CA1307579C

CA1307579C - Method and apparatus for reducing acoustical distortion

Info

Publication number: CA1307579C
Application number: CA000551676A
Authority: CA
Inventors: Gary L. Ward
Original assignee: Epic Corp
Current assignee: Epic Corp
Priority date: 1986-11-13
Filing date: 1987-11-12
Publication date: 1992-09-15
Anticipated expiration: 2009-09-15
Also published as: US4811402A; AU1087288A; WO1988003740A1

Abstract

Abstract A method and apparatus for reducing distortion of an acoustical waveform by locating a plurality of microspheres to interact with interfering acoustical waveforms are described.

Description

- 1 30757q METHOD A~D APP~RATVS FOR R~:DUCING
ACOUSTICA~ DISTORTION
Field Of The Invention This inve~tion relates to a method and apparatus 05 ~or reduc~ng acoustical distor~ion of the output of an electro-acoustic~l transducer.

Background All electro-acoustic transducers provide some degree of und~sired change in acoustical waveform, i.e.
distortion. Distortion is common~y divided into three types, i.e. frequency distortion, amplitude di~tor~ion (harmonic distortion~ and phase distortion. Harmonic and phase distortion are particularly troublesome when the output acoustical transducer is located in a con-fined space or cavity, for example, in a hearing aid, sound head set or telephone receiver. Often the cavity has a "tuned" frequency and the materials in the cavity have resonant frequencies which, when coupled with the waveform from the transducer, result in paaks or spikes in the waveform correspondiny to harmonic fre~u~ncies ` of the waveform, i.e. harmonic distortion. Addi-tionally, phase shifts in the waveorm can occur which produce distortion and also result in harmonic distor~
tion where the resonant peaks persist for a period of tlme after the desired pulse. ~hese effects can be heard by the listener as an annoyin~ ringing.
With amplified hearlng devices, such as hearing aids, the input slgnal is amplified so that the wearer of the aid receiveæ an amplified signal which should correspond to the waveform of the input signal~
However, noise and othex extraneous signals are al50 amplified which create a problem of clarity and make it difficult for the wearer of the aid to "focus" on the desired sound. It has recently been found that much of the difficulty associated with focusing is due to the 3~ ' 1 30757q presence of harmonic distorti~n in the amplified sig-nal. Minimizing harmonic and phase dlstor~ions provide much greater cl~rity in the amplified sound and allow the listener using the ampli~ioation device to more 0~ readily ~ocus on the desired sounds.
Feedback to the input transducer can also be a probiem with devices such as hearing aids in which the input transducer is located in close proximity to the output transducer. The amplification of such ~eedback : 10 or resonance waves can result in "ring~ng" which can be unpleasant to the wearer of ths hearing aid. Addi-tionally, ln the real world, the amount of usable gain available wlth a hearing aid varies depending upon the complexity of the signal being amp~ified. H. C.
Schweitzer, Hearin~ Instruments, Yolume 37, Nos. 1 and 2, 1986. Consequently, distortion can result in a lower output of the hearing aid and, therefore, a lower usable gain available for amplification.
To date, efforts to remedy the problems associated with lack of clarity and distortion in amplified sig-nals have primarily focused on modifications in the electronic csmponents and in physical placemen~ of such components. The effect that materials of construction might have were considerad in the past but wer~ not ~ound to be significant. It has been reported that:
"Ear mold material was once considered a factor in the acoustic performance [of~ ear molds. Excspt for the way in which the material might in1uence the tightness of the seal in the ear canal, it appears insignificant 3~ acoustically. Il S.F. Lybarger, "Earmolds", Handbook of Clinical Audiology, J. Katz, Editor, 1972, The Williams and Wilkin Company. Materials such as sintered pel-lets, mesh screens, lamb's wool and ootton have been used as acoustic obstructions (filters) in the earmold and earphone tubing or earhook to increase acoustic ~' ,. " .,.,, '' ~.

~ 30757q resistance to modlfy response peaks. Heariny Aid Assessment and Use in Audiolo~lc Habilitationt William R. Hodgson, Editor, 3rd Ed. p. 85 and p~ 93 (1986).
These obstructions, however, can cu* down gain and out-05 put and can add distortion at higher acoustic pres-sures.
Althou~h great advances have been made in provid-in~ electronic components which reduce distortion and improve clarity, lack of clarity in the output of 1~ acoustical transducers and difficuties associated with focusing on ~ounds continue to-be problems. Con-sequently, there is a need for methods and apparatus for minimizing the distortions which can occur when acoustic waveforms are generated particularly in a con-fined space.
It has now been found that the above-described problems associated with harmonic distortion and feed-back can be minimized by the use of a plurality of microspheres located in relation to the output transducer to interact with interfering waveforms.
When the microspheres are used, a significant decrease in the total harmonic distortion is achieved par-ticularly when th~ transducer or its output waveforms are in a confined space, such as an ear canal. Addi-tionally, when the microspheres are uqed in the ~hell or housing to contain the input and output transducers, amplifier and associated electronics, significant reductions in total harmonic distortion and feedback are observed.
Both solid and hollow microspheres are well known as fillers in the plastics industry. They are commonly used as extenders and the hollow microspheres find ap-plication where it is desirable to reduoe the weight of the polymeric product and improve stiffness and buoyancy. However, the reduction in distortion of acou~tic waYeforms is totally unexpected in view of the reported acoustical properties of cellular polymers.
AS set forth in the Encyclopedia o~ Polymer Technology:
"The acoustical propert~es of polymers are 05 altered considerably by ~heir fabrication into a cellular structure. Sound transmi~--sion ~s altered to only a minor extent since it depends predominantly upon the density of the barrier (in this case, the polymer phase~. Cellular polym~rs are, the,refore, very poor materials to use by themselves in order to produce sound transmission. They are ~-quite effective in absorbing sound waves of certain frequencies (24). Materials with open cells on the surface are part~cularly effective in this respect. n Encyclopedia of Polymer Scie~ce and Technology, Herman F. Mark, Editor, 1970. As set orth in Volume 12, page 716, of the same series, "open-celled foams provide '~
good sound deadeniny whereas hard, closed-cell ~oams have only slight absorption"; and on page 706, "since widespread friction of the air in the ~oam is impor-tant, closed-cslled foamed polymers are in general not suitable for air-borne sound absorptlon." Accordingly, there is no suygestion in the known art o the advan-tages of the instant invention.

