U.S. patent application number 09/167624 was filed with the patent office on 2001-08-16 for acoustic filter apparatus for an electonic device.
This patent application is currently assigned to HEWLETT-PACKARD COMPANY. Invention is credited to HICKMAN, SCOTT N., STERNER, JOHN R..
Application Number | 20010014163 09/167624 |
Document ID | / |
Family ID | 22608117 |
Filed Date | 2001-08-16 |
United States Patent
Application |
20010014163 |
Kind Code |
A1 |
HICKMAN, SCOTT N. ; et
al. |
August 16, 2001 |
ACOUSTIC FILTER APPARATUS FOR AN ELECTONIC DEVICE
Abstract
An apparatus for reducing noise emitted by an electronic or
other device and such devices incorporating the noise reducing
apparatus. A mechanism for acoustically filtering undesired noise
from an electronic device, particularly noise generated by a
cooling mechanism is disclosed. In a preferred embodiment, noise is
filtered at least in part with an appropriately dimensioned
compressible air space. The noise reducing or filtering mechanism
may be utilized with portable and non-portable computers, stereos,
entertainment equipment and other devices.
Inventors: |
HICKMAN, SCOTT N.;
(CORVALLIS, OR) ; STERNER, JOHN R.; (ALBANY,
OR) |
Correspondence
Address: |
HEWLETT PACKARD COMPANY
P O BOX 272400, 3404 E. HARMONY ROAD
INTELLECTUAL PROPERTY ADMINISTRATION
FORT COLLINS
CO
80527-2400
US
|
Assignee: |
HEWLETT-PACKARD COMPANY
|
Family ID: |
22608117 |
Appl. No.: |
09/167624 |
Filed: |
October 6, 1998 |
Current U.S.
Class: |
381/71.5 ;
181/224; 381/71.11; 381/71.8 |
Current CPC
Class: |
G10K 11/161 20130101;
G10K 11/172 20130101 |
Class at
Publication: |
381/71.5 ;
381/71.8; 381/71.11; 181/224 |
International
Class: |
A61F 011/06; G10K
011/16; H03B 029/00 |
Claims
1. An electronic device, comprising: an input device; an output
device; processing circuitry coupled between said input device and
said output device; a function performing mechanism that produces
sound waves of audible noise; and a noise reducing mechanism that
acoustically filters the sound waves produced by said function
performing mechanism to thereby reduce the noise generated by said
function performing mechanism.
2. The apparatus of claim 1, wherein said function performing
mechanism includes an exhaust pathway and said noise reducing
mechanism is at least part of said exhaust pathway.
3. The apparatus of claim 1, wherein said noise reducing mechanism
includes a compressible air chamber.
4. The apparatus of claim 3, wherein said noise reducing mechanism
further includes a duct coupled between said function performing
mechanism and a duct output.
5. The apparatus of claim 2, wherein said noise reducing mechanism
includes a volume that attenuates sound waves of undesired
frequencies.
6. The apparatus of claim 4, wherein said duct is coupled to said
air chamber.
7. The apparatus of claim 5, wherein said volume is approximately
equal to or less than (194645.a/f.sub.0).sup.2/1' mm.sup.3, where a
is the approximate radius of said pathway, f.sub.0 is the
approximate threshold frequency of said undesired frequencies and
1' is the approximate length of said pathway.
8. The apparatus of claim 1, wherein said noise suppression
mechanism suppresses sound waves above at least approximately 400
Hz.
9. The apparatus of claim 1, wherein the function performing
mechanism is a cooling mechanism that cools said processing
circuitry.
10. A cooling apparatus for use with an electronic device,
comprising: a cooling mechanism having an output pathway; and a
noise reducing mechanism coupled to said pathway that acoustically
filters noise caused by said cooling mechanism.
11. The apparatus of claim 10, wherein said noise reducing
mechanism includes a volume that attenuates sound waves of
undesirable frequency.
12. The apparatus of claim 10, wherein said noise reducing
mechanism includes a compressible air chamber.
13. The apparatus of claim 12, wherein said noise reducing
mechanism includes a duct coupled to said air chamber, said chamber
and said duct being arranged so as to attenuate sound waves of
undesirable frequencies.
14. The apparatus of claim 3, wherein said compressible air chamber
has a volume approximately equal to or less than
(194645.a/f.sub.0).sup.2/1' mm.sup.3, where a is the approximate
radius of said pathway, f.sub.0 is the approximate threshold
frequency of said undesired frequencies and 1' is the approximate
length of said pathway.
