United States Patent [i9j
`Andrea et al.
`
`[54] NOISE CANCELLATION APPARATUS
`
`[75] Inventors: Douglas Andrea, Old Brookville;
`Martin Topf, Brooklyn, both of N.Y.
`
`[73] Assignee: Andrea Electronics Corporation, Long
`Island City, N.Y.
`
`[21] Appl. No.: 912,459
`Aug. 18, 1997
`[22] Filed:
`
`Related U.S. Application Data
`
`[60] Division of Ser. No. 485,047, Jun. 7, 1995, which is a
`continuation-in-part of Ser. No. 339,126, Nov. 14, 3994, Pat.
`No. 5,673,325, which is a continuation-in-part of Ser. No.
`968,380, Oct. 29, 3992, Pat. No. 5,383,473.
`[51] Int. Cl.6 ................................................. G10K 11/16
`[52] U.S. Cl.........................381/71.6; 381/71.7; 381/71.13
`[58] Field of Search ............................... 381/71.6, 71.7,
`381/71.13, 72, 74, 93
`
`[56]
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`2/1965 Leale .
`6/1987 Clough .
`8/1992 Kimura et al. .
`3/1998 Andrea et al. .
`
`3,170,046
`4,672,674
`5,138,664
`5,732,143
`
`FOREIGN PATENT DOCUMENTS
`0390386 10/1990 European Pat. Off. .
`
`US005825897A
`[ii] Patent Number:
`[45] Date of Patent:
`
`5,825,897
`Oct. 20, 1998
`
`Primary Examiner—Forester W. Isen
`Attorney, Agent, or Firm—Frommer Eawrence & Haug
`EEP; Thomas J. Kowalski; I. Marc Asperas
`ABSTRACT
`[57]
`This invention relates to a method and an apparatus for
`reducing ambient noise for use with a headset or a boom
`headset attached to a boom microphone device or the like.
`The apparatus can include a sensor microphone to detect a
`background noise signal, a desired input audio transmission,
`and signal processing means for canceling the noise signals
`to create an inverted anti-noise signal within an acoustical
`waveguide located adjacent to the earphone of headset. The
`method for reducing noise according to this invention is
`provided by an open loop circuit allowing the input audio
`signal from an operator or caller to be transmitted to the
`user’s ear without the disturbance of unwanted ambient
`noise. The method provides adjustments to the gain and/or
`phase of a noise signal for canceling the noise component
`detected, within an acoustical waveguide to produce a quiet
`zone for the desired audio speech to be transmitted. The
`apparatus can also include a noise cancellation microphone
`transmitter system having a first and second microphone
`arranged such that the first microphone receives a desired
`speech input and the background noise present in the vicin­
`ity of the speech, and the second microphone receives
`substantially only the background noise. The background
`noise from the second microphone is converted into a
`corresponding electrical signal and subtracted from a signal
`corresponding to the speech and background noise obtained
`from the first microphone so as to produce a signal repre­
`senting substantial the speech.
`5 Claims, 30 Drawing Sheets
`
`LGE EXHIBIT NO. 1004
`
`- 1 -
`
`Amazon v. Jawbone
`U.S. Patent 8,467,543
`Amazon Ex. 1004
`
`

`

`U.S. Patent
`U.S. Patent
`
`Oct. 20, 1998
`Oct. 20, 1998
`
`Sheet 1 of 30
`Sheet 1 of 30
`
`5,825,897
`5,825,897
`
` S3N17
`
`INOHGS194
`
`WOUS
`
`
`
`SIN17SNOHd3Tal
`
`OL
`
`- 2 -
`
`

`

`Oct. 20, 1998
`Oct. 20, 1998
`
`SINI7INOHdIT4LJNOHd39131
`
`U.S. Patent
`U.S. Patent
`
`OL
`
`foLe4
`
`40388
`
`
`
`
`
`Sheet 2 of 30
`Sheet 2 of 30
`
`5,825,897
`5,825,897
`
`SANT1SNOHd3TAL
`NOUSQi
`
`LINA
`
`ocOd
`
`8ANOHdITIL
`
`|
`
`r
`
`2eeeVo
`
`0]LASGNVH
`
`- 3 -
`
`
`
`

`

`U.S. Patent
`U.S. Patent
`
`Oct. 20, 1998
`Oct. 20, 1998
`
`Sheet 3 of 30
`Sheet 3 of 30
`
`5,825,897
`5,825,897
`
`F !G. 3A
`
`SPEECH
`
`D1 RECTION
`
`FIG. 3B
`
`DIRECTION
`
`OF SPEECH
`feTzAllLon
`Cip2aET,RETESTZL §
`
`
`
`
`
`
`
`
`
`
`- 4 -
`
`