Summary_0~ The Invention In one ambodiment, the instant invention compri~es a method for reducing acoustical distortion of an acoustical waveform produced by an electro-acoustical transducer. The method comprises providing a plurality of microspheres ad~acent to the transducer to interact with interfering wa~eforms.

.

. .
.. - ' ' ' , ' '~' ' ,' ~ 307579 In another embodiment, the instant in~ention com-prises a method for reducing acoustical distortion of an acoustical waveform produced by an acou~tical trans-ducsr. The method $nvolves placing the transduc~r 05 within a composite which comprises a polymeric matrix and microspheres.
In another aspect, the instant invention comprises a method for reducing distortion in an in-the-ear hear-ing aid having an input transducer, an ampli~ier and an - 10 output transducer. The method involves encasing the transducers and amplifier in a shell which cornpris~s a polymeric matrix containing microspheres. u In a further embodim~nt, the instant invention in-volves an acoustical output assembly having a housing 15 which contains a) a means for producing an acoustical waveform, and b) a plurality of restrained micro-spheres.
In a stil} further embod~ment, the instant lnven-tion involves an in-the-ear hearing aid which comprises 20 a microphone to convert acoustical waveforms to electrical waveforms. The microphone is connacted to an mplifier to amplify the electrical waveforms and supply the amplified waveforms to a receiver electri-cally connected to the amplifier. The amplified 25 electrical waveforms are converted to acoustical sig-nals by the receiver. The mlcrophone, amplifier, and receiver are located within a shell which is composed of a polymeric matrix containing microspheres.

30 Description Of The Drawings Fig. 1 is a cross-sectional schAmatic repre sentation of an acoustical output transducer with a microsphere composite proximately located to said transducer.

1 30757~
Fig. 2 i~ a cros~-seational ~ahemati¢ repre~entation of an ln the-~ar hearing aid having a ~hell comprise~ of a matrix/miaro~phore aompo~ita.
Fig. 3 is a aros~-~aational schemati~ repra~entation of an ln-the-ear hearing ald having a mlcro~phere/-polymeric matrix composite coatlng on ~he $nterior ~urface of the shell and on the surface of the tube to the hearing cavity.
Fig. 4 i~ a oro~s sectior~al 3ahematic representation of an earmold of a behind-the-ear hearing aid formed ~rom a micro~phere/polymeric matrix compo3ite.
Detai~ Des CEip~iQ~_Q~ Ths_Inv~n~lo~
The term~ "acoustical output mean~", "output transducer" and "receiver" are used interchangeably herein to refer to devices for converting electxical waveforms to acou~tical waveforms.
The term~ "input transducer" and "microphone" ara used herein to refer to devices for converting acoustical waveforms to electrical waveforms.
It has been found that aooustical distortion particularly due to harmonic distortion can ba decreased by plaaing microsphere~ ~o that they interact with potentially interferlng waveform~. Signifloank i~provs-ment~ i~ ¢larlty of sound produaed with, for example, an in-the-ear hearing ald aan be obtained. The dearea~ in total harmonia di~tortion obtained prOVi~eB a greatflr u~eful gain in the deviae3. Al~o, the " foau~" o~ tha listener to the de~ired ~ound is greatly improved.
While not wishing to ba bound by the theory~ it i~
believ~d that tha microsphere~ aat to "break up" sta~ding waves and prevent bui ld up of ~ransient nodes.
The miarospheres u ful in the in~tant invention are materials whi~h are commonly used as filler in the pIastic industry. The micro~phere~ can be ~olid or hollow and aan be made of a variety of matarlal~, e.g.

:;, - ~.

