EXHIBIT B
`
`

`

`Exhibit B
`
`Initial Expert Report on US Patent No. 5,181,252
`
`

`

`I.
`
`Introduction and Background
`
`| have read and understand the specification and clatms of US Patent No.
`
`3,18 1.252 (the “252 patent”) (Attachment 1), having a title of “High Compliance
`
`Ifeadphone Driving.” | have ocen asked to give my opinion on whether the
`
`mventions recited in Claims 1,2, and 5 were publicly knownor obvious (to one
`
`having ordinary ski] in the acoustics arts) more than one vear before August 23,
`
`1989, the effective date of filing of the *252. based on howthe claimterns are
`
`used tn the specification and their meaning in the acoustic arts.
`
`] understand from Phitek’s legal counsel that a legal finding of obviousness may
`
`be found by showing that the prtor art teaches. suggests. or mottvates one of
`
`ordinary skill in the art, at the time ofthe invention, to combine elements found in
`
`two or more priorart references.
`
`Attached as Attachment 2 ts a current CV. including myqualifications and list of
`
`publications. My conipensation agreement ts for $150/hr ($225/hr for testifying).
`
`| have not testified as an expert in the last 4 vears.
`
`i].
`
`Summaryof Conclusions
`
`The headset recited in Claim | combines an active noise reduction system
`
`(CANR™) with a high compliance driver. As defined in the "252 patent, a high
`compliance driver ts a driver having a compliance that ts greater than the
`
`compliance ofthe rear cavity.
`
`Myopinionis that it was obvious to combine ANR with any headphone where
`
`noise reductionis desirable. Because the prior art (materials existing before
`
`August 23. 1988) included many headsets having driver compliances greater than
`
`their rear cavity compliancees, it was obvious to make the combination deseribed
`
`in Claim | more than a year before the *252 patent wasfiled.
`
`6.
`
`Clatm 2 recites a limiting structure that limits diaphragm excursion.
`
`In addition to
`
`it being obvious to use a mechanical stop to limit excursion, this feature was
`
`publicly known mthe acoustic arts at Ieast as carly as 1981.
`
`It was obvious to use
`
`

`

`such mechanical stops on anyheadset, and in particular on thosethat include high
`compliance drivers with their typically floppy diaphragms.
`7. Claim 3 revites indentations in the diaphragm “suchthat the diaphragmrecovers
`its shape if collapsed.” The prior art disclosed diaphragms with such indentations
`
`It was obvious to use
`as carly as 1928 to strengthen speakers to prevent collapse.
`such structure with any headset, and in particular with those that had a driver
`
`compliance greater thanthat ofthe rear cavity.
`
`HE.
`Summaryof the ‘252 Patent and Its Claims 1, 2, and 5
`8. The °252 patentis directed to high conipliance drivers in active noise reducing
`headsets, Col. 1:14-15.
`It is particularly directed to structures for protecting the
`diaphragmofthe driver, Col. 1:16-18. The patent specification defines “high
`comphance™ as meaning that “the driver compliance is greater than the rearcavity
`complianee.” Col, 2:58-59.
`
`%.
`
`‘The structure ofthe headset is schematically represented in Figure 2. which shows
`the driver 13. front cavity 11. and rear cavity 112.
`
`10, Claim | reeites a headset having an earcup with front andrear cavities having
`respective front cavity and rear cavity compliances, a baffle that separates the
`front and rear cavities, a high compliance driver, and an ANR system. My
`understanding is that the central issue is whether it was obvious to combine ANR
`
`with a high compliance driver.
`of Claim } recites
`
`Inits entirety. the high compliance driver clement
`
`“a igh compliance driver with a driver compliance that is greater
`than said rear cavity compliance having a diaphragm joined to a
`voice coil normallyresiding in a gap mounted on the baffle”
`
`11. Claim 2 adds to Claim | “limiting structure limiting the maximumexcursion of
`the diaphragmsothat the voice coil remainsat least partiallyin said gap.”
`12. Claim 3 adds to Claim 1 “means for recovering from collapse ofthe diaphragm
`including indentations in the diaphragm suchthat the diaphragmrecoversits
`shape if collapsed.”
`
`

