
[0045] FIG. 23B is a plan view of the tubular portion constituted
of an outer tube, an inner tube, and an opening.
[0046] FIG. 24A is a perspective exploded view of a lattice member
attached to a roof inner panel of the vehicle.
[0047] FIG. 24B is a side view of the lattice member in a direction
F in FIG. 24A.
[0048] FIG. 25 is a graph showing the simulation result on the
panel/diaphragm resonator by using different surface densities of
the vibrator, thus calculating sound absorption coefficients in
connection with frequencies.
[0049] FIG. 26 is a perspective view of a corrugated panel
according to a fifth variation.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0050] The present invention will be described in further detail by
way of embodiments and variations with reference to the
accompanying drawings.
1. First Embodiment
[0051] FIG. 1 is a perspective view showing the exterior appearance
of a vehicle 100, i.e. a four-door sedan, equipped with an acoustic
resonance device according to a first embodiment of the present
invention. FIG. 2 diagrammatically shows a cabin/compartment 105 of
the vehicle 100. Herein, a bonnet (hood) 101, four doors 150 (which
serve as entrance doors of the compartment 105), and a trunk door
103 are fixed to a chassis (serving as a skeletal structure of the
vehicle 100) in an open/close manner. The chassis of the vehicle
100 includes a base 104, center pillars 120 (which extend upwards
from the base 104), front pillars 130, and rear pillars 180 as well
as a part of a roof 110 (which is supported by those pillars). The
compartment 105 is circumscribed by the doors 150 in the vehicle
100. The compartment 105 is a room space accommodating a
driver/passenger who gets into the vehicle 100. A rear package tray
220 is installed in the rear side of the vehicle 100. The rear
package tray 220 covers a partition (not shown) between the
compartment 105 and a trunk. As shown in FIG. 2, the front side of
the vehicle 100 corresponds to the forward direction (or running
direction) of the vehicle 100, while the rear side of the vehicle
100 corresponds to the backward direction of the vehicle 100.
[0052] The compartment 105 includes a driver/passenger space in
which a driver and/or passengers reside in the vehicle 100. Similar
to the conventionally-known interior structure of a car, the
driver/passenger space of the compartment 105 includes front seats
140 and rear seats 190. Specifically, the front seats 140 include a
driver's seat 140A and its adjacent seat 140B. The driver/passenger
space of the compartment 105 accommodating a driver and/or
passengers is determined in advance in the design phase. The four
doors 150 include two front doors 150A fixed adjacent to the front
seats 140 and two rear doors 150B fixed adjacent to the rear seats
190. The doors 150 are equipped with side windows 153. When the
side windows 153 are closed as shown in FIG. 1, they are disposed
at top positions of the front doors 150A.
[0053] An acoustic resonance device is installed in the vehicle 100
so as to reduce low-frequency sound in the compartment 105. The
acoustic resonance device includes a resonator which resonates to
attenuate sound in the compartment 105. The first embodiment adopts
a panel/diaphragm resonator for use in the acoustic resonance
device.
[0054] FIG. 3 diagrammatically shows the exterior appearance of the
panel/diaphragm resonator 1. FIG. 4 is a cross-sectional view taken
along line in FIG. 3, showing the inside of the panel/diaphragm
resonator 1.
[0055] The panel/diaphragm resonator 1 is essentially divided into
a housing 10 and a vibrator 15. The housing 10 is a rectangular
parallelepiped member whose upper section is opened as an opening
12. The housing 10 is constituted of the opening 12 and a
rectangular parallelepiped cavity 13, i.e. a hollow space
communicating with the opening 12. The housing 10 is made of woods;
but this is not a restriction. That is, the housing 10 can be made
of hard materials, such as a synthetic resin and metal, which are
harder than the material of the vibrator 15. The vibrator 15 is a
rectangular member having elasticity, such as a panel or a
diaphragm. For example, the vibrator 15 is a panel made of an
elastic material causing elastic vibration, such as a synthetic
resin, metal, and fiber board, or the vibrator 15 is a diaphragm
made of an elastic material or a polymer compound. The edge of one
surface of the vibrator 15 is supported by the housing 10 so that
the vibrator 15 closes the opening 12 of the housing 10. Since the
opening 12 of the housing 10 is covered with the vibrator 15, the
cavity 13 is formed inside the panel/diaphragm resonator 1. The
cavity 13 serves as a layer composed of gaseous particles,
practically, an air space including air molecules.
[0056] The panel/diaphragm resonator 1 is arranged in the
compartment 105 such that it communicates with a space subjected to
sound attenuation. In other words, the cavity 13 of the
panel/diaphragm resonator 1 is positioned in a space experiencing a
sound pressure which should be attenuated. When sound occurs in
this space, the panel/diaphragm resonator 1 resonates to the sound
pressure. Owing to resonance, a pressure difference occurs between
the sound pressure of the space and the internal pressure of the
cavity 13 of the panel/diaphragm resonator 1. The pressure
difference causes the vibrator 15 to vibrate so that acoustic
energy is being consumed; subsequently, acoustic energy is radiated
again. This operation works on the surface of the panel/diaphragm
resonator 1 so that sound pressure is reduced in a space in
proximity to the vibrator 15.
[0057] The frequency at which sound pressure is reduced by way of
resonance of the panel/diaphragm resonator 1 depends upon a
resonance frequency of a spring-mass system based on a mass
component (i.e. the weight of the vibrator 15) and a spring
component of the cavity 13. The vibration of the spring-mass system
refers to "piston oscillation". Since the vibrator 15 having
elasticity has a small area, the property of a bending system
additionally emerges due to elastic vibration at a part of the
vibrator which is constrained by being supported by the housing 10.
That is, the panel/diaphragm resonator 1 possesses the vibrator 15
experiencing "bending oscillation" and the cavity 13 disposed in
the backside of the vibrator 15.
[0058] Next, setup conditions of the panel/diaphragm resonator 1
will be described with respect to a resonance frequency of piston
oscillation and a resonance frequency of bending oscillation.
[0059] The resonance frequency f of the piston oscillation is
expressed via equation (1), wherein .rho..sub.0 [g/m.sup.3] denotes
a density of a gaseous medium, i.e. an air density; c.sub.0 [m/s]
denotes sound velocity; .rho. [kg/m.sup.3] denotes a density of a
vibrator; t [m] denotes the thickness of the vibrator; and L [m]
denotes the thickness of an air layer.
f = 1 2 .pi. { .rho. 0 c 0 2 .rho. tL } 1 / 2 ( 1 )
##EQU00001##
[0060] The resonance frequency f of both the piston oscillation and
the bending oscillation is expressed via equation (2), wherein the
vibrator has a rectangular shape whose one length is "a" [m] and
whose other length is "b" [m]; E [Pa] denotes Young's modulus of
the vibrator; .sigma. [-] denotes the Poisson ratio of the
vibrator; and p, q are positive integers representing mode degrees.
This resonance frequency f is occasionally employed in
architectural acoustic design.
f = 1 2 .pi. { .rho. 0 c 0 2 .rho. tL + [ ( p a ) 2 + ( q b ) 2 ] 2
[ .pi. 4 Et 3 12 .rho. t ( 1 - .sigma. 2 ) ] } 1 / 2 ( 2 )
##EQU00002##
[0061] As described above, the panel/diaphragm resonator 1 causes
resonance owing to the piston oscillation and resonance owing to
the bending oscillation. Herein, the piston oscillation and the
bending oscillation do not occur independently of each other. When
their resonance frequencies are close to each other, the resonance
of the spring-mass system and the resonance of the bending system
cooperate to determine the overall resonance frequency of the
panel/diaphragm resonator 1. When the resonance frequency of the
spring-mass system differs from the resonance frequency of the
bending system, they operate independently of each other while they
may partially affect each other. For this reason, the fundamental
oscillation of the bending system cooperates with the spring
component of the cavity in the backside, so that a large amplitude
oscillation is driven in a frequency band between the resonance
frequency of the spring-mass system and the fundamental frequency
of the bending system, thus increasing the attenuation of sound
pressure.
[0062] The panel/diaphragm resonator 1 of the first embodiment
satisfactorily works to reduce sound pressure in a frequency band
whose center frequency is set to a relatively low resonance
frequency. We (i.e. inventors of the present invention) made
various experiment in which a fundamental frequency fa of the
bending system is expressed via equation (3) while a resonance
frequency fb of the spring-mass system is expressed via equation
(1). We found that the panel/diaphragm resonator 1 whose parameters
are adjusted according to equation (4) is able to adequately reduce
sound pressure.
fa = 1 2 .pi. { ( p a ) 2 + ( q b ) 2 } { .pi. 4 Et 3 12 .rho. t (
1 - .sigma. 2 ) } 1 / 2 ( 3 ) 0.05 .ltoreq. fa fb .ltoreq. 0.65 ( 4
) ##EQU00003##
[0063] Since the fundamental oscillation of the bending system
cooperates with the spring component of the air space in the
backside so that a large amplitude vibration is driven in a
frequency band between the fundamental frequency of the piston
oscillation and the fundamental frequency of the bending
oscillation, thus causing a resonance phenomenon where (fundamental
frequency of bending oscillation) fa<(peak frequency of
attenuation of sound pressure) f<(fundamental frequency of
piston oscillation) fb. This causes the panel/diaphragm resonator 1
to radiate an anti-phase reflected wave, thus reducing sound
pressure on the surface of the vibrator 15.
[0064] When the above parameters of the panel/diaphragm resonator 1
are adjusted to meet equation (5), the peak frequency of the
attenuation of sound pressure further decreases in comparison to
the fundamental frequency of the piston oscillation.