` 1 307579 ~illceouR, ceramic, gla~s, polymeric and mineral~ suoh a~
~llica and alumina. Depending upon whether the mi~ro-; s ~pheres are hollow or solid and the material o~ ¢onstruc-tion, the diameter of the mlcroRpheres aan rang~ from about 5 up to about 5000 microns. Solid gla~ micro-spheres oan be manufactured from a Yarlety of glas~
types, for example A-gla~s. The silicate--6a-based microspheres have compositions wh~ch can be modified with organic compounds. These are commonly supplied as holl~w microspheres. ~he polymeric materials can be formed from thermoplastic as well as 05 ther~oset resins. Commonly, phenolic thermoset resins are used to prepare these materials. Ceramic micro-spheres are ~ommonly alumino-silicate ceramics although other ceramic compositions can be used. It is also contempl~ted that objects with shapes other than ~pherical, e.g. rectangular, cubic, etc., as well as ob~ects with sizes greater than 5000 microns, can be used ~o reduce harmonic distortion and increase the clarity of sound~ For aase of fabricat~on and co~mer-cial availability, the smaller ~ize spheres are 1~ preferred.
In the instant invention, it is preferred that hollow microspheres be used. Preferably the micro-spheres have a diameter of about 5 to about 1000 mic-rons. More preferably, the diameter of the micro-20 spheres is between about 10 and about 200 microns.
Normally the microspheres are produced with a distribu-tion of sizes. When the microspheres are used in an in-the-ear hearing aid, it has been found that good results can be obtained with microspheres having a mean 25 ~iameter between about 50 and about 100 mi~rons and partiaularly about 70 microns. It is also preferred that hollow glass microspheres be used.
In the practice of the instant inventivn, the microspheres are placed so as to interact with inter-fering acoustical waveforms. It has been found that a reduction in distortion can be obtained when the micro-spheres are used to coat the inside surface of a hous-ing containing an acoustical output transducer. The most effective location for the microspheres can be readily determined with minimal exp2rimentation by a ,,,. ~, ,,. ~
, skilled person. Nurmally, it is preferred that the microspheres be placed proximately tc the output transducer, and most preferably that the microspheres substantially surround the output transducer. For a 05 given amount of microspheres, the effect is normally maximized if the output transducer ic substantially surrounded by the microspheres, i.e. that the micro-spheres be placed in proximity to at least four of the six sides of a rectangular transducer. Of course, it is contemplated that a pathway for the acoustical out-put is provided from the transducer. The microspheres can be used in the form of a coating of a housing, shell or transducer case as described hereinabove or can be included as a component in the housing or shell as in a telephone receiver housing or a hearing aid shell.
For convenience, it is preferred that the micro-spheres be contained in a polymeric matrix. The com-position of the polymeric matrix is selected based on the end use according to the physical properties of the polymeric matarial and its formabllity. Also, the physical properties of the final composite comprising the matrix and the microspheres must be considered in view of the end use. For example, for uses such as in a telephone receiver, the polymeric material should be xigid and tough to provide the necessary structural in-tegrity. In uses where the mater~al will be in in-timata contact with the human body, for example, an in-the-ear hearing aid, factQrs such as allergic response to the polymeric material or monomers and addi tives contained therein must be taken into acco~mt. For uses re~uiring a rigid, tough ma trix, resins such acrylonitrile-butadiene-styrene (ABS), polystyrene, polyethylene, polypropylene, polyamides, polyamide-imides, polyesters, polyurethanes, etc., can be used.

` 1 307579 These materials can be cross-linked or contain other fillers and additives ln addition to the microspheres.
Commonly for uses such as ear molds, more flexible materials can be used which can include silicones, 05 polyvinyls, both hard and soft acrylics such as poly(methyl methacrylate) and the like.
The loading of the microspheres in the polymeric matrix depends upon the end use ~f the resulting com-posite material. Other thlngs being equal, the extent to which disruptive signals are damped increases as the level of microspheres increases. Normally, the amount of microspheres in the polymeric matrix ranges from about 5 to about 75 volume percent of the resulting composite. However, as the loading level of micro-spheres in the polymeric matrix increases, there can bea detrimental effect on certain physical properties of the matrix, e.g. a decrease in tensile strength. Con-sequently, the physical properties which are required for the composite determine the upper level of micro-spheres which can be incorporated into the matrix. Ad-ditionally, at the lower levels of microsphere loading a decrease in the effect of the microspheres on the distortion can be observed. Therefore, sufficient levels of microspheres must be incorporated ln order to obtain the desired results depending upon the amount of composite material which can be used. Therefore, if the polymer matrix/microsphere composite is used in comblnation with or as an insert in other materials which do not contain microspheres, it is ordinarily desirable to use higher loadings of microspheres to ob-tain the desired result. In ordinary operation in an in-the-ear hearin~ aid, it ls preferred that the micro-spheres comprise between about 10 and about 50 volume percent and most preferably about lO to about 45 volume percent of the polymer matrix/microsphere composite.

, .

