U.S. patent application number 10/529013 was filed with the patent office on 2005-10-13 for parametric ring emitter.
Invention is credited to Croft, James J., Norris, Elwood G..
Application Number | 20050226438 10/529013 |
Document ID | / |
Family ID | 28452331 |
Filed Date | 2005-10-13 |
United States Patent
Application |
20050226438 |
Kind Code |
A1 |
Norris, Elwood G. ; et
al. |
October 13, 2005 |
Parametric ring emitter
Abstract
A sound emitting device (10) for providing at least one new
sonic or subsonic frequency as a by-product of emitting a waveform
of at least two ultrasonic frequencies whose difference in value
corresponds to the desired new sonic or subsonic frequency. The
device includes a parametric emitting perimeter or plurality of
emitter segments (13) positioned around a central open section
(15). This open section (15) is structured with a diagonal width
greater than a cross-sectional diagonal of the parametric emitting
perimeter. An ultrasonic frequency source (60) and sonic/subsonic
frequency generator (62) arc coupled together to a modulating
circuit (61) for mixing an ultrasonic frequency signal with an
electrical signal corresponding to the at least one new sonic or
subsonic frequency. The modulator output is coupled to the emitting
perimeter (64) which comprises ultrasonic frequency emitting
material for propagating the mixed waveform into air for
demodulating the waveform to generate the at least one new sonic or
subsonic frequency.
Inventors: |
Norris, Elwood G.; (Poway,
CA) ; Croft, James J.; (Poway, CA) |
Correspondence
Address: |
Vaughn W North
Thorpe North & Western
P O Box 1219
Sandy
UT
84091-1219
US
|
Family ID: |
28452331 |
Appl. No.: |
10/529013 |
Filed: |
September 17, 2004 |
PCT Filed: |
March 18, 2003 |
PCT NO: |
PCT/US03/08311 |
Current U.S.
Class: |
381/77 ;
381/75 |
Current CPC
Class: |
H04R 2217/03 20130101;
F41H 13/0081 20130101; H04B 3/56 20130101; H04R 27/04 20130101;
G10K 15/02 20130101; H04R 27/00 20130101 |
Class at
Publication: |
381/077 ;
381/075 |
International
Class: |
H04B 003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 18, 2002 |
US |
10/101426 |
Claims
I claim:
1. A parametric speaker sound emitting device for providing at
least one new sonic frequency as a by-product of emitting at least
two ultrasonic frequencies from an ultrasonic frequency emitter,
comprising: an emitting perimeter of ultrasonic emitting material
having an outer radius and an inner radius respectively surrounding
an interior open space, wherein a ratio of (i) a difference between
the inner radius and the outer radius of the emitting perimeter to
(ii) the outer radius of the emitting perimeter is within a
numerical range of 0.1 to 1.0.
2. A device as defined in claim 1, wherein the ratio is within the
numerical range of 0.2 to 0.4
3. A device as defined in claim 1, wherein the emitting perimeter
comprises a substantially continuous ring of emitter material.
4. A device as defined in claim 1, wherein the emitting perimeter
comprises segments of emitter material.
5. A device as defined in claim 1, wherein the emitting perimeter
comprises an array of piezoelectric emitters forming at least one
ring of emitting material around the open space.
6. A device as defined in claim 1, wherein the emitting perimeter
comprises at least one electrostatic membrane.
7. A device as defined in claim 1, wherein the emitting perimeter
includes piezoelectric film material.
8. A device as defined in claim 1, wherein the emitting perimeter
comprises separated emitter elements which are displaced from
adjacent emitter elements along a length of the emitting perimeter,
thereby spacing the emitter elements with gaps wherein no
ultrasonic emissions are occurring.
9. A device as defined in claim 8, wherein the gaps are within a
range of 0.2 to 2.0 cm.
10. A device as defined in claim 9, wherein the gaps are within the
range of 0.5 to 1.5 cm.
