CA2040115A1 - Noise suppression system - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A noise cancellation system, comprising a symmetrical assembly of microphone inputs is disclosed. A controller receives the output of the microphone assembly and generates an electrical cancellation signal having a polarity opposite the polarity of a portion of a noise to be cancelled and a magnitude equal to the magnitude of the portion of the noise to be cancelled. An actuator receives the electrical cancellation signal and outputs an audio cancellation signal.

Description

8 NOISE SUPPRESSIO~ SYSTEM

~,.
16 TECII~ICA~ FIEL~
17 The presant invention relatea to the field o~ dy~mic noi 18 aancellation systems of the typa in whiah ~ auqio ~ign~
19 ls produced for the purpose of cancelling noi~e ~t a, siv$n 20 locatlon.

22 BACKGROU~D

2~ In a wide variety of situations, envlronmental noise 24 presents substantial problems ranging from ~treqs, safety hazards and annoyance to physiological da,~age,~ Unt,il 26 recently, efforts at noise control have oent~red ~ri~arily - .

'~ f~ 5 ~ -2 1 àbout elther reducing the a,mount o~ noise a~te~ or usln~', 2 sound absorbing materlals ta abaorp and deq~ e~yirq~men- ' 3 tal noise.
D, Far example, in the ca6e of an automobile/ ~nqin~ n~ise i~
6 ~irst suppressed through the use of a mu~f~r. It then 7 remalns to prevent residual ~ngine nol6e~ ~p~ se~ wl nd 8 noise and the llke from enterlng the passe~ ca~partment 9 of the vehlole. Typlcally~ this ls donq ~y ~ th~
aabin area of thQ vehlcle with sound ab~ox~i~y ~nd ~ou~
hlelding materlal. Such material~ are ~p~ q to the 12 fioor~ the ceiling and sid'ewalls o~ the cabi~ are~, 14 These material~ generally perform two ~u~ct~on~ n~ely~
the function of shleldlng the pas~enger`'c~b~ om nols~
16 outside the vehicle and absorbing any noi~e~ which ,enter 17 the passenger cabin.

19 ~hlle this sort o approach does achleve a la~ge ~egree o~
24 success in protec-ting the passenger fro~ ~vi~on~ent~l 21 noise, still a substantial amount o~ noise r~aln~, 23 In other areas of technology ! conventional ~oise reductio~
24 techniques are of little or no value. For exqmpl~, in th,e case of a dentist's chair, the above tec~niques, provide 26 little or no relief from the stress in~u,icing ~olse$

1 producad by the dentist's drlllt ~hlla t~ ~om~ ~xt~nt a 2 portion of the noise creqt~d, ~y the da~ti~ dr~ 9 3 transmitted through the tis~ue~ in the hea~ ~ the pa,tie~t 4 to the ear, thi~ repres~nts ~ relativaly ml~or p~t ,~ the problem. Neverthele~s, ~ecau~ o~ t~ dl~ic~lties 6 involved in approaching the remalnillg ~ op~gated 7 repetitive noise, vi~tually nothing ha~ ~e~ dona ln 8 addressing the problem of the remalning nol~
"
Turning to another area in the health a~ lc~r t~
11 extremely high levels of noi~e experienaed ~y t~ p~ie~
12 during the opera-t,ion o~ a nuclear ma~netic :reqo~ance 13 imaging device is of an extremely high l~vel, ~hi~l 14 coupled ~ith the possibly very ~eriou~ ~,a~tur~ o~ th~
illnes~es involved, combine to create ~ e~tre~ely hi~h 16 level of physical and psychological di~comfq~t. In 17 addition, because o~ the nature of th~ ~e,qul~ent~
18 includiny both its physical conflguration ~d ~lect~onic 19 characteristics, conventional nol~ reduai~g ~ppro~che~
cannot be employed.

22 In the past, dynamic noise cancellation sy~tems pave bee" ' 23 devised. Such systems generally involve the generation of 24 a second audio signal which is equal in m~nitude to the noise to be eliminated but opposite in ~ig~ ,at the poi~t 26 where one desires to achieve noi~e aanc~llati 0~7 2 ~,~, dr ~ 'ii. '' l Typiaally, a mlcrophone is po~itioned at ~ pqint ~here 2 cancellation 18 des1red. The mia~phone ge~ t~ a ~ignal 3 which is indlcatlve o~ the amplitude o~ ~pl~ at that 4 point, and thl~ slgnal is ~ent to ~ p~poe~s~or which generates the cancellatlon ~ign~ and ~ 8 it ~0 an 6 actuator whlch iG o~ten a conven~lon~l lo~ ea~r~ ~hlch 7 - in turn producas a cancellatlon audio 6ign~ at the ~oi~t 8 whero quiet is dQsired.

~hlle thl~ ~ort o~ approach certalnly doe~ qq ~ g ~i~y 11 reducing anvironmental nole~ problQm~ ah ~y~m~ hay 12 ~ome limitatlon~ when lt com~ to achiev~ olqe 13 cancellation over a dQsired range o~ area~. I
1~ :
A pos~ibly ma~or problem in dynamic n~ic~ ca~cel~atlo~
16 systems i~ the posltionlng o~ a mlcrophone ~ar the point 17 where one wishes to achieve ef~ective ~yn~mlc noi~

l~ cancellation. This re~ults in a numbq~ o$ opyio~
l9 problems~ namely, the introductlon of microphqnes cl~se to/
for example, the ears of an individual in ~ ca~ or other 21 vehicle. This introduces potential safety ~qziard~ ia~ well 22 as inconvenience and potentlal discomfort.

24 In addition, such approaches present aesth~etlc problems which, for example, in the context of a ~asseng~r 26 automobile, are an important negatlve co~ideratlo~ to 1 potentlal buyers. More importantlyl protrudln~ microphon~s 2 and tha llke, be~ides presenting a hazar~ to the safe 3 operation of the vehicle, as noted abovel ~lsql in the 4 event of an accident may do damags to th~ eyes pf an indlvidual in th~ automobile.