1 30757q No~mally when incorporating microspheres into a polymeric matri~, a coupling agent is used to assure effective bonding between the polymeric matrix and the microspher~. Ordinarily with siliceous microspheres, a 05 ~ilane coupling agent can be used to treat the mlcro-spher~s prior to incorporation into the polymeric matrix. Any such coupling agent normally used for this purpose can be used in the insta~t invention. However, ln the e~ent the material is to be in contact wi th human tissue, the pharmacological effects of the material must be considered.
As is well known by those ~killed in the art, other additives can be incorporated into the polymeric matrix. For example, other fillers to affect or modify the physical properties of the matrix material can be incorporated. ~dditionally, additives such as an-tioxidants, stabilizers, lubricants, mold release agents , etc ., can be us2d as appropriate .
The matrix/microsphere composite can be formed into the desired shape by any method known in the art for such forming. For example, as appropriate, the composite can be injection molded, cast lnto a mold form, or milled. Selection ~f the appropriate molding process depends upon the pol~meric matr~x b~ing used and the end use of the product. For example, if ABS is usad as the housiny ~or a telephone receiver, it is ex-pected that the composite would be inJec-tion molded into the proper form. However, in the event that the final article is an in the-ear hearin~ aid, it is ex-pected that a mold of the actual ear canal would beprepared and the polymeric material, for example polymethyl~ethacrylate, would be cast into the ap propriate shape using the female mold of the ear canal.
The electronics, includin~ the output txansduc~r, would then be attached to the composite material.

--10~

~ 30757q In a preferred embodlment of the instant inven-tion, the matrix/microsphere composite substantially surrounds the output transducer. By "substantially" is meant that the composite surrounds at lsast four sides 05 of the transduc~r h~wever, a pathway i5 provided through which the acoustic waveforms produced by the 7 transducer can travel. The location of the composite material in this relationship to the transducer acts to dampen distorting vibrations which occur as the result 10 of the transducer continuing to vibrate after acti~a-tion as well as harmonic waveforms which are generated by resonance in the surrcunding space and other materials in the space. ~hese vibrations can result in out-of~phase secondary signals which produce harmonic 15 distortion and/or feedback to the input transducer.
Preferably, the composite material is formed into a housing for the output transducer and, more preferably, serves as a housiny or shell to encase the output transducer and associated electronics, including the 20 amplifier and input transducer.
With an in-the-ear hearing aid it is preferred that the co~posite material be used as the material of construction for the shell of the hearing aid.
However, it is contemplated that the use of the com-25 posite material can be limited to its location around the output transducer with othex material serving as the shell of the hearing aid unit. It is also con-templated that, as described hereinabove, the composite can be used as a coating on the surface of the housing 30 or shell. For a behind-the-ear hearing aid, the com-posite material can be used as the housing for the electronics and/or it can be located in the conduits which conduct the amplified signal to the ear canal, and/or it can be used in an ear mold which fits in tha 35 ear canal.

Referrlng now to Fig. 1, a schematic, r2pre-sentation of a transducer 1 is depicted with a com-posite material 2 composed o~ a polymeric matrix 3 con-taining microspheres 4 dispersed throughout the matrix 05 locatod proximately to the transducer. When the transducer is activated by an electrical signal passing through connector 5, acoust~cal waveforms are gen-erated. Secondary signals produced as the result of the transducer 1 continui~g to vibrate after activation are reduced by the composite 2. As depicted by dotted line 6, it is preferred that the composite substan-tially surround the transducer.
An in-the-ear hearing aid is schematically depicted in Fig. 2. The shell 10 is shown inssrted in the ear canal. Within the shell 10 is contained an in-put transducer ll, an amplifier 12 and an output transducer 13. The transducers and amplifier are in electrical communication with one another. Optionally, the amplifier can be connected to a control means 14 which can serve to adjust the gain or output of the amplifier. Other electronic circults and/or components can be incorporated as appropriate, but these are not represented. The output transducer 13 generates an acoustical signal into tube 15. These signals travel into the ear cavlty 17 and impact on the ear drum 18.
Commonly in such in-the-ear devices, a ~ent tuba 19 can be provided to allow for equalization of pressure and minimize discomfort to the wearer. As depictad in Fig.
2, the polymeric matrix/microsphere composite is used to form the shell or housing of the hearing aid and serves to encase the electronic components, however, it is contemplated that the composite material can be used to simply surround the perimeter of the ~utput transducer with another material used to form the remaining portion of the shell or housing. It is .

0757q pre~erred that the ~hell or hou~ing be prepa~ed ~rom th~
polym~ri¢ matrix/miaro~phere aomposit~. Thi~ s~rve~ to minimize harmonia di~tortion a~ the result o~ vibrations trans mi tted throllgh the matsrial. Al~o, ik minimizes S feedbaak which oacurs a3 the result o~ transmi~sion o acoustic slgnals from the ear cavity 17 through tha vent tube 19 and to the input transducer 11 a~ well a leaking between the shell and the ear canal.
Fig. 3 ~chamatically depicts a~ in-tha~ear hearing-aid. The shell 10 ha~ a coatiny 22 o~ a compo~ite material 2 composed of a polymaria matrix 3 containing di3per~ed microspheras 4. The tube 15 al30 ha~ a coating 20 of composite 2.
Fig. 4 depict~ an earmold 24 formed of a composite material 2 composed of a polymeric matrix 3 containing disper~ed micro~pheres 4. A conduit 25 conducts the amplified signal to the earmold from the output tran~-ducer (not 6 hown ) .
It has been found by 6pectral analysis that an electronic device (input a~d output tran~duoer~ and amplifier) encased in poly(methyl methacrylate) without microspheres 6hows a phase shift accompanied by a time lag. ~hi i~ thought to result from the combination of the applied ~ignal adding wlth noi~o background ln standing wave area~ throughout the ~peatrum. In contrast, the use of miorosphere~ in ths pvly(m~thyl methaarylate) matrlx wlth the 3ams alectronlc device wa~
~ound to provide a slgnal which, while ~howing some 6mall degree of phase ~hi~t, was approximate to the origlnal slgnal. Thi~ e~fect reduces ringing and unwanted spikes theraby adding appreciably to the clarity of the ampl i ~i ed s ound.
The polymeric matrix/microsphere composite can be prepare~ by method~ well know~ to khose ~killed in the art. For example, when the matrix material i~
poly(methyl methacrylatel, the ~hell can be prepared by 1 .~0757q slush mol di ng by ~i rs t prepari ng an i mpres~ion of the cavity. A ~emale cavity ls then prepared to mirror the imprassion. Commonly, ~he acrylia used ~or ~lush moldlng the shell i8 a two-part catalyst cured sy~tem. The base material i~ ~ast polymerizir3g polymer commercially available in powder ~orm and commonly u~ed in the dental indu~try. The powder which contain~ the microspher0 is mixQd w~th methyl methacrylata monomer. The resulting slurry is poured into the mola and allowed to -13~-cure. Thls can be repeated to bu~ld up layer~ o~ the acrylic polymer to the desired final thickness. Un-reacted monomer can be remove~ by heating the resinous body in hot water.
05 The following examples are lntended by way of il-lustration and not by way of limitation.