`

`U.S. Patent
`U.S. Patent
`
`Oct. 20, 1998
`Oct. 20, 1998
`
`Sheet 4 of 30
`Sheet 4 of 30
`
`5,825,897
`5,825,897
`
`L3SQNVH|*It@INOHdaTaL|t-|bb222WaWWadS
`||4|Ol
`
`FIG. 4
`
`22
`
`|||||}of||
`
`INOHdS141.
`
`a7aL|ANOHS13}9222-)(+
` 8ssiSNOWY
`
`S3NIT|=|
`
`|-
`
`- 5 -
`
`
`
`
`

`

`U.S. Patent
`U.S. Patent
`
`
`qWoHdTa]INOHdS1aCoeSFO¥Is
`SANIT
`OL|ONALTI!|20S2191M|oo¢
`
`|+\6¢eeoh_|GOld
`
`Oct. 20, 1998
`Oct. 20, 1998
`
`NOUS7|
`
`NOHTal:
`SINITah=!
`
`—
`
`Sheet 5 of 30
`Sheet 5 of 30
`
`5,825,897
`5,825,897
`
`
`
`CTTTTTTNN7|oyylfya,T=bOIN|!I||!g0e
`|OlL380
`
`/8JNOHdITIL
`
`- 6 -
`
`
`

`

`U.S. Patent Oct. 20, 1998 Sheet 6 of 30
`
`5,825,897
`
`DIRECTION
`
`FIG.6C
`
`146
`
`- 7 -
`
`

`

`U.S. Patent
`U.S. Patent
`
`Oct. 20, 1998
`Oct. 20, 1998
`
`Sheet 7 of 30
`Sheet 7 of 30
`
`5,825,897
`5,825,897
`
`FIG.7A
`
`FIG. 7A
`
`FIG.7B r—~b/2Sme
`MIC2
`
`r+b/2Sme
`
`“QI
`~
`—_
`
`™
`—
`—_—
`
`MIC|
`
`2
`C
`MI
`
`- 8 -
`
`

`

`U.S. Patent
`U.S. Patent
`
`Oct. 20, 1998
`Oct. 20, 1998
`
`Sheet 8 of 30
`Sheet 8 of 30
`
`5,825,897
`5,825,897
`
`MIC1-MIC2—_
`
`CJ>
`
`FIG.8
`
`=a
`
`o
`@
`
`- 9 -
`
`

`

`U.S. Patent
`U.S. Patent
`
`Oct. 20, 1998
`Oct. 20, 1998
`
`Sheet 9 of 30
`Sheet 9 of 30
`
`5,825,897
`5,825,897
`
`FIG.IB
`
`FIG.9A
`
`-10 -
`
`- 10 -
`
`

`

`U.S. Patent
`U.S. Patent
`
`Oct. 20, 1998
`Oct. 20, 1998
`
`Sheet 10 of 30
`Sheet 10 of 30
`
`5,825,897
`5,825,897
`
`FIG.9E
`
`FIG.9C F/G.9D
`
`-11-
`
`- 11 -
`
`

`

`U.S. Patent
`U.S. Patent
`
`Oct. 20, 1998
`Oct. 20, 1998
`
`Sheet 11 of 30
`Sheet 11 of 30
`
`5,825,897
`5,825,897
`
`
`
`FIG.9F
`
`-12-
`
`- 12 -
`
`

`

`U.S. Patent
`U.S. Patent
`
`Oct. 20, 1998
`Oct. 20, 1998
`
`Sheet 12 of 30
`Sheet 12 of 30
`
`5,825,897
`5,825,897
`
`Cout
`
`o
`
`+=
`
`—=o
`
`So
`
`s
`—
`co
`
`wri
`co
`
`o
`©
`
`ja
`
`Sis
`
`+
`=
`
`<
`wo
`
`{i
`
`i
`
`oe
`
`pe
`
`oN
`
`as
`a
`
`ll
`
`a
`
`a
`
`i
`
`co
`
`CO
`O
`
`>C
`
`a
`
`9
`
`ae(5 ww
`ic
`
`Ss
`co
`
`MIC|
`
`S
`
`es
`
`; Pod
`
`oe
`
`ws
`e>
`=
`
`I
`
`—_
`C
`>=
`MI
`
`- 13 -
`
`nS
`ra)
`
`=a
`a
`
`=oo
`cx
`
`|
`
`co
`oS
`oo
`
`&
`
`coOd
`
`=
`
`\!
`
`=
`NX
`
`2
`
`Hi
`
`MIC2
`
`oS
`
`ZI
`S
`~
`® —
`
`FIG. ΙΟΑ
`
`OL
`=
`
`- 13 -
`
`