`

`IV.
`
`CompHance
`
`13.
`
`‘The patent claims and specification use the term “compliance,” In the acoustic
`
`arts, the word compliance is used both for acoustic compliance and mechanical
`
`comphance. The specification does not address this distinction.
`
`In the one
`
`example where units are provided, acoustical complhance is used
`(meters)/(Newtons).
`(Col. 4:31-33). However, in the prosecution ofthe
`application, Bose’s patent attorney, in response to the examiner’s request for the
`
`definition of compliance, supplied a definition of mechanical compliance.
`
`“A physical structure is said to be a mechanical comphance Cy; if, whenit is
`
`acted on bya foree, it is displaced in direct proportion to the force. The unit is the
`
`meter per newton.” Beraneck, Acoustics, (Acoustical Society of America, 1996),
`
`page 53 (Attachment 3). “Acoustic comphanee is a constant quantity having the
`dimensionsof meter® per newton.
`It is associated with a volumeofair thatis
`
`compressed by a net foree without an appreciable average displacementofthe
`
`center of gravity of air in the volume.” Beranck, Acoustics, at page 65
`
`(Attachment 3).
`
`. The concepts are related by the square ofthe effective area of the diapbragm
`
`acting on the Volume. Therefore. because Claim | focuses on a driver compliance
`
`greater than that ofthe rear cavity, analysis of the claims does not change whether
`
`mechanical or acoustical complianceis used.
`
`LG.
`
`Rear cavity compliance means the actual compliance ofthe air constrained within
`
`arear cavity. See, D’Appolito, Testing Loudspeakers (Audio Amateur
`
`Publications 1998), Chapter 2. page 16, “air spring compliance depends on both
`
`the enclosed volume and the piston area.” (Attachment 10).
`
`. The inverse (reciprocal) of complianceis referredto as stiffness.
`
`‘These terrosare
`
`used to describe the same physical properties; they are simply reciprocals of each
`
`other. Some references choose to describe their systems in terms of compliance,
`
`and some in terms ofstiffness.
`
`

`

`Vv.
`
`The Prior Art Contains All Limitations of The Claims
`
`18,
`
`It is my opinion that. more than a year belore August 23. 1989, it was obvious to
`
`one of ordinary skill in the acoustic arts (one who hasat least a graduate degree in
`
`ee
`
`acoustics and several years of experience) to combine ANR with any headphone.
`
`l‘irst, a headphone is the initial place one of ordinaryskill tn the art
`
`(a “PEIOSHITA”), at the time of the invention (svell before 1987) would try to
`
`tmplement ANR. This ts because of the difficulty of implementing ANRinlarge
`
`spaces, such as the passenger compartment o)'an airplane.
`
`In fact. a myriad of
`
`prior art discusses ANRand tts benelits. and a PIIOSTVA knewthat ANR was
`
`suitable for any headphone application where notse reduction was desirable. As
`
`just one example, L:urepean Patent Application Publication No. 0195641,
`
`published on September 24, 1986 (Attachment 4), in describing its ANR
`
`invention, states
`
`“Ht will also be appreciated that although the particular
`embodiment of ANR| specifically described ts applted to a
`ctrcumaural earphone structure te arvention may also be
`applied to other Ovo cavity earphone structures such as of
`the supra-aural type” (Page 8. lines 13-17, emphasis
`added.}
`
`19,
`
`Similarly, it ts my opinion that a PHIOSITA would, in implementing ANR,first
`
`try iton existing headphones, Moreover, Bosestates, in the Background of the
`
`Invention ofthe ‘252 patent, that It was known to combine ANRtn a headphone
`
`having front and rear cavities separated bya balfle carrying a driver.
`
`(Col. 1:8-
`
`20.) Given this admission, and that it was obvious to combine ANR with any
`
`headphone, the only question, then, ts whether the high compliance driver of
`
`Claim 1 existed in headphones more than one year before August 23, 1989.
`
`If it
`
`did, then the invention of Claim |
`
`ts obviaus.
`
`20.
`
`] have reviewed several prior art patents which disclose the “high compliance
`
`driver’ of Clann |.
`
`Indeed. some ofthese patents explicitly disclose the ratio of
`
`the driver and rear cavity compliances (or stiffnesses).
`
`. For example. US Patent No. 2,714,134 Cssued to Touger on July 16, 1955)
`
`(Attachment 5), at Col. 4:40-45, discloses that “1t
`
`ts cssenttal that the acoustic
`
`

`

`cavity behind the diaphragm have a reflected stiffness magnitude ... very much
`
`greater than the diaphragm mechanical stiffness.
`
`{f this relationship exists,
`
`the
`
`headphone internal
`
`impedance will be governed bythe back cavity stiffness.”
`
`Touger goes on disclose “a ratio of reflected acoustic stiffness to diaphragm
`
`stiffness of about 35 to 1.7 (Col. 8, lines 15-18.) Therefore. because stiffness is
`
`the inverse of compliance. Pouger discloses a headset with a high compliance
`
`driver. Following is a chart detailing Touger’s relationship to the ClaimI:
`
`