EXPERIMENTAL
For the following tests, four instruments were as-sembled on open face plates. Two of the in~truments had B-l response curves, 40dB ANSI gain and lO9dB MP0 using Knowles electronics 1739 receivers as the output transducers. The other two instruments were assembled ~ , to have the same B-1 response curves with 40dB ANSI ~r, 15 gain and 117dB MP0 l~sing Knowles electronics 1912 !~
receivers as the output transducers. Knowles -~
electronics 1842 input transducers were used ~or all four instruments. The amplifiers were standard LTI 505 chip~. j Four shells were made for the right ear, two prepar~d from poly(methyl methacrylate) without micro-spheres and two from poly~methyl methacrylate) contain-ing 35 volume percent hollow microspheres. The micro-spheres were bubble type B 23/500 from 3M Company which are reported to have chemical properties similar tc~ a soda-lime-borosilicate gla~s. The mlcrospheres are reported to have a crush strengt,h of at least 500 pounds per square inch (34 Bars). The dlameters of the microspheres range from about 1~ to about 140 microns r.
with an average diameter of about 70 microns. The microspheres (35 volume percent~ were mixed by tumbling for 5 minute~ at room temperature with the methyl methacrylate polymer (65 volume percent). The poly(methyl msthacrylate) used was Audacryl ~TC pol~mer 35 grade 650 Z 2064 from Esschem Company having a reported 1 30757q molecular weight of about 400,000 to 500,000. Two parts by volume o~ the polymer-microspheres mixture were mixed with one part by volume methyl methacr~late monomer. The resulting mixture was stirred in a con 05 tainer for 30 seconds. The container with the mixture was then placed in a vess~l ~or 2 minutes under 0.5 at-mospheres pressure. The mixture was again stirred for 30 seconds and then poured into a mold cavity. The mixture was slushed and cured at room temperature until a matrix wall thickness of about 2.5 to 3.5 millimeters was obtained. The remaining mixture was poured from the mold cavity. The solid matrix was removed from the mold cavity and placed in a pressure vessel containing water at 180F and allowed to cure under 20 pounds per square inch gauge pressure for 30 minutes. No addi-tional heat was added to the vessel so that the con-tents of the vessel cooled during the cure time. The matrix was then placed in boiling water for 20 minutes to complete the cure. Each of the resulting shells was finished by grinding and buffing to be as identical as possible.
Testing was done on the Frey electronics "phonix"
5500Z elactro-acoustic test set. Battery voltage was calibrated at 1.35VDC with the test box being leveled and calibrated to standards once every houx of use.
Tubing length and couplerJaid p~sitioning were dupli-cated to as close to identical positions as could be maintained. Each ~ace plate was loaded to the shell, checked and run in the chamber. Volume controls were locked in "full-on" position. Electronics were changed after each test run to the next shell for a total cross check shell to shell, electronics to el0ctronics. TAe tests were run according to ANSI S 3.22 1982 except as indicated in the following TablesO

-lS-The results of tests comparing material with microspheres to material without mlcrospheres are given in Tables I through XII.

Table I
With Microspheres Without Microspheres Total Total Aid Harmonic Aid Freq. Aid ~larmonic Aid Freg Gain Dist. In In Gain Dlst. In In db 96 dB K~Z dB ~ dBK~IZ
4.5 ~ 70 0.100 8.0 700.100 15.5 70 0.125 ~2.0 7t~0;1~5 17.5 70 0.160 14.5 700.160 2:2.5 73 0.200 19.5 700.200 2~.() 70 0.250 22.5 700.250 30.5 70 0.315 24.5 70~.315 34.5 70 0.400 26.5 700.400 38.0 10 70 0.500 27.5 8 700.500 40~5 13 70 0.630 29.5 19 700.63~
41.0 70 0.710 30.0 700~710 41.5 7 70 0~800 30.0 12 700.800 43.0 13 70 1.000 32.0 23 701.000 44.5 8 70 1.250 34.5 18 701.250 46.0 70 1.500 35.~ 701.500 46.5 19 70 1.600 36.0 22 701.600 39.0 70 2.000 38.5 702.000 39.0 70 2.500 38.S 702.500 37.0 70 3.150 36.0 703~150 35.0 70 4.000 34.5 704~.000 35.0 70 S.000 33.5 705.000 21.0 70 6.31~0~1.0 706.300 19.0 70 8.000 10.5 70B.000 3.0 '70 9.999 3.0 70 9.g99 ~ __ . . .._ _ ~

