UNITED STATES INTERNATIONAL TRADE COMMISSION
`WASHINGTON, D.C.
`
`Before Honorable Charles E. Bullock
`Administrative Law Judge
`
`
`
`In the Matter of
`
`CERTAIN NOISE CANCELLING
`HEADPHONES
`
`Investigation No. 337-TA-626
`
`
`
`COMPLAINANT BOSE CORPORATION’S OPPOSITION TO RESPONDENT AUDIO-
`TECHNICA’S SUPPLEMENTAL NOTICE OF PRIOR ART FOR U.S. PATENT
`5,181,252 AND U.S. PATENT 6,597,792 AND MOTION FOR LEAVE TO SUPPLEMENT
`THE EXPERT REPORT OF ITS EXPERT MARSHALL BUCK
`
`Complainant Bose Corporation (“Bose”) hereby opposes Respondent Audio-Technica
`
`U.S., Inc.’s (“Audio-Technica”) Supplemental Notice of Prior Art and its accompanying Motion
`
`for Leave to Supplement the Expert Report of its Expert Marshall Buck, both filed on the eve of
`
`the close of fact discovery, and some 15 days after the initial expert report was due. Because
`
`allowing the requested supplementation would severely prejudice Bose for no good cause, both
`
`Audio-Technica’s Supplemental Notice of Prior Art and its Motion for Leave to Supplement Dr.
`
`Buck’s Initial Expert Report should be denied.
`
`It is disingenuous for Audio-Technica to claim on June 12 (the date on which it filed the
`
`underlying motion for leave) that its expert, Marshall Buck, had “just uncovered” “new” prior
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`art1: an alleged noise reducing headset from Active Noise and Vibration Technologies, Inc.
`
`(“ANVT”), Model NQ100 (“NQ100”).2 In reality, Audio-Technica and its expert, Marshall
`
`Buck, have had knowledge of and easy access to the NQ100 since Dr. Buck was hired by Audio-
`
`1 Bose’s use of the term “prior art” here and throughout this opposition should not be
`construed as an admission that the NQ100 is prior art vis-à-vis the patents at issue.
`2 It is actually unclear throughout Audio-Technica’s motion whether it means to request
`leave to supplement as to the NQ100 or as to some ANVT AQ100 device, which is curiously
`mentioned twice as often (16 times) in Audio-Technica’s motion than the NQ100 (7 times).
`Bose has not received any documentation or notice regarding an ANVT AQ100 device.
`
`

`
`Technica in March 2008, and even before that, because the NQ100 was allegedly purchased by
`
`Harman International, Dr. Buck’s former employer, way back in 1994 while Dr. Buck was still
`
`supposedly Harman’s Chief Acoustic Engineer. It is telling how easily Dr. Buck describes being
`
`able to get the NQ100 headset that Audio-Technica now seeks to bring into this case. All he had
`
`to do was contact his former colleague from Harman, which he did not do until around June 2,
`
`2008, six weeks after respondents’ Notice of Prior Art was due (yet prior to filing his initial
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`expert report on invalidity). (See Buck Decl. at ¶¶ 11-12). Audio-Technica was not even
`
`delayed by the ordinary discovery procedures involved in issuing subpoenas to third parties.
`
`Apparently, Dr. Buck simply made a friendly request to his former colleague, something he
`
`could just as easily have done when he was first retained in this case. Indeed, nearly the entirety
`
`of Dr. Buck’s declaration is a testament to how familiar he has been with the NQ100, allegedly
`
`since 1994. (Id. at ¶¶ 4-9.)
`
`Even if Dr. Buck did not alert Audio-Technica to the existence of the NQ100, Bose’s
`
`document production should have. In fulfillment of Bose’s discovery obligations, Bose
`
`produced numerous documents to Audio-Technica early in discovery which identified the
`
`NQ100. These documents include an article from Mechanical Engineering featuring the NQ100
`
`product (BOSITC052355 – 052360, produced on Feb. 29, 2008) (Ex. A), and a scientific paper
`
`entitled “Comparison between subjective and objective measures of active hearing protector and
`
`communication headset attenuation” which discusses the NQ100 (BOSITC056462 – 056467,
`
`produced on Feb. 29, 2008) (Ex. B). As a result, Audio-Technica was aware of the NQ100
`
`months prior to the Court-ordered deadlines of April 21 for filing notices of prior art and May 28
`
`for submitting initial expert reports.