`

`U.S. Patent
`U.S. Patent
`
`Oct. 20, 1998
`Oct. 20, 1998
`
`Sheet 13 of 30
`Sheet 13 of 30
`
`5,825,897
`5,825,897
`
`fout10OUTPUTINTERFACE CKT
`
`FIG.//
`
`R3
`
`100
`
`V+
`
`-14-
`
`- 14 -
`
`

`

`U.S. Patent
`U.S. Patent
`
`Oct. 20, 1998
`Oct. 20, 1998
`
`Sheet 14 of 30
`Sheet 14 of 30
`
`5,825,897
`5,825,897
`
`Cout
`
`INTERFACE
`
`TOQUTPUT
`Lo
`
`KT
`
`800
`
`FIG.12
`
`FIG. 12
`
`-15 -
`
`- 15 -
`
`

`

`U.S. Patent
`
`Oct. 20, 1998
`
`Sheet 15 of 30
`
`5,825,897
`
`eg
`
`50.000Hz Y;-43J5dB ZA;LIVE CURVE preompff rlU.
`
`X;
`
`- 16 -
`
`

`

`U.S. Patent
`
`Oct. 20, 1998
`
`Sheet 16 of 30
`
`5,825,897
`
`FIG. I3B
`
`RELATIVE
`RESPONSE (dB)
`
`TYPICAL FREQUENCY RESPONSE(Hz)
`
`- 17 -
`
`

`

`U.S. Patent
`U.S. Patent
`
`Oct. 20, 1998
`Oct. 20, 1998
`
`Sheet 17 of 30
`Sheet 17 of 30
`
`5,825,897
`5,825,897
`
`
`
`
`
`OlOIA
`
`FIG. 14
`
` Yslidsd
`916
`
`~¥(2DIW-1IW)4905
`
`M+S
`
`be6——¥
`
`KO1
`
`- 18 -
`
`- 18 -
`
`

`

`U.S. Patent Oct. 20, 1998 Sheet 18 of 30
`
`5,825,897
`
`FIGI6B
`
`k TO FINAL
`>SUMMARY
`AMPLIFIER
`
`n
`
`- 19 -
`
`

`

`U.S. Patent
`
`Oct. 20, 1998
`
`Sheet 19 of 30
`
`5,825,897
`
`F/GJ7A
`PRIOR ART
`
`- 20 -
`
`

`

`U.S. Patent
`U.S. Patent
`
`Oct. 20, 1998
`Oct. 20, 1998
`
`Sheet 20 of 30
`Sheet 20 of 30
`
`5,825,897
`5,825,897
`
`
`
`FIG. 18
`
`-21-
`
`- 21 -
`
`

`

`Oct. 20, 1998
`Oct. 20, 1998
`
`Sheet 21 of 30
`Sheet 21 of 30
`
`5,825,897
`5,825,897
`
`U.S. Patent
`
`ore
`U.S. Patent 1H/OI
`
`-22 -
`
`- 22 -
`
`

`

`U.S. Patent
`U.S. Patent
`
`Oct. 20, 1998
`Oct. 20, 1998
`
`Sheet 22 of 30
`Sheet 22 of 30
`
`5,825,897
`5,825,897
`
`10226
`aco”94oboe\
`
`090%
`
`elOIW
`
`(INOU4)|INI
`
`- 23 -
`
`Ate
`
`Y001
`Wee
`
`64
`
`Lu
`
`oe__a
`
`Nl
`
`kyova)
`
`|HiatWu
`
`OWeNI
`
`- 23 -
`
`
`
`
`

`

`U.S. Patent
`U.S. Patent
`
`Oct. 20, 1998
`Oct. 20, 1998
`
`Sheet 23 of 30
`Sheet 23 of 30
`
`5,825,897
`5,825,897
`
`1210
`
`FIG.2/PRIORART
`
`-24 -
`
`- 24 -
`
`

`

`U.S. Patent
`U.S. Patent
`
`5,825,897
`5,825,897
`
`Oct. 20, 1998
`Oct. 20, 1998
`
`Sheet 24 of 30
`Sheet 24 of 30
`
`ObE|
`
`-25 -
`
`- 25 -
`
`

`

`U.S. Patent
`U.S. Patent
`
`Oct. 20, 1998
`Oct. 20, 1998
`
`Sheet 25 of 30
`Sheet 25 of 30
`
`5,825,897
`5,825,897
`
`F1G.238
`FIG.23A
`
`- 26 -
`
`- 26 -
`
`

`

`U.S. Patent
`U.S. Patent
`
`Oct. 20, 1998
`Oct. 20, 1998
`
`Sheet 26 of 30
`Sheet 26 of 30
`
`5,825,897
`5,825,897
`
`
`
`FIG. 24
`FIG. 24
`
`-27 -
`
`- 27 -
`
`