11. A sound emitting device for providing at least one new sonic
frequency as a by-product of emitting at least two ultrasonic
frequencies from an ultrasonic frequency emitter, said device
comprised of: a plurality of ultrasonic emitting perimeter segments
coupled together at adjacent edges and positioned around a central
open section, said emitting perimeter having a directional
orientation along a transmission axis; an ultrasonic frequency
signal source for generating a first ultrasonic signal; a sonic or
subsonic frequency generator for supplying an electrical signal
corresponding to the at least one new sonic or subsonic frequency;
modulating means coupled to the ultrasonic frequency signal source
and sonic or subsonic frequency generator for mixing the first
ultrasonic frequency signal with the electrical signal
corresponding to the at least one new sonic frequency to thereby
generate a waveform including the first ultrasonic frequency signal
and a second ultrasonic frequency signal; said emitting perimeter
comprising ultrasonic frequency emitting material coupled to an
output of the modulating means for (i) propagating a waveform
embodying both the first and second ultrasonic frequency signals,
and (ii) generating the at least one new sonic frequency as a
by-product of interaction between the first and second ultrasonic
frequency signals.
12. A device as defined in claim 11, wherein at least one of the
segments can be decoupled from its adjacent segment and wherein the
plurality of segments can be collapsed together to a smaller volume
for storage.
13. A device as defined in claim 13, wherein the plurality of
segments comprise rectangular shapes having one edge which includes
a hinge member for coupling to a hinge member of an adjacent
segment, said open section forming a rectangular opening.
14. A device as defined in claim 12, wherein the smaller volume of
the plurality of segments forms a box shape providing a convenient
storage configuration.
15. A method for enhancing efficiency of a parametric speaker sound
emitting device for providing at least one new sonic frequency as a
by-product of emitting at least two ultrasonic frequencies from an
ultrasonic frequency emitter with respect to energy output based
upon emitter surface area, said method comprising the steps of: a)
forming an ultrasonic frequency emitting perimeter around an open
region which is substantially void of ultrasonic emitting material;
and b) emitting ultrasonic frequency from the emitting perimeter to
generate sonic or subsonic sound within surrounding air as part of
a parametric speaker system.
16. A method as defined in claim 15, further comprising the step of
forming the emitter material with individual emitter elements
positioned along the emitting perimeter and spacing the emitter
elements at separated distances from adjacent emitter elements,
thereby avoiding closed configuration of the emitter elements and
reducing power losses resulting from shock effect of localized
emitter energy at an air interface with the emitter elements.
Description
[0001] This is a continuation-in-part application of copending
application Ser. No. 09/135,732 filed Aug. 18, 1998, entitled
Parametric Ring Emitter (U.S. Pat. No. 6,359,990) and Ser. No.
08/846,637, entitled "Light Enhanced Bullhom", filed Apr. 30, 1997
(U.S. Pat. No. 5,859,915).
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This invention pertains to parametric sound projection
devices which incorporate acoustic heterodyning as basis for
generating audio output. More particularly, the present invention
relates to a device and method for enhancing a directional
parametric speaker power output.
[0004] 2. State of the art
[0005] Recent developments have been made involving sound
propagation from parametric speakers, acoustic heterodyning, and
other forms of modulation of multiple ultrasonic frequencies to
generate a new frequency. In theory, sound is developed by the
interaction in air (as a nonlinear medium) of two ultrasonic
frequencies whose difference in value falls within the audio range
or subsonic range. The resulting compression waves are projected
within the air as a nonlinear medium. The present inventor has
succeeded in advancing parametric audio devices from a state of
curious research to commercially acceptable speaker systems which
offer unique advantages over all other forms of audio devices.
Applications are now expanding to general audio systems for home,
office and automobile, military communications systems, weapons
devices, point of purchase advertising sources and numerous other
specialty devices.
[0006] A brief explanation of the theoretical parametric speaker
array is provided in "Audio spotlight: An application of nonlinear
interaction of sound waves to a new type of loudspeaker design" by
Yoneyama et al as published in the Journal of Acoustic Society of
America, 73(5), May 1983. Although technical components and the
theory of sound generation from a difference signal between two
interfering ultrasonic frequencies is described, the practical
realization of a commercial sound system was apparently
unsuccessful. This weakness in the prior art remained despite the
assembly of a parametric speaker array consisting of as many as 547
piezoelectric transducers yielding a speaker diameter of 40-50 cm.