0.05 .ltoreq. fa fb .ltoreq. 0.40 ( 5 ) ##EQU00004##
[0065] In order to adequately reduce sound pressure in a frequency
range from 160 Hz to 315 Hz (corresponding to a center frequency of
one-third octave), the panel/diaphragm resonator 1 needs to set the
above parameters, such as .rho..sub.0=1.225 [kg/m.sup.3],
c.sub.0=340 [m/s], .rho.=940 [kg/m.sup.3], t=0.0017 [m], L=0.03
[m], a=b=0.1 [m], E=1.0 [GPa], .sigma.=0.4, and p=q=1.
[0066] Next, a method for determining an installation location of
the panel/diaphragm resonator 1 will be described in detail. FIG.
5A is a perspective view of the front seats 140A whose center
position is observed in a diagonal-rear direction in the
compartment 105, and FIG. 5B is a graph showing natural vibration
(or a normal mode of vibration) spread in a width direction
(corresponding to the lateral width of the vehicle 100) in the
compartment 105. The graph of FIG. 5B shows distribution of sound
pressure in a one-dimensional mode of vibration regarding standing
waves (or axial waves) in which sound pressure is spread in the
width direction of the vehicle 100. The wavelength of an axial wave
is roughly twice the width of the compartment 105. The natural
vibration depends upon the width of the compartment 105, wherein
the natural frequency thereof is relatively low at 167 Hz, for
example. The horizontal axis of the graph of FIG. 5B represents the
position of a dotted line H in FIG. 5A, i.e. the height of a head
(or ears) of a person seated at the front seat 140, while the
vertical axis represents sound pressure in the one-dimensional mode
of vibration.
[0067] We, the inventors, presumed that a low frequency of 170 Hz
or so, which a person residing in the compartment 105 can recognize
as noise, greatly depends upon the natural vibration. In general,
numerous modes of vibration condense in an audio frequency range in
a diffuse sound field; hence, sound pressure is spread uniformly in
the sound field, explicitly indicating the uniform distribution of
sound field at each position in the sound field on the frequency
axis. In contrast, some modes of vibration which are difficult to
be attenuated occur in a sound field of a small space such as the
compartment 105 of the vehicle 100. In other words, some modes of
vibration are isolated from each other on the frequency axis in the
compartment 105. At low natural frequencies, antinodes of sound
pressure are spread in a rarefactional manner in the compartment
105; hence, an antinode of sound pressure may emerge at a specific
position of the sound field at which sound pressure is
significantly increased compared to other positions. The isolated
mode of vibration corresponds to the one-dimensional mode of
vibration (causing axial waves), presenting high acoustic energy
which is difficult to be attenuated. Compared to other modes of
vibration, the one-dimensional mode of vibration leads to a small
number of incidence of sound waves at a wall surface per unit time,
so that acoustic energy is rarely absorbed by the wall surface.
[0068] We found a simple solution to attenuate sound at a specific
natural frequency in a small sound field, wherein a position
corresponding to an antinode of sound pressure of the specific
natural frequency needs to be specified and reduced in sound
pressure. This solution effectively reduces low-frequency sound in
a small sound field. In other words, when a position corresponding
to an antinode of natural vibration is specified and subjected to
attenuation of sound pressure, it is possible to weaken natural
vibration in a sound field. A resonator can be employed as a
constituent element for reducing sound pressure, wherein the
opening of the resonator is positioned in proximity to the position
of an antinode of sound pressure. Herein, the term "proximity"
refers to a distance which suffices the need of reducing sound
pressure at an antinode. A small distance may reduce sound pressure
at a specific natural frequency, wherein it may be set to one-sixth
of a wavelength or less, for example.
[0069] We performed the following measurement testing in order to
confirm whether or not a low-frequency sound pressure is actually
reduced in a small sound field by way of the above working
principle.
[0070] FIG. 6 shows the details of the measurement testing, which
diagrammatically shows natural vibration in which sound pressure is
spread in a height direction of a rectangular parallelepiped sound
field. Specifically, FIG. 6 shows a two-dimensional mode of
vibration in which a low natural frequency of 158 Hz occurs owing
to the height dimension of the sound field. Hatching portions with
slashes indicate positions at which maximum sound pressure emerges
or at which sound pressure increases maximally; hence, these
positions matches antinodes of sound pressure. Other hatching
portions with vertical lines indicate positions at which minimum
sound pressure occurs or at which sound pressure decreases
minimally; hence, these positions correspond to nodes of sound
pressure. Other blank portions (or non-hatching portions) indicate
positions at which sound pressure remains in an intermediate level.
The two-dimensional mode of vibration of FIG. 6 is computed by way
of sound-field simulation adopting a finite element method
(FEM).
[0071] We designated fifteen circular marks serving as evaluation
positions, at which sound pressure is being measured, with numerals
"1" through "15". A microphone is positioned at each evaluation
position. Evaluation positions 1 through 9 are laid along an edge
line extending in the height direction of the sound field, wherein
they are positioned with equal spacing therebetween. Evaluation
positions 9 through 15 are laid along an edge line extending in the
width direction or a baseline of the sound field, wherein they are
positioned with equal spacing therebetween. The evaluation position
9 is set at a corner of the sound field, while a sound source is
positioned at a farthest corner from the evaluation position 9.
[0072] FIG. 7 is a graph showing the results of the measurement
testing, which are produced in such a way that microphones disposed
at respective evaluation positions receive sound emitted from the
sound source so as to detect sound pressure. In FIG. 7, the
horizontal line represents the evaluation positions 1 through 15,
and the vertical line represents sound pressure in units of
decibels (dB) in a 160 Hz band corresponding to a one-third octave
band whose center frequency is 160 Hz. Herein, a solid line
represents a measurement result A in which sound pressure is
attenuated at an antinode of natural vibration by way of resonance,
wherein four resonators are arranged at four corners of a
horizontal plane whose height corresponds to the evaluation
position 5 in the sound field. Specifically, four resonators, each
of which has one open end (communicating with its cavity) and the
other closed end, are arranged such that the open ends thereof are
positioned at four corners. Each resonator resonates at a
predetermined resonance frequency in the 160 Hz band. A dotted line
represents a measurement result B in which sound pressure is
attenuated at a node of natural vibration by way of resonance,
wherein four resonators are arranged at four corners of a
horizontal plane whose height corresponds to the evaluation
position 7. A dashed line represents a measurement result C in
which no resonator is arranged.
[0073] The measurement result A (see solid line in FIG. 7) clearly
shows that sound pressure significantly decreases at the evaluation
position 5, corresponding to an antinode of natural vibration,
which is closest to the open end of a resonator, wherein sound
pressure is reduced to approximately 62 dB. At the evaluation
positions 3, 4, 6 and 7 which are close to the evaluation position
5, sound pressure is around 90 dB; hence, sound pressure is lower
than the measurement result C (see dotted line in FIG. 7) produced
without using resonators. At the evaluation positions 8 through 15
which are distant from the positions of resonators, sound pressure
is lower than the measurement result C produced without using
resonators, by approximately 20 dB. The above measurement result A
shows that sound pressure at an antinode of natural vibration can
be greatly reduced by use of resonators, while sound pressure at
other positions, which are distant from positions of resonators,
can be reduced as well. This proves that resonators can improve the
quietness/noiselessness in a sound field occurring in the
compartment of a vehicle. This effect will be referred to as a
"mode suppression effect" in the following description.
[0074] The measurement result B (see dotted line in FIG. 7) clearly
shows that sound pressure significantly decreases at the evaluation
position 7, corresponding to a node of natural vibration, which is
closest to the open end of a resonator, wherein sound pressure is
reduced to approximately 76 dB. In contrast, no mode suppression
effect is found at other evaluation positions in comparison with
the measurement result C. The measurement result C shows that sound
pressure cannot be sufficiently reduced by use of resonators which
are arranged at a node of natural vibration; hence, it is very
difficult to obtain a mode suppression effect in the sound
field.
[0075] Referring back to FIG. 5A illustrating the one-dimensional
mode of vibration in which sound pressure is spread in the width
direction of the compartment 105, we found that an antinode of
sound pressure emerges around the height of a head (or ears) of a
driver/passenger seated at the front seat 140A/140B. Antinodes may
emerge around opposite ends of the width direction of the
compartment 105, wherein they may be proximate to the side windows
153 of the front doors 150A. The wavelength of a natural frequency
corresponding to natural vibration may be twice the width of the
compartment 105. For example, the wavelength of a natural frequency
of 167 Hz is about 2.0 m, while the width of the compartment 105
ranges from 0.8 m to 1.5 m in a general size of a vehicle.
[0076] An antinode of sound pressure, which emerges around the side
window 153 of the compartment 105 undergoing a normal mode of
vibration, does not necessarily occur via a standing wave (or an
axial wave) propagating in the width direction. We could estimate
that an antinode of a sound wave may occur via an axial wave
spreading sound pressure in the width direction dependent upon a
one-dimensional mode of vibration. Strictly speaking, an antinode
of sound pressure is connected with an axial wave spreading sound
pressure in a forward-backward direction of the vehicle 100 (see
FIG. 2); in other words, an antinode of sound pressure possibly
emerges due to a tangential wave dependent upon a two-dimensional
mode of vibration. In addition, an antinode of sound pressure
possibly emerge due to a slanted wave dependent upon a
three-dimensional mode of vibration in connection with an axial
wave spreading sound pressure in the height direction of the
compartment 105. Regardless of which type of vibration being
involved, we found a fact that an antinode of sound pressure owing
to a natural vibration emerges around the front seats 140 and the
side windows 153.