`

`U.S. Patent
`U.S. Patent
`
`Oct. 20, 1998
`Oct. 20, 1998
`
`Sheet 27 of 30
`Sheet 27 of 30
`
`5,825,897
`5,825,897
`
`(1T3NNVHO)
`
`01
`
`
`40Luvd0191
`
`IH/WdSpay4¢[77OVIMNdS=¢2yIH/QIW
`171H/1¥8Todi
`
`7OI7I¥8aie
`
`
`saat119N
`
`2Oldny
`
`ON
`
`- 28 -
`
`- 28 -
`
`

`

`U.S. Patent
`U.S. Patent
`
`Oct. 20, 1998
`Oct. 20, 1998
`
`Sheet 28 of 30
`Sheet 28 of 30
`
`5,825,897
`5,825,897
`
`¢
`
`it
`
`401W¥deR
`
`(1TANNYH9)!
`
`1
`
`ONOW r¢310N33S
`1N0034315
`/NI
`
`ATH/IOINNGOII°
`
`yolive
`
`OTASINYEG4
`
`-29 -
`
`96OldL7-90Obl
`
`FIG. 26
`
`0NA002
`
`INGAp(Si)
`
`- 29 -
`
`
`

`

`U.S. Patent
`U.S. Patent
`
`Oct. 20, 1998
`Oct. 20, 1998
`
`Sheet 29 of 30
`Sheet 29 of 30
`
`5,825,897
`5,825,897
`
`
`
`nylava)\posspeea338
`
`~AYd31000"a|ASE||401
`if|LayQ310N
`LethIe
`+AU0aM804o4'—YRdUNY
`
`NOLAHSNOIAHS
`0¢9SOLWNAZHe%OV)ooesixd\poeelya“dO.InceACE
`
`
`soysey]SOU110010yomayoOlge922avedO¢N?-I
`rigda)01L3LON33S
`eee|heh
`.C59)
`idA
`
`seyVedBeeIN
`
` +s06siXdyWON|_|43S8by
`
`ZOHA
`
`FIG. 27
`
`p60dndJz.
`
`- 30 -
`
`- 30 -
`
`
`

`

`U.S. Patent
`U.S. Patent
`
`Oct. 20, 1998
`Oct. 20, 1998
`
`Sheet 30 of 30
`Sheet 30 of 30
`
`5,825,897
`5,825,897
`
`
`
`
`
`WALSASOlONY.0661og6l
`
`82Old3NOLIUS
`
`
`~NYWAISASINOHdOYDIN
`
`See0¢eltWAISAS\MYHL19104
`:’056!VVOlONY|OLLNdLNO|apyccp|____»9onanY|
`
`WOU4FLAdNIWNOILISOd0161C161086]
`QA1VINWIS ¢SNOSSINSNYHL006!winnisBIC6|Ld~0261
`
`
`CeUNVWLSASdQOUVS
`iAanga]W's°oIn
`
`9061-mdWVWALSAS
`
`
`
`océloun|NOILISOd|opelr¢06!NYHLIVENOILISOdSION
`p06!Au
`]oNT¥as’YNY7Ud
`G26ls106}
`3Ly9WIOA
`
`
`
`TWNOISHodad$=
`
`AYHLYI¥L
`
`JMS
`
`0961104LNO9
`
`NIV)1061
`
`Sits*F
`
`- 31 -
`
`- 31 -
`
`
`