15. The apparatus of claim 10, wherein said cooling mechanism
includes a fan.
16. The apparatus of claim 10, wherein said noise reducing
mechanism provides low pass acoustic filtration.
17. A noise reducing apparatus for reducing noise generated by a
function performing mechanism of an electronic device, comprising:
an output pathway coupled to a function performing mechanism; and a
noise reducing mechanism coupled to said pathway that acoustically
filters noise generated by said function performing mechanism.
18. The apparatus of claim 17, wherein said function performing
mechanism is a cooling mechanism.
19. The apparatus of claim 17, wherein said noise reducing
mechanism includes a compressible air chamber.
20. The apparatus of claim 19, wherein said noise reducing
mechanism includes a duct coupled to said air chamber, said chamber
and said duct being arranged so as to attenuate sound waves of
undesirable frequencies.
21. The apparatus of claim 20, wherein said undesirable frequency
includes frequencies above approximately 400 Hz.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to noise suppression or
filtering in an electronic device. While applicable to all
electronic devices, the present invention is particularly
applicable to portable electronic devices because of their size and
physical feature constraints.
BACKGROUND OF THE INVENTION
[0002] There has been a continual effort to develop new features
and improve existing features performed by electronic devices. The
features may include, but are not limited to, communication,
document production, information storage and retrieval, navigation,
entertainment, etc. This effort has been at least in part promoted
by advances in integrated circuit technology that have produced
more powerful processing circuitry. As the complexity of integrated
circuits increased, however, the need to adequately cool these
devices also increased. While various approaches have been brought
forth, cooling by electric fan is the most common technique for
integrated circuit and overall electronic device cooling.
[0003] While beneficial as a cooling mechanism, conventional fans
are disadvantageous in that they produce audible noise at
frequencies that are unpleasant to the human ear. While a problem
in desk top environments, such as in a desk top computer, the
problem is more acute in portable electronic devices. One reason
for this is that components are more tightly coupled in a portable
device leading to thermal build up. In addition, due to their
limited size and weight it is generally more difficult to design
new features (such as noise suppression) into a portable
device.
[0004] Hence a need exists for suppressing or reducing noise
generated by the cooling mechanism of an electronic device.
SUMMARY OF THE INVENTION
[0005] Accordingly, it is an object of the present invention to
reduce or filter noise generated by a cooling mechanism of an
electronic device.
[0006] It is another object of the present invention to reduce or
filter noise generated by a cooling mechanism of a portable
electronic device.
[0007] It is another object of the present invention to provide
noise reduction that filters out frequencies that are unpleasant to
a human ear.
[0008] It is also an object of the present invention to create a
mechanism or structure in a cooling mechanism output path that
absorbs, compresses or otherwise attenuates sound waves of
particular frequencies.
[0009] These and related objects of the present invention are
achieved by use of a acoustic filter apparatus of an electronic
device as described herein.
[0010] The attainment of the foregoing and related advantages and
features of the invention should be more readily apparent to those
skilled in the art, after review of the following more detailed
description of the invention taken together with the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a perspective view of an electronic device having
noise suppression in accordance with the present invention.
[0012] FIG. 2 is a partial perspective view of an electronic device
cooling system in accordance with the present invention.
[0013] FIG. 3 is a graph of sound power level (SPL) versus
frequency.
[0014] FIG. 4 is a side view of the cooling system and other
componentry of FIG. 2 in accordance with the present invention.
[0015] FIG. 5 is an equivalence acoustic circuit diagram for the
configuration of FIGS. 2 and 4 in accordance with the present
invention.
[0016] FIG. 6 is a diagram illustrating the parameters M.sub.A and
C.sub.A for the embodiment of FIGS. 2 and 4 in accordance with the
present invention.
[0017] FIG. 7A is a perspective view of an alternative embodiment
of a cooling system noise suppression mechanism in accordance with
the present invention.
[0018] FIG. 7B illustrates a perspective cross-sectional view of
the compressible air chamber of FIG. 7A in accordance with the
present invention.
DETAILED DESCRIPTION
[0019] Referring to FIG. 1, a perspective view of an electronic
device having noise suppression in accordance with the present
invention is shown. As illustrated in FIG. 1, the electronic device
is a portable computer, such as a notebook computer. This
embodiment, however, is a representative embodiment and it should
be recognized that the present invention is applicable to any
electronic device, including audio receivers, amplifier units,
etc., in which it is desired to reduce noise.