`
`The ease with which Audio-Technica could have (and should have) become aware of the
`
`NQ100 through Dr. Buck, his former work colleague, and Bose’s document production greatly
`
`
`BOSE’S OPPOSITION TO AUDIO-TECHNICA’S MOTION FOR LEAVE TO FILE SUPPLEMENTAL PRIOR ART
`NOTICE AND EXPERT REPORT—PAGE 2
`
`

`
`undermines Audio-Technica’s assertion that it did not discover the NQ100 until June 2, 2008.
`
`Thus, Audio-Technica has not shown good cause to be allowed to supplement its prior art notice
`
`and its expert report well past the deadlines. Therefore, its motion for leave should be denied.
`
`Allowing Audio-Technica to supplement its expert report with “prior art” which it had no
`
`good cause to ignore until this late point in the investigation would severely prejudice Bose.
`
`First, fact discovery has closed and, with only six weeks until the hearing, this case is well
`
`beyond the point where Bose could conduct counter-discovery to investigate this alleged prior art
`
`(for example, by subpoenaing its manufacturer to determine its features and whether it was in
`
`fact on sale to qualify as prior art, and by deposing Dr. Buck’s source to determine whether the
`
`device has been altered in any way). In addition, Bose’s expert witness, Dr. Durand Begault has
`
`not yet had a meaningful opportunity to analyze the NQ100, despite Audio-Technica’s claim that
`
`it made the NQ100 available for inspection as of June 6, 2008 (on a Friday afternoon only 5 days
`
`prior to rebuttal expert report deadline of July 11). Dr. Begault has already been deposed. If
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`Audio-Technica were granted leave to serve its supplemental report on this new prior art, Dr.
`
`Begault would most likely have to write another rebuttal report and sit for deposition again, thus,
`
`greatly delaying the end of discovery in this case and jeopardizing the Court’s, the Staff’s, and
`
`the parties’ ability to adequately prepare for the hearing, which is now only six weeks away.
`
`Audio-Technica’s initial expert report was due three weeks ago and its prior art notice
`
`nearly two months ago. Allowing Audio-Technica (and all the other respondents by default) to
`
`add the NQ100 to its prior art disclosure at this point would amount to a de facto extension of
`
`nearly two months from the deadline of April 21, 2008, for Respondents to identify their prior
`
`art. The Court’s deadlines serve the purpose of giving structure and order to the discovery
`
`process. They cannot be so cavalierly disregarded. Moreover, the speed of an ITC investigation
`
`does not allow for such delay, whether intentional or by neglect. And, most importantly, such a
`
`
`BOSE’S OPPOSITION TO AUDIO-TECHNICA’S MOTION FOR LEAVE TO FILE SUPPLEMENTAL PRIOR ART
`NOTICE AND EXPERT REPORT—PAGE 3
`
`

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`delay would cause substantial prejudice to Bose’s ability to prepare its case as Bose would not
`
`have the time or the opportunity to develop facts rebutting this new alleged prior art. Put simply,
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`Audio-Technica seeks to spring new prior art upon Bose well after the Court-mandated
`
`deadlines, and with no good cause. Accordingly, Audio-Technica’s notice of supplemental prior
`
`art should be stricken and its motion for leave to supplement Dr. Buck’s initial expert report
`
`should be denied.
`
`For the Court’s convenience, a Proposed Order is included herewith.
`
`
`
`
`
`
`
`
`
`Respectfully submitted,
`
`
`
`BOSE’S OPPOSITION TO AUDIO-TECHNICA’S MOTION FOR LEAVE TO FILE SUPPLEMENTAL PRIOR ART
`NOTICE AND EXPERT REPORT—PAGE 4
`
`
`
`FISH & RICHARDSON P.C.
`
`/s/ Autumn J.S. Hwang
`
`Ruffin B. Cordell
`Andrew R. Kopsidas
`Jeffrey R. Whieldon
`Autumn J.S. Hwang
`FISH & RICHARDSON P.C.
`1425 K Street, N.W.
`11th Floor
`Washington, D.C. 20005
`Telephone: (202) 783-5070
`Facsimile: (202) 783-2331
`
`Charles Hieken
`Gregory A. Madera
`FISH & RICHARDSON P.C.
`225 Franklin Street
`Boston, MA 02110
`Telephone: (617) 542-5070
`Facsimile: (617) 542-8906
`
`Jordan T. Fowles
`FISH & RICHARDSON P.C.