[0077] In the compartment 105, plural isolated modes of vibration
occur on the frequency axis in a low-frequency range, particularly,
in a 160 Hz band, so that sound pressure is actually spread
according to those modes of vibration in a sound field. We found
that, among those isolated modes of vibration, a certain mode of
vibration (see FIG. 5B) spreading sound pressure in the width
direction needs to be suppressed in order to achieve a high noise
reducing effect in the compartment 105. That is, it is possible to
significantly improve a noise reducing effect at a
driver/passenger's position of hearing sound when an antinode of
natural vibration, which is determined based on the
driver/passenger's position and which emerges around the front seat
140 and the side window 153, is selectively controlled in sound
field. Considering the interior specification of the vehicle 100
having a generally-known structure and dimensions, it is necessary
to embed a resonator in the front seat 140 or at a selected
position of an interior surface close to the front seat 140 in the
compartment 105.
[0078] The position of an antinode of natural vibration depends
upon the material and shape of the compartment 105; hence, it can
be easily measured without actually driving the vehicle 100. In
actuality, a measurement sound having a predetermined frequency is
emitted from a speaker which is installed in a generally-known
compartment of a vehicle and is received by a microphones disposed
at predetermined positions in the compartment; subsequently, sound
pressure is detected based on the result of measuring the
measurement sound, thus producing the sound pressure distribution
shown in FIG. 5B. Generally speaking, conventional vehicles adopt
similar shapes and dimensions of compartments; hence, it can be
said that an antinode of sound pressure emerges around front seats
in a driver/passenger' space undergoing a natural vibration.
[0079] Next, the positioning of the panel/diaphragm resonator 1
arranged in the compartment 105 will be described in detail. The
positioning of the panel/diaphragm resonator 1 is set up to realize
mode suppression with respect to a 160 Hz band based on a natural
vibration. Specifically, the resonance frequency of the
panel/diaphragm resonator 1 is roughly set up in conformity with
the natural frequency.
[0080] FIG. 8 is a perspective exploded view of the vehicle, and
FIG. 10 is a perspective view whose center shows the backside of
front seats 140A in a slanted direction in the compartment 105. In
the present embodiment, numerous panel/diaphragm resonators 1 are
attached to respective positions inside the vehicle 100.
Specifically, the panel/diaphragm resonators 1 are attached to the
roof 110, the center pillars 120, the front pillars 130, the front
seats 140, and the front doors 150A. Among them, the roof 110, the
center pillars 120, the front pillars 130, and the front doors 150A
are constituent parts of the compartment 105. The panel/diaphragm
resonators 1 are positioned in proximity to reduce sound pressure
at an antinode which emerges in the compartment 105 undergoing a
natural vibration. Specifically, they are positioned within a small
distance (e.g. 30 cm) roughly corresponding to the wavelength of a
natural frequency from the antinode of natural vibration. The
panel/diaphragm resonators 1 are each positioned such that the
cavity 13 communicates with the compartment 105 via the opening
12.
[0081] In the following description, the term "upper side"
indicates a higher position in a height direction of the
compartment 105, while the "lower side" indicates a lower position
in the height direction of the compartment 105. The term "left
side" indicates a left portion of the vehicle 100 in a running
direction, while the "right side" indicates a right portion of the
vehicle 100 in the running direction. In addition, the position of
the side window 153 refers to the upper end of the side window 153
which is closed, wherein the height thereof roughly matches the
height of a driver/passenger who is actually seated in the front
seat 140.
[0082] Next, the constitution of the roof 110 will be described in
detail. FIG. 10 is a cross-sectional view taken along line
VIII-VIII in FIG. 2, showing the roof 110 of the vehicle 100.
[0083] As shown in FIGS. 8 and 10, the panel/diaphragm resonators 1
are positioned on the ceiling, just above the driver/passenger's
space on the front seats 140A and 140B, within the root 110.
Specifically, two sets of three panel/diaphragm resonators 1
linearly aligned in the forward-backward direction of the vehicle
100 are embedded in the roof 110. The panel/diaphragm resonators 1
need to be arranged in the roof 110 since an antinode of sound
pressure emerges at a high position close to the side window 153 of
the front door 150A. In the width direction of the vehicle 100, the
panel/diaphragm resonators 1 are each positioned such that the
vibrator 15 is positioned close to the side window 153.
[0084] The roof 110 is attached to a part of the chassis serving as
the basic structure of the vehicle 100, wherein the roof 110
includes a roof inner panel 114 composed of a polypropylene resin.
The roof inner panel 114 has a base material 111 made of a wooden
fiber board. Surface materials 112, which are composed of cloth
materials allowing sound pressure to transmit therethrough, are
arranged in the roof inner panel 114 in proximity to the
compartment 105. The panel/diaphragm resonators 1 are embedded
inside recesses 113 formed on the upper surface of the base
material 111, wherein the panel/diaphragm resonators 1 are fixed to
the roof inner panel 114 via the adhesive. The fixing measure for
fixing the panel/diaphragm resonators 1 to the roof inner panel 114
is not necessarily limited to the adhesive; hence, it is possible
to adopt other fixing measures such as screws and nuts, and belts.
In short, it is possible to adopt any fixing measures adaptive to
the fixation between the panel/diaphragm resonator 1 and the roof
inner panel 114. The panel/diaphragm resonators 1 are each attached
to the base material 111 such that the vibrator 115 communicates
with the inner space of the compartment 105 via the surface
material 112. In addition, the other panel/diaphragm resonators 1
are embedded and fixed inside recesses 115 which are formed at
opposite ends of the width direction in the roof inner panel 114,
wherein they are embedded in slanted portions of the ceiling in
proximity to the side windows 153. Specifically, the
panel/diaphragm resonators 1 are positioned in proximity to an
assist grip 200, which is attached to a side portion of the ceiling
close to the driver/passenger's position in the vehicle 100 having
a generally-known structure. When the panel/diaphragm resonators 1
are positioned in proximity to the assist grip 200, the vibrators
15 are positioned very close to the side window 153, thus further
improving a sound attenuating effect with respect to an antinode of
sound pressure. The panel/diaphragm resonators 1 embedded in the
roof 110 effectively achieve mode suppression with respect to
natural vibration.
[0085] Next, the constitution of the center pillar 120 and the
constitution of the front pillar 130 will be described in detail.
FIG. 11 is a cross-sectional view of the center pillar 120 which is
cut in a plane perpendicular to the longitudinal direction. The
center pillar 120 is constituted of a center pillar outer panel 121
(serving as a part of the chassis) and a center pillar inner panel
122 (which is fixed to the center pillar outer panel 121 via pins
122A). A surface material 123 composed of a cloth material allowing
sound pressure to transmit therethrough is attached to the inner
portion of the center pillar inner panel 122 in proximity to the
compartment 105.
[0086] The panel/diaphragm resonator 1 is embedded in the center
pillar 120 such that the vibrator 15 faces the center pillar inner
panel 122. Plural holes 124 are formed on the inner portion of the
center pillar inner panel 122. Sound occurring in the compartment
105 reaches the vibrator 15 of the panel/diaphragm resonator 1 via
the holes 124. As shown in FIG. 9, the center pillar 120 is
positioned in proximity to the front seat 140A and the front door
150A. The panel/diaphragm resonator 1 embedded in the center pillar
120 effectively achieve mode suppression in the compartment
105.
[0087] FIG. 9 shows that another panel/diaphragm resonator 1 is
embedded in the front pillar 130, wherein the fixing structure
thereof is similar to the above structure for fixing the
panel/diaphragm resonator 1 inside the center pillar 120. Since the
front pillar 130 is positioned in proximity to the front seat 140A
and the front door 150A, the panel/diaphragm resonator 1 embedded
in the front pillar 130 effectively achieve mode suppression in the
compartment 105.
[0088] Next, the constitution of the front seat 140 will be
described in detail. FIG. 12A is a lateral sectional view taken
along line A-A on the front seat 140A in FIG. 9, and FIG. 12B is a
vertical sectional view taken along line B-B on the front seat 140A
in FIG. 9. The surrounding space of the front seat 140 constitutes
the compartment 105.
[0089] The front seat 140 is divided into a head rest 141 and a
seat back 142. The head rest 141 is attached to the seat back 142
via legs (not shown) which are inserted into the seat back 142. The
head rest 141 is adjusted in position with an occipital region of a
head of a driver/passenger seated in the front seat 140. The front
rest 141 supports a driver/passenger's head. A head rest bag 143
made of leather or synthetic leather is filled with stuffing such
as low-resilience urethane foam. The head rest bag 143 is covered
with a head rest cover 144. In the seat back 142, a seat back bag
145 is filled with stuffing such as urethane foam. The surface of
the seat back bag 145 is covered with a seat back cover 146. Both
the head rest cover 144 and the seat back cover 146 are made of a
cloth material allowing sound pressure to transmit
therethrough.
[0090] As shown in FIG. 12A, two panel/diaphragm resonators 1 are
embedded in the heat rest 141 such that the vibrators 15 are
directed to opposite ends of the width direction of the compartment
105. Since an antinode of sound pressure owing to a natural
vibration emerges in proximity to the side window 153, the
vibrators 15 of the panel/diaphragm resonators 1 need to be
positioned close to the antinode of sound pressure. Since the
vibrators 15 are arranged inwardly of the heat rest cover 144 to
communicate with the compartment 105, they are not visualized by a
driver/passenger with ease. In addition, the panel/diaphragm
resonators 1 are fixed in position with respect to the head rest
141, wherein the panel/diaphragm resonators 1 are fixed to legs or
a frame (not shown) via which the heat rest 141 is attached to the
seat back 142.