`

`
`
`|
`
`|
`CLAIMED
`COMMENTS
`|
`PRIOR ART (TOUGER £134)
`LIMITATION
`(Cha)
`po
`
`“En thts particular embodiment. the carphone |
`| comprises a housing 3 of a design suitable for
`use ina headset or aviator's helmet...” (col. 6.
`
`1.A headset
`_ comprising:
`
`“at least one carcup
`having
`
`
`
`
`
` | “acoustic cavity comprising the ear cavity and
`
`
`Earphone 1 (see Fig 1) maybe part of a
`headset with a close fitting eareap that is
`“placed over the ear, in such a manneras to
`prevent sound leakage betweenthe earcap of
`the earphone and the head ofa user...” (col.
`| 3. lines 17-19). See also housing 3. Figures]
`
`
`
`2
`
`|
`
`
`The claimed “front
`| cavity” is the car cavity
`and the space defined
`- bythe earcap of the
`Tougerpatent.
`| The claimed “rear
`_ cavity”is the acoustic
`cavity behind the
`__________{ diaphragmofTouger.
`|
`
`“The acoustical stiffness of the car cavity thus
`| Front cavity
`provided is shown bythe expression pC°/V."
`| compliance is the
`with front cavity and
`| (Formula 1) (col. 3, lines 22-25).
`- reciprocal of Formula
`rear cavily
`_ “it is essential that the acoustic cavity behind
`l.
`compliances
`the diaphragm have a reflected stiffness
`| The rear cavity
`| respectively,
`magnitude (A*S,) very muchgreater than the
`| complianceis the
`| diaphragm mechanicalstiffness (Sc).” (col. 4.|reciprocal ofA*S,
`
`lines 40-43). |
` |TheBosebaffle
`"separates the front and
`i
`
`at front cavity
`
`-.
`~
`|
`‘the space defined bya close fftting earcap
`, has volume V, (Col 3:13-33)
`
`ws
`
`and rear cavity
`.
`ees
`
` ‘the acoustic cavity behind the diaphragm”
`.
`col. 4, lines 40-43).
`
`
`
`| rear cavities and carries
`
`i
`abafile separating the ; As seen in Touger Figure 2, the diaphragm 9 1s
`front and rear
`' supportedat its periphery between annular
`the driver. (col. 1, lines
`cavities,
`_ spacing rings 23. These spacing rings are the
`53-56) Also, Bose
`baffle. Col 7:5-8.
`admits that this
`|
`' structure ts known,
`Lo _(ol.1.lines18-20) —
`
`
`
`
`
`

`

`
`
`
`
`PRIOR ART (TOUGER‘134)
`
`COMMENTS
`
`i
`
`i
`
`|
`
`
`|
`
`
`
`
`CLAIMED
`LIMVPATION
`
`_ Tongerstates. “itis essential that the acoustic
`
`_ cavity behind the diaphragmhave areflected
`a high compliance
`stiffness magnitude (A°S,) very michgreater
`driver with a driver
`
`
`' compliance thatis / than the diaphragm mechanicalstiffness (S,).”|TP rear cavity stifiness 1s
`
`greater than said rear | (col. 4, lines 40-43). See also example ratio of|greater thanthat ofthe
`cavity compliance
`35:1 at col 8:15-18.
`driver, then the
`compliance ofthe
`The driver is the well known diaphragm, voice | driver is greater than
`; coil, magnetic and mechanical structure.
`that ofthe rear cavity.
`Touger showsthat its “voice coil 10 is attached | because stiffness is the
`having a diaphragm
`
`joined to a voice coil|to the central dome portion 27 ofthe reciprocal of
`
`| normallyresiding ina|diaphragm 9. The diaphragm 9 [via spacing | compliance.
`| sap mounted on the
`rings 23] is mounted onthe outer pole piece 13 |
`| baffle, and
`with the voice coil 10 freely disposed within
`|
`cctesnniavennneftheairgap 21." (ol. Tines8-12).
`
`
`
`Well known, See, ¢.g.. Bose patent no.
`: 4.644.581. combining active noise reduction
`| circuitry with a conventional headphone.
`
`an active noise
`_ reduction system
`_ coupled to said
`driver.
`
`
`
`ANRis a generally
`applicable headphone
`technologythat ts
`suitable for use with
`| virtuallyall
`' headphones. A
`/ PHOSITA would
`| combine it with any
`priorartheadphone. |
`
`