`1717 Main Street
`Suite 5000
`Dallas, TX 75201
`Telephone: (214) 747-5070
`
`
`
`
`
`
`Dated: June 18, 2008
`
`

`
`Facsimile: (214) 747-2091
`
`Attorneys for Complainant
`Bose Corporation
`
`
`
`BOSE’S OPPOSITION TO AUDIO-TECHNICA’S MOTION FOR LEAVE TO FILE SUPPLEMENTAL PRIOR ART
`NOTICE AND EXPERT REPORT—PAGE 5
`
`

`
`CERTIFICATE OF SERVICE
`
`I hereby certify that on June 18, 2008, a copy of
`
`COMPLAINANT BOSE CORPORATION’S OPPOSITION TO RESPONDENT AUDIO-
`TECHNICA’S SUPPLEMENTAL NOTICE OF PRIOR ART FOR U.S. PATENT
`5,181,252 AND U.S. PATENT 6,597,792 AND MOTION FOR LEAVE TO SUPPLEMENT
`THE EXPERT REPORT OF ITS EXPERT MARSHALL BUCK
`__________________________________
`was served on the following as indicated:
`
`
`
`Marilyn R. Abbott
`Secretary
`U.S. International Trade Commission
`500 E. Street, S.W., Room 112-F
`Washington, DC 20436
`
`
`
` Via Hand Delivery
` Via U.S. Mail
` Via Overnight Delivery
` Via Electronic Mail
` Via Facsimile
` Via Electronic Docket Filing
` Not Served
`
` Via Hand Delivery
` Via U.S. Mail
` Via Overnight Delivery
` Via Electronic Mail
` Via Facsimile
` Via Electronic Docket Filing
` Not Served
`
` Via Hand Delivery
` Via U.S. Mail
` Via Overnight Delivery
` Via Electronic Mail
` Via Facsimile
` Via Electronic Docket Filing
` Not Served
`
` Via Hand Delivery
` Via U.S. Mail
` Via Overnight Delivery
` Via Electronic Mail
` Via Facsimile
` Via Electronic Docket Filing
` Not Served
`
`
`The Honorable Charles E. Bullock
`Administrative Law Judge
`U.S. International Trade Commission
`500 E Street, S.W., Room 317-I
`Washington, DC 20436
`
`
`
`T. Spence Chubb, Esq.
`Christopher G. Paulraj, Esq.
`Office of Unfair Import Investigations
`U.S. International Trade Commission
`500 E Street, S.W., Room 404-I
`Washington, DC 20436
`
`
`
`William B. Nash, Esq.
`Daniel D. Chapman, Esq.
`Mark Fassold, Esq.
`Jackson Walker L.L.P.
`112 E. Pecan Street., Suite 2400
`San Antonio, TX 78209
`
`Counsel for Respondents Phitek Systems
`Limited, GN Netcom, Inc., Creative Labs, Inc.,
`and Logitech Inc.
`
`
`
`
`
`
`
`
`
`
`
`
`
`
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`BOSE’S OPPOSITION TO AUDIO-TECHNICA’S MOTION FOR LEAVE TO FILE SUPPLEMENTAL PRIOR ART
`NOTICE AND EXPERT REPORT—PAGE 6
`
`

`
`
`Alan Cope Johnston, Esq.
`G. Brian Busey, Esq.
`Cynthia Lopez Beverage, Esq.
`Morrison & Foerster LLP
`2000 Pennsylvania Ave., N.W., Suite 5500
`Washington, DC 20006-1888
`
`Counsel for Respondents Phitek Systems
`Limited, GN Netcom, Inc., Creative Labs, Inc.,
`and Logitech Inc.
`
`
`James P. White, Esq.
`J. Aron Carnahan, Esq.
`Welsh & Katz, Ltd.
`120 South Riverside Plaza, 22nd Floor
`Chicago, IL. 60606
`
`Counsel for Respondent Audio-Technica U.S.,
`Inc.
`
`
`Arthur Wineburg, Esq.
`Daniel E. Yonan, Esq.
`Akin Gump Strauss Hauer & Feld LLP
`1333 New Hampshire Ave., N.W.
`Washington, DC 20036
`
`Counsel for Respondent Audio-Technica U.S.,
`Inc.
`
`
`Daniel Ebenstein, Esq.
`Abraham Kasdan, Esq.
`Joseph Casino, Esq.
`David A. Boag, Esq.