7 SUMMARY OF TI~E I~VE~TIO~
The present invention as clalmed, is lnte~d~ t~ proyide a ~ remedy. It ~olves the problem oP how to con~ol the ~ha~e of the zone in whlch relative c~ulet i~ to b~ a~hi~ye~
11 samQ is achieved by providlng nois~ sen~in~ deyipe~ a~
12 plurallty o~ point~. The pointq are po8ltl~n~ to 13 configuration which, togather with tha char~cteristi~s q~
14 the cancellatlon actuator, de~ine a region pf ~lative~
1~ effective noise cancellation.

17 Relatively effective cancellatio" o~ Gausq~n ~oi~e is 18 achieved through the use of numarouq micropho~ put~
1~ accordance with the preferrsd embodlment~ ~uc~ numerou~
inputs are provided by a tubular ~haped mem~er ~a~ing a 21 plurality of holes defined therein and ori~nted at 22 positions to achieve maximum ~ignal-to-noise ~atio for the 2~ cancellatlon surface being gener~ted. At t~e q~me time~
24 the use of a tubular member results in acou~tic averagi~g o~ Gaussian noise and thus minimizatlon of th~ Gaussi~n 26 noise component.

, .
.

2 In accordance with the pref~rred empodiment~ p,o,int~ are 3 arranged in a closed loop and are provlded at the ,end of q 4 focusing port which generally dir~ats the 4utp~t of the actuator forward, At the SamQ tlme~ the abq~ a~fi~ura-6 tlon also has the advantageous a~feGt of moyln~ ~hs 7 cancellatlon surfacQ away from the m~croph~e ~nd the 8 actuator, thus minimizlng reactlve component~ pf ~e nolse 9 cancellation problem and maximi~ing the e~f~ptly~nefi~ of 10 cancellatlon.

12 Applicatlons o~ the inventlon in~lude housaho~ ni~ure~
13 dental chairs, automobile seats, an~ th~Wher~ lo~
14 levels o~ environmental noise are de~ired.
15 ~:
16 In the particular case o~ a nuclear magnetic resonancq 17 imaging devica, the lnventive ~ystem provide~ pa,rticula~ ;
18 value insofar as fabrlcatlon may be made wlt~ pl~stic 19 materials which are substantially transparent becau~ of the electronic character~stics o~ nucl~r ,magnetic 21 resonance imaging syBtems.

23 ~RI~F DESCRIPTIo~ OF THE DRAWI~GS
24 One way of carrying out the inYention is ~esc,ribe~ in detail below with reference to drawings whlc~ i~lus~rate 26. only one specific embodiment of the invention and in 1 whichj-2 Figure 1 is a vi~w of ~ ~eat i~co~or~a,tin~ the 3 lnventlve noise cancellatiny ~y~tem;
4 Figure 2 1~ a top ViQW of th~ ~aat o~ Fl~ura ~ ~howlng it ln use by an individual~
6 Flgure 3 is an enlarged detail vieW Q~ o~a q~ the 7 components of the nol~e canculling ~y~t~m i~u~ated in Figure l;
9 Figure 4 i~ a detail along line~ 4-4 of ~g~ 3;
Figure 5 1~ a ~ida view partlally in crq~ t:L~
11 along line~ 5-5 o~ Figure 3t ' 12 Flgure 6 is a bloak diagram o~ the inventive noi~e 13 cancelliny ~ystem;
14 Figure 7 is an altarnative embodiment o~ a ,m"icro~hon5e aasembly for u~e in ths ~y~t~m o~ Figure l;
16 Figure B is an alternative embodi~ent o~ t~,e 17 invention, provldlng a relatlvely flat pro~ top 1~ plan view;
19 Figure 9 ls yet another alternativ~ haad~st ~yst,e;m;
~0 Flgure 10 is an embodiment with a ~ead po~ition 21 sensing sy~tem;
22 Figure 11 an alternative embodlment of the i~yention~
23 Figure 12 is a detail o~ an alternative 24 microphone;
Figure 13 is a view along lines 13-13 o~ ~igure 12;
26 Figure 14 is a top plan vieW of another ~lter~ative;

1 ` Figure 15 is a noise ca~cslli~g madical ~y~m;
2 Figure 16-~7 show a ported ~e~ de~ign; ~d 3 Figure 1~ shows a wide ranga portecl de~

BE~T MODE ~OR CARRYING OU~ T~l~ INVEN~IO~
6 A seat 10 incorporating a noise cancelling ~ad~st 12 is, 7 illu~trated in Flgure 1. Generally! hq~dr~t 12 iq 8 incorporated into the back o~ a conventlonal ~e~J ~uch ~q 9 an automobile ~eat or the illustrated ~ing b~ chai~ 14 ~q illu~trated most clearly 1~ Figure 2.

i2 AB illustrated ln Figures 1 and 2, noi~ ~an~
13 headrest 12 comprises'a pair of actuator~ 1~ which ~a~ p~
; 14 conventional loudspea~ers. These lou~spea~r~ typically have a diameter in the range of ten to twenty ce~tim~ter~.
-16 Actuators 16 and 1~ are po~itioned behlnd tha ~ront 17 surface~ 20 and 22 o~ headrest 12. Disp~se~ on front 1~ sur~ace~ 20 and 22 are microphone assembliR~ 2~ a~d 26 raspactively.

22 Microphone assemblies 24 and 26 are substantially 23 identical. Microphone assembly 2~ is i~lustrated in detail 24 in Figures 3-5.

26 ~icrophone assembly 24 generally comprises a hollo~ tubular , .

