COMMUNICATING WITH ACllVE NOISE REDUCING
HEADSET
The present invention relates in general to corainimieivting wtli a noise reducing headset and roore pmiiculai'ly concenis novel apparatus ai^d techniques using an active noise reducing headset having headphones selectively connectable betvc'cen a connector for receiving external electrical signals and a microphone for transducing speech outside the headset.
BACKGROUND OF THE mVBNTION For background refensneeis made to Pubiicatipn US 2005/021.3774 A1 published September 29, 2005, the information set forth in paragraph [002] thereof, pending US Application No. 1(^868,318 filed June 15, 2004, now Publication US 2005/0276421A1 publi.shed December IS. 2005, and Japanese Unexamined Patent Application Publication No. 1:18-70493 published Miai-ch 12,1996, all incorporated by reference herein.
Sl)?vl\:L4RY OF THE INWNTION According to the invention, an active tioise reducing headset hsis headphone.^ .selectively intercotinected between a comiector for receiving external electrical .signals and a microphone for transducing speech outside the headphorieSi
Other features, objects and advantages of the invention will become apparent from ihe ibllovving detmled description when reiul in connection witb tlie accompaityit>g driiwing in VfMch:
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
FIG I is a block diagram of tlie logical iirrangement of a system according to the invention;
FIG. 2 shows a headset 'Virilhi microphones on cach headphone receiving outside speech; aiid
FIG 3 i,s a block pictorial diagram of an emlx)diment of the intention using feed forward active noise reduction.
Witii reference to the drawing atid more pMiculariy FICt 1 tliereof' tliere is shown a block diagram iliustnsting the logical arrangement of a systein according to (he iiiveBtion. Cn this embodiment a sigml combiner 30 aigebraicaliy combines the signal desired to be. reproduced by the headphone on input terminiil 24 connected to switch tenninai SI A with switch SI connected i\s shown with the feedback signal provided by internal microphone preamplitier 35. Signal combiner 30 provides the con>bined signal to compressor 31 which Umits the level of high level signals, llie output of compressor 51 is applied to compeiisator 3.1 A. Compensator 31A includes compensation circuits to ensure that tlie open loop gain meets tlie Nyquist stability criteria so that the system wll not Oxscillate when the bop is closed. The system shown is duplicated once each for the left and right ears.
Power amplifer 32 amplifies the signal from compensator 3IA energizes headphone dnver 17 to provide an acoustic signal in cavity 12 that is combined with an outside noise .signal that enters cavity 12 fri:im a region repre-sented as acoustic input ierminal 25 to produce a combined acotistic pressure signal in cavity 12 represented as a circk^ 36 applied to ittid transduced by internal microphone II. Ititemai microphone preajnpHfier 35 ampHfies tlte trfmsduced signal mtd delivers it to signal combiner 30.
With switch SI connected to terminal SIB, a iramduced .signal from outside microphone 41 coupled through outside microphone preamplitter 42, prefe.ra.bly havirtg a bandpass restiicted to tl'ie speech spectnmi, is delivered to sigiiaJ combiner 30.
The invetition has a nurnber of advantage.'* when used wlh an active noise reducing headset, such as the Bose* QuietComfort Acoustic Noise Cancelling^' headphones having an attached microphone. The wearer, such as an airplane passenger, may move switch .SI to receive die fansduced speech signal of a flight attendant, for e.xample, that i.*; clcitfly heard with the benefit of the active noise reduction. Moving the switch to connect to terminal SI A allows the user to listen to an eieciricai audio .signal on .input 24, such as music or the sound track of a movie or, alternatively, xviti) no signal applied, enjoy Uie ts-anquility of significantly reduced noi.se In a noi.sy atiTiosphere, such as that of an aircraft.
Referring to FIG, 2, there is shown a diagranmatie view of outside microphones, suchas4l or41', attached to headphone cups, such as 43 and 44.
Referring to FKj. 3, tliere is shown a bbck-pictoriaJ diagram or an emooaimeiH or the im'eatioti usiiig feed fbnvard vvrth aii extenial feed forvi'ard micTophone .I T that is coupled by aii inverting aivplifler 51 and filter 52 tliat typically selectively trajismits spcctral components within a predetermined band of audio frequencies to effect noise reduction in that band. The output of filter 52 is coupled to one input of combiner 36'. The other input of combiner 36' is coiipled to tlie artn of switch. SI" tliat selectively reeeives either audio input signal on terminal SIA" or the ainpiilled sound signal transduced by outside microphone 4J" on terminal S.IB". The output of combiner 36' is coupled to power aniplilTer 32' that drives headphone driver 17". Feed Ibrwaixi microphone 11' is always coupled to an input of coniblner 36' to effect active noiiie reduction.
There has been described novel apparatus and techniques ibr improving communication in a noisy enviromiient. It is evident that tliose skilled in the ait may now make numerous uses and modifications of and departures from the specific apparaiiis and techmqiies herein disclosed without departing from the inventive concepts. C-onsequei^ti)', tlie invention is to be consti-ued a.s embracing each and every novel feature and novel combination of features present in or possessed by apparatus and techniques herein discIo.sed GSCIUPT10N OF THE SEVERAL VIEWS OF THE DRAWINO
FIG 1 is a block diagram of the logical iirrangement of a system according to the invention;
FIG, 2 shows a headset willi microphones oa each headphone receiving outside speech; and
FIG 3 is a block pictorial diagram of an embodiment of the intention using feed forward active noise reduction.