[0091] As shown in FIG. 12B, the panel/diaphragm resonators 1 are
embedded in the sear back 142 such that the vibrators 15 are
positioned at an upper surface and left/right-side surfaces
(preferably, at a height close to the side window 153). The
vibrators 15 of the panel/diaphragm resonators 1 are arranged
inwardly of the seat back cover 146 to communicate with the
compartment 105, wherein they are not visualized by a
driver/passenger with ease. The panel/diaphragm resonators 1 are
fixed to a frame (not shown) of the seat back 142 and are thus
fixed in position. Since the vibrators 15 of the panel/diaphragm
resonators 1 are embedded in the front seats 140 in proximity to
the side windows 153, it is possible to effectively achieve mode
suppression in the compartment 105. In particular, the front seats
140 occupy the driver/passenger space in the compartment 105, thus
making it possible to position the vibrators 15 of the
panel/diaphragm resonators 1. Thus, an improved sound attenuating
effect at a driver/passenger's position at which a driver/passenger
actually hears sound is highly expected.
[0092] Even when the head rest 141 and the seat back 142 are
integrally unified as a single seat, it is possible to arrange the
panel/diaphragm resonators 1 in a manner similar to the separate
type of the front seat 140.
[0093] Next, the constitution of the front door 150A will be
described in detail. In the present embodiment, the panel/diaphragm
resonators 1 are installed in the front doors 150A, while no
panel/diaphragm resonator is installed in each of the rear doors
150B.
[0094] FIG. 13 is a vertical sectional view of the front door 150A
which is cut in a plane perpendicular to the width direction of the
compartment 105.
[0095] The front door 150A has a base material 151, which installs
the side window 153 to be movable in a vertical direction of the
front door 150A. A surface material 154 made of a cloth material
allowing sound pressure to be transmitted therethrough is attached
to the inner surface of the base material 151 defining the
compartment 105. The base material 151 of the front door 150A has a
glass storage 151A storing the side window 153 when being opened.
The base material 151 of the front door 150A has an inner space S
arranged internally of the glass storage 151A. The panel/diaphragm
resonators 1 are installed in the front door 150A such that the
vibrators 15 communicate with the inner space S. Plural holes 155
are formed on the inner portion of the base material 151 of the
front door 150A, so that the inner space S communicates with the
compartment 105 via the holes 155.
[0096] Since sound occurring in the compartment 105 enters into the
inner space S via the holes 155, it is possible to reduce sound
pressure at an antinode of natural vibration by way of resonance of
the panel/diaphragm resonators 1. The panel/diaphragm resonators 1
are set up in position such that the vibrators 15 are positioned
close to the side window 153 which is installed in the upper side
of the front door 150A. In the present embodiment, the
panel/diaphragm resonators 1 are positioned in the upper side of
the inner space S, while no panel/diaphragm resonator is positioned
in the lower side of the inner space S close to the floor of the
compartment 105.
[0097] The acoustic resonance device of the first embodiment is
constituted of the panel/diaphragm resonators 1 which are attached
to the front seats 140 (located within the driver/passenger space
of the compartment 105) as well as the roof 110, the center pillars
120, the front pillars 130, and the front doors 150A which serve as
surrounding walls of the compartment 105 in proximity to the
driver/passenger space. In the compartment 105, an antinode of
sound pressure corresponding to a low natural frequency is located
in proximity to the front seats 140 (particularly, at a height of a
driver/passenger's head) as well as the side windows 153 of the
front doors 150A. For this reason, the panel/diaphragm resonators 1
each positioned close to an antinode of sound pressure can
effectively achieve mode suppression in the compartment 105. As
described above, the first embodiment is designed to reduce sound
at an antinode of sound pressure, which is closest to the
driver/passenger space, among antinodes of sound pressure owing to
a natural vibration.
[0098] The first embodiment is designed to reduce low-frequency
sound in the compartment 105, thus improving
quietness/noiselessness thereof, particularly, at a
driver/passenger's position at which a driver/passenger actually
hears sound.
2. Second Embodiment
[0099] Next, a second embodiment of the present invention will be
described with respect to an acoustic resonance device installed in
the vehicle 100, which is constituted of a resonance pipe unit 2
including resonance pipes.
[0100] FIGS. 14A and 14B show the constitution of the resonance
pipe unit 2. FIG. 14A shows the exterior appearance of the
resonance pipe unit 2, which is constituted of five resonance pipes
21 (i.e. 21-1 through 21-5). The resonance pipes 21 are aligned in
an alignment direction perpendicular to their longitudinal
direction, wherein they are unified together via fixing measures or
adhesive. The resonance pipes 21 are each composed of a metal or a
synthetic resin, which is shaped in a pipe form. Each of the
resonance pipes 21 is constituted of a closed end 22, an open end
23 and a hollow space 25; hence, it is a closed pipe having one
open end and one closed end. The open ends 23 of the resonance
pipes 21 are linearly aligned so as to adjoin together. A neck
portion of the open end 23 of the resonance pipe 21 can be closed
with a flow resistor 24 having a flow resistance, i.e. an
air-permeable material such as a glass wool, a cloth, or gauze. It
is preferable to select an appropriate material as the flow
resistor 24 when reducing sound pressure in the hollow space
25.
[0101] Next, a sound attenuation effect of the resonance pipe unit
2 will be described with reference to FIG. 14B.
[0102] FIG. 14B shows two adjacent resonance pipes 21-j and 21-k
(where k=j+1) having closed ends 22-j, 22-k, open ends 23-j, 23-k,
and flow resistors 24-j, 24-k within the resonance pipe unit 2.
Herein, L1 denotes the length of the hollow space 25 of the
resonance pipe 21-j, and L2 denotes the length of the hollow space
25 of the resonance pipe 21-k, where L1=L2 since all the resonance
pipes 21 have the same length of the hollow space 25. When a sound
wave is incident at the open ends 23-j, 23-k of the resonance pipe
21-j, 21-k from the compartment 105 of the vehicle 100, they are
introduced into the hollow spaces 25 and reflected at the closed
ends 22-j, 22-k, so that they are emitted from the open ends 23-j,
23-k. At this time, sound waves, whose wavelength .lamda.c (i.e.
L1=L2=.lamda./4) is four times longer than the lengths L1, L2 of
the hollow spaces 25, causes standing waves S1, S2. During the
repetition of oscillation of sound waves inside the resonance pipes
21-j, 21-k, acoustic energy is consumed due to friction on interior
walls of the resonance pipes 21-j, 21-k and due to viscosity of air
molecules at the open ends 23-j, 23-k, so that sound pressure is
being reduced in proximity to the open ends 23-j, 23-k with respect
to a center frequency corresponding to the wavelength .lamda.c. In
FIG. 14B, the length L1=L2 is equal to 0.53 m so that the
wavelength .lamda.c is equal to 2.12 m, for example.
[0103] The resonance pipe unit 2 is arranged such that the hollow
spaces 25 of the resonance pipes 21 communicate with a
predetermined space subjected to sound attenuation. Upon reception
of sound, the resonance pipes 21 resonate to sound entering into
the open ends 23, thus reducing sound pressure in proximity to the
open ends 23. Herein, resonance frequency f is set to reduce sound
pressure in the 160 Hz band; hence, the length of the hollow space
25 of the resonance pipe 21 is set to a quarter of the wavelength
corresponding to the frequency of 160 Hz. That is, the length of
the hollow space 25 of the resonance pipe 21 may range from 40 cm
to 80 cm, for example.
[0104] Sound waves reflected at the closed ends 22-j, 22-k and
emitted from the open ends 23-j, 23-k are diffracted at the open
ends 23-j, 23-k, thus emitting sound energy. A part of sound energy
is emitted from the open end 23 of one resonance pipe 21 and
re-entered into the open end 23 of the other adjacent resonance
pipe 21. That is, coupled oscillation occurs mutually between the
adjacent resonance pipes 23-j, 23-k, thus interchanging sound
energy with each other. During couples oscillation, sound energy is
consumed due to friction on the interior walls of the hollow spaces
25 and due to viscosity of air molecules at the open ends 23-j,
23-k of the resonance pipes 21-j, 21-k, thus reducing sound
pressure. This coupled oscillation can be presumed as an
opposite-end closed pipe mode in which the two adjacent resonance
pipes 21-j, 21-k are unified together, wherein it is possible to
reduce sound pressure with respect to a center frequency
corresponding to the wavelength depends upon the total length of
L1+L2.
[0105] The resonance pipe unit 2 of FIG. 14A is constituted of the
five resonance pipes 21; but this is not a restriction. It is
possible to arbitrarily set the number of resonance pipes included
in the resonance pipe unit 2. In the following description, the
second embodiment is designed to use the resonance pipe unit 2
constituted of the five resonance pipes 21 or the resonance pipe
unit 2 constituted of only one resonance pipe 21.
[0106] Next, the structure for arranging the resonance pipe unit 2
in the compartment 105 will be described with reference to FIG. 15.
The resonance pipe unit 2 installed in the compartment 105 is set
up to achieve mode suppression at a specific frequency, i.e. a
natural frequency of a 160 Hz band. That is, the resonance
frequency of the resonance pipe unit 2 is approximately set to the
natural frequency of natural vibration.
[0107] FIG. 15 is a perspective exploded view of the vehicle 100
equipped with the resonance pipe units 2. FIG. 16 is a perspective
view showing the rear sides of the front seats 140 in a diagonal
direction, whose center position matches the center of the rear
side of the front seat 140A, in the compartment 105 of the vehicle
100. As shown in FIGS. 15 and 16, a plurality of resonance pipe
units 2 is installed in the compartment 105 at various positions,
which are similar to the installation positions of the
panel/diaphragm resonators 1 of the first embodiment (see FIG. 9).