:

2 ~

_9_ 1 member mada of flexible plastic tubing 28. ~uch tubing i~
2 ganerally avallable in stral~ht la~gths and i~ a~paple o~
3 balng bent i"to a curve~ loop~ suah a~ t~,e circl~e 4 illustrated ln Flgura 3 wlthout kinking or b~ak~g. Suoh plastic tublng typlcally ha~ a thlckn~ on ~ o~,der of ~2 6 centimeters and an lnner diameter o~ app~pxi~ely 2~5 7 centlmeter~. Acceptable material~ inclu~e polyyinyl 8 chloride tubing, which ~ay ba eaaily at~r_ha~ to it~lf ~t 9 seam 30 to provide a contlnuous clo~ed loq~ ~ubing alao ha~ a plurality of holes 32! ~lola~ 32 ~ r~ typioal~
11 posltioned on the sur~ace o~ tubing 28 ~hiah i~' op~osl~
12 th~ surfaae of tubing 28 at ~hich tublny 2B i~ ~u~pox~,d 13 front surEace 20 a6 illu6trated in Flgure ~. ' 14 ;, While~ ln prinaiple, a single microphon~ lg ~uf~ialent ~o~' 16 microphone assembly 24, in accordance ~lth ~he ~re~erre~
17 ~mbodlment of the inventlon a plurality o~ microphone~
18 such as microphone~ 34-37, are employed.

A~ can be seen in Figure 5~ mlcrophone~ 34-~7 a~e mountad 21 in holes, 6uch as hole 40, made ~ithin t~lng 2~, 22 Typically, the front surface of a microphone such as 23 sur~ace 42 of microphone 36 i8 mounted to be ~lus~ with t~e 24 inner surface of tubing 28 as illustrated in ~igure 5.

26 During use, the system illustrated in Fi~ures 1-5 i~

1 assoalated with appropri~te co~troller el~ctr~nlc~
2 lllu~trated ln Figure 6. Ger~erally~ the cont~ol ~yst~m ~
3 comprises an electronic dynamic nolsQ contro~er 46, ~hich 4 has lts output~ coupled to ampli~iers 45 an~ 48~ which i~
turn have their output~ coupled to actuato~ a~ 18, 6 ~ha lnput o~ dynamlc noiee oontroll~r 46 i~ ~pup~d to the - 7 mlxed output of microphone a~emblles 24 an~ 26 ? Dy~amic 8 noise controller 46 may be of c~nventional d~ign~ puring g op~ration o~ the ~y~tem, any environmental ~q~e~ ens~
by mlcrophone as~Qmblies 24 and 26 and gq~r~s ~rrq~
11 slgnals which are couplad vla re~i~tlva or ot~er`~ix~s ~7 1~ and 49 and lines 50 a~d 51 to the input~ o~ ~ont~ol~r 4~
13 which, in turn, generates noise aontrol ~lgna~ w~ich drly~
14 actuatars 16 and 1~ to yenerate aud1o ~lg~ u,~l in amplitude but opposite in sign to the en~iro~me~tal noi~
16 which one wi6hes to cancel, ~hi~ re~ults in the ~ne~atlqn 17 of a cancellation ~urface at ths holss 32 Whio~ com~rl~
18 the audio inputs to the mlcrophone as6emblles~ Al~ern~tlve-19 ly, mixers 47 and 49 may be replaced by a sin~le 4pera,tio~'.
al ampllfier with eight inputs.

22 In additlon, the cancellatlon 6urface defined py the ~ystem 23 extends away from holes 32 along a palr~o~ genera~ly conveX
24 cancellation surfaces 52 and 54, as de~ine~ ~y p~,antom lines in Figure 2.

,C~ 3 ~ ~
:L 1 1 Cancallat1On sur~aces 52-54 are gener~lly ~ph~ic~l in fo,r~
2 and indicate the 10~UB o an ~ra~ o$ maxlmum ~anc~ellationr 3 typically on the order of about ~i~teen d~cipel~ o~e 4 maasure~ cancallation at point~ remoyed in either directlon ~rom ~ur~ace~ 52 and 54, noi~e lev01~ gradual~ rise, 7 In th~ case of an actuator which has a theqretl cal poi~t 8 source location at polnt~ 56 and 58, th~ ca~cellatio~
9 sur~aces 52 and 54 sub~tantlally take the ~o~ of ~ph~rlc~l ~ur~acee whose center of rotation i~ loaata~ at poi~ts 5 11 and 58 r~apactively. In thla particul~ t,h,~
12 canaellation sureace~ 52 a~d 56 arff th~ ~en~al~y 13 ~pherical segments with a circular ba~e whtc~ ~ub~tan~ y 14 calncides ~ith the center line~ o~ hol~ 3~ in the resp~ativs microphone assembly.

17 As noted above, th~ ~f~ective ~ur~ace o~ maxi~u~ canc,ell~-1~ tion i9 a part of a sphsre and the ring ~hap~ q~ th~
19 microphone assembly provides a signal to the cont~oller whlch ls the lntegrated aVQrags no1se pr~ur~ ln th,e 21 vicinity o~ the microphone as~embly along a line p~rpen-22 dicular to the circle de~ined by the m~crophon~ aqsembly.