`

`22. Similarly, US Patent No. 4.041.256 Ussued to Ohta on August 9. 1977)
`
`(Attachment 6) discloses a headset.
`
`including a headset having a closed rear
`
`cavity with a driver compliance higher than the rear cavity.
`
`(Col. 3:9 to Col.
`
`4:33.) More specifically.
`
`the Ohta reference discloses a driver source |
`
`comprising a driver unit 12 with a stiffness of SO (Col. 3,
`
`lines 10-15).
`
`Following is a chart detailing Ohta’s relationship to the claims at issue:
`
`CLAIMED
`
`
`
`
`LIMITATION
`
`1.A headset
`* comprising:
`
`||
`
`at least one earcup
`having
`E
`
`
`_Vigure|.headphone10,case 11
`
`i -
`- The claimed “front
`_eavity”is the “front air |
`_ chamber 25”
`| The claimed “rear
`cavity” is the “internal
`_ Figure 1. internal space 22 ofattachment 19
`| space 2? of attachment
`(Col. 3:56-57)
`19
`|
`
`Front cavity
`
`with front cavity and|The front air cavity has a stiffness S, (Col. compliance is the
`rear cavity
`3:32)
`reciprocal of S..
`compliances
`Rear cavity
`respecuvely,
`; compliance is the
`| reciprocal of Sp
`
`
`a front cavity
`
`| Figure |. front air chamber 25 (Col. 3:32-33)
`
`and rear cavity
`
`The rear cavity (internal volume of
`| attachment 19) has a stiffness S, (Col. 3:21)
`
`
`

`

`PRIOR ARF (OHTA ‘256)
`COMMENTS
`
`
`:
`
`
`
`‘The Bose baffle
`separates the front and
`
`rear cavities and
`| carries the driver. (col,
`|
`|. lines 53-56) Also.
`| Bose admits that this
`structure is known.
`
`CLAIMED
`
`(CLA
`
`LEIMIFATION
`
`ELCON’T)|
`
`.
`,
`a baffle separating
`the front and rear
`cavilles,
`
`i
`
`|
`
`Supporting ring 36 (Col 3:9, Figure 4)
`
`
`
`driver with a driver
`| comphanee that is
`greater thansaid rear
`' cavily compliance
`
`having a diaphragm
`| joinedto a voice coil
`normally residing in
`a gap mounted on
`the baffle. and
`
`| an active noise
`reduction system
`coupled to said
`driver.
`
`|
`
`The suffness $, of the driver is neghgible in
`comparison with that of the front and rear
`cavities (the front cavity stiffness S, 1s 50
`umes greater than Sg}. Sp, therefore, but not
`S, and S, beeause they are not negligible, is
`nat taken into consideration in formula 2.
`| If rear cavity stiffness
`Col 3:31-57. The rear cavity stiffness
`1s greater thanthat of
`depends on the volume ofthe attachment [9.
`which can be designed as desired.
`ligure 3
`' the driver, then the
`(Col 3:67 ~ Col 4:33) characterizes the
`comphanee of the
`driver is greater than
`| performance withthe rear cavity off and then
`on with 3 different volumes(or stiffnesses),
`' that of the rear cavity,
`fPhus, Ohta teaches that a range ofrear
`- because stiffness 1s the
`_ cavities having stiffnesses greater than that of|
`reciprecal of
`| the driver, and a zero stiffness if the back
`comphance.
`attachment 19 1s removed.
`
`_ The driver unit 31 comprises a vibrating
`diaphragm32 with a voice coil. (Col 5:5-6)
`
`/ Well known. Sce, ¢.g.. Bose patent no.
`| 4,644,581, combining active noise reduction
`circuitry with a conventional headphone.
`
`
`
`
`ANRis a generally
`applicable headphone
`technologythat is
`suitable for use with
`virtually all
`headphones. A
`PHOSHVA would
`combine it with any
`_.priorartheadphone,
`
`i
`
`