Virtually all prior research in the field of parametric sound has
been based on the use of tightly clustered conventional ultrasonic
transducers, typically of bimorph character.
[0007] A common structural feature of prior art attempts to develop
an effective parametric speaker is to form a substantially
continuous array of transducers across the surface of a support
plate. The natural assumption appears to be that filling in the
interior area of the support plate with the maximum number of
transducers is appropriate to maximize sound pressure level (SPL).
Conventional speaker theory would suggest that increasing the
number of transducers would indeed contribute to increased SPL.
Accordingly, prior art parametric speakers are typically
illustrated with bimorf transducers compactly positioned in
honeycomb array. Until demonstration of the parametric ring concept
as set forth in the parent patent applications, a general
perception has existed that an increase in emitter surface was a
primary factor for increasing SPL of a parametric emitter
device.
[0008] Although not related to parametric audio production as
presented in this application, a prior examination in the US Patent
and Trademark Office of a parent application of the present
invention discussed U.S. Pat. No. 4,418,248 by Mathis. The Mathis
patent illustrates (patent FIGS. 1, 2 and 3) stereophones which are
designed for operation in the audio spectrum. The inner radius 13
comprises a diaphragm which is designed to operate at audio
frequencies greater than 1000 Hz. This frequency range corresponds
to the upper audio frequency band. A second transducer comprising
diaphragm 25 covers the lower frequency range of the audio
spectrum. See column 3, lines 13 through 17. The outer radius 33
simply comprises ports which pass the lower frequency range audio
vibrations within the stereo headphone. Accordingly, both the inner
and outer radii are merely transmitting audio sounds in a
conventional manner to enhance both upper and lower audio
bandwidth.
[0009] In contrast, a parametric speaker projects ultrasonic
emissions which are decoupled within the air for audio output. The
principles of operation between conventional audio speakers as
represented by Mathis and the present invention which involves a
parametric speaker are very unrelated. It is important to
distinguish between (i) conventional audio speakers that directly
propagate audio sound by vibration of a diaphragm at a
corresponding audio frequency range and (ii) parametric speakers
which vibrate a diaphragm at ultrasonic frequencies of 25 Khz or
greater and demodulate the ultrasonic output in air to indirectly
produce audio output. It will be apparent to those skilled in the
art that a ring of emitters producing audio output directly into
the air such as Mathis will not correspond to a ring of ultrasonic
emitters whose output is pumped into the air, which then operates
to decouple an audio sideband frequency as audio output. In the
former case, the audio speaker operates as a two-dimensional or
point source of origination of the sound. In the later parametric
embodiment, the audio sound source is similar to a
three-dimensional column of air molecules which project out like a
beam of light from the ultrasonic emitter. In essence, this column
of air becomes the vibrating speaker element. Accordingly, prior
art versions of audio speaker rings would not be relevant to the
dynamics involved in a parametric ring emitter.
SUMMARY OF THE INVENTION
[0010] These and other objects are realized in a parametric speaker
device for providing at least one new sonic frequency as a
by-product of emitting at least two ultrasonic frequencies from an
ultrasonic frequency emitter. The device includes an emitting
perimeter of ultrasonic emitting material having an outer radius
and an inner radius respectively surrounding an interior open
space. The ratio of (i) the difference between the inner radius and
the outer radius of the emitting perimeter to (ii) the outer radius
of the emitting perimeter is approximately within a numerical range
of 0.1 to 1.0.
[0011] The invention is also represented by a method for enhancing
efficiency of a parametric speaker system with respect to energy
output based upon emitter surface area, comprising the steps of a)
forming an ultrasonic frequency emitting perimeter on a support
base around an open region which is substantially void of
ultrasonic emitting material; and b) emitting ultrasonic frequency
from the emitting perimeter to generate sonic or subsonic sound
within surrounding air as part of a parametric speaker system.
[0012] Other objects, features and benefits will be apparent to
those skilled in the art, based on the following detailed
description, in combination with the accompanying drawings.
DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 illustrates a perspective view of a bullhorn device
incorporating a circular parametric emitting perimeter.
[0014] FIG. 2 depicts perspective view of a rectangular emitting
perimeter utilizing PVDF emitting film.