24 The advantage here is that a minimlzed ~ub~tantially spherical zone of silence is provided at th~ ear poqition 26 of an individual without the need, for pr4yiding ~

,~
2 ~

1 protruding miarophone at th~ RCtu~l aar Po~itl~n~
2 previou~ da~ign~. A~ note~ ~povet ~he uq~ o~ ot,r,udi~g .
.~ 3 miarophon~ ot th~ mo~t aaa~p~ble app~ah to mo~
4 u~er~ in that lt produas~ ~ yary ~all 0ph~ q~ q~.ena~
~hiah mu~t be loaat~d at th~ e~r ~q~ti~ to ~oy~e ~e~
; 6 a~na~lla~lon, I~ addition, he~d mqY~tl~ t~ o~ i 7 o~ tha hair of tha u~er into th~ patb ~l~ns whlo~ t~
~ 8 miorophone ia deteatlng sound~ and tha lik~ ~y ~ t ~ ~
ad~r~e~ly a~cs~ thq ~er~o~ na~ o~ pri~r ~ Sy~

lQ ~he~e und~irable ash~raat~ tlc~/ ln ad~ t~l t~
11 unoom~o~table nature o~ 6suoh 6Sy~tem~s an~ po~ ti~ y ~
12 hazard~s in certain applicSa~lonES make~ the lny~stiv~ ~y~t~

13 partiaular~y valuable a~s aompared to prlor Ar~ ~'Yfi't~
,. i: 1i..:

Turning to thQ ~ueaklon o~ blocka~e by ~air or ~pe ~iks~
1~ th~s ~a~sking 0~ a par~lcular ~oint on a mioro~honq ~Sq~mb~
17 do~sES no~ greatly a~ect the s~erall ~ignal pr~uc~d by thq-rlng m~orophone a~ssembly, Thi~ o, ~Qa~s~ t~
21 uno~qtructed area produca~ ~ co~p~rable ~ l Whi~h, i~

22 Eti.ll ~f~Qctively the lntegrated a~rage o~ the ~em~inin~
23 unblocked radius. While the amplituds'of t~ ~ignal m~y 24 change ~omewhat, the phase angl~ o~ ~he ~ al is ~till e~sentially correct and the transfer function mod~lin~
26 employed in modern controller~ iB abl~ to apmps~sat~ a~
~"; r~

; 2~ [~ $ j 13- ;

I part o~ the real time modelli~ o~ tha ~icro~ho~ ~eedbac~.
2 path, 4 A~ notad abovo, in connHctlon with ~0~n ~oi~
eliminatlon~ thl~ a~pect i~ partia~ ly lm~t~t ~ t~
6 aaBe ~h~ra th~ ~ nventive ~y~te~ m~ ntq~ i~t~
7 automobilu ~at whar~ wlndow~ may pe p~ioqiR~l~y o~ne~
8 or wh~ro the automobile may be a aonY0~tihlerl~hiQh i~
9 drlven wlth the top down. ~nsrally~ Wl~d q~fa~s/ whic~.
10 ~r~ ths ~tronge~t Gau~qlan ~o~a pr~ d ~p~i 11 tho ~epetitiVe nol8e problem~ a~oclated ~it~ t~m~bi~
12 engine) are relatlvely e~ctiv~ly de~ it~ ~Y ~he ~lti-,, . , ~ . . . . . .
13 portad m~crophone a~semblie~ o~ the ~nsta~t 1~yen~io~
1~ ' ': ,' ~ '' I.5 ~ we ~on~idar the aa~e o~ an indlvldu~lt60r ~ u~trat~e,d' 16 in Flgur2 2 r it i~ noted th~t the ~ack 62 o~ tb~ h~q~re~t 17 comprise~ a comfortable ~oft resllle~t ~ aa~ ln t~
18 manner o~ a conventional chair ~hll~ at ~h~ ~am~ tl~
19 proyldlng a cancallation ~ur~ace ad~acent t~ ea,~i 64 a~
66 o~ the individual 60.
21 ,. ~ :
22 ,~nother preferred embodlment iB lllu~trate~ in ~ig~ 7t' 23 Generally, similax parts or parts per~ormi~g q~al~gou~
24 corre~ponding or identical functions are n~ered h~erei~
~ith numbers which dif~er ~rom ~ho~ o~ . th~ e~ ,r 26 e~bodiment by multiples of one hundred, 2 ~ ~ i3 J. ~
~a . 14 a A ~ariant approach to th9 ~anu~ ur~r ~ ~ miar3~ko~i3 3 a~sqembly 1B llluatrated 1~ r~3 7, ~r~ ~ ~icr~phon~
4 assambly 124 i~ providad wlth an auqio ilnp~t ~le,~32 ~hi~C~
i~s loaat~d along an lmagl~ary ~ 16~ ~hia~ e~t~nd~
~ b~tW~ tha ae~t3r 170 o~ tubl~g 12~ ~nq t~s ~nt~ ~72 oP
7 the ear 16~ o~ an l~dividu-~l 160, It i~ e~ th~ in S a~cordanca wlth an ld~allz~d de~ig~ the ~anp~lla~lo~
u~ 152 ~oul~ aolncide wl~ hol~ ,a~ r,~ 73 t, 10 ~ner~lly ~ th~a ob~eot o~ thl~ yPria~t app~p~q~ iq t~
11 maxl~lze qignal piak-up giv~n th~ ~lightly di~c~ion~.
12 charactar1~tics o~ audio pick-up hol~ 132, ;

14 In aaaordance with a ~urther pre~err~d~omb4q~ 4~ t4 ~5 invention~ varyl~g the pha~ o~ t~e canc~ tiq~ ~ign~
16 and/or lts component~ i~ u~sd to ~urthex ~on~ro~ th~
17 positlon and ~hape o~ the ~ur~aca o~ ~a~l~u~ ~na~ lo 18 Further control of the eur~ace aan b~ a¢hlov~ t~ou~ th~
19 u~e o~ ported outpUt,B ~upported by ~lç~lbl~ ~ay~ ~ide~
whiah are conflgured to pe a p~t o~ t~etlaally 21 speclfied contour Bhape~.

2~ 9uch an alternative embodiment of th0 ~pvention ~S
24 illu~trated in Figure 8. Here the l~yentlye ~y~tem i~
lncorporated into an automoblle headre~t 212~ Seat pack 26 ~62 i~ o~ a less concay~ ~hape in orde~ to improye, : ;~

1 vi~ibillty ~or the indivi~u~l 260 ~eatad 1n the iny~tiy~
; 2 auto~obile ~eat 214. ~ .