`Amster, Rothstein & Ebenstein LLP
`90 Park Avenue
`New York, NY 10016
`
`Counsel for Respondent Panasonic
`Corporation of North America
`
`
`Tom M. Schaumberg, Esq.
`Jamie D. Underwood, Esq.
`Adduci, Mastriani & Schaumberg, LLP
`1200 Seventh Street, N.W., Fifth Floor
`Washington, DC 20036
`
`Counsel for Respondent Panasonic
`Corporation of North America
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
` Via Hand Delivery
` Via U.S. Mail
` Via Overnight Delivery
` Via Electronic Mail
` Via Facsimile
` Via Electronic Docket Filing
` Not Served
`
` Via Hand Delivery
` Via U.S. Mail
` Via Overnight Delivery
` Via Electronic Mail
` Via Facsimile
` Via Electronic Docket Filing
` Not Served
`
` Via Hand Delivery
` Via U.S. Mail
` Via Overnight Delivery
` Via Electronic Mail
` Via Facsimile
` Via Electronic Docket Filing
` Not Served
`
` Via Hand Delivery
` Via U.S. Mail
` Via Overnight Delivery
` Via Electronic Mail
` Via Facsimile
` Via Electronic Docket Filing
` Not Served
`
` Via Hand Delivery
` Via U.S. Mail
` Via Overnight Delivery
` Via Electronic Mail
` Via Facsimile
` Via Electronic Docket Filing
` Not Served
`
`BOSE’S OPPOSITION TO AUDIO-TECHNICA’S MOTION FOR LEAVE TO FILE SUPPLEMENTAL PRIOR ART
`NOTICE AND EXPERT REPORT—PAGE 7
`
`

`
`
`
`
`
`/s/ Patrick Edelin, Jr.
`
`
`
`BOSE’S OPPOSITION TO AUDIO-TECHNICA’S MOTION FOR LEAVE TO FILE SUPPLEMENTAL PRIOR ART
`NOTICE AND EXPERT REPORT—PAGE 8
`
`
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`
`

`
`
`
`
`
`UNITED STATES INTERNATIONAL TRADE COMMISSION
`WASHINGTON, D.C.
`
`Before Honorable Charles E. Bullock
`Administrative Law Judge
`
`In the Matter of
`
`CERTAIN NOISE CANCELLING
`HEADPHONES
`
`Investigation No. 337-TA-626
`
`[PROPOSED] ORDER NO.: ______
`
`DENYING RESPONDENT AUDIO-TECHNICA’S SUPPLEMENTAL NOTICE OF
`PRIOR ART FOR U.S. PATENT 5,181,252 AND U.S. PATENT 6,597,792 AND MOTION
`FOR LEAVE TO SUPPLEMENT THE EXPERT REPORT OF ITS EXPERT
`MARSHALL BUCK
`
`Having considered Respondent Audio-Technica’s Supplemental Notice of Prior Art for
`
`
`
`
`
`U.S. Patent 5,181,252 and U.S. Patent 6,597,792 and Motion for Leave to Supplement the Expert
`
`Report of its Expert Marshall Buck, and Bose’s Opposition thereto, it is determined that Audio-
`
`Technica’s motion should be, and hereby is, DENIED.
`
`
`
`So ORDERED this ______ day of June, 2008.