That is, the resonance pipe units 2 are embedded in a roof 110a,
center pillars 120a, and front pillars 130a as well as the front
seats 140 and the front doors 150A. The resonance pipe units 2 are
arranged such that the open ends 23 of the hollow spaces 25 of the
resonance pipes 21 communicate with the compartment 105. The effect
of the resonance pipe unit 2 is similar to the effect of the
panel/diaphragm resonator 1.
[0108] Next, the structure of the roof 110a for installing the
resonance pipe units 2 will be described with reference to FIG. 17.
FIG. 17 is a cross-sectional view taken along line VIII-VIII in
FIG. 2.
[0109] As shown in FIGS. 15 and 17, the resonance pipe units 2 are
embedded in the ceiling portion of the roof 110a just above the
driver/passenger space on the front seats 140A and 140B. Each of
the resonance pipe units 2 includes five resonance pipes 21, whose
alignment direction is the forward-backward direction of the
vehicle 100. Since an antinode of sound pressure emerges in
proximity to the side window 153 of the front door 150A, the open
ends 23 of the resonance pipes 21 are directed to the side window
153, thus improving a sound attenuation effect at the side window
153. In other words, the resonance pipe units 2 are arranged inside
the compartment 105 such that the open ends 23 of the resonance
pipes 21 are directed toward proximate interior walls of the
compartment 105 in the width direction.
[0110] As shown in FIG. 17, a plurality of holes 116 is formed in a
roof inner panel 114a of the roof 110a in proximity to the open
ends 23 of the resonance pipes 21 of the resonance pipe units 2.
These holes 116 communicate with an upper space above the roof
inner panel 114a. Sound occurring in the compartment 105 enters
into the open ends 23 of the resonance pipes 21 via the holes 116.
Other resonance pipe units 2 are attached to the side portions of
the roof inner panel 114a just behind the assist grips 200, wherein
they are each constituted of a single resonance pipe 21 whose
longitudinal direction lies along the forward-backward direction of
the vehicle 100. Other holes 117 are formed in the side portions of
the roof inner panel 114a so as to introduce sound occurring in the
compartment 105 into the open ends 23 of the resonance pipes 21.
Similar to the first embodiment, the second embodiment can
effectively achieve mode suppression in the compartment 105.
[0111] Next, the constitution of the center pillar 120a and the
constitution of the front pillar 130a will be described with
reference to FIG. 18. FIG. 18 is a cross-sectional view of the
center pillar 120a taken in line D-D in FIG. 16. The center pillar
120a includes a center pillar inner panel 122a attached to the
center pillar outer panel 121 (see FIG. 11). The front material 123
is attached to the interior surface of the center pillar inner
panel 122a in proximity to the compartment 105. An inner space Sa
is formed between the center panel inner panel 122a and the surface
material 123. In order to form the inner space Sa, a recess 125 is
formed in the upper side of the center pillar inner panel 122a such
that the back portion thereof project toward the outside of the
vehicle 100 in the width direction. A hole 126 is formed in the
lower end of the recess 125. The resonance pipe unit 2 is embedded
in the center pillar 120a such that the open end 123 of the
resonance pipe 21 is engaged in the hole 126 of the recess 125.
Sound occurring in the compartment 105 enters into the open end 13
of the resonance pipe 21 via the surface material 123 and the inner
space Sa. The resonance pipe unit 2 resonates to sound occurring in
the compartment 105 so as to reduce sound pressure at an antinode
of natural vibration, thus achieving mode suppression in the
compartment 105.
[0112] As shown in FIG. 16, the resonance pipe unit 2 is embedded
in the front pillar 130a as well. The structure for arranging the
resonance pipe unit 2 in the front pillar 130a is similar to the
structure for arranging the resonance pipe unit 2 in the center
pillar 120a; hence, the front pillar 130a equipped with the
resonance pipe unit 2 can achieve mode suppression, and a detailed
explanation thereof will be omitted.
[0113] Next, the constitution of the front seat 140 equipped with
the resonance pipe units 2 will be described with reference to FIG.
16.
[0114] The resonance pipe units 2 are arranged in the head rest 141
and the seat back 142 in the front seat 140. Specifically, two
resonance pipes 21 are vertically arranged in the seat back 142 of
the front seat 140 such that the openings 23 are each directed
toward the upper surface of the seat back 142. That is, the
resonance pipe units 2 are arranged in the seat back 142 of the
front seat 140 such that the hollow spaces 25 of the resonance
pipes 21 communicate with the compartment 105 via the open ends 23,
wherein sound occurring in the compartment 105 enters into the open
ends 23 of the resonance pipes 21 via the seat back cover 146.
Another resonance pipe unit 2 is arranged in the heat rest 141 of
the front seat 140, wherein in order to adequately secure the
overall length, the resonance pipe 21 is folded in the head rest
141. The open end 23 of the resonance pipe 21 embedded in the head
rest 141 of the front set 140 is directed towards the interior wall
of the compartment 105.
[0115] Next, the constitution of the front door 150A equipped with
the resonance pipe unit 2 will be described with reference to FIG.
19. In this connection, no resonance pipe unit is arranged in the
rear door 150B.
[0116] As shown in FIG. 19, the resonance pipe unit 2 is vertically
arranged in the base material 151 of the front door 150A such that
the open ends 23 of the resonance pipes 21 are directed toward the
side window 153. The open ends 23 of the resonance pipes 21 is
positioned in the upper side of the base material 151 of the front
door 150A so as to improve a sound attenuation effect at an
antinode of sound pressure which emerges in proximity to the side
window 153. An opening is formed in the upper side of the base
material 151 of the front door 150A, thus allowing sound to easily
enter into the open ends 23 of the resonance pipes 21. It is
preferable that the opening of the base material 151 of the front
door 150A be processed not to be visualized by a driver/passenger
with ease.
[0117] Since an antinode of sound pressure at a specific frequency,
i.e. a natural frequency in a 160 Hz band, emerges in proximity to
the driver/passenger space, the second embodiment adopting the
above arrangement of the resonance pipe units 2 can achieve mode
suppression similarly to the first embodiment. That is, the second
embodiment attenuates sound pressure at an antinode closest to the
driver/passenger space among antinodes of sound pressure which may
emerge in proximity to the front seats 140 and the side windows
153.
[0118] When the resonance pipe unit 2 is constituted of plural
resonance pipes 21 causing coupled oscillation, it is possible to
reduce sound pressure at other frequencies different from a natural
frequency, thus further improving quietness/noiselessness in the
compartment 105.
3. Third Embodiment
[0119] A third embodiment of the present invention is characterized
by using a Helmholtz resonator 3, which is installed in the
compartment 105. The third embodiment is similar to the first
embodiment with respect to the overall structure of the vehicle 100
and the installation positions of resonators in the compartment
105, wherein the same constituent elements are designated the same
numerals accompanied with a subscript "b"; hence, a detailed
description thereof will be omitted.
[0120] The Helmholtz resonator 3 is employed as an acoustic
resonance device of the third embodiment. FIG. 20A is a perspective
view showing the exterior appearance of the Helmholtz resonator 3,
and FIG. 20B is a cross-sectional view taken along line E-E in FIG.
20A. The Helmholtz resonator 3 is constituted of a body 31 and a
tubular portion 32. A hollow space is formed inside the body 31 and
the tubular portion 32 and communicates with an opening 33 of the
tubular portion 32.
[0121] A cavity is formed inside the body 31, which is made of
fiber-reinforced plastics (FRP) and which is formed in a
cylindrical shape. The tubular portion 32 is an open tube made of
vinyl chloride, whose opposite ends are opened. The tubular portion
32 is unified with the body 31 such that the tubular portion 32 is
inserted into a center hole of the body 31. The Helmholtz resonator
3 is arranged such that the hollow space formed inside the body 31
and the tubular portion 32 communicates with the space of the
compartment 105 subjected to sound attenuation. When sound enters
into the opening 33, the Helmholtz resonator 3 resonates to sound
so as to reduce sound pressure in proximity to the opening 33.
Specifically, the Helmholtz resonator 3 is a spring-mass system in
which a mass component corresponds to an air (or a gaseous body)
disposed inside the tubular portion 32, and a spring component
corresponds to a cavity of the body 31. Sound energy is converted
into thermal energy due to friction of air on the internal wall of
the tubular portion 32, thus reducing sound pressure while
increasing particle speed in proximity to the opening 33. A
resonance frequency f of the spring-mass system corresponding to
the Helmholtz resonator 3 meets equation (5), in which Le denotes
an effective length of the tubular portion 32. As shown in FIG.
20B, the effective length Le is calculated by measuring the length
of a cavity of the tubular portion 32 (ranging between opposite
ends) and by correcting it with an open end correction value. In
addition, V denotes the volume of the cavity formed in the body 31,
and Sc denotes an area of the opening 33.
f = c 0 2 .pi. ( S LeV ) 1 / 2 ( 5 ) ##EQU00005##
[0122] In this connection, the Helmholtz resonator 3 is not
necessarily equipped with a single tubular portion 32; but it is
possible to unify two tubular portions 32 with the body 31. In
addition, it is possible to close the opening 33 of the tubular
portion 32 with a flow resistance material having air permeability,
such as a glass wool, a cloth, and gauze.