4 Improvsd operation le achleyed ~y proyi~ at~to~ 216 -~ 5 and ~l~ With tubular cyli"dria~l ~ocu~t~intg ~ior~ ~7~ ~d 6 276 a~ illu~trated ln aro~q. ~eatiQn in ~ e ~t ~h~
7 ~oou~t~ing port~ have the ~eat o~ ai~ h~ o~ d 8 n~ar-~ield audio B~ea~ o~ aCtuatQr~ a~ o~
9 particularl~, in the r~gio~ medl~t~ly ~d~e~ t~ aon~
o o~ th~ ~atu~tor( th~ aQ~ity~ ~a~ and ~1 ~ ia~y 11 air ~urroun~ng th~ aotuator ~a~ oharact~ri~t ~ e ~io~ g 12 rl~e to imaglnary compona~t~ a~ well ~ ra~ q~pc~nt~
13 For e,xampla, the vl~ao~ity o~ th~ alr ,may b~ yl~d ~ th~i 1~ an~log o~ eleatrlaal resi~anae W~ ot~r ~;pmp~ne~
be equated to aapaaitanoe~ and lnduata~c~ By r~
1~ mlarophone a~emblie~ 224 a~d 226 ~rom the ~Bar ~ d 17 the ~peaker~ the~e near ~ield e~eat~ w~ich g~nq~ te~
}8 to aau~e pha~e problem~ Wlth re~pqct to ~ouhd ~ltted py-~ 19 the ~atuators, may be mlnlmized, In ~ddi~io~/ t~
~ymmetrlaal nature of mlcrophone ~ m~lie~ 22~ a~ 226 21 aleo tend~ to remov~ ~omu og th~ imagl~a~y ~om~,on&~t~ a~
: ?2 the ~ystem charaat~ri~ic. In connection wl~h this ~ lt 1~, 23 al~o noted that the u8e of a~ ~ctuator Wit~ a co~o~ly~
2~ ~iymmetrlc microphone as~embly tends to r~duq~ Gau~sia~ or random nolss effect~, thus re~ulting i~ high ley~el of.
26 performance in the inventive syste~, .

~, .. ~ .. . . .

C~ 3 4~
~.--16~

2 In aacordance ~rith the ambo~iTne~t ~ qt~ata~ ig}~re ~ ~;
3 unlike the embodimant illu~tra,te~ in ~igur~ 6 I t~e 4 a~gnal ~ent to aGtuator~ 216 ar~d, 21~ ot pal~ la~d ~o 5 r~ult in a cana~llation ~ur~aae ~hi~a~ Qolna~ thl pole~
.. ~ ~ . ~ . . . .

6 232 o~ mi¢rophon~ a~Qmbll~ ~2d~ ~,nd~ 2~fi t R~th~
.,~ ................................................ I .

7 indlyldual ~requenay aompon~ntq oP th~ ~naq?~ati~n ~ n~l 8 output by the aontxoller ar~3 delayed or ~d~ ce~ ha~

9 ,by an amount whicll ~eault~ in th~ir ~q~ , up ir~
o tlnd~l~ye~ ~ol~e aanaell~,tion ~içtn~ k 11 ¢ancallatlo~ ~ur~aces 252 and 25~, ~hl~ ~a~t~
12 aub~t~ially greater ~ro~ection o~. th~ cance~ti~n.
13 ~urEac~ out ~rom the aotuator~ allowi~g ~h~.~ea~ d~ign~F
14 additional latitude with re~e~t to aa~th~a and ~h~
15 ~eAture~ in the de~ign o~ the ~at.

17 Additional aeethetic conaer"q may p8 aa~mmodate~ ~y~
18 variatlon o~ the shape o~ tha paak o~ th~ t. Ho~ve~
19 to qome extent, volume~ 27~ and 280 b~hi~d ~ctuator~ 21~
and 218~ re~pectivalyJ mu~t ~e ~hq~ed i~ a~eordancq with , .
~1 kno~ de~ig~ techniques ~8~q by ~ud~peakax:~e6igner~ to, 22 accommodate aoou~tical re~o~ant oh~r~cte~i~tics which 23 result in e~ficient tran~mi~ion of .audia 60unds ~ro~
24 actuator~ 216 and 218 withln the de~lred noi~ cancellation frequency range.
26 .

3 L ~' 3 - -~".

1 ~ore particularly, ln t~ ca~e o~ an a~omobll~ ~e~
2 headre~t, it ha~ been ~ound t~a~ ~b~ pr~do~inant ra~e o~
3 ~ound to be cancelled 1~ ln th~ r~n~ ~ ~ to 700 ~rt~
4 Acaordlnglyl ~peaker~ havl~g ~ q~noy r~on~ ln thi~
r~nge may be u~ed a~ actuator~ A~ yolu~n~ 27n and 2~ a~
6 tuneq ~or ths~o ~requenaie~ aollt~p~t~d th,~ th@
7 l~v~ntive headr~s~ de~lgn may be integ~ d ~to the ~pp~
~8 part o~ a aonv~ntional ~at ~lth a ~light i~ea~E i~ ~e~
9 back hsight and Width at tha top ~Q~t ~o~tl~ o~ th~ ~e~, 10 bac~ 't~
' 11 .' n the càsa o~ an automobll~ nolae ~uppree~io~ ~y~te~ ~q.~
13 inaorporated in the headr~t o~ om~hi~
. }4 relati~ely ~imple method o~ pushlng out th~ cancel~tla~
j ~r ,~, .
~ur~ace ~rom th~ actuatur may be ~mploye~ parti~la~
16 the actuator may be modl~led ~y seeklng out t~ predo~i~a~^
17 ~re~uency compon~nt o~ th~ r~qui~e~ cana~ ti~n ~lgn~ a~d~
18 qimply d01aylng the antlre output ~ignal by ~ ~ime ey~l ta 19 the time which lt take~ the ~lgnal to travel ~rom a ~ol~t on the ~phere de~lned by the input port h~ 232 q~ t~@
21 microphon0 a8sambliee to point~ on th~ di8p~aced~
22 canoellation sur~aces 252 and 25~, ~hlS approach 23 represent~ a good first order approxlmatlo~ ~r the entire 24 ~ignal in ~imple noise environment~ andr Wl~h respect to the ~undamental, represente a substa~tl~ly accurat~
26 solutlon.