`
`
`
`
`
`
`
`
`
`Hon. Charles E. Bullock
`Administrative Law Judge
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`

`
`
`
`EXHIBIT A
`
`EXHIBIT A
`
`

`
`Comparison between subjective and objective measures
`of active hearing protector and communication
`headset attenuation
`Jan Zera,a) Anthony J. Brammer, and George J. Pan
`Natlonal Research Council of Canada, Ottawa, Onlario K]A OR6, Canada
`
`(Received 17 April 1996; revised 13 December 1996; accepted 29 December 1996)
`
`A marked-threshuid and a loudness-balance method have been developed to estimate the attenuation
`of communication headsets and hearing protectors with buik-ln active noise reduction (ANt)
`systems. Both methods ere used to estimate the attenuation of the ANt systems and the
`masked-threshold method is also used to estimate the total attenuation (active plus parsive) of the
`device. The procedures ere designed to be used in the presence of environmantal noise, and to
`mlnlm~z’ e the noise exposure of subjects during the measurements. For comparison, physical
`mearurements of insertion loss have also been performed using a miniature microphone in the
`concha‘ Experiments showed that the masked-threshold method tends to give increased estimates of
`the attenuation if the noise reduction of the let and right eercup ANR systems differs, as commonly
`occurs in practice. In conR-ast~ the loudness-balance method reduces the estimates of the active
`attenuafion. Insertion loss measurements may be influenced by the position of the microphone,
`owing to the epatial variability of the sound field under an earmuff when the ANR system is
`operating. Differences between physical and subjective measurements of up to 20 dB have been
`obtained in this study at frequencies of 250 Hz and below for a device in which the sound pressure
`varied subsmufiaRy neer, and within, the ear canal. [$0001-4966(97)02205-4]
`PACS numbers: 43.50.Hg, 43.50.Ki [GAD]
`
`INTRODUCTION
`
`"[’here ere two commonly used designs for hearing pro-
`tectors and headsets (protectors incorporating a communica-
`tion channel) with built-in active noise reduction (ANR) sys-
`tems. One employs a lerge cL~umanral eercup with a
`compllant cushion. In this device, the AN~ system is used to
`increase the attenuation in the frequency range below 500
`Hz. At mid and high frequencies, the headset displays con-
`sidemble passive attenuation. The other tyge of device em-
`ploys Hghtweight, often supra-anral construction. The ANR
`system of this headset provides most of the headset attenua-
`tion at frequencies from 50 to 1000 Hz. All these active
`devices differ from maditional parsive devices in several
`ways that ere impo£tant for the me~u’ing methods used for
`their assessment. Firstly, the presence of external (environ-
`mental) noise is raquired for their proper operation. Sec-
`.anally, the attenuation of the ANR system often intentionally
`ch~ugar with the exteraalnoise level. Thirdly, the electronic
`noise of the system may cause edditianal marking in renl-
`ear-at-threshold (REAT) measurements,1-3 lendlng to the
`overestimation of attanuatianf’~ Thus, an active hearing pro-
`tector, or headset, cannot be tested at noise levels corra-
`sponding to the absolute threshold of headug, nor can the
`device be arsumed to be lineer over a wide range of sound
`levels. These factors suggest the need for measurement
`methods spedfically designed for devices with ANR
`syatemsf, v,4,s
`There ere, at present, few repoV.s evaluating the perfur-
`mance of active hearing protectors or headsets using subjec-
`
`=)Cunrnt address: C~ntral I~sti~to fo~Labour Pmte~on, uL Czemiakowskn
`16, 00-701 Wamaw, po]aM.
`
`rive methods. Forshaw et aL9 used a masked-threshold and a
`Ioudueas-balence method to arsars the active attenuation of
`an A.NR headset, and Crab[zea and RylandsI° have also used
`a Ioudnees-balanea method for this purpose. Carall and
`Robinson4 have discussed the difficulty of ar tablishing a urg-
`form, standa~ized procedure for measuring the attenuation
`of all types of active heariug protectors, and proposed a hy-
`pothetical hybrid procedure sukable for devices in which the
`ANR is used only to increase the attenuation at low frequen-
`cies. According to their proposal, the smuderdized tEAT
`method would be used for subjective measurement of the
`passive attenuation of the device, while objective measure-
`ment would be used to determine the tom1 (active+passive)
`attenuation and the ANR.
`We believe that subjective and objective methods should
`be dsveloped independently for the measurement of total
`tenuatinn, which is the most impo£tant parameter to the user,
`ar well ar for the active component (ANt), which has to be
`determined during device develupment. Because an ANR
`headset or hearlug protector should be tested at noise levels
`similer to those at which it wfil be used, suprathreshold psy-
`choacoustic methods would appear to be required for this
`purpase..
`The purpose of this reseerch was to develop and test
`methods of measurement sultuble for the ANR devices, in an
`attempt to foster the development of smudardlzed methods of
`measurement. We present here two subjective methods for
`estimating the active attenuation of an ANR headset or hear-
`ing protector:, a marked-threshold procedure and a Ionduess-
`balance procedure. The masked-threshold procedure may
`also be used to estimate the total attenuation, and is designed
`to min~ize the subject’s expesure to noise. The Iouduess-
`
`HG. i. Three drvices used in the eXlx~dmenls.
`
`balance procedure differs from its traditional form by em-
`ploying a two-altematlve forced-choice (2-AFC) design, and
`is implemented using an adaptive technique. This afiows us
`to simplify the experiment for inexperienced llsteners and so
`improve their decisions. The r~ts of the subjective men-
`surements are then compered with objective measurements
`of the attenuation recorded by a miniature microphone lo-
`cated either in the conchaIt’m or within the eer canal.