~16--~ 30757q Table II
With Microspheres Without Microspheres Total Total Aid Harm~nic Aid Freq. Aid ~armonic A~ d Freg Gain Disto In In Gain Dis-t. In In dB ~ dB K~Z db ~ dB KHZ
7.5 70 0.100 8.0 70 0.100 11.5 70 0.12512.5 70 0.125 13.5 70 0.16016.0 70 0.160 19.0 70 0.2~0~1.0 70 0.200 21.0 70 0.25022.0 70 0.250 23.5 70 0.31525.5 70 0.315 25.0 70 0.40~27.0 70 0.400 26.5 ~1 70 0.500~ .5 17 70 0.500 27.5 16 70 0.63030.0 35 70 0.630 ~8.5 70 0.71030.5 70 0.710 28.5 12 70 0.80031.0 ~8 70 0. ~00 3~.5 25 70 1.00033.0 44 70 1.000 32.5 21 70 1.25034.5 30 7~ 1.250 34.0 70 1.50035.5 70 1.500 34.5 19 70 1.60036.0 24 70 1.600 36.5 70 2.00039.0 70 2.000 38.5 70 2.50039.0 70 2.500 35.0 70 3.15036.0 70 3.150 32.5 70 ~ .00034.5 Y0 4.000 31.5 70 5.00034.5 7~ 5 000 23.5 70 6.30021. ~ 70 6 300 10.5 70 8.00010.0 70 8.000 6.0 70 9.999 -1.0 70 9.999 Table III
With Micr~spheres Witho~lt l~i C=~sD Are-A d Total db ~ dB In 5 0 75 0 125 l2.0 75 0 125 9 0 75 0.250 16.0 75 160 ~ ~ 2 75 D 530 25~ 5 ~ _~c 38 . 522 75 2 . 500 ~7. 531 75 l . 600 3.0 75 5 00O 33 0 75 4 0D ~

1 30757q Tabl~ IV
, With M1crospheres Without Microspheres Total Total Aid Harmonic Ald Freq. Aid Harmonic Aid Freq.
Gain Dist. In In Gain Dist. In In db ~ dBK~Z dB % dB KHZ
14.5 75 0.100 9.0 ~ 75 0.100 16.5 75 0.125 13.0 7S 0O125 19.0 75 0O160 15.5 75 ~ 0 24 0 75 0.~00 19.0 75 0.200 '.
27 0 75 0.~50 21.5 75 0.250 ':
30 S 7S 0~31S 23.5 75 0.315 34 0 75 0O400 25.0 75 0.400 ..
3~ S 41 75~.50026.5 37 7~ 0.~00 ~.-39 Q 41 750.63027.S 45 75 0.630 39.5 750.71028.0 75 0.71~ -~0 0 40 750.80028.~ 49 75 ~.800 ~ --41 5 46 751.00030.5 5~ 75 1.000 ~2 0 38 751~25031.5 44 75 1.250 :
42 5 751.50031.5 75 1.500 t - -42.5 35 751.60032.~ 35 75 1.~00 ~ .
44 0 752.00034.0 75 2.000 44 0 752.50034.5 75 2.5Q0 42 5 753.15032.0 75 ~.150 y 40 0 754.00030.0 75 4.000 ,ir .
40.5 755.00030.0 75 ~.000 .-27 0 75`6.30017.0 75 6.300 7 0 758.000 7.5 75 8.00 3.0 759.9g9 3.5 75 9.999 ;