.

. . 20~0 ~
l B - ~, . . , ~ ; . .

1~ 2 F1 rlallyr i~ ~he aa~e o~ t4~ $.5~Qhi~ ~sat i~luatr~d i1n -3 Fig~re 8 ~ lt may b~ deair~bl~ ~o ~PYi~ th~ ~am~ W~t) - 4 upholstery ~ac~d~ 2~2 !
: 5 6 Still another po~ lq appro~ah i~ n Fl~ t 7 Ir~ p~,rt:lcu~ar, aq an alt~r~ly~ ~Q . ~ ay~ th~ ri niarophone a~a~mbly may b~ brought alo~ ~Q ~ ~ar ~a ~
~ a contaat mlcrophono po~ltiorlacl i~ th~ q~ to ~Qd,~
.0 C~no~ t~ rial~y o~ Ha?~

11 lnv~tiye ~ol~a cancelling he~dr~t 3~f~ hA~ Q
.12 piozoel~atrlf3 actu~tore 383 and 3A5 at ~h~ e~ 316 ,~
., . ... ~ , , , . . ~ . ~ .
13 o~ a pair o~ hollow ~lexlbla tube~ 3~4 an~ 3~ in P~

14 the loudepeaker type aatuato~ h~ at~tor~ 38~

3~5 are drlyen ~lth a ~ourca o~ aanae~tio~`poi~Qt`~d~l ?: ' 16 316 ~nd 318 ars eupported by a plurall~y o~ ~lexlbl~ ~rm~., 17 38~ ~ia~ a~r~ ge~erally ~hapad to ~it t~ rm ~ a~y~

1~ de~ d haadre~t aontour. ~huq, ~h~n ~overe~ W

19 UphOlf3tBry ~acade 3~2, A pleaeant app~arance i~ glve 21 ~e~rring to Figura 10, yet ~other ~lt~r~at~ye embo~i~ent 22 of the lnventlve nol~e aa~celll~g ~ea~est 412 i~
23 lllustrated. G~nerally, in accor~anc~ with th 24 embodiment, tubes 484 and 486 are placed with their end~

416 and 418 ~ubstantially flush ~ith ~hR baek 462 of th~ .
26 headr~st 412/ and are driven at their o~o~ite ends by a~

';

~19 1 aco~tia ~ourco of nolse ca~c~ g ~udio~
3 U~lng eithar of t~e pha~e dsl~y t~hni~ d~aribed ~bovs~
4 th~ a~na~ tlon ~-lr~aae~ 45~ an~ 4~4 ~ pU~d outw~dly~
Moraovsr~ ln aaaordana~ wlth thi~ d~ t- ~ ~o~iql emitter 49~ ~y ~l~o be u~ed t~ n ~uq~ to~ Whick i~7-7 detQcted by ~onia deteator~ 4~2a-~ w~h ~ po~itlon~d B oppo~lte ~lde~ o~ th~ ~onla emltt~r 490 7 .,' 9 .'.~
i~ lq ~y d~aotln~ th~ ampli~ud~ o~ t~ ~4d~ p~duoe~by ~ 11 e~i~t~r 4~0 at tha varlou~ pQint~ W~ d~atorq ~2a~
.: . ;

12 are ~o~itip~ad~ a rqlati~ely ~im~ n~ :euc~ aq 13 loaa~i~g the d~t~ator receiyi~g tb~ u~ pli~ud~

14 reve~1 the po~ition o~ the pBad oP ~n i~diyi~al u5i~g th~
i~e~tive head~a~t 41~ For ~x~n~ 4E ~ ound ~ourc~
16 ~ua~ aq e~ittsr 490 diractly i~ ~ront o~ th~ head, i~ the.
1~ ~lgn~l deteated by detector~ 4~ 4~ 7.~nd 492f 1~ ;
lB ralativ~ly low ~hile the signal datqat~d hY the ~ther lq d~t~ator~ iq relatively high~ the hea~ o~ thq.~individual i~
20 ad~aa~t detector~ 9s2d, 492~ and 492~, Aa~q~dingly~ it i5 1 the~ neaes~ary to redua~ t~ Q~ ~phe~laal.~.
22 ¢anaellatlon surfacs 454 and lncre~eq th~ radiu~ o~
23 sphQrical cancellatlon ~urfaca 452 tP acc~modat~ ~hls 24 di~erent head po6ition. In thls mannBr ~ he~ movement may`
ba compensatad for while maintalni~g e~c~ive ~oise.
26 cancellation.