[0020] Electronic device 10 preferably includes a display 12 and
may include speakers 14 or other output devices including, but not
limited to, an information panel or the like (with or without light
emitting diodes, etc.) for an audio receiver or related devices.
Electronic device 10 also preferably includes a keypad 16 and a
pointing mechanism 18 (e.g., a touch pad, track ball, mouse, joy
stick, etc., for a computer implementation) or other input devices.
Processing circuitry 22 and memory 24 are shown in phantom lines as
is cooling system 30 which is discussed in more detailed below. The
exhaust of cooling mechanism 30 exits the electronic device through
exhaust openings 51.
[0021] Referring to FIG. 2, a partial perspective view of an
electronic device cooling system in accordance with the present
invention is shown. Cooling system 30 preferably includes a cooling
mechanism 32 and a noise suppression mechanism or structure 40
(hereinafter referred to as open "noise reduction mechanism 40")
that suppresses or reduces noise created by the cooling mechanism
preferably by acoustic filtering. In a preferred embodiment, the
cooling mechanism is an electric fan of the type known in the art
for cooling electronic devices and components therein. As such,
cooling mechanism 32 is also referred to herein as fan 32 (though
the cooling mechanism may be other than a fan without deviating
from the present invention).
[0022] Fan 32 is preferably coupled to a heat sink 34. A circuit
board 25 with a heat producing integrated circuit such as
processing circuitry 22 is positioned proximate heat sink 34. Arrow
A indicates that the circuit board and processing logic are
preferably positioned underneath the heat sink (from the
perspective of FIG. 2). Heat sink 34 is preferably formed of an
inexpensive, lightweight material that has good thermal conductive
properties. Die cast aluminum is an example of such a material.
[0023] Fan 32 has an input 31 and a plurality of output openings 33
which are coupled via ducts to exhaust openings 51. The ducts 36
are preferably separated by dividers 38 and their top surface (not
shown in FIG. 2) may be provided by the housing of electronic
device 10 as shown in FIG. 4. While dividers and a plurality of
openings 51 are shown, it should be recognized that a singular duct
and opening 51 or other arrangements could be provided.
[0024] An attenuation orifice 41 is provided in each duct for the
purpose of connecting the duct to a compressible air chamber or
volume 45 (shown in FIGS. 4 and 6). The arrangement of the
attenuation orifice and compressible air chamber serves to
dissipate or attenuate noise at undesirable frequencies. Suitable
dimensions for the ducts and the compressible air chamber to
achieve a desired noise suppression are discussed below.
[0025] Referring to FIG. 3, a graph of sound power level (SPL)
versus frequency is shown. Studies of the human ear have shown that
the range of human hearing is approximately from 20 Hz to 18 KHz.
Studies have further shown that humans are less sensitive to
frequencies from 20 to 350 Hz than from 350 Hz to 18 KHz. Thus, if
a low pass acoustic filter can be established for the fan or other
cooling mechanism of an electronic device, than that device will
produce significantly less objectionable noise.
[0026] Equations related to designing for noise suppression include
the following. Equation no. 1 indicates that the cutoff frequency
of such a low pass filter is inversely proportional to the square
root of M.sub.A times C.sub.A, where M.sub.A is the acoustic mass
and C.sub.A is the acoustic compliance as defined by Leo L. Beranek
in his book entitled "Acoustics" published by the Acoustic Society
of America (1954,1993). The American Institute of Physics has
accepted Beranek's work as a standard in the acoustics field.
Equation no. 1 provides:
f.sub.0=1/(90 (M.sub.AC.sub.A).sup.1/2) Eq. 1
[0027] where
M.sub.A=(.rho..sub.01)/(.pi.a.sup.2); Eq. 2
C.sub.A=V/(.rho..sub.0C.sup.2); Eq. 3
[0028] and
1=1'+2(0.85a). Eq. 4
[0029] In these equations, .rho..sub.0 and C are physical constants
having the following values:
.rho..sub.0=1.18 Kg/m3 (density of air); Eq. 5
[0030] and
C=345,000 mm/s (speed of sound). Eq. 6
[0031] The design parameters of cooling system 30 (i.e. for noise
suppression mechanism 40) include 1'=length of the exhaust ducts,
1=effective length of duct corrected for air loading of flanged
opening, a=equivalent radius of the exhaust ducts (a
cross-sectional area indicator) and V=volume of the compressible
air chamber.