`In the following sections, we first inrcoduea the ANR
`devices, measuring system, and subjects. Then, the subjec-
`tive and objective measuring methods ere darcribed and ra-
`suits reviewed. This order was chosen since it allowed us
`more opportunity to discuss the measurement methods.
`
`I. APPARATUS AND SUBJECTS
`A, Hearing proton-tot and headsets
`
`Measurements were conducted in an anechoic chamber
`(inner dimensions 5,6X3.SX3.4m) located on the campus of
`the National Rareerch Council in Ottawa. A rpecial noise
`source was constructed for the measurements, consisting of
`four loudspeaker systems located in a horizontal plane at the
`comers of a rectangle t.8 m by 1.75 m (see Figs. 2 and 3).
`Each loudspeakcr unit included a subwoofer (State of Art
`~leatrenik, 300 W), a midrange section (PSB-800 100-W
`two-way loudspeaker system), and an Audax super tweeter.
`The Audax super tweeters were used in addition to the tweet-
`ers of the PSB speakers to enhance the performance of the
`system at high frequencies. A Brystun active crossover
`(model 10B) was used to divide the ~equency range into low
`(20-100 Hz), mid (100-4500 Hz), and high (4500-20 000
`Hz) frequency bands. The low- and midrange speakers were
`Two communication headsets and one he~-ing protector,
`powered by four Bryston 4B amplifiers (250 W per channel).
`representing various design concepts, were selected for the
`Bryston 2B amplifiers (50 W per channel) were used to drive
`experiments (see Fig. 1). These were a Peltor headset (model
`the Audax super tweeters.
`7004), a Quiet.Men headset (mauufactured by IvlNC, Inc.),
`The noise source was capable of generating broadband
`and a hearing protector, modeINQl00, manufactured by Ac-
`(25-20 000 Hz) pink noise of 110 dB suund-prassuxe level
`rive Noise and ¥ibmtinn Techuologiar (ANV’f).
`The Peltur 7004 is a circumaural headset with a lerge
`volume (approximately 130 cm3) enclosed by the eercup (see
`Pig. 1, the sample to the left). A combined liquid-filled ~ud
`foam cushion provides en effective seal between the earanp
`and the head. The ANR system of this headset is designed to
`imprave its attenuation at frequencies below 300 Hz.
`The QuietManheadset (see Fig, I, the middle sample) is
`also a circumaural device, but with a smaEar volume under
`the lightweight eercup and a pertial air seal between the eer-
`cup and the head. The attenuation of this headset at frequen-
`cias below I000 Hz is entirely dependent on the performance
`of the ANR system.
`The ANVT NQ100 hearing protector (see Fig. 1, sample
`to the right) is a supra-aural device of very fightweight can-
`srraction with the ANt system acting in a restricted fre-
`quency range (70-400 Hz), end with some parslve attenua-
`tion above 3000 Hz.
`
`FIG, 2. ~1oor plan of the exlx~dmental setup in the anechoi~ chamfer. NI-
`N4: four-~l~al~r source: of pink noise, LSI: sl~.aker
`dgna] when the headse¢ was not worn by ~ m~bje~
`
`B. External noise source
`
`HG, 3. E.xpefimental setup iu t~ anechoic chamber, S~e~. ker LSI in n~
`shown,
`
`

`
`(sPL) at a reference point corresponding to the center-head
`position w’~’th the subject and chair absent, Before experi-
`ments commenced, the noise level measured fix one-thlrd oc-
`tave bends at the centar-head position (with subject end chair
`absent) was adjusted electrenicaffy to be within -+3 dB of the
`target p~ noise specR’um, using a Technics Stereo Equal-
`izar model SH-9010. If necessary, the positions of the high-
`frequency tweeters were also adjusted. The diffuseness of the
`sound field at the subject’s head was increased by intreduc-
`hag a 25-ms delay betwean midfrequency speakers using a
`Klark-Teknik modal DNT00 delay line.