`

`1
`NOISE CANCELLATION APPARATUS
`
`This application is a division of application Ser. No.
`08/485,047, filed Jun. 7,1995 which in turn is a continuation
`in part of application Ser. No. 08/339,126, filed on Nov. 14,
`1994, now U.S. Pat. No. 5,623,325 which in turn is a
`continuation in part of application Ser. No. 07/968,180, filed
`on Oct. 29, 1992 now U.S. Pat. No. 5,381,473.
`
`BACKGROUND OF THE INVENTION
`1. Field of the Invention
`Hie present invention relates to method and apparatus for
`noise canceling and noise reducing by attenuating unwanted
`ambient noise from reaching the eardrum and canceling
`background acoustic noise received from a boom micro­
`phone or directional microphone, when used with a headset
`or boom headset or the like.
`Hie invention further relates to an active noise reduction
`system for use in headsets, particularly in the earphone
`vicinity where the system utilizes a sensor microphone to
`detect unwanted, background noise. Uris noise signal out­
`putted by the sensor microphones is processed by electro­
`acoustical means to produce an inverted signal so that a quiet
`zone is created in an acoustical waveguide located between
`the output transducer, and the eardrum. Therefore the
`desired original audio signal is not disturbed by noise when
`transmitted to the ear of the user. Hie acoustical waveguide
`absorbs any sound returning to the microphone from the ear
`(preventing feedback) and deadens any sound returning
`from the microphone to the ear.
`This invention also relates to a noise cancellation
`apparatus, for use with a telephone handset or a boom
`microphone or directional microphones or the like, where
`the system utilizes two microphones, a first microphone for
`receiving sound comprised of speech and background noise,
`and a second microphone for receiving sound comprised of
`substantially background noise, with the means for subtract­
`ing the second signal from the first signal.
`Hie microphone in the noise cancellation system of the
`present invention utilizes a two terminal system, in which
`the output audio signal comprised of speech and the power
`support input used to drive the system are transmitted on one
`terminal and the second terminal is grounded.
`Hie noise cancellation apparatus of the present invention
`also relates to a directional microphone used in a far-field
`microphone device having the ability to accept acoustical
`sounds in certain directions better than in other directions.
`Hie noise cancellation and noise reduction system of the
`present invention may be enhanced by the inclusion of an
`automatic audio microphone transmission feature, a sidetone
`feature to transmit a portion of the signal to the earcup of the
`speaker, and a feature to convert an active noise cancellation
`microphone to a standard omni-directional microphone by
`removing voice microphone from the circuit, and the
`increasing the gain of the noise microphone amplifier. This
`enhancement allows all audio from external surroundings to
`be transmitted to the earcup of the speaker by increasing the
`sidetone channel gain without the addition of any other
`microphone elements..
`2. Description of the Prior Art
`As is to be appreciated, in numerous situations, the
`presence of background acoustic noise is undesirable. As an
`example, consider the situation in which an operator is
`attempting to conduct a telephone conversation from a
`telephone or such similar device located in a noisy area. In
`
`5
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`5,825,897
`
`2
`this situation, loud acoustic background noise is received by
`a microphone in the handset of the telephone and converted
`to an electrical signal which is supplied to the telephone(s)
`of the person(s) having the conversation with the operator
`and is converted thereat to an acoustic signal. As a result, the
`person to whom the operator is communicating constantly
`hears the loud background noise. Further, when the person
`is speaking, such speech is combined with the background
`noise and, as such, may be difficult for the other person(s) to
`understand. As a result, the operator may have to shout into
`the microphone of the telephone. Furthermore, the signal
`representing the background noise is also supplied from the
`microphone in the operator’s handset to the speaker in the
`operator’s handset as sidetone. Thus, the operator also
`constantly hears the background noise from the speaker in
`the operator’s handset and, when the other person is
`speaking, may impair the understanding thereof.
`As another example, consider the situation in which a
`pilot who is operating a helicopter or the like wishes to
`communicate with another person by way of radio frequency
`(RF) communication. In this situation, the pilot typically
`speaks into a so-called boom microphone or boom headset
`which is coupled to a radio transmitting/receiving device
`whereupon the speech is converted into RF signals which
`are transmitted to a second receiving/transmitting device and
`converted therein to speech so as to be heard by the other
`person(s). As with the above situation of a telephone located
`in a noisy area, the loud background noise from the heli­
`copter is received and converted into an electrical signal by
`the boom microphone or headset device and thereafter
`supplied to the receiving device. As a result, the person(s)
`communicating with the pilot hears the loud background
`noise. This may be particularly annoying when the pilot
`leaves the radio transmitting/receiving device in the “ON”,
`(the hot mike) position while operating the helicopter.
`As yet another example, consider voice verification and/
`or recognition systems into which an operator must speak
`for access, for instance to a physical facility or, to operate a
`computer or automatic teller machine. Background noise
`can prevent access (no recognition or verification due to
`background noise) or can provide false access by false
`verification.
`In an attempt to reduce background noise so as to improve
`performance of a telephone or a boom microphone or
`headset or the like located in a noisy environment or the like,
`pressure gradient microphones may be utilized. Basically, a
`pressure gradient microphone responds to the difference in
`pressure at two closely spaced points. When used in an
`environment where the pressure gradient of the background
`noise is isotropic, the electrical signal produced by the
`pressure-gradient microphone due to such background noise
`is effectively zero. However, in most actual situations, the
`pressure gradient of the background noise is not isotropic
`and, as a result, in these situations, the performance of the
`pressure-gradient microphone is adversely affected.
`Additionally, since voice or speech propagates in more than
`one direction, the electrical signal produced by the micro­
`phone which corresponds thereto is often degraded. Thus,
`even if a pressure gradient microphone is utilized in either
`a telephone handset or a boom microphone, the desired
`amount of background noise cancellation may not be suffi­
`cient and the performance may not be adequate.
`Furthermore, since two opposite sides of a pressure­
`gradient microphone respond to acoustic pressure, as pre­
`viously mentioned, the handset of an existing telephone
`would have to be substantially modified so as to enable these
`two sides of the microphone to respond to the acoustic
`
`- 32 -
`
`