[0123] Next, the structure for arranging the Helmholtz resonator 3
in the compartment 105 of the vehicle 100 will be described in
detail. Similar to the first embodiment, a plurality of Helmholtz
resonators 3 is installed in a roof 110b, center pillars 120b and
front pillars 130b as well as the front seats 140 and the front
doors 150A. Since the third embodiment can adopt the same
installation positions as the first embodiment, the Helmholtz
resonators 3 are arranged such that the hollow spaces communicate
with the compartment 105 via the openings 33. The Helmholtz
resonators 3 can demonstrate similar effects as the panel/diaphragm
resonators 1 employed in the first embodiment. As an example of the
installation position, the roof 110b will be described below.
[0124] FIG. 21 is a cross-sectional view of the roof 110b taken
along line VIII-VIII in FIG. 2. A plurality of panel/diaphragm
resonators 1 is arranged on a planar portion of a roof inner panel
114b of the roof 110b, while a plurality of Helmholtz resonators 3
is arranged on inclined side portions (whose areas are smaller than
the area of the planar surface and which are positioned just behind
the assist grips 200) of the roof inner panel 114b. Thus, it is
possible to effectively arrange different types of resonators on
the roof 110b.
[0125] The third embodiment can demonstrate a similar effect as the
first embodiment.
4. Noise Reduction Effect
[0126] FIG. 22 is a graph showing the result of the measurement
testing on a noise reduction effect owing to the resonators of the
foregoing embodiments installed in the compartment 105 of the
vehicle 100. This graph shows frequency characteristics of sound
pressure (or noise level) measured in a driver's seat, wherein a
solid line represents the measurement result using resonators, and
a dotted line represents the measurement result using no resonator.
The measurement testing is performed by actually running a vehicle
at a speed of 60 km/h, wherein the measurement testing is performed
in terms of audibility characteristics (or A-characteristics) sound
pressure by use of a one-third octave band-pass filter, thus
precisely detecting frequency characteristics close to actual
auditory sensation.
[0127] FIG. 22 clearly shows that a noise level is reduce in a
frequency range between 125 Hz and 200 Hz. In particular, a noise
reduction of 5 dB or more is detected at a 160 Hz band, indicating
a significant reduction of sound pressure in a low-frequency range.
Compared with the technology which reduces sound pressure at other
positions different from antinodes of natural vibration, the
foregoing embodiments adopting various resonators directed towards
antinodes of sound pressure are able to improve
quietness/noiselessness in the compartment 105, thus demonstrating
an outstanding noise reduction effect at the driver/passenger
position at which a driver/passenger suffers from noise. In
addition, the foregoing embodiments are designed to carefully
select the "effective" installation positions of resonators
dedicated to a noise reduction effect; this prevents excessive
resonators from being arranged in insignificant positions.
5. Variations
[0128] The present invention is not necessarily limited to the
foregoing embodiments, which can be appropriately combined together
or which can be further modified in various ways as follows.
[0129] (1) First Variation
[0130] The first embodiment adopts the panel/diaphragm resonators
1; the second embodiment adopts the resonance pipe units 2; and the
third embodiment adopts the Helmholtz resonators 3. Of course, it
is possible to combine the panel/diaphragm resonators 1, the
resonance pipe units 2, and the Helmholtz resonators 3, which are
selectively installed in the compartment 105 of the vehicle 100.
The types of acoustic resonance devices are not necessarily limited
to them, since the present invention simply requires that acoustic
resonance devices have hollow spaces communicating with the
compartment 105 via openings. It is preferable that acoustic
resonance devices be able to reduce sound pressure at an antinode
closest to a driver/passenger space by positioning openings in
proximity to an antinode of sound pressure. It is further
preferable that openings of acoustic resonance devices be directed
toward the driver/passenger space.
[0131] The foregoing embodiments are each designed such that
acoustic resonance devices are arranged in the roof 110, the center
pillars 120, the front pillars 130, the front seats 140, and the
front doors 150A. It is possible to limit the installation
positions of acoustic resonance devices among them. In the
compartment 105 shown in FIG. 5A, acoustic resonance devices are
arranged only in the driver's seat 140B while no acoustic resonance
device devices are arranged in the next passenger's seat 140A. In
addition, an acoustic resonance device having a large size can be
installed across a plurality of installation positions in the
compartment 105.
[0132] (2) Second Variation
[0133] The foregoing embodiments are designed to control sound
pressure at an antinode of natural vibration, because a
one-dimensional mode of vibration dominates an antinode of sound
pressure spreading in the width direction, which may presumably
emerge in proximity to the side window. Without targeting on a
specific mode of vibration, it is possible to reduce sound pressure
at any antinode actually emerging in the driver/passenger space.
This may also demonstrate a similar sound attenuation effect as the
foregoing embodiments. Regardless of antinodes of sound pressure
depending upon different modes of vibration, it is possible to
achieve an outstanding mode suppression effect in any types of
compartments suffering from low-frequency sounds.
[0134] It is possible to focus on a natural vibration occurring in
the compartment 105 in connection with a front-rear length of the
vehicle 100 in a forward-backward direction. Since the length of
the vehicle 100 is longer than the width of the vehicle 100, a
low-frequency antinode of sound pressure may emerge in the
compartment 105 undergoing a secondary one-dimensional mode of
vibration spreading sound pressure in the forward-backward
direction of the vehicle. Specifically, antinodes of sound pressure
may occur at end portions of the front-rear length of the vehicle
100, such as the center pillars 120, the rear pillars 180, and the
rear package tray 220 (see FIGS. 2 and 5A) in the compartment 105
undergoing a natural vibration. It is possible to arrange
resonators in proximity to end portions of the front-rear length of
the vehicle 100, thus achieving mode suppression. In the case of a
secondary one-dimensional mode of vibration, an antinode of sound
pressure may be located around the center position of the
compartment 105 in the forward-backward direction of the vehicle
100; hence, it is necessary to arrange resonators at the front
seats 140A, 140B, thus achieving mode suppression.
[0135] The foregoing embodiments are designed to arrange acoustic
resonance devices reducing sound pressure at an antinode of sound
pressure closest to the driver/passenger space; but this is not a
restriction. It is possible to arrange acoustic resonance devices
at other positions. Regarding natural vibrations different from a
primary mode of vibration, antinodes of sound pressure are
positioned very close to the driver/passenger space, whereas they
are not necessarily the one closest to the driver/passenger space.
The measurement results of FIGS. 6 and 7 clearly show that,
regardless of modes of vibration (e.g. a one-dimensional mode, a
two-dimensional mode, and a three-dimensional mode) and orders of
vibration (e.g. a primary order, and a secondary order), the
present embodiment is able to reduce low-frequency sound pressure
of the compartment 105 and to improve a noise reduction effect at
the driver/passenger's position at which a driver/passenger
actually hears noise because an acoustic resonance device is
arranged to suppress sound pressure at an antinode of sound
pressure emerging in proximity to the driver/passenger space.
[0136] (3) Third Variation
[0137] It is possible to modify the third embodiment in such a way
that the tubular portion 32 of the Helmholtz resonator 3 can be
freely varied in length. FIGS. 23A and 23B show a modified example
of the Helmholtz resonator 3 having a variable-length tubular
portion 32a. FIG. 23A is a cross-sectional view of the tubular
portion 32a, and FIG. 23B is a front view of the tubular portion
32a having an opening 323.
[0138] The tubular portion 32a is constituted of an outer tube 321
and an inner tube 322. The inner tube 322 is a tube-shaped member
having an external thread on the external periphery thereof. The
inner tube 322 of the tubular portion 32a is rotated and fixed to
the body 31. The outer tube 321 is a tube-shaped member whose inner
diameter is larger than the diameter of the inner tube 322 and
which has an internal thread on the interior surface thereof. The
tubular portion 32a is assembled in such a way that the inner tube
322 is screwed into the outer tube 321. The length L of the tubular
portion 32a depends upon what length the inner tube 322 is screwed
into the outer tube 321. As shown in FIG. 23B, the outline shape of
the outer tube 321 is a hexagonal shape; hence, the user can adjust
the screwed length by use of a mechanical tool such as a wrench,
thus freely changing the length L of the tubular portion 32a. Since
the resonance frequency of the Helmholtz resonator 3 depends upon
the length L of the tubular portion 32a, it is possible to adjust
the resonance frequency as necessary.
[0139] FIGS. 23A and 23B show that the tubular portion 32a adopts a
screw structure in the outer tube 321 and the inner tube 322, thus
freely adjust the length L; but this is not a restriction. The
tubular portion 32a can be composed of three or more screw
elements. Alternatively, it is possible to provide a corniced tube
as the tubular portion 32a of the Helmholtz resonator 32. That is,
the tubular portion 32a can adopt various structures having
flexibility of expansion and contraction. The outline shape of the
outer tube 321 is not necessarily formed in a hexagonal shape; but
it is preferable that the shape of the tubular portion 32a allows
the user to easily adjust the length thereof.
[0140] The third variation allows the user to easily select a
frequency greatly suppressing sound pressure even when the selected
frequency dedicated to an improvement of quietness/noiselessness
differs dependent upon different materials and structures adapted
to the compartment 105 and different types of vehicles.
[0141] (4) Fourth Variation
[0142] It is possible to employ a lattice member 4 instead of the
resonance pipe unit 2. FIGS. 24A and 24B show the lattice member 4
serving as an acoustic resonance device according to a fourth
embodiment. FIG. 24A is a perspective exploded view of the lattice
member 4, and FIG. 24B is a side view of the lattice member 4 in a
direction F shown in FIG. 24A.