`

`23. Furthermore, adding the limiting structure of Claim ? to the elements of Claim |
`was obvious, because floppy diaphragms (typically in high com es drivers)
`travel farther than stiffvratateeeaiohesineRACE
`
`drivers, a well known problem called “over excursion”can arise.
`
`24. The prior art disclosed the solution of limiting structure at least as carly as 1981]
`US Patent No, 4,297,537, issucd to Babb (Attachment 7). Babb shows: “The
`
`in
`
`resilient shockabsorbing bumper 54 is cooperatively disposed to engage the apex
`of the dust cap 38 whenever the voice coil 40 travels to the forward end of the
`
`annular flux gap 30, whereupon the bumper 54 compressesto bring the acoustic
`radiator assembly 16 to a quiet stop without allowing the bearing 44 to travel
`beyond the forward most edge of the cylindrical surface of the center pole 28.”
`Col 3:29-37. Babb notes thatit is necessary to control “excessive excursions”
`
`forward and rearward where one uses a highly compliant driver suspension. Col
`2:41-55,
`
`25. Similarly, US Patent no. 4,399,334 (Attachment8), issued on August 16, 1983,
`In
`discloses structure for limiting over excursion of a diaphragm in a headphone.
`particular, a protector [5 includes projections [5b which engage a diaphragm 13
`and to prevent damage that can be caused if the diaphragm moves beyond its
`normal range.
`(See, Figures 2 and 3, and Col 2:56 ~ Col 3:50.)
`
`26. [t would have been obvious to one having ordinary skill in the art, at the time the
`invention was made, to combinethe structure ofeither one ofthese patents with
`an ANR headphonehaving a high compliancedriver.
`
`27. Also, it is simply obvious to use a mechanical stop to limit travel of a mechanical
`element.
`
`28. The specification does not describe any structure that correspondsto the
`indentations of Claim 5.
`‘The specification deseribes prior art grooves and
`
`corrugations (Col. 2:19-27}, and then states that the shape ofthese grooves or
`corrugations may be changed by including indentations 17. Col.3:59-62.
`
`However, neither the drawingsnor the text provide any description of these
`indentations.
`In fact, the specification states that the “grooves 17” allow collapse
`
`

`

`recovery. Col. 4, lines 21-24. H thus admits that the prior art “grooves” provide
`
`the claimed recovery function.
`
`29. Furthermore, US Patent No. 1,807,225 (Attachment 9), for example, among many
`
`other references, discloscs a wide range of corrugations and grooves.
`
`(Sec,
`
`Figures 1, 6, and 8 wherein the corrugations add “strength and rigidity.” Page
`
`2:33-45.) Ht would have been obvious to a PHOSITAto include features on a
`
`diaphragm to recover from collapse, and in particular on a high comphance
`
`driver’s diaphragm, which is typically very floppy and knownto be prone to
`
`collapse.
`
`30. [ reserve the right to address any theories, opinions, arguments or evidence
`
`that Bose may advance in support of any contention that the claims of the asserted
`patents are not invalid or unenforceable.
`In addition, | have reviewed other prior
`art found in the Joint Notice of Prior Art and reserve the right to use the other
`
`prior art in addressing any new theories, opinions, arguments or evidence.
`
` </7 6 /o#
`
`outlas Winker, Ph.D.
`
`Date
`
`[2007 Rotherhan
`
`Austin, Texas 78753
`
`

`

`APPENDIX OF ATTACHMENTS TO EXHIBIT B
`
`Attachment |
`
`Attachment 2
`
`Attachment 3
`
`Attachment 4
`
`Attachment 5
`
`Asserted Patent, US 5.181.252
`
`Douglas Winker, Ph.D., CV
`
`Beranck. Acoustics, (Acoustical Society of America, 1996)
`
`Prior Art, EPO Patent Appheation Publication No. 019564
`
`Prior Art Patent, US 2.714.134
`
`Attachment 6
`
`Prior Art Patent, US 4.041.256
`
`Attachment 7
`
`Attachment 8
`
`Attachment 9
`
`Attachment 10
`
`Prior Art Patent, US 4,297,537
`
`Prior Art Patent, US 4,399,334
`
`Prior Art Patent, US 1,807,225
`
`D’ Appolito, Testing Loudspeakers (Audio Amateur
`Publications 1998), Chapter 2, page 16
`
`