[0015] FIG. 3 graphically illustrates an additional embodiment of
the present invention incorporating an array of emitter strips to
form a polygon configuration.
[0016] FIG. 4 shows a cross section of the array of FIG. 3, taken
along the lines 4-4.
[0017] FIG. 5 shows a annular disk with a spaced array of emitter
elements in two rings.
[0018] FIG. 6 illustrates a block diagram of typical circuitry
associated with a parametric speaker.
[0019] FIG. 7 graphically depicts an array of four speaker segments
joined to enclose a square opening in accordance with the present
invention.
[0020] FIG. 8 illustrates the array of segments of FIG. 7 uncoupled
at one junction to form a linear array.
[0021] FIG. 9 shows the linear array of FIG. 8 folded or collapsed
to a storage configuration.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0022] FIG. 1 illustrates one embodiment of a parametric speaker
system useful for sound propagation. It will be apparent that this
specific structure is intended to represent many different types of
projection devices such as general speakers, stereo systems, PA
systems, megaphones, etc., particularly where a direction
orientation in a narrow beam is desired.
[0023] This basic system comprises a sound emitting device 10 for
providing at least one new sonic or subsonic frequency as a
by-product of emitting at least two ultrasonic frequencies from an
ultrasonic frequency emitter 11. This is in accordance with the
general principles of acoustic heterodyning as referenced above. A
support plate 12 forms a base or housing for supporting an audio
emitting perimeter 13 of ultrasonic frequency emitting material 14.
The support plate may be comprised of virtually any material which
operates to stabilize the emitter 11 in its desired perimeter
configuration. Plastics, metals, dielectrics, ceramics and woods
are illustrative of this broad choice of compositions. FIG. 1 shows
a bullhorn application with a handle 16, circuitry housing 17 with
control pad 18, and a support housing 19 for supporting the support
plate with emitting perimeter.
[0024] The emitter material 14 comprises bimorf transducers of
conventional design and is configured for attachment to the support
plate around a central open section 15 which is at least partially
bounded by the emitter material. The significance of developing a
parametric speaker having the emitting perimeter format arises from
the ability of the parametric speaker to supply unusually efficient
sound output, despite the use of emitter material only at the
perimeter. This unique feature of parametric speakers enables a
perimeter emitter to provide comparable audio output to a fully
embodied emitter array with emitter material extending across the
full area of the support plate. Because the perimeter configuration
has a substantially reduced number of ultrasonic transducers or
emitter surface area, less drive voltage is required and enhanced
efficiency results.
[0025] Various forms of emitter devices may be used in this
perimeter configuration. Traditionally, parametric speakers have
utilized bimorf transducers. The present inventor has developed
effective parametric output with polyvinyl? PVDF film, as well as
electrostatic emitter structures. The selection of material will be
a function of desired shape of the support plate, as well as the
type of audio range desired. For example, FIG. 2 illustrates a
midrange speaker using piezoelectric or PVDF film 20, a substrate
21 for supporting the film in suspended state above a cavity 22,
and a voltage source with attendant audio signal 23. The
rectangular configuration is suitable for a film-type emitter
because the film can be placed in tension across the opposing sides
or diametric edges 24 to provide proper tension in the film. For
determining roll off parameters for low range frequencies, the
diameter of the speaker is measured along the horizontal axis 25 or
vertical axis 26. Normally, the longer diameter (in this example,
25) will control.
[0026] The central section 27 is an open portion in the substrate
21 and emitter 20. The horizontal diameter 28 of the opening is
approximately twice the distance 30 across a cross-section of the
emitting perimeter. This forms a ratio of 0.5 for this orientation.
The vertical opening spans a distance 29 which is {fraction
(5/4)}ths the distance 30, equivalent to a ratio of approximately
0.4, a more preferred ratio based on empirical results.
[0027] FIGS. 3 and 4 illustrate a hexagon shape, representative of
a general polygon configuration. In this example, electrostatic
emitters 32 are supported on a stator substrate 33 over a cavity
34, and are arranged along the respective straight diametric edges
35 of the polygon. Each stator 33 is powered in parallel from a
driver 36 which is coupled to an audio signal source (not shown).