[0143] As shown in FIG. 24A, the lattice member 4 is constituted of
a single partition 4A (which is elongated in a single direction)
and six crossed partitions 4B (which are crossed with the partition
4A and elongated perpendicularly to the partition 4A). The lattice
member 4 is attached to the upper surface of the roof inner panel
114 such that the partition 4A lies in the forward-backward
direction of the vehicle 100 while the crossed partitions 4B lie in
the width direction perpendicular to the forward-backward direction
of the vehicle 100. Thus, the lower end of the lattice member 4 is
closed with the roof inner panel 114, while the upper end of the
lattice member 4 is covered with a part of the chassis serving as
the skeletal structure of the vehicle, such as a roof outer panel
160 which is combined with the roof inner panel 114.
[0144] The lattice member 4 has ten hollow spaces which are defined
between the adjacent crossed partitions 4B and which have openings
directed in the width direction, thus realizing an acoustic
resonance device whose constitution and functionality may roughly
resemble those of the resonance pipe unit 2. In this connection, it
is possible to close both the upper end and the lower end of the
lattice member 4 or either the upper end or the lower end of the
lattice member 4. The lattice member 4 replaces the resonance tube
unit 2 attached to the ceiling (i.e. the roof 110) of the vehicle
100. It is possible to arbitrarily change the number of the crossed
partitions 4B in light of a desired number of hollow spaces.
[0145] (5) Fifth Variation
[0146] FIG. 26 shows a corrugated panel 5 composed of a flexible
material such as a resin, which has a plurality of recesses
virtually serving as a plurality of resonators. The corrugated
panel 5 can be attached to the ceiling portion or the interior wall
of the compartment 105, so that a plurality of resonators absorbs
sound at the ceiling portion or the interior wall of the
compartment 105. The corrugated panel 5 having flexibility can be
easily deformed in conformity with the curved surface; hence, it is
possible to facilitate a plurality of resonators at a desired
position of the compartment 105 with ease.
[0147] (6) Sixth Variation
[0148] The panel/diaphragm resonator 1 of the first embodiment is
constituted of the rectangular housing 10, the vibrator 15 closing
the opening 12 of the housing 10, and the cavity 13 formed inside
the housing 10. The outline shape of the housing is not necessarily
limited to a rectangular shape, which can be replaced with a
circular shape or a polygonal shape. Irrespective of the outline
shape of the housing 10, it is preferable that a concentrated mass
altering a condition of vibrating the vibrator 15 be located at a
center portion of the vibrator 15.
[0149] The panel/diaphragm resonator 1 has a sound absorption
mechanism constituted of a spring-mass system and a bending system.
We performed experiments on sound absorption coefficients at
resonance frequencies by changing the surface density of the
vibrator 15.
[0150] Specifically, we prepared a sample of the housing 10, in
which the cavity 13 has a length of 100 mm, a width of 100 mm, and
a thickness of 10 mm, and a sample of the vibrator 15 has a length
of 100 mm, a width of 100 mm, and a thickness of 0.85 mm, wherein
the center portion (which has a length of 20 mm, a width of 20 mm,
and a thickness of 0.85 mm) of the vibrator 15 is varied in terms
of the surface density. FIG. 25 is a graph showing the simulation
result of the panel/diaphragm resonator 1 in terms of a normal
incidence sound absorption coefficient. We adopt a simulation
method according to the Japanese Industrial Standard, JIS A 1405-2
(titled "Acoustics--Determination of sound absorption coefficient
and impedance in impedance tubes--Part 2: Transfer-function
method"), in which the panel/diaphragm resonator 1 is arranged in a
sound chamber so that its sound field is determined via the finite
element method, thereafter, sound absorption characteristics are
calculated using a transfer function. Specifically, the graph of
FIG. 25 shows five characteristic curves (1) through (5) based on
different surface densities (at the center portion of the vibrator
15) such as (1) 399.5 [g/m.sup.2], (2) 799 [g/m.sup.2], (3) 1199
[g/m.sup.2], (4) 1598 [g/m.sup.2], and (5) 2297 [g/m.sup.2]; the
same surface density of 799 [g/m.sup.2] at the peripheral portion
of the vibrator 15; and different average densities of the vibrator
15 such as (1) 783 [g/m.sup.2], (2) 799 [g/m.sup.2], (3) 815
[g/m.sup.2], (4) 831 [g/m.sup.2], and (5) 863 [g/m.sup.2]. This
simulation result clearly shows that peaks significantly appear in
frequencies of 300 Hz through 500 Hz and around a frequency of 700
Hz in terms of the sound absorption coefficient.
[0151] The sound absorption coefficient is locally maximized around
the frequency of 700 Hz owing to the resonance of the spring-mass
system composed of the mass component of the vibrator 15 and the
spring component of the cavity 13. The panel/diaphragm resonator 1
absorbs sound with a peak sound absorption coefficient at a
resonance frequency of the spring-mass system, wherein even when
the surface density of the center portion of the vibrator 15
increases, the total mass of the vibrator 15 is not significantly
changed; this indicates that the resonance frequency of the
spring-mass system is not greatly varied irrespective of the
surface density of the center portion of the vibrator 15. The sound
absorption coefficient is maximized in the frequency range between
300 Hz and 500 Hz owing to the resonance of the bending system
caused by a bending oscillation of the vibrator 15. The
panel/diaphragm resonator 1 causes a peaked sound absorption
coefficient of the low-frequency side at a resonance frequency of
the bending system, which becomes lower as the surface density of
the center portion of the vibrator 15 increases. In general, the
resonance frequency of the bending system is determined by an
equation of motion dominating an elastic oscillation of the
vibrator 15, wherein it is inversely proportional to the density
(or the surface density) of the vibrator 15. The resonance
frequency of the bending system is greatly affected by the density
of antinodes of natural vibration (at which amplitude becomes
maximal). That is, the resonance frequency of the bending system is
varied because the above simulation varies an antinode region of
1.times.1 eigenmode with a different surface density of the center
portion of the vibrator 15.
[0152] The above simulation result indicates that within peaked
sound absorption coefficients, a peaked sound absorption
coefficient of the low-frequency side moves to a lower frequency as
the surface density of the center portion of the vibrator 15 is
increased larger than the surface density of the peripheral portion
of the vibrator 15. This indicates that a peaked sound absorption
coefficient can be moved to a lower frequency or a higher frequency
by changing the surface density of the center portion of the
vibrator 15. Compared to the technology in which the vibrator 15 is
formed in a panel shape composed of the same material as the
panel/diaphragm resonator 15 so that a sound absorption frequency
is changed by increasing a total mass of the panel/diaphragm
resonator 1, the present technology can freely lower the sound
absorption frequency without changing the total mass of the
panel/diaphragm resonator 1 because the sound absorption frequency
corresponding to a peaked sound absorption coefficient can be
changed by simply changing the surface density of the center
portion of the vibrator 15 in the panel/diaphragm resonator 1.
[0153] It is possible to change the resonance characteristics by
filling the cavity 13 of the panel/diaphragm resonator 1 with a
porous sound absorbing material (e.g. a foaming resin, a felt
material, and a cotton fiber such as polyester wool). This
modification is able to cope with variations of noise
characteristics in the compartment 105 due to changes of modes of
vibration (e.g. changed numbers and shapes of persons and baggage)
and changes of noise (e.g. changed tires and variances of road
conditions).
[0154] (7) Seventh Variation
[0155] The first embodiment adopts the same shape to all the
panel/diaphragm resonators 1; but it is possible to adopt different
shapes as the panel/diaphragm resonators 1. Thus, it is possible to
broaden a frequency range reducing sound pressure because the
resonance frequency of the panel/diaphragm resonator 1 differs
dependent upon the dimensions of the housing 10. It is possible to
set different resonance frequencies to the front seats 140A and
140B. In addition, it is possible to set different resonance
frequencies to the roof 110 and the center pillars 120. This
decreases sound pressure in a broader frequency range, wherein it
is possible to reduce sound pressure at an optimum frequency
suiting to each position. That is, various groups are each formed
using a single resonator or a plurality of resonators, wherein each
group of resonator(s) has a different resonance frequency.
Similarly, it is possible to employ various types of resonance pipe
units 2 having different resonance frequencies and various types of
Helmholtz resonators 3 having different resonance frequencies.
[0156] The second embodiment employs a closed pipe as the resonance
pipe 21 having one open end 23 and one closed end 22. It is
possible to use an open pipe whose opposite ends are opened as the
resonance pipe 21. Alternatively, it is possible to mix closed
pipes and open pipes in the resonance pipe unit 2.
[0157] (8) Eighth Variation
[0158] The foregoing embodiments applies acoustic resonance devices
to the vehicle 100 such as an automobile; but it is possible to
apply acoustic resonance devices to other types of vehicles such as
trains, ships, aircrafts, space stations, and gondolas. The term
"vehicle" includes transportation devices which carry people and/or
baggage. In addition, the term includes other non-transport
carriages and equipment used in amusement parks, such as Ferris
wheels. The application of acoustic resonance devices is not
necessarily limited to compartments in which people reside in
vehicles; hence, acoustic resonance devices can be applied to
machinery rooms and luggage rooms which are separated from
compartments of vehicles. There is a possibility that a person may
enter into a machinery room or a luggage room. Some vehicles are
not equipped with seats in the driver/passenger space of a
compartment. Many passengers do not use seats in gondola cars,
busses, and trains. In those vehicles which include passenger
spaces, it is possible to achieve mode suppression at antinodes of
sound pressure suited to passenger spaces, thus achieving similar
effects as the foregoing embodiments.