`
`C. Subjects
`Seven subjects, aged from 20 to 24 years, pasdcipated fix
`the experknents. Before experiments commenced their heas-
`ing thresholds were measured using a clinical audiometer
`(Madsen, modal OB 40) in accordance with ANSI $3.6-
`1989. Subjects had normal hearing, with less then 10 dB HI.,
`throughout the f~equency range from 125 Hz to 8 kHz. Five
`subjects ($1-$5) participated in both the initial psychen-
`coustical tests and the objective measurements described fix
`Secs. H end ]H. Two subjects ($6 end $7) participated fix
`measurements of the spaffal variability of the sound field
`under the eareup described fix Sec. IV. The number of sub-
`jects was chusen so that, within tho time consh’aints avaffuble
`for the study, measurements could be repeated for each sut of
`experimental conditions.
`A subject, wearing en ANR device, was seated in a chair
`at the center of the four-speaker source (see Fig. 2). The
`subject’s head position was referenced in the horizontal
`plene to the midpoint of the Ioudspeakar array, which was
`defined by the Iocatlon of the tweeters of the PSB speakers.
`The reference point was maintained by two (harlzentul end
`vartlcal) laser pointers, with en accuracy of -+0.5 cm. The
`chair was equipped with a support to position the back of the
`subject’s head during measurements (Fig. 3). For safety rea-
`sons, end to improve communication between the subject
`end the experimenter, a video camera was mounted fix the
`anechoic chamber. It allowed the subject to be seen by the
`experimenter, who continuously monitored the subject’s
`head position during the measurement session. A measure-
`ment session, involving one headset or the hearing protector,
`was completed in 3 h.
`2"he subjects had no prior experience of psychoecousti-
`calmeasurements end were i~tially trained for about 5-10 h
`until leamlng effects were not observed.
`
`II. SUBJEC~VE METHODS
`A. Masked-threshold method
`In the masked-threshold method, the difference in
`threshold between that determined fix a noisy eavlronment
`when the headset, or hearing protector, is worn and when it
`is not worn provides a measure of the attenuatiun of the
`davica.I~,ll The complication associated with udug en addi-
`tional sound source may explain why tho masked-threshold
`method has never been stendardized, end is infrequently used
`to evaluate passive hearing protectors. Active hearing protec-
`tors end headsets am already equipped with en earphone to
`
`serve as the secondary source for active noise cenceliation,
`In headsets, and some active hearing protectors, the easphone
`is also used to deliver signals from a communication chan-
`nel. In these elrsumstances, it is feasible to use rids chaunel
`to present the test signals for a masking procedure without
`compromising the performance of the ANR system.
`When a conventional masked-threshold method is em-
`ployed, masking noise of up to 100 dB SPL may be required
`in order to measure the device’s parformence under realistic
`operating conditions. A health and ethical prublem then
`arises as to how to protect subjects from excessive exposure
`to high noise leveis, end to prevent temporary threshold shift
`from influencing the res-ults. White noise, or bendlimired
`white noise, has been used in most masking experiments.14
`However, the shape of the hearing damage risk contours as a
`function of frequency~ suggests that white noise would pro-
`duce either insufficient sound leveis at low frequencies, or
`excessive sound levals at high frequencies. For the purpose
`of the present experiments, pink noise would appear to pro-
`vide a reasonable balence between energy at high and low
`frequencies, and was therefore adopted for the masking
`noise. During the experiments the level of broadbend
`noise was set to a maximum of LI=90 dB SPL~ for the
`Paltor end QuietMen headsets. The A-welghted sound level
`did not exceed 87 dB, to comply with Cenadien Occupa-
`tlonal Safety end Health Regulations (1991) for eight hours
`daffy exposure. The maximum noise level was only 80 dB
`SPL for experiments involving the NQ100 headug protector,
`because distortion (clipping) of the ANR system was ob-
`served at higher leveis.
`
`Stimulus control
`The masked-threshold procedure described here is da-
`signed to minimize a subject’s exposure to noise, by permit-
`ting exposures only to levels not greater then those experi-
`enced when the ear is fully protected by the ~ headset or
`heating proteetur. The goal of ~g a subject’s expo-
`sure to noise was achieved by decreasing the levul of the
`masktug noise when measurements were taken with the
`ANK system not operating, or the headset or hearing protec-
`tor not worn (unprotected ear). The externalnoise source was
`used to generate the masking noise.
`The measurement procedure involves three steps (see
`Fig. 4). In step one, the device is worn and the ANR system
`is operating. The noise outside the device is kept at loyal
`LD which should be the highest sound level permitted dur-
`ing testing. The subject is presented with a pure-tone test
`signal dellver~d through the earphone, and the masked
`threshold of this signal is determined by adjusting its sound
`pressure.