`

`5,825,897
`
`3
`pressure. Moreover, as a result of using such a microphone
`in a telephone handset, the electrical signals produced there­
`from should be amplified. Thus, to replace the conventional
`microphone in a telephone handset of an existing telephone
`with a pressure-gradient microphone would typically neces­
`sitate replacing the handset with a new handset and, as such,
`would be relatively expensive.
`As an alternative to using pressure-gradient microphones,
`an acoustic feed-back type system may be utilized. Such a
`system normally includes compensation filters which are
`used to equalize the transfer function of the output trans­
`ducers. Since the characteristics of the speakers are tightly
`controlled by these filters, the cost of the filters is relatively
`high. As a result, such acoustic feed-back systems are
`typically relatively expensive.
`Many microphones used with noise cancellation and noise
`reduction apparatus are inherently nondirectional or
`omnidirectional, such as the electrostatic, piezoelectric,
`magnetic and carbon microphones. With omnidirectional
`small microphones, at low frequencies there is sufficient
`diffraction of sound around the microphone so that dia­
`phragm motion is insensitive to the direction of the sound.
`At high frequencies, and correspondingly shorter
`wavelengths, the microphone becomes acoustically larger
`and shows a preference for sound arriving perpendicular to
`the diaphragm. Thus, the smaller in size of the microphone,
`the higher in frequency its behavior remains omnidirec­
`tional. Hence, the omnidirectional microphones are small
`compared to the wavelength and the microphone case
`shields the rear side of the diaphragm from receiving certain
`sound waves at different angles. As a result, these prior art
`microphones are referred to as pressure microphones since
`pressure is a scaler, and not a vector quantity. Thus, a
`directional microphone response able to increase the sensi­
`tivity of sound in a far-field region from a variety of
`directions is desired for a microphone device in an active
`noise cancellation system. That is, to achieve a directional
`microphone response by adding the outputs of the omnidi­
`rectional pattern and bidirectional or “figure-eight” pattern,
`and then simply adjusting the amplitude and phase of the
`summed output signal to produce the desired pattern. The
`figure-eight pattern is also known as a cosine pattern and is
`mathematically expressed a p=COS Θ, in polar coordinates.
`In directional microphones, distance is a factor. The distance
`factor measures how much farther away from a source a
`directional microphone may be used, relative to an omnidi­
`rectional pattern, and still preserve the same ratio of direct
`to reverberant pickup. Thus, the prior art has failed to
`provide a directional microphone in an active noise reduc­
`tion apparatus based on the omni-directional patterns and the
`cardioid patterns where the sound pressures arriving at a
`determined point are added vectorially.
`In devising the circuitry for an active noise cancellation
`apparatus for use with a boom microphone device or a
`directional microphone device comprising at least two
`microphones, it is known to use a three terminal microphone
`configuration. That is, a noise cancellation system having
`two or more microphones connected to an amplifier, for
`example, requires circuitry having three terminals: a power
`supply input terminal, an audio signal output terminal, and
`a ground terminal. In an effort to reduce the complexity and
`cost of the noise cancellation system utilized in the
`microphone, or boom microphone or the like which option­
`ally may be used with a headset of the noise reduction
`apparatus, a two terminal microphone configuration is
`desired. It is desired to have a microphone configuration
`where the DC voltage supplied from a power supply is
`
`5
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`4
`inputted on the same terminal as the AC audio signal
`outputted from the microphones, whereby the AC signal is
`superimposed on the DC signal. Thus, the prior art has failed
`to provide a two terminal microphone configuration for use
`in an active noise cancellation apparatus, where the power
`and signal are superimposed on the first terminal and the
`second terminal is grounded.
`In yet a further attempt to reduce background noise so as
`to improve the intelligibility of electro-acoustic communi­
`cation using headsets with a microphone, a technique has
`been developed, called active noise reduction that utilizes a
`sensor microphone placed between the speaker and the ear
`in the sound field of the speaker, and which senses the
`background noise and programs audio. With this active type
`headphone device, a negative feedback loop is used whereby
`the electrical signals converted from the external noises by
`a microphone unit are fed back in a reverse phase for
`reducing the noise in the vicinity of the headphone unit. A
`feedback circuit utilizing a closed loop system as shown in
`the prior art provides a “quiet zone” between the speaker and
`the ear which eliminates the background noise. This is
`because in a noisy environment, the ear will detect not only
`the output of the speaker, but also the background noise.
`Reference is made to the following documents providing
`a closed loop active noise reduction system, which docu­
`ments are hereby incorporated by reference:
`U.S. Pat. No. 2,972,018 to Hawley et al.
`U.S. Pat. No. 3,098,121 to Wadsworth
`U.S. Pat. No. 4,833,719 to Carme et al.
`U.S. Pat. No. 5,138,664 to Kimura et al.
`Japanese Patent Abstract No. 3-169199 to Saeki.
`The above-referenced patents illustrate a variety of noise
`canceling devices. For instance, Hawley et al. relates to a
`noise reduction system for earphones having a plastic casing
`located between the speaker and the microphone; Wad­
`sworth provides an earphone having a microphone located
`on top of the headband; Carme et al. is directed to an
`earphone having a hollow annular part located between the
`speaker and the microphone; Kimura et al. calls for a noise
`reduction headphone having a cup member located between
`a speaker and a microphone; and Saeki relates to a noise
`canceling headphone having a microphone located between
`two oppositely facing loudspeakers.
`However, there exist various disadvantages in the con­
`ventional active noise reduction systems. The prior active
`noise cancellation systems, for instance, utilize closed loop­
`type circuits governed by the associated equations:
`
`where
`P=output
`S=standard audio signal
`H1=high pass filter
`H2=speaker at headset
`N=noise component
`B=variable gain/ phase control
`The conventional closed loop noise reduction system is
`not ideal as a very large direct transmission gain (1+BH1H2)
`is required in order to reduce the noise component (N) to
`zero at the output (P). This system suffers from the problem
`of instability. This creates drawback of oscillation, i.e.,
`squealing due to the unstable loop conditions caused by
`
`- 33 -
`
`