[0032] Combining equations 1-6 provides that the cutoff frequency,
f.sub.0, is equal to
194645 (a/(1'V).sup.1/2. Eq. 7
[0033] Assuming that the four ducts 36 of the embodiment of FIGS. 2
and 4 have a cross-sectional area of 100 mm.sup.2, then the
equivalent radius for this area if it were circular is
r=(.pi..100).sup.1/2 or 5.6 mm. The length of the ducts may be
established at 25 mm, thus causing 1' to have a value of 25 mm. If
the desired cutoff frequency is set at 316 Hz (e.g., below a 350 Hz
limit), then substituting the values of a and 1' into Eq. 6
provides a compressible air chamber volume of 4.times.10.sup.5 mm.
This volume may be achieved, for example, in a chamber that is 10
mm.times.200 mm.times.200 mm and a great number of other
configurations, including those that are not uniformly dimensioned.
Implementation of such a volume in the cooling system discussed
with reference to FIG. 2 is now presented.
[0034] Referring to FIG. 4, a side view of the cooling system and
other componentry of FIG. 2 in accordance with the present
invention is shown. Fan 32 is provided on or proximate a heat sink
34 and processing circuitry 22 is coupled by a thermal joiner 42 to
heat sink 34. Thermal joiner 42 is provided for efficient
conduction of heat away from processing circuitry 22 to the heat
sink. A plurality of inlet openings 54 are provided in housing
cover 53 (not shown in FIG. 2) that is coupled to or formed
integrally with the remainder of the housing 52. One of the
attenuation orifices 41 is shown connecting a duct 36 to the
compressible air chamber or volume 45. Volume 45 may have the
dimensions of 10 mm in height, 200 mm in width and 200 mm in depth
(into the page) to achieve a cutoff frequency (in combination with
the duct length and cross-sectional area discussed above) of 316
Hz.
[0035] While volume 45 of FIG. 4 has generally uniform dimensions,
it should be recognized that these uniform dimensions are provided
in part because they permit easier mathematical analysis than
non-uniform dimensions. Nonetheless, the present invention may be
implemented with curved, round, punctuated and other non-uniform
shapes. Furthermore, the volume may be established from otherwise
unused air space in the electronic device. As such it is possible
that the volume may contain components including other circuitry
therein. Accordingly, a representative circuit board 61 with a
component 62 provided thereon is shown in FIG. 4. It should be
recognized that while the equations provided herein are helpful in
cooling system design (particularly from a mathematical or
theoretical perspective), the ultimate selection of component
layout and dimensions is preferably established empirically.
[0036] Referring to FIG. 5, an equivalence acoustic circuit diagram
for the configuration of FIGS. 2 and 4 in accordance with the
present invention is shown. The term C.sub.A refers to the
compressible air space while the M.sub.A terms refers to the duct
sections before and after the attenuation orifice(s). This
equivalence circuit and others like it can be implemented such that
the compressible air chamber is accessed by penetrating the heat
sink (as shown in FIG. 4) or such that the compressible air chamber
is coupled to the output duct(s) other than through the heat sink,
i.e., coupled to the top of the duct(s) or provided around the
duct(s) as in FIG. 7 below.
[0037] Referring to FIG. 6, a diagram illustrating the parameters
M.sub.A and C.sub.A in accordance with the present invention is
shown.
[0038] Referring to FIG. 7A, a perspective view of an alternative
embodiment of a cooling system noise suppression mechanism in
accordance with the present invention is shown. FIG. 7A illustrates
one wall of an electronic device housing 152 having a cooling
system coupled thereto. Illustrated components include a fan or
other cooling mechanism 132, a heat sink 134 and processing logic
122. Processing logic 122, heat sink 134 and fan 132 function in
substantially the same manner as components 22, 34 and 32 discussed
above. In the cooling system of FIG. 7A, however, the compressible
air chamber 145 is configured as a hollow disk or the like that is
placed around the fan exhaust duct. Attenuation orifice(s) 141
preferably couples duct 136 to the interior of chamber 145.
[0039] FIG. 7B illustrates a perspective cross-sectional view of
compressible air chamber 145 in accordance with the present
invention.
[0040] While the invention has been described in connection with
specific embodiments thereof, it will be understood that it is
capable of further modification, and this application is intended
to cover any variations, uses, or adaptations of the invention
following, in general, the principles of the invention and
including such departures from the present disclosure as come
within known or customary practice in the art to which the
invention pertains and as may be applied to the essential features
hereinbefore set forth, and as fall within the scope of the
invention and the limits of the appended claims.
* * * * *