[0159] The automobile-type vehicle is equipped with installation
structures, which are able to install acoustic resonance devices,
such as the roof, center pillars, front pillars, front seats, and
front doors, while other types of vehicles are not always equipped
with those installation structures. However, it is possible to
attach acoustic resonance devices to counterpart structures of
other vehicles which may be comparable to installation structures
of the automobile-type vehicles. Acoustic resonance devices are not
necessarily attached to installation structures which are already
incorporated into the vehicle and the compartment 105. Before
installation structures are unified with the vehicle 100 and the
compartment 105, it is possible to install acoustic resonance
devices in the vehicle 100 and the compartment 105.
[0160] The present invention does not matter installation positions
of acoustic resonance devices, which are not necessarily limited to
surrounding walls of the compartment 105 and seats of the
driver/passenger space. It is possible to attach acoustic resonance
devices to any positions dedicated to a reduction of sound pressure
at an antinode of natural vibration.
[0161] (9) Ninth Variation
[0162] It is possible to modify the third embodiment such that the
tubular portion 32a of the Helmholtz resonator 3 is automatically
adjusted. This requires an automatic adjustment device including a
microphone, a frequency analyzer, a controller, and a driver. In
this automatic adjustment device, the microphone receives sound,
and subsequently, the frequency analyzer analyzes received sound so
as to specify a frequency significantly increasing noise. The
controller calculates the length of the tubular portion 32a of the
Helmholtz resonator 3 based on the specified frequency; then, it
outputs a drive signal representing the calculated length to the
driver such as a solenoid. The driver adjusts the length of the
tubular portion 32a of the Helmholtz resonator 3 in response to the
drive signal, thus reducing sound pressure particularly at the
specified frequency significantly increasing noise. In this
connection, it is possible to apply feedback control to the
controller driving the tubular portion 32a.
[0163] It is possible to apply an expansion/contraction mechanism
to the Helmholtz resonator 3, thus varying the dimensions of the
body 31. This varies the volume of the cavity of the body 31 so as
to change the resonance frequency of the Helmholtz resonator 3.
Similarly, it is possible to apply an expansion/contraction
mechanism to the resonance pipe unit 2 so as to adjust the length
of the resonance pipes 21.
[0164] (10) Tenth Variation
[0165] The foregoing embodiments arrange acoustic resonance devices
at selected positions corresponding to antinodes of sound pressure
at specific natural frequencies of natural vibration, wherein
resonance frequencies are set to increase reduction values of sound
pressure at antinodes of natural frequencies. It is possible to set
resonance frequencies attenuating sound pressure at other
frequencies different from natural frequencies.
[0166] During a running mode of the vehicle 100, tires serve as an
excitation source (causing a vibration in the compartment 105) so
as to have the vehicle 100 undergo a vibration at a certain
frequency (hereinafter, referred to as an excitation frequency),
which in turn causes noise in the compartment 105. Even when the
compartment 105 has a natural frequency of 167 Hz, sound pressure
is maximized at a frequency of 155 Hz in the compartment 105;
hence, those frequencies may belong to the same frequency range
subjected mode suppression, but they slightly differ from each
other. Herein, the frequency range subjected to mode suppression is
equal to a 160 Hz band, for example. The foregoing embodiments
select the positions of acoustic resonance devices in light of a
natural vibration, wherein they can determine resonance frequencies
in light of sound caused by an excitation source. That is, when a
specific natural frequency differs from an excitation frequency
which is applied to the compartment 105 due to external conditions
(e.g. friction of tires running on roads), resonance frequencies
can be determined to achieve a sound attenuation effect at a high
frequency which is increased due to an excitation at the excitation
frequency. In actuality, acoustic resonance devices are positioned
in proximity to antinodes of sound pressure in a 160 Hz band based
on a natural vibration, thus having acoustic resonance devices
resonate to a frequency of 155 Hz. Since both the excitation
frequency and the natural frequency may belong to the same
frequency range, acoustic resonance devices need to be adjusted at
resonance frequencies reducing sound pressure at those frequencies;
hence, resonance frequencies are not necessarily limited to the 160
Hz band.
[0167] It is possible to implement an automatic control of the
ninth variation in the tenth variation in such a way that resonance
frequencies are each set to a peak frequency caused by excitation
at an excitation frequency in a running mode of the vehicle 100. In
general, automobile-type vehicles undergo variations of excitation
frequencies while running on roads so that excitation frequency
characteristics are varied from time to time while natural
frequency characteristics are unique to each sound field; hence,
natural frequency characteristics do not always emerge in
compartments. Therefore, a microcontroller such as a microcomputer
automatically controls acoustic resonance devices to adjust
resonance frequencies in response to excitation frequencies, thus
effectively reducing noise in a compartment. Herein, the
microcomputer is able to calculate excitation frequency based on
various parameters such as a running speed, an engine speed, an
accelerator opening, and a gear position.
[0168] (11) Eleventh Variation
[0169] Resonance frequencies of acoustic resonance devices do not
need to be fixed to natural frequencies; instead, acoustic
resonance devices reduce sound pressure at natural frequencies by
way of an interaction due to coupled oscillation between the space
arranging an acoustic resonance device and the internal space of
the housing of an acoustic resonance device. In a broad
interpretation, the structure arranging an acoustic resonance
device can be regarded as a secondary resonator connected to the
acoustic resonance device. Owing to coupled oscillation via a
correlation between an acoustic resonance device and a secondary
resonator, sound energy is interchanged between a compartment and
the acoustic resonance device plus the secondary resonator, thus
achieving an additional sound attenuation effect in another
frequency range.
[0170] (12) Twelfth Variation
[0171] The resonance pipe unit 2 consumes sound energy by way of
viscous resistance and friction between the interior wall and air
molecules. Consumption of sound energy increases at the position
undergoing a high particle velocity of a sound wave. For this
reason, it is possible to effectively reduce sound pressure when
the resonance pipe unit 2 is arranged at the position undergoing a
high particle velocity. It is possible to specify the position of a
high particle velocity by way of the measurement testing which
measures a particle velocity in addition to antinodes of sound
pressure.
[0172] (13) Thirteenth Variation
[0173] The foregoing embodiments arrange acoustic resonance devices
to reduce sound pressure at antinodes of a natural vibration; but
it is possible to arrange acoustic resonance devices only for the
purpose of increasing a motion velocity of medium such as particles
(i.e. a particle velocity). Specifically, the motion velocity of
particles is the speed at which particles vibrate.
[0174] At an antinode of sound pressure in the compartment 105
undergoing a natural vibration, sound pressure is maximized while a
particle velocity is minimized. Increasing a particle velocity at
an antinode of sound pressure may vary a natural vibration, thus
improving the quietness/noiselessness in the compartment 105. This
causes resonance in the medium at an antinode of sound pressure in
which sound pressure increases due to a natural vibration; thus, it
is possible to achieve similar effects as the foregoing
embodiments.
[0175] A resonance pipe may suffice the above acoustic resonance
device according to the thirteenth variation. Even though a
standing wave is resided in the hollow space of a resonance pipe in
agreement with a boundary condition in which a particle velocity
becomes zero at the opening of the resonance pipe, the particle
velocity at the opening of the resonance pipe is maximized at a
primary resonance frequency (namely, a minimum resonance
frequency). That is, it is possible to increase the particle
velocity at the opening of a resonance pipe which is identical to
or proximate to an antinode of sound pressure owing to a natural
vibration. When a resonance pipe is used to increase the particle
velocity, it is preferable not to use a flow resistor. Because, a
resonance pipe not using a flow resistor is able to cause a high
particle velocity by way of resonance. Instead of a resonance pipe
(or the resonance pipe unit 2), it is possible to employ the
panel/diaphragm resonator 1 or the Helmholtz resonator 3, wherein a
particle velocity can be increased at the vibrator 15 of the
panel/diaphragm resonator 1 or the opening 33 of the Helmholtz
resonator 3.
[0176] The above structure increasing a particle velocity is merely
one example; hence, it is possible to employ other types of
resonators having a capability of increasing a particle velocity by
way of resonance. In short, the thirteenth variation is designed to
determine the arrangement of resonators to thereby increase a
particle velocity at an antinode of sound pressure owing to a
natural vibration.
[0177] (14) Fourteenth Variation
[0178] Instead of improving quietness/noiselessness around the
front seats 140, it is possible to improve quietness/noiselessness
in a passenger space on the rear seats 190 undergoing an antinode
of sound pressure owing to a natural vibration. In this case,
acoustic resonance devices are arranged to control sound pressure
at antinodes of natural vibration which emerge in proximity to the
back-ceiling portion just above the rear seats 190, the rear doors
150B, and the rear pillars 180. The present invention is not
necessarily limited to the arrangement of acoustic resonance
devices improving quietness/noiselessness in the driver/passenger
space on the front seats 140; hence, it is possible to control
sound pressure at antinodes of natural vibration dependent upon any
spaces of the compartment 105.
[0179] Walls embedding acoustic resonance devices are not
necessarily limited to partitions between the compartment 105 and
the outside of the vehicle 100; hence, it is possible to install
acoustic resonance devices in other walls communicating with the
compartment 105, such as doors and support members.
[0180] The foregoing embodiments focus on antinodes of sound
pressure in a 160 Hz band based on a natural vibration; but it is
possible to focus on other natural frequencies.
[0181] A region of a reduced sound pressure (via resonance of an
acoustic resonance device) and a region of an increased particle
velocity are dependent upon the position of an opening. Those
regions are not necessarily located in the compartment 105 but at
any positions of the vehicle 100.
[0182] As described heretofore, the present invention is not
necessarily limited to the foregoing embodiments and variations,
which can be further modified in various ways within the scope of
the invention as defined in the appended claim.
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