--lg--Tabl~ V
w-e~E~s Without Micro~ph0res AidHarmonic Aid Freq~ Aid Harmvnic Aid Freq Gain Dlst. In I GainDist. n In 1158 o5 75 0 12513.5 75 0 125 2~,0 75 0 20 21 75 0-160 26 5 42 75 0 630 27 5 51 75 0 ~30 27.5 58 75 1.250 3l 5 52 75 1 250 30.5 35 75 1 600 32.0 35 75 1 600 l9.5 75 8.~00 l~ 75 9,999 . --Table VI
W h Micros~heres With ut Mic~ospheres Total Total Aid Harm~nic Aid Freq. Aid Harmonic Aid Fr~q GainDist. In In Gain Dist. In In ~B % dB KHZ db ~ dB KHZ
12.5 75 0.100 15.0 75 0.-l~0 1~.5 75 3.125 17.5 75 0.125 16.0 75 0.16~ 18.5 75 0 160 18.0 75 0.~00 21.0 75 0 200 18.5 75 0.250 22 5 75 0.25 21.5 75 ~.315 2~ 0 75 0.315 22.5 75 0.400 25.0 75 0.400 24.0 6 75 0.500 26.0 18 75 0 500 25.016 75 0.630 27.0 34 75 0 630 25.5 75 0.710 27.0 75 0 710 26.~13 75 0.800 27.5 23 75 0 800 27.519 75 1.000 30.0 40 75 1.000 30.516 75 1.250 32.0 30 ~5 1 250 34 027 75 1 500 3~ 0 31 75 1 500 36.5 75 2.000 37.0 7~ 2 000 37.5 75 ~.500 37.5 75 2 500 35-5 75 4.000 31.0 75 5.000 17.5 75 ~.300 18.5 75 ~.300 -10.0 75 ~ 999 -7 5 75 8.000 Table VII
With Microsp_~eres Without Micro~heres Total Total Aid Harmonic Aid Freq. Aid Harmoni Aid FreS
Gain Dist. In In Gain Dist. In In dB ~6 dB KHZ db % dB KHZ
12. 5 80 0. 100 14. 5 80 0. 100 14. 5 Bû 0.125 16. 5 80 0.125 16 . 0 80 0. 160 17 . 5 ~0 0. 160 17 . 0 80 0. 200 19 . ~ ~0 0. 200 18 . 0 80 0. 250 20 . 5 80 0. 250 20 . 5 80 0. 315 21 . 5 80 0 . 315 21 . 5 80 0 . 400 22 . 5 80 0 . 400 22 . 5 34 80 û. 500 2~. 0 40 ~0 0O 500 23 . 5 48 80 0. 630 25 . 051 80 0. 630 24 . 5 80 0. 710 25. 5 80 0. 710 25 . 0 56 8G 0. 800 26 . 058 80 0. 800 27 . 5 68 80 1 . 000 2.g . 0 ~ 80 1 . 000 29 . 0 52 80 1 . 250 30. 0 57 ~0 1 . 250 ~9 . 5 80 1 . 5~0 30. 0 80 ~ . 500 30. 0 43 80 1 . 600 30. 5 44 80 1 . 600 32.0 80 2.000 32.5 80 2.000 33. ~ 80 2. 500 33 . 0 ~0 2 . 500 31 . 0 ~0 3 . 150 31 . 0 80 3 . 150 26 . 0 80 4 . û :)0 26 . 0 80 4 . 0~0 28 . 0 80 5 . 000 27 . 5 80 5 . 000 14 . 0 80 6 . 300 15 . 0 B0 6 . 300 -2 . 5 80 B . 000 -4 . 0 80 8 . 000 -11 . 0 ~0 g . 999 -8 . 5 80 9 . 999 .. . ..

-` 1 307579 Tabl e VI I I
.
With Microspheres Without Microspheres Total Total AidHarmonic Aid Freq. Aid Harmonic Aid Freq Gain Dist. In In GainDist. In In dB 96 dB KHZ db ~ dB KHZ
4 . 0 80 0 . 100 11 . 0 80 0 . 100 4 . 5 80 0. 125 12 . 0 ~ 0. 125 4.5 B0 0,160 15.5 80 0.160 10.0 B0 0~200 16.0 80 0.200 13 . 0 80 0. 250 18 . 0 80 ~ . 250 l9 . 0 80 0 . 315 21 . 0 80 0 315 23 . 5 80 0. 400 22 . 0 ~0 0 400 26. 5 21 80 0. ~00 23. 537 80 0. 500 27 . 535 80 0. 630 25 . 0 ~9 80 0. 630 27. 5 ~0 0. 710 2~ . ~ 80 0 710 27 . 5~1 80 0. 800 26 . 5 60 ~0 0 800 30. 0 63 80 1 . 000 30 . 0 74 80 1 . 000 30. 5 43 80 l . 250 30. 5 57 80 1 . 250 31. 0 80 1. 500 31. 0 8G 1. 500 32 . 036 80 1. 600 31. 541 8D 1. 600 34. 0 80 2 . 000 34 . ~ 80 2 . 000 34 . 0 80 2 . 500 34 . 0 80 2. 50û
31 . 5 80 3. 150 31 ~ 5 80 3. 150 27 . O ~0 4 . 000 27 . 0 80 4 ûO0 30. 5 80 5 . 000 30. 0 80 5 000 10. 5 80 6 . 300 ll . 5 80 6 . 300 -8. 5 ~0 8. 000 ~ . 5 80 8 . 000 -10. 5 80 9. 999 -4. 5 80 9 . 999 Tabl e IX
Aid Fre~. Total Harmonic Di~tortion d _ K Z _ __ Micro~s~heres Microspheres ~00 1~ 1 6 1000 15 ~2 1600 14 ~7 . _ . _ . . .

I 3~7579 Table X
Aid Freq.Total Harmo~ic Distortion In In With Without dB ~HZMicrospheres Microspheres 63D 16 lB
~0 800 ll 20 1000 ~4 69 . . .
: Table XI
A~d ~req.Total Harmonic Distortion In In With Without dB _ KHZMicrospheres Microspheres 630 ll 20~ .
8~0 17 3~
1000 16 74 -:
1250 16 67 ~
1603 63 91 `-.. _ . _ ~_ __ - ---- ~ ;
Table XII
Aid Fre~.Total Harmonic Distortion %
In InWith Without dB__ _ KHZ_ _ _ Microspheres _Mlcrospheres 630 10 ~3 gO 800 19 46 1250 1~ 65 gO 1600 55 84 ~ --n _ .
While various embodiments of the present invention have h~en described in detail, it is apparent that modifications and adaptations of those embodiments will occur to those skilled in the art. HoweYer, it i3 to be expressly understood that such modifications and adaptations are within the spirit and scope of the present invention as set forth in the following claims.