This embodiment is representative of electrostatic speakers
generally, and may include a separate biasing circuit 38, as well
as electret materials which can be pre-charged to a desired
condition. It will be apparent that virtually any speaker shape can
be implemented by segmenting the emitter perimeter into a
combination of straight segments and/or curves, and by positioning
these in end-to-end orientation to circumscribe an open, central
region 40. Such shapes need not be symmetrical, but may be of
virtually any shape. This flexibility enables the present invention
to conform to unusual room shapes and positioning requirements for
speaker use. An advantage of the FIG. 3 embodiment is that this
configuration can be folded for compact storage by providing hinge
connections 42 between the respective segments (represented by 33
and 35). By releasing one or more of the hinged connections, the
remaining segments can be folded upon each other.
[0028] FIGS. 7, 8 and 9, for example, demonstrates that a
four-square speaker array 43 can be folded to a collapsed volume of
{fraction (4/7)}ths of the total volume of the ring configuration
of FIG. 7. Hinge members 42a, b, c, and d provide attachment of the
four emitter segments 45a, b, c, and d to form a rectangular
configuration of the speaker system, surrounding an open section
46. By detaching segment 45a from segment 45d, the segments can be
configured in a linear array for storage on a low-height shelf.
FIG. 9 suggests that the linear array can be reconfigured to a
square shape by collapsing the base portions of 45a and 45b against
the base portions of 45c and d respectively. Dashed line 47 of FIG.
7 represents the spacial volume of the array based on diagonal
edges extending from corner to corner of the circumscribing speaker
segments. Based on this volume, the volumes of FIGS. 8 and 9 are
{fraction (4/7)}ths that of FIG. 7. If the rectangular volume
represented by dashed line 48 is used as a reference, the volumes
of FIGS. 8 and 9 are only half that of FIG. 7. Such flexibility is
particularly useful for minimizing the volume of these speaker
elements during shipping and storage. Other prior art speaker
systems generally remain constant in the volume requirements for
use and storage.
[0029] FIG. 5 shows a circular ring 50 with an array of bimorf
transducers 52 disposed in a double ring format. This is in direct
contrast to conventional practice which would dictate that the
internal region 53 be filled with transducers to maximize the audio
output. The amount of open space in this embodiment has been
configured with a ratio of 0.3, based on the relationship of the
difference between the outer radius r.sub.o and the inner radius
r.sub.i. This is represented by the expression
(r.sub.o-r.sub.i)/r.sub.o. Hereagain, it will be apparent that
various numbers of rings could be selected, as well as differing
ratios as desired.
[0030] The open sections 27, 40, and 53 have primary significance
in the present invention with respect to parametric speaker
systems. As mentioned above, prior art attempts to develop a
commercial parametric speaker have been frustrated by low SPL and
nominal performance, particularly at low frequencies. Prior art
solutions to these deficiencies have involved maximizing the amount
of emitter surface area by packing transducers into a tight cluster
or honeycomb configuration. It was believed that by increasing the
surface area of radiating speakers, increased air movement would
supply a corresponding increase in SPL output. This is consistent
with conventional speaker design characteristics for both dynamic
and electrostatic speaker systems.
[0031] The unexpected phenomenon of the present invention as
represented recognizes that ultrasonic emitting elements within a
perimeter of the parametric speaker can be removed without
seriously affecting the SPL and operation of the speaker device.
Indeed, some fringe distortion around the primary frequency and
transmission axis appears to be reduced with the elimination of
internal emitter devices. Air molecules contained within the b earn
o r column of air appear to be energized, even though the only
source of ultrasonic radiation is a virtual circumscribing tubular
perimeter of energy. The process of filling the integral region on
the support plate with additional ultrasonic emitter material does
not appear to offer a proportional increase in SPL. Therefore, the
efficiency of the parametric speaker is enhanced by use of a
perimeter emitter configuration, as opposed to a continuous
emitting surface.
[0032] Another possible explanation for the surprising efficiency
of the parametric ring configuration of the present invention
relates to the shock limit of air with respect to acoustic loading.
When intense energy levels are localized at the interface of air
with the transducer, air may be driven to its limit of response.