e ~

2~a..~

,, , ,Jj,.~. ., l ~ . . .
- 2 0 i :
". 3 ,,, .
2Still arlother po~Elibility i~ th~ U~ q~ r o~' ultra-`
3 Bonia ranging d~ylae~ at oP~o~ id@~ o~ th~ usur ' ~ head .
multar~ou~ e~l~ti~n q~' P~th ~ W~ thU~ ~ho~ ~h~
, ~ ~ right and l~'t ~imi~ O~ h~ q~i~iQn, ~ in~ to 6 E~ig~r~ it m~y ~e qe~ b~ ,gh~e~y~ pcellatiol~ ~
7 particlular ~oiqe~ hav~ ng strong compc?~ or exa~ple, 8 the lo~ f'requency audio range. ~ nay be more 'eatiyaly ~,chl~y~d by t~llorill~ th~ erl~ fl O~r, 10 tub~q ~8~ and 5a6 to m~toh, t~ a~ c~q~a~ stlc~ ~hiol~
il orle i~ attempting ta canael u~ing ~hq ln~ro31~ive head~e~t 12 512 i In the pa~tic:ular aaE~e o~' th~ ~y~t~enq ~h~n ln Flgur~.
13 '11~ 1o~r f'r~ ale~ ao~ld p~tt~ p~ ~Qm~ ated u~lr!Ç~ !,;j ,rg~r dla,m~ter tu,b~EI 584 ~d 586l whla~ ~y range ~rom,~

15 1~ivs to tl~irtee ntimeter~ 3t~ illuatrated 16 Nayartheles~ ported apeaker aotuator daql~ uch a~ tho~`

17 de~cribed bslo~ ~ill be mo~e ef~eative, i ..

In a manner ~imilar to the tuhe ~nq ~ct~3~or~ u~ed in.
0 Figures 9~ it may al~o be d~lr~blq ~4 ~uq~ ~cou~tic ~ave ,t ~ " ,, '~ : 21 guide~ to carry ~ound from the ~laropho~ $~be a~embly.
" i~ '.',:;! ;, ;, ... . .. ..
22 In partlcular, as lllustrated in ~lg~e~ ~2 and 13~ a 23 microphone a~embly 624 may be proylded Wlth a tube 24 recelving hole 540, whlch would ~eceiy~ eumatic llne . ; 2S 59~ which would carry audlo input throug~ ho~ in tubular . 26 member 628 to a remo~e microp~ona ~t ~h~ other e~ of , `` . ` : 2 ~

~21-1. ~oou~tio tubular ~y~guld~ h~ 1 ~ Th~ po~ llity al~o e~l~t~ ~0 in~oe ~ lred eignal 4 l~to the e~yironment ~ithout ~n~ ,panaellatlon.
5 The proae~q o~ i~plementin~ ~ ~t~ $~e by ~lng 6 tho l~war frequanaie~ in t~ ra~g~ Q tq ~00 Hz o~ th~
7 add~d audio ~ignal wlth th~ con~roll~ aond higher ~re~u8ncy Bpeak~r ~ aqded ~0 ~nd~ the higher ,~
9 f~qu~ale~ A cro~-oVer nRtwq~k 1~tq aap~
lo ~h~ two b~nq~ ~ the audi~ ~1gn~aa~e Q~ a~
11 repetltive ~ontroller, the cont~oll~r ign~ the a~dio, , . 12 ~ig~ nd ~reat~ it a~- randol~ Poi~e~ Fpr a ra~do~$
: ~ 13 aontroller~ tha ~oi~e i~ add~d ~ ~q~lti~na~?.!lnput to thq;
14 ra~dom aontroller ~nd ~ubtract~d (wit~ the propar .
aomp~n~ation~ ~rom t~e aontroller out~ut ~ driving the 16 actu~tor~. Thusl 1~ desired( th~ ~y~te~ aA~ inaorporate, .. ...
17 a~ aatuator~, conventional aoaxia~ high ~idq~ty spsaker~, 18 716 and 718~ which include hi~h ~idality ao~ial tweeters 19 796 and 798~ re~peatively~ a~ illu~t~Rte~ i~ Figure 14.
~0 ~uch a noi~e cancelling headre~t 712 h~ it~ actuator 21 modi~ied to the extant that the ~ct~ r Wq~d recognizes 22 the desired entertainment mu~la or audio pro~am beinq ~ed 23 to aatuators 716 and 718 ~hereby thlq pr~gram i8 not 24 cancelled, thu~ leaving only the progra~ to b~ heard by the individual 760 using the headrest 712~ Suc~ ~ sy~tem ~ould 26 also have the added advantag~ of ma~ h~ ~esidual nqise . ~. ~.h .. : .

1 ramai~lng ~ter aancellatlo~, ;
2 :
3 ~he applicatlon o~ a porteq ~nc~o~ e~ lmilar to ~ tho~ u~ed ln loud~peaker d~ t~ d o~ dynamlc ~ nol~ aanaell~lo~ e~hana~ pppllaatlon~
6 wh~ra thq aancel~ation noi~q ~o~pq~nta mu~t bo 7 loaate~ a di~t~nae away ~ro~ th~whsr~ noias 8 cancollation i~ r~quired. One ~uc~ ap~ Q~ i~ A ~oi~e 9 a~a~lllng ~y~t~ de~igned ~or ~ar ma~netia lO~ reè4~ana~ ~pplio~tlon~ thi~ ~p~h~ ~U~:~
11 th~ m~ohlnq ~au~uq th~ pati~nt d~o~Po~ ~n~ nead~ ~n be 12 .ca~aelled. ~e~au~e o~ ~he n~tur~ Q~ th~ ~oh~e~ m~gn~tic 13 3na~e~ia,1 aa~not ~e po~itio~q~ i~ th~ ~ ual~ar magn~ic 14 re~onanae mea~ureme~t zon~ For ~ pp~lio~on, a ported 15 ena10~ura ~a~ign made o~ plaqti~ d~l bin that the 16 ~p~aker and microphona elemen~ ¢q~ p~ loc~t~ a di~tance 17 away ~ All o~ th,e material~ ln ~ me~U~ nt zone ara 18 pla~tic and hence transparent to tha ~u~ar mag~atic 19- re~o~anae proce~. Figure 16 ~owq ~ diagrammatic 2 ra~re6e~tatlan of an extended port~d ~cl~ura for an ual~ar magnetio re~onance ayqte~ 810 i~al~ g a patient 22 bed 811, . .
24 1 See for ~xample, ~i~he ~d Dlmension;
; 25 Symmetrically Loaded~ by Jea~ Margera~d~ aker Builder, .: 26 June~ 1988 and references c$ted th~r~