-~4-

Claims

1. A method for reducing distortion of an acous-tical waveform produced by an acoustical transducer located within a polymeric matrix said method compris-ing locating a plurality of microspheres in contact with said matrix to interact with interfering wave-forms.

2. The method of Claim 1 wherein said micro-spheres are located in a coating on the interior sur-face of a housing which contains said transducer.

3. The method of Claim 1 wherein said micro-spheres are substantially dispersed in a composite.

4. The method of Claim 1 wherein said micro-spheres are located in a conduit which conveys said waveform from said transducer.

5. The method of Claim 3 wherein said composite comprises a polymeric resin matrix with said micro-spheres comprising from about 5 to about 75 volume per-cent of the total volume of said composite.

6. The method of Claim 1 wherein said micro-spheres have a mean diameter between about 5 to about 5000 microns.

7. The method of Claim 1 wherein said micro-spheres have a mean diameter between about 20 to about 200 microns.

8. The method of Claim 1 wherein said micro-spheres comprise a material selected from the group consisting of ceramic, glass, mineral and phenolic resins.

9. The method of Claim 6 wherein said micro spheres are hollow glass beads.

10. The method of Claim 6 wherein said micro-spheres are solid glass beads.

11. The method of Claim 3 wherein said composite substantially surrounds said transducer.

12. The method of Claim 5 wherein said micro-spheres comprise between about 10 and about 50 volume percent of said composite.

13. The method of Claim 12 wherein said micro-spheres have a mean diameter between about 5 microns and about 5000 microns.

14. The method of Claim 12 wherein said micro-spheres are hollow glass beads with a mean diameter be-tween about 10 and about 200 microns.

15. The method of Claim 5 wherein said polymeric matrix is selected from the group consisting of sill-cones, polyvinyls, acrylics, polyolefins, polyamides, polyesters and polyurethanes.

16. The method of Claim 15 wherein said polymeric matrix is a silicone or poly(methyl methacrylate).

17. An acoustical output assembly comprising a housing containing:
a) a means for producing an acoustical waveform;
and b) a plurality of restrained microspheres.

18. The assembly of Claim 17 wherein said micro-spheres are located within a composite material which comprises a polymeric matrix.

19. The assembly of Claim 18 wherein said com-posite material is coated on the inside surface of said housing.

20. The assembly of Claim 18 wherein said com-posite material substantially surrounds said means for producing an acoustical waveform.

21. The assembly of Claim 18 wherein said housing comprises said composite.

22. The assembly of Claim 18 wherein said micro-spheres comprise between about 5 and about 75 volume percent of said composite.

23. The assembly of Claim 17 wherein said micro-spheres have a mean diameter between about 5 microns and about 5000 microns.

24. The assembly of Claim 22 wherein said micro-spheres comprise a material selected from the group consisting of ceramic, glass, mineral and phenolic resins.

25. The assembly of Claim 17 wherein said as-sembly is an in-the-ear hearing aid; said housing com-prises a composite material which comprises a polymeric matrix and between about 5 and about 75 volume percent of substantially dispersed microspheres; and said means for producing an acoustical waveform is an electro-acoustical output transducer said transducer being in electrical connection with an amplifier suitable for amplifying electrical signals received from an electro-acoustical input transducer.

26. An in-the-ear hearing aid comprising a shell containing:
a) a conversion means for converting a first acoustical waveform to an electrical waveform;
b) an amplifier in electrical connection with said conversion means to amplify said electrical wave-form; and c) a means in electrical connection with said amplifier for receiving said amplified electrical waveform and producing a second acoustical waveform, said shell comprised of a sufficient amount of micro-spheres to interact with acoustical waveforms which in-terfere with said second acoustical waveform and to reduce harmonic distortion in said second acoustical waveform.

27. The hearing aid of Claim 26 wherein said shell consists essentially of a polymeric matrix con-taining between about 10 and about 50 volume percent of said microspheres.

28. The hearing aid of Claim 26 wherein said microspheres are hollow glass beads having a mean dia-meter between about 10 and about 1000 microns.

29. The hearing aid of Claim 26 wherein said microspheres are solid glass beads having a mean diameter between about 10 and about 1000 microns.

30. A behind-the-ear hearing aid comprising:
i) a housing containing:
a) a microphone means for converting a first acoustical waveform to an electrical waveform;
b) an amplifier in electrical connection with said microphone means to amplify said electrical waveform; and c) a receiver means in electrical connec-tion with said amplifier to convert an amplified electrical waveform to a second acoustical waveform, and ii) a conduit attached to said housing to conduct said second acoustical waveform from said receiver means to an ear canal, the improvement comprising providing a plurality of restrained microspheres in proximity to said conduit to interact with interfering acoustical waveforms and reduce distortion of said second waveform.