`

`5
`variations in the transfer function of the speaker, feedback
`microphone and acoustic cavity containing these elements
`and user headgear. The degree of noise cancellation gener­
`ated by the conventional closed loop noise reduction device,
`at any frequency, is directly related to the direct transmission
`gain at that frequency. However, the higher the gain the more
`susceptible the device is to instability.
`The conventional active noise reducing headphone device
`also has the drawback that when mechanical vibrations such
`as impact, frictional induced vibrations from connecting
`cords, user jaw movement induced vibrations etc., are trans­
`mitted to the noise feedback microphone, these vibrational
`noises are converted to electrical signals by the microphone.
`These signals are amplified and cause instability and other
`non-linear effects, for example, audio interruption, loud
`noises or pressure surges.
`Another drawback of conventional active noise reducing
`headphone devices is the complexity added to the device to
`avoid canceling the desired audio signal, which signal is
`inputted as an electrical signal. The desired audio signal (S)
`of the conventional device is input into two summing nodes
`to create the signal transmitted to the user’s ear. The first
`summing node adds the negative feedback microphone
`signal to the desired input audio signal. But, in a conven­
`tional closed loop feedback device, the signal feedback from
`the microphone contains the desired audio signal as well as
`the ambient noise signal which is desired to be canceled.
`This feedback signal is subtracted from the desired input
`audio signal to create the anti-noise signal, with zero desired
`audio signal content. Then, a second summing node is used
`to add the desired audio signal back into the loop so it can
`be transmitted to the output transducer. This method of
`generating the desired audio signal adds complexity and cost
`to the conventional noise reducing device. The additional
`summing node processing in the conventional device also
`increases chances of creating distortion in the desired audio
`signal as well as increasing the possibility of instability.
`In addition, various other prior art headphone configura­
`tions have been developed for creating an active noise
`reduction device, where the input and output transducers are
`positioned in relation to the ear, such as the following three
`documents, which are incorporated by reference:
`U.S. Pat. No. 5,134,659 to Moseley.
`U.S. Pat. No. 5,117,461 to Moseley.
`U.S. Pat. No. 5,001,763 to Moseley.
`Moseley (’659) relates to a noise canceling system for
`headphones having a baffle, two speakers, and two micro­
`phones wherein the baffle serves to impede noise from
`traveling directly from a noise source to the input transducer
`by forcing the noise to travel a longer distance around the
`baffle and through a foam barrier. Moseley (’461) is directed
`to an electroacoustic function including noise cancellation
`for use with headbands having a microphone mounted on the
`headband to face in same direction of the ear canal. Moseley
`(’763) relates to a noise cancellation system for headbands
`having a speaker, microphone, and a baffle.
`Thus, in general, the Moseley patents are concerned with
`the location of the speaker, being the output transducer, and
`the microphone, which is input transducer. In fact, the
`patents require that the speaker and microphone be in the
`same plane or substantially aligned in the same plane. Also,
`the patents teach that the processed signal output is substan­
`tially in the same time domain as the original acoustic wave,
`that is the signal is in phase.
`In contrast to the Moseley patents, the present invention
`is not per se concerned with the alignment of the speaker and
`microphone in the same plane (although such alignment
`
`5
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`5,825,897
`
`6
`need not be explicitly excluded). The output transducer and
`microphone utilized in the open loop active noise reduction
`of the present invention may be perpendicular, tangential, or
`in any other location out of the same plane (as well as in the
`same plane). The present invention provides a noise reduc­
`tion system having the capability to transmit the original
`input audio signal to the speaker without the readdition of
`the input audio signal. This is because the sensor
`microphone, which is the control action of the open loop, is
`so disposed from the audio signal, that the audio signal is not
`detected by the pickup or sensor microphone. That is, in the
`open loop system of the present invention, the original
`desired audio signal is transmitted to the speaker indepen­