`In step two, the ANR system is not operating (i.e.,
`switched off). The impcrtent chenge from step one is that the
`test signal at the ear is now kept eoustent at the previously
`detemfined threshold level. The masking noise is varied to
`determine a new level, L-z, which just masks the test signal.
`If the noise caueelling system increases the attenuation of the
`device, then level L’2 should be lower then the initial level
`used fix step one (LI). The difference fix levels, L~--L2, is a
`subjective measure of the active attenuation of the device.
`
`was depressed after each pair of trials. The duration of the
`test tones and the interstlmulas interval was 200 ms. The
`tones were ramped with a 10-ms sine squared function.
`Feedback was provided after each response, end there were
`20 trials in each adaptive run.
`In each step seven threshold measurements were made.
`The mean thl~hold was est~nated by calculating the average
`of the interquastile results, that is, after excluding the lowest
`and the highest observed values. The meen threshold men-
`sured fix step one (device worn, ANR switched on), was used
`to set the loyal of the test tone in steps two (device worn,
`ANR system switched off), and three (daviee not worn). In
`these steps the maximum-likelihood procedure was used to
`adjust the level of the masking noise.
`Device attenuation was determined three times by each
`subject for eight test frequencies: 63, 125, 250, 500, 1000,
`2000, 4000, end 8000 Hz. During measurements, the mask-
`ing noise bendwidth was reduced to two octaves below end
`above the test frequency. Fikering out nuise bends which did
`not contn’ente to masking affowed us to llmit further the
`subject’s exposure to noise.
`Stimulus presentation, timing, end response recording
`were controlled by en IBM-PC microcomputer equipped
`with a DSP card end external modules from Tuckar-Davis
`Technologies (System II). The test tones were generated us-
`ing a 50-kHz sampling rate and were low-pass filtered at 10
`kHz. The pink noise was generated by a Bruel & Kjuer noise
`generator (modal B&K 1405); its level was adjusted by at-
`tenuators cenlrnlled by the computer (module PA4 of Sys-
`tem II).
`
`3. Calibration
`Cal~mfion of the device’s alectroacoustie amplifcafion
`was required to aeaount for the differences fix gnin between
`the ANR-on end ANR-off conditions. Similarly, calibration
`of the loudspeaker LS1 was needed to compensate for its
`frequency response.
`Calibration was performed during a separate session end
`invulved physical measurement of the SPI~ using a minia-
`ture mierephune (Knowles BL 1785) placed in the middle of
`the subject’s concha. The sequence of test tones used during
`the masked-threshold measurements was played ten times
`through the earphone under the two operating eundifiens
`(A.NR on end ANR off), end from the loudspeaker in front of
`the subject. Since the position of the devica on a subject’s
`head was the most significant factor influencing the resdts of
`measurements, the subject was required to doff end don the
`device between measurements. ~ procedure increased the
`stendard deviation of measurements but reduced bias that
`might result from controlled mounting of the device on a
`subject’s head. Thus, the results are intended to represent the
`performance to be expected during normui use of the head-
`set. Reeordlngs were takenhoth from the left end right ears,
`end the data were averaged.
`The dlfferenees between the SPLs recorded under the
`three measurement conditions were used to equalize the elec-
`~eal input to the headset, hearing protector, or loudspeaker,
`fix order to obtain the same sound pressure in the eeneha with
`the headset worn and ANR switched on. The difference in
`
`Finaffy, in step three, the headset or hearing protector is
`not worn. The test signal is presented from loudspeakar LS1,
`located in front of the subject. The test signui is again pre-
`sented to the ear at the threshold levul determined fix step one
`of the procedure, end the level of the masking noise, L3, is
`determined that just masks the test signal. Loyal L3 should
`be consldembly lower then levelly, if the headset produces
`meaningfu! protection from noise. The level difference L1
`-L3 is a subjective measure of the total attenuation of the
`device.
`The level of the test signal presented fix step two has to
`be corrected for eny change fix electroaeoustie gain of the
`headset or hearing protector between the AN-R-on end ANR-
`off eendltiens. Also, fix step three, the gain of the lend-
`speaker ehaunel LS1 t~s to be adjusted to obtain the same
`leval of the test signal as the threshold level obtained fix step
`one, The required caffbrations are descn’bed in Sec. II A 3.
`In the REAT method, one-third octave-bend noise is rec-
`ommended for the test signal, in order to obtdu results inte-
`grated over a range of frequencies, For the masked-thrashold
`method’ it may be