When this limit is reached, a shock effect occurs, leading to
distortion of the acoustic output, as well as energy losses. With
prior art use of bimorf transducers in parametric speakers, the
practice was to concentrate the transducers in tight clusters in
hopes of reaching acceptable commercial levels of sound
reproduction. It is possible that such strategies were counter
productive because the intense localized energy near the
transducers exceeded the shock limit of the air, thereby wasting
acoustic energy. The use of the parametric ring configuration
avoids such intense loading of the air by opening the center of the
speaker array. As a consequence, the open ring system generates SPL
which approaches that of a fully driven plate of transducers
typified by the prior art, yet with fewer transducers and less
required power input.
[0033] Based on empirical studies, maximum efficiency is realized
with a bimorf array as shown in FIG. 5, wherein the emitting
perimeter has an outer radius r.sub.o and an inner radius r.sub.i
which falls within the ratio of (r.sub.o-r.sub.i) /r.sub.o having a
value within the numerical range of 0.1 to less than 1.0. The
preferred efficiency of 0.3 is produced with a preferred range of
0.2 to 0.4. Other emitter configurations and materials will likely
vary from these exemplary ranges for the disclosed bimorf array. In
general terms, the present invention is characterized in part by
the ratio of (i) a difference between the inner radius and the
outer radius of the emitting perimeter, to (ii) the outer radius of
the emitting perimeter being within a numerical range of 0.1 to
1.0, or within a more preferred numerical range of 0.2 to 0.4.
[0034] In view of the foregoing relationships, it is apparent that
the direction of propagation is a function of both the ring
diameter and the space configuration of the internal region. A
planar relationship for the emitter materials offers the most
efficient system for several reasons. First, this planar
configuration requires the least number of emitters to circumscribe
the maximum area. Secondly, the planar relationship maximizes the
in-phase relationship between each emitter. This is significant, in
order to reduce SPL loss from phase cancellation.
[0035] FIG. 5 also illustrates an additional feature of the present
invention wherein the bimorf emitters are spaced from each other to
provide a surrounding separation distance from adjacent emitters.
Such a concept of spaced positioning appears to offer further
economy by reducing the amount of emitter surface within defined
rings of specific diameters. In other words, by reducing emitter
material with the specific ring configuration, a further reduction
in cost is achieved, yet proportional reductions in SPL do not
occur. These open segments 55 can be empirically adjusted to
optimize the parametric output, while maintaining the desired
radial or diametric relationships mentioned above. Generally, the
gaps formed by this displacement will range from 0.5 to 2.0 cm, and
more preferably, from 0.2 to 1.5 cm. This concept is developed
further in a continuation in part application to be filed by the
present inventor.
[0036] A description of the remaining speaker components will
briefly identify operating elements generally necessary to drive a
parametric speaker as shown in FIG. 6. An ultrasonic frequency
signal source 60 is coupled to a modulating device 61 for providing
a first ultrasonic frequency signal. Typically, this frequency is
considered the carrier signal and will operate at a specific value
within the ultrasonic range from 40 Khz to approximately 80 Khz.
Actual frequency value, however, will be a function of desired
operation parameters. For example, higher frequencies will be
absorbed in air more rapidly than lower frequencies. Therefore, the
desirable energy of higher frequencies is mitigated by loss of
active interference or interaction along the ultrasonic beam. Lower
frequencies will extend the length of the ultrasonic radiation,
thereby extending the length of active interference or interaction
which converts the ultrasonic energy to indirect audio output.
[0037] A sonic or subsonic frequency generator 62 is provided for
supplying an electrical signal corresponding to the new sonic or
subsonic frequency. This may be music, audio of general form, or
even subsonic radiation. This sonic or subsonic source is mixed
with the carrier signal in a modulating device such as a
conventional AM modulator 61. A modified waveform having the first
ultrasonic frequency as a carrier with single or double sidebands
as the second ultrasonic frequencies is thereby provided to a power
amplifier 63, and is directed to the emitter ring 64. Parametric
output is developed in accordance with principles as described
above.
[0038] It will be apparent to those of ordinary skill in the art
that the foregoing example are merely exemplary of the inventive
principles disclosed herein. Accordingly, these specific
embodiments are not to be considered limiting, except as defined in
the following claims.
* * * * *