`dent of the ambient noise detected by the microphone. In
`addition, in the present invention an acoustical material can
`be located between the output transducer and the eardrum of
`the user to create an acoustical waveguide for the transducer
`by coupling the audio signal to the ear of the user. The
`acoustical material located between the output transducer
`and microphone acts as an acoustic filter to decrease the
`open loop gain by placing an acoustical impediment in the
`path of the pickup microphone and the output transducer.
`The acoustical material isolates the desired original inputted
`audio signal from the noise detected and canceled by the
`pickup microphone. The background noise signal detected
`by the pick-up microphone is inverted through electric-
`acoustical processing means producing an anti-noise signal,
`which signal is transmitted to the acoustical waveguide to
`create a quiet zone. This quiet zone is located between the
`output transducer and the eardrum of the user.
`Thus, the prior art has failed to provide a relatively
`low-cost means for reducing background noise to an accept­
`able level for use with communication systems or the like,
`and a cost-effective means for enabling existing audio
`communication systems to reduce background noise to an
`acceptable level.
`
`OBJECTS AND SUMMARY OF THE
`INVENTION
`An object of the present invention is to provide an active
`noise cancellation apparatus and an active noise reduction
`apparatus to create a noise reducing system which over­
`comes the problems associated with the prior art.
`More specifically, it is an object of the present invention
`to provide an active noise cancellation apparatus and active
`noise reduction apparatus which reduce background noise to
`an acceptable level.
`Another object of the present invention is to provide noise
`reduction apparatus for use with a headset device and boom
`microphone or to provide a noise cancellation microphone
`device or the like.
`It is still another object of the present invention to provide
`noise reduction and cancellation apparatus and an active
`noise reducing system as aforementioned which is relatively
`inexpensive.
`It is yet another object of the present invention to provide
`a relatively low-cost noise reduction and cancellation appa­
`ratus for use with telecommunication systems which is
`operable with standard available on-line power.
`Another object of the present invention is to provide an
`enhanced active noise cancellation and noise reduction
`headset by adding a talk thru feature, which enables the user
`to hear the microphone audio signals as well as the external
`audio from the surrounding environment, without the physi­
`cal addition of any other microphone elements. The object of
`the present invention is to have an active noise cancellation
`
`- 34 -
`
`

`

`7
`and noise reduction headset where all the audio from exter­
`nal area is transmitted to the earcup of the speakers by
`increasing the gain of the sidetone channel. This active noise
`cancellation microphone of the present invention is con­
`verted to a standard omni-directional microphone by remov­
`ing the voice microphone from the electronics and increas­
`ing the gain of the noise microphone amplifier.
`A still further object of the present invention is to provide
`a relatively low-cost noise cancellation apparatus which is
`readily adaptable to handsets of existing communication
`systems and which is operable with standard available
`on-line power.
`A yet further object of the present invention is to provide
`a relatively low-cost noise reduction apparatus for use with
`audio communication systems which enables the user to
`selectively amplify a received signal or, which may be used
`in a boom microphone with a headset or, which may be used
`as a noise canceling microphone.
`In many applications as described herein, microphones
`with other-than-omnidirectional characteristics are desired.
`Such microphones reject signals from certain directions and
`thus yield an improvement of the signal-to-noise ratio. The
`directional microphones based on summation scheme,
`which is that of the present invention, may depend on the
`algebraic combinations of the sound pressure signals with
`phase differences which are exclusively due to the electron­
`ics of the system. As opposed to gradient-type microphones,
`the directivity of such microphones is dependent on the ratio
`of linear dimensions to wavelength.
`When two or more microphones are fed into the same
`amplifier, it is possible that signals from a sound source at
`distance from the microphones may arrive at the micro­
`phones 180° out of phase, canceling each