`

`ATTACHMENT 1
`
`

`

`CACOREEE
`USO05181252A
`.
`11] Patent Number:
`5,181,252
`119)
`United States Patent
`Sapiejewski et al,
`[453 Date of Patent:
`Jan, 19, 1993
`
`
`[54] HIGH COMPLIANCE HEADPHONE
`DRIVING
`
`
`
`Inventors: Roman Sapiejewski, Boston. Jetn J.
`Breen, Southbors, both of Mass.
`,
`.
`.
`(73] Assignee: Bose Corporation, Framingham,
`Mass.
`[21] Appl. No: 782,874
`(221 Filed:
`Oct. 16, 1991
`
`7/1948 Eokardheee 181/166
`2,379,891
`
`ow 183/166
`9/1947 Eklov 2...
`2,427,844
`771963 Bleazey et alo ose 181/32
`3,073,411
`8/1983 Kakiuchi cial.
`.
`we 381/194
`4,399,434
`6/1984 Bose et ah oe SBITE
`4,455,675
`4,581,496 4/7986 Sweany |
`4,644,581
`2/1987 SapiejewSki oon IBIVIET
`4,922,542
`§/1990 Sapiciewski oe 3817187
`FOREIGN PATENT DOCUMENTS
`0195641
`3/1986 European Par. Off.
`.
`8101815 11/1981 Netherlands oe SBIS19F
`3,
`{
`11224534
`6/1983 United Kingdom .
`ienti
`21882104
`Related U.S. Application Data
`3/1987 United Kingdom .
`
`[63]|Continuation of Ser. No. 138,095, Dec. 28, 1987, Pat. 2187361 9/1987 United Kingdom wu... 381/74
`
`No. 4,922,542, and a centinuation of Ser. No. 398,133,
`.
`.
`Aug. 23, 1989, abandoned.
`Primary Examiner-—James L. Deyer
`.
`Assistan: Examiner-~Jason Chan
`Int. CE veerHOFR 25/00; HOSR 7/00
`Attorney, Agent, or Firm—Fish & Richardson
`UWS. Cheects: SBE/ISF: 381/183,
`381/158; 181/166
`[57]
`ABSTRACT
`Field of Search ............... 381/181, 183, 158, 197,
`An active noise reducing headset has a high compliance
`381/74, 202; 181/166, 171,172
`diaphragm. Structure limits the maximum excursion of
`References Cited
`the diaphragm so that the voice coil does not escape the
`.
`air gap. Struciure, such as indentations in the dia-
`US. PATENT DOCUMENTS
`phragm, prevent unrecoverable diaphragm collapse.
`Re. 26,030 $/1966 Marchand ef al ow. SBISI9T
`
`1,807,225
`S/1931
`Pack ween
`tiveness 181/164
`
`6 Claims, 2 Drawing Sheets
`
`
`
`

`

`U.S, Patent
`
`Jan, 19, 1993
`
`Sheet 1 of 2
`
`5,181,252
`
`
`
`

`

`U.S. Patent
`
`Jan. 19, 1993
`
`Sheet 2 of 2
`
`5,181,252
`
`FIG. 2
`
`FIG. 4
`
`
`
`