Widi refbrence io the drawing and more particularly FKi 1 tliereof, tliere is shown a block diagnmi illustTating the logical arrangement of a systeni according to the i'iivenijoti, Cn this embt>dimcnt a signal combiner 30 aigebraically comfeines t&e signal desired to be reproduced by the headphone on input temiinal 24 connected to switcii tennifld SI A with switch SI connected as showi with the feedback signal provided .by internal microphone preamplitier 35. Signal combiner 30 provides the coti^bined signal to compreissGr 31 which h'mits the level of high level sigi^als. Ilie output of conipre^;sar 31 is applied to compeiisator 3.1 A. Compensator 31A inciude« con:ipensation circuits to ensure thai tlie open loop gain meets tlie Nyquist stability criteria so that the system mil not oscillate when the loop is closed The system shown is duplicated once each fi.)r the left and right ears,
Power iimplifler 32 amplifies the signal from compensator 31A and energizes headphone diiver 17 to pravide aii acoustic signal in cavity 12 that is combined with ati outside noise signal that enters canity 12 from a region represented m acouisiic input terminal 25 to produce a combined acoustic pressure signal in cavity 12 represented as a circle 36 applied to imd transduced by internal microphone 11. Internal microphone preamplifier 35 iunplifies the traiisduced signal and delivers it to signal cosnbiner 30.
With switch SI connected to terminal SIB, a transduced signal from outside microphone 41 coupled through outside microphone preamplifier 42^ preferably havirtg a bandpass resti-icted to tlie speech apectnmi, is delivered to signal combiner 30.
The invention has a number of advantages when used with an active noise reducing headset, such as the Bose*' QuietComfort Acoustic Noise Cancelling* headphones having an attached microphone, "fhe wearer, such, as an airplane passenger, may move switch SI to receive tlie transduced speech signal of a tlight attendant, for e.Kan.rpIe, that is cleitfly heard with the benefit of the active iioisc reduction. Moving the switch to connect to terminal SI A allows the user to listen to jm elecirical audio signd on input 24, such as music or the sound track of a movie or, alternatively, xvitl^ rio signal applied, enjoy die tranquility of significantly reduced noise In a noisy atmosphere, such as that of an aircraft.
Referring to FiG. 2, there is shown a diagranmatic view of outside microphones, such as 41 or 41', attached to headphone cups, such as 43 and 44.
Refaing to FIG. 3, tliere is shown a biock-pictoria! diagram of an emhodimejit of itneation Uisiiig feed i^wward v\it!i an extenial feed for'W-'ard micrOphme IF lliat is soupied by ajv inverting aiwplifier 51 and filter 52 tliat tj'pically seiectivdy transmits spccti-a} components within a predetermined band of audio frequencies to effect noise reduction in that band. The output of filter 52 is coupled to one input of combiner 36', The other input of combiner 36' is coupled to tlie artn of switcii Si" tliat selectively reeeives either tlie audio input Mgnal on terminal SI A" or the mnpiified souiid signal txansduced by outside micrtjphcjne 41" on terminal SIB". The output of combiner 36' is coupled to power aiDplifier 32' that drives headphone driver 17'. Feed forwani microphone 11' is always coupled to an input of combiner 36' to elTect active noise reduction.
There has been described novel apparatius and teohnique.s ixvr improving communication in a noisy environment. It is evident that tliose skilled in the ast may now make numerous Usses and. modifications of and departures from the specific apparauis and techniqiies herein disclosed without departing from the inventive caricepts. Consequent!}', the invention is to be construed as embracing each and every novel feature and novel combination of features present in or possessed by apparatus and techniques herein disclosed and Hmiteti only by the spirit ajiid scope of the appended claims.

WBMMIS CLAIMED IS:
1, C/OniiTumjcation apparatus compdsiiiig, a noise .i-edwcing headphone,
an input terminal for receiving an electxical inpul signai, an outside microphone attiiched to said headphone coiistmcted and aixanged to eleclmacoustically tnuisdx^ce a signal external to the headphone into a corresponding electilcai speech signal Uirough a bandpass filter restricted to the speech spectRun,
a switch coupled to Siud headphone ha\dng a first temiinal coupled to said input terminal and a second terminal coupled to said outside microphone constructed and arranged to selectively couple said headphone to only one of vsaid first tenninal and said second terroina!,
and a noise reducing microphone for eiectroacousticaliy transducing an unde.sired acoastic signal into a corresponding undesired acoustic eiectrieal signal, a combiner constructed and arranged to combine the desired signal on that one of the first and second terjniniUs which said switch has then selected with said undcsired acoustic electrical signal to provide a combined signal, and a. power amplifier coupling said combined signal to said headphone to reduce the audibility of said undesired aconstie signal to a user of said headphone.
2, Convmunication apparatus in accordance with claim 1 w^lierein said noise reducing microphone is inside said headphone imd comprises a negative feedback circuit conatrucied and iirninged to reduce the audibility of said undesired acoustic signa! to a user of said head phone.
3, Communication apparatus in accordance witl^ claim 1 wherein said noise reducing microphone is outside said headphone and coinprises a feed fonvard circuit constructed and arranged to reduce the. audibili ty of said undesired acoustic signal to a user of said headphone^
4, Commutiication apparatus in accordance with claim 1 and further comprising a second headphone, wherein said switch is coupled to both said headphones to
sd' couple .said headphones to oiily one of said first terniinal and said second lermijiM.
5. C..omniujiication app^tws in aceordancc mtii claim 4 aiid further comprising a second outside microphone atoched to said second headphone constructed and Ranged to ekcti'oaccoustically transduce a signal external to tlie second headphone into a corresponding electiical speech signal through a second bandpass fiiter restricted to the speech spcctram.