`

`1
`
`5,181,252
`
`2
`tronic circuitry comprising a system corresponding
`substantially to the active noise reducing system dis-
`closed in U.S. Pat. Nos. 4,644,581 and 4,455,675 incor-
`porated herein by reference.
`Referring to FIG. 2, there is shown a diagrammatic
`sectional view generally patterned after the sectional
`view of the aforesaid U.S. Pat. No. 4,644,581 with head-
`phone cup structure added to betterillustrate the rela-
`tionship among the front cavity, rear cavity, high com-
`pliance drive and raised portions on the basket surface,
`Baffle 11 separates front or inside cavity 11F from rear
`or outside cavity LER and carries high compliance drive
`13 having diaphragm 14 and mayhave the driver basket
`surface 13B formed with raised portions 23R.
`Having described the physical arrangement of an
`exemplary embodiment,
`it
`is appropriate to consider
`certain principles. It is convenient to refer to the cavity
`nearer the user and encompassing his ear with head-
`phonesproperly positioned as the front or inside cavity
`and the cavity further from the user as the rear or out-
`side cavity. It is desirable to keep the front cavity vol-
`ume as small as practical to maximize the sound pres-
`sure that the small driver produces at the ear canal to
`cancel low frequency noise. However, to increase pas-
`sive transmission attenuation for ambient noise penetrat-
`ing an ear cup sealed around the ear by a cushion,it is
`desirable to make the front cavity volume large.
`It has been discovered that the effective air volume
`which determines this transmission attenuation is not
`simply the volume of the front cavity but also a funetion
`of the driver compliance (below its free air resonance
`frequency) and the volume of the rear cavity. If Cris the
`compliance of the front cavity air volume, C, is the
`compliance of the rear cavity air volume and Cy is the
`compliance of the driver, then the effective compliance
`Coyprdetermining passive transmission attenuation is the
`front cavity compliance in series with the parallel com-
`bination of the driver compliance and the rear cavity
`compliance, or
`
`0
`
`us
`
`2335
`
`35
`
`HIGH COMPLIANCE HEADPHONE DRIVING
`
`CROSS-REFERENCE TO RELATED
`APPLICATION
`
`This application % a continuing application of co-
`pending application Ser. No. 07/138,095, filed Dec, 28,
`1987, of Romau Sapiejewski entitled HEADPHONE
`COMFORT, rlow U.S. Pat. No, 4,922,542 granted May
`1, 1990, and is a continuation of Ser. No. 398,133 filed
`Aug. 23, 1989, now abandoned.
`BACKGROUND OF THE INVENTION
`
`invention relates to high compliance
`The present
`drivers ir: active noise reducing headsets. Particularly,it
`relates 10 an apparatus for protecting the driver dia-
`phragm.
`In active noise reducing headphonesit is known to
`use a headphone having front {inside} and rear (outside)
`cavities separated by a baffle carrying a small driver.
`SUMMARY OF THE INVENTION
`
`According to the invention, the driveris a high com-
`pliance driver. According to another feature of the
`inveution, there is structure limiting the maximum ex-
`cursion of the diaphragm. According to another feature
`of the invention, the diaphragm is formed with indenta-
`tions having a componeut
`transverse to the circular
`grooves or corrugations uear the diaphragm periphery.
`According 10 another aspect ofthe invention, the basket
`surface under the diaphragm has raised portions.
`BRIEF DESCRIPTION OF THE DRAWING
`
`Other features and advantages of the invention will
`become apparent from the following detailed descrip-
`tion when read in connection with the accompanying
`drawing in which:
`FIG. 1 is a plan view of a high compliance driver
`with the headphone cup generally illustrated to show
`the environment of the invention; and
`FIG, 2 is a diagrammatic axial sectional view ofele-
`ments in FIG, 4.
`FIG. 3 is a plan view of another embodiment of the
`invention corresponding to FIG. 1 illustrating a fine
`wire mesh screen for limiting diaphragm excursion; and
`FIG. 4 is a block diagram illustrating the logical ar-
`rangement of an active noise reduction system embody-
`ing the invention.
`DETAILED DESCRIPTION
`
`With reference now to the drawing, and more partic-
`ularly FIC. i thereof, there is shown an embodiment of
`the invention. The invention includes a baffle II that
`separates a front or inside cavity from a rear or outside
`cavity and carrics high compliance driver 13 having
`diaphragm 124. Plastic fingers 15 are equi-angularly
`spaced about the driver axis, extend radially inward and
`are positioned along the driver axial direction of motion
`so as to limit displacement of the diaphragtn from its
`center or rest position to a plane sufficiently close to the
`rest plane with the diaphragm centered so that a portion
`of the voice coil is always in the air gap and sufficiently
`far from the central plane so that the diaphragm is free
`to translate axially without obstruction when normally
`reproducing sound with the headphones properly
`mounted on the head of the user. An active noise reduc-
`tion syStem mounting struciure 16 carries a microphone
`(FIG. 4} near the diaphragm used with associated elec-
`
`45
`
`$0
`
`&
`
`Cyr Cp Cy Ca(Cy + Cg}
`below the free air resonance of the driver.
`Since compliance of an enclosed quantity of air is
`proportional to the volume, for a given ear cup volume
`divided into front and rear cavities, it can be shown that
`the effective compliance Cyris maximized by maximiz-
`ing the driver compliance. Thus, a driver with very
`high compliance (low stiffness) and low mass (so as to
`resonate with the high compliance at as high a fre-
`quency as practical), effects significant improvements in
`passive transmission attenuation below driver free air
`resonance without audibly affecting sound reproduc-
`tion. In the limit, if the compliance ofthe driver is much
`greater than the compliance ofthe air in the rear cavity,
`the effective compliance is equal to the sum of the rear
`cavity and front cavity compliances, Cr+-C,.
`High compliance herein means the driver compliance
`is greater than the rear cavity compliance.
`Another advantage of high compliance drivers is that
`at very low frequencies (below the rear cavity port
`resonance whentherear cavityis ported), higher driver
`compliance results in higher system efficiency. This
`increase in efficiency reduces the electrical power re-
`quired 10 generate sound pressures needed to cancel
`high levels of low frequency noise. This feature is par-
`ticularly advantageous in battery-powered active noise
`reduction headsets and hearing protectors.
`
`

`

`5,181,252
`
`4
`from collapsing to the
`sure situations, preventing it
`poimi that permanent damage or change in shape oc-
`curs.
`
`3
`When the ear opening in the headset is sealed agains1
`the head or any other surface, motion of the earcup
`relative 10 thal surfaee changes the volume ofthe front
`cavily. Shght changes in volume result in tremendous
`subsonic pressures. If the voluine is increased, such as
`when the earcup is removed from the head after ihe
`cushion was sealed tightly to the head, the under-pres-
`sure generated ieuds to pull
`the driver diaphragm
`toward the opened end of the earcup. Since high com-
`pliance, low mass drivers move very freely, this pres-
`sure can very easily pull the voice coil outside of the
`gan beyond its norma] maximum range of excursion,
`with the risk that 11 may catch on the driver basket or
`magilet and 101 return to its nominal rest position upon
`release of the under-pressure.
`If the volume is de-
`creased, Such as when the earcup is pushed suddenly
`against the head, the over-pressure generated can cause
`the thin, flexible diaphragm to collapse from its normal
`Shape. Drivers with diaphragms formed from thin plas-
`tic films usually are formed with angled grooves or
`corrugations in the outer annulus between the voice coil
`and the edge of the diaphragm. These grooves expand
`and contract as the voice coil moves and help assure
`linearly, piston like motion. Under the over-pressure
`conditions described above, these grooves may irrev-
`ersably change shape, and prevent the driver diaphragm
`from returning to its norma! shape and position,
`The invention avoids the suction or under-pressure
`problem by locating a structure in the earcup over the
`diaphragms 1o limi! voice coii excursion, This structure
`15 is positioned such that, during the normal range of
`excursion of the driver diaphragm, the diaphragm does
`not touch structure 15 and motion is unimpeded. Struc-
`ture 15 is located close enough to the driver such thatit
`contacts the diaphragm before it is pulled so far that the
`voice coil is pulled fully from the gap. Since the voice
`coil
`is not pulled from the gap, when the suction is
`released, the coil will return to its normal rest position
`and not hang up on the basket. The structure ¥5 is pref-
`erably small enough so that it does not cause diffraction
`or otherwise affect the sound pressure detected by the
`active noise reduction system’s microphone except at
`high frequencies {above 10 KHz). The present inven-
`tion accomplishes this by using three small fingers of
`plastic 15 positioned to symmetrically contact the dia-
`phragm along the circle where the voice coil is glued to
`it. Contacting the diaphragm with smal] point-like fin-
`gers anywhere but along the voice coil might risk possi-
`bly puncturing or otherwise damaging the diaphragm.
`An alternative embodiment for the structure to stop
`diaphragm motionis a fine wire mesh screen 16° shaped
`So as to contact as muchofthe surface of the diaphragm
`as possible at its position of maximum allowed outward
`excursion. By contacting over a large area, the pressure
`al any point is small enough so as not to damage the
`driver.
`The present invention avoids the driver collapse or
`over pressure problem by using a driver whose dia-
`phragm recovers its shape when collapsed. Changing
`the shape of the grooves or corrugations by including
`indentations 17, liaving a radial component in the dia-
`phragm such that the diaphragm recovers its shape if
`collapsed, prevents unrecoverable collapse. An alterna-
`tive solution is to change the shape of the metal basket
`to which the diaphragm is attached or to add a structure
`to the basket. Commouly the basket surface under the
`diaphragm is flat. By raising this surface at some points
`
`oO
`
`A preferred form of the invention involves combin-
`ing the driver mounting structure, active noise reduc-
`tion system microphone mounting structure, and driver
`under-pressure excursion stops into a single plastic
`piece molded in one shot. This approaeh reduces the
`effect of mechanical tolerance build-up and positions ail
`parts accurately so as to provide consistent perfor-
`mance, This structure could be further combined with
`the baffle separating front and rear cavities.
`The specific apparatus functions as follows. When the
`headset
`is removed from the head causing an under
`pressure situation,
`limitation elements 15 limit the ex-
`cursion of diapliragm 14 so that the voice coil doesn’:
`escape the air gap. This structure ensures that dia-
`phragm 14 will return to its nominal position. These
`limitation elements 15 do not interfere with the normal
`range of motion of diaphragm 14.
`In an over-pressure situation such as when the head-
`set is pressed against the head, grooves ¥7 in the surface
`of diaphragm 14 cause the diaphragm 14 to recoverits
`original shape if collapsed by the increase in pressure. In
`another embodiment,
`raised points underneath the
`diaghragm 14 supportit during over-pressure situations
`preventing a collapse.
`In a specific embodiment of the invention, the front
`cavity volume is approx