, 2 ~ a . . "

In thi~ de~lgn~ the m?~ C ~p~a,k~r ~cfi and metal 2 miaro~phon~ ~36 ~ro locateq ~yç~at fro~ the nuclear 3 magr~tla re~onanae measur~m~t 7,on~ ¢~nt ths hsad 860 4 o~ the ~atieT~t, ~ha portad ~p~ q cho~en ~ing 5 a 1 to 2 ma~er long, ~l~t~n ~n~ ltt ~3F ~ t~r plaa~ic 6 port 874, A ~lng mlarophon~ a~m~y' ~ at the ~nd o~
7 ~?ort ~74 i~ w3eq to pro~ect t~ ?b~ na~ t~Qn ~rom 8 a~embly 824 about ~Ive ca~tlmet~q t~ ~ha ear o~ the 9 raalining patle~t, A vented ~enqln~ ~u~ 4 connect~ to - s; lQ ~th~ a~op~ mh~y ~ iarophon~ ~
11 be loaat~d a di~t~nce aWay, Wh~n u~n~ ~ ~en~in~ tube, 12 typio~lly~ g~ancY compeneation 1~ ~mploy~d t~ cor~oct , 13 ~or ~e no~ ear ~requency ~e~pon~ o~ the tube.

~ typlaal oon~i~uration ~or a por~q ~y~em o~ thie type 16 u~in~ ~ aomm2ralAlly avall~bl~ driyer ~o~ employ a 16.5 17 ce~t1mster Polydax HD17825 ~p~ak~r ~q ~ ~ct~ator. For 1~ thi~ de6ign tha front volum~ ~15 i~ 4~72 llter~, th~ rear 19 volume 817 i~ 10,28 liter~ a~d the len~th Of the 182 cm2 cro~-6ectio~al area hemholtz port ~74 i~ 127 cm. The ~1 frequency range ~or thi~ de~lgn i~ ~bou~ 40 to 200 Hz, It 22 ~houl~ be noted that the use ~ erqnt ~peaker~ and 23 volume conflyurations can proYl~e ~ ~ider freq4ency 24 response. Altarnatlvely, the u~a o~ a multi-chambered de~ign, a~ will be descrlbed below~ can ~l~o produce wider 26 frequency range cancellation, , ' : , ii"

-:

3 ~ ~ jb~

' ' ' 1 2 Flg~ra 16 and Figura 17~ ~iob i~ ectlonal vieW
~ alo~g llne 17-17 o~ Figur~ h~ ~n~her altarnative 4 noi~f~ canaalling ~eat 914 i~a~ headre~t 912.
5 Thi~ ~?Pr~h i~te~at~Fiqn~y load~d por~ed ~ ~eAk~ de~ign into th~ a~ail~ g~n~lona to allow 7 dy~ a aana~ lon to ~e ~d~ h~n exi~ting ~at ~ contour wlthout ~y lnar~a~f~ in ~dimen~ion~, A
~ g rin~icrophone a~embly 924 1~at th~ en~ o~
;'k ~ q 1' t~ pprt; ~d p~yld~ the ~mR pa~ t~

12. T4i~ da~ig~ ~ di~erent.~rotn r~r po~ ~alo~ur~ uc~ a~
tha~ o~ th~ ur~ 1 de~lgn, in thqt the ~r v~lume ~17~
14 Pront yolume 915 and hemholt~ tu~ ~o~t ~74 all dater~inf3 . . .
- ~ 15 th~ quenoy oharaatsrl~tiae.
~ "
1 ~i , 7 . ' 17 ActU~tor ~16 i~ plaa~d ln~ide a ~ar yplutn~ 917 Which ie r ~ 18 de~inad ~y ~all 919. Rear yolum~ 9~7 h~ a depth 919 o~
.l ' 19 ~iyf~ centlmqt~r~ and a height 921 o~ 31 c~ntimetar~
~: 20 Astuator~ 916 ~d 91~ ~aye ~ ~lAm~t~ bout ~ig~teen ; 21 ce~timetQr~ lmholz port ~7~ pi~aular pipe Wlth a .~ 22 length of abaut aeven centlmeter~ and ~ diameter of ten : !
23 centimeters. ~he thicknea~ 923 of 6eat ~10 ~ about nine 24 centimeters~ wlth an lnside dimension of about eight centimeters.

;~; '. .: .

:' .

2 ~t ~ 3 ",,` -?~~
.
q`he Ixequency llmlt~ ~or ~ gl~ 16, 5 l~ch ac:tuator i~ 95 2 to ? 65 Hz, To provlds the ~ o~r~G~ n rangt3 poBEIible 3 ir~ dynamlo noiE~e canc~llatlo~J ~ ~U~tlp~ aonaentria port 4 arrangement ~uch a~ that o~ ulr~d-, . , , , ,, ~ . .
~ i~; 6 El~r,a thts ~aond cona,s~trla port ~ iP~ Qll oompri~i~g a ..
. 7 hlghq~ ~requ~a~ay aatll,s,tor 1~01 i~ pste r~ax volums 8 1002 de~ln~d by barrier lOû~i driY~q ~ ~pi~,rate h~imholtæ
~ port tube 1004. Tube 1004 1~ cona0ntr7to W~ port 1074 and -~ `i.-1 . ' t~ lP s d~iY~ b~ ~OOJ~ Yla e ~aaon~ yq~ g .~04 ~ .py Rrri~ 10~5, ~ort ~ctio~ 1011 1~ t~d to ~alrar ~he . 1~. ran~ ~rom above 265 ~z to ~oun~ ~oO ~ he controll~r pr~o,yi~2~ pro~ ar logia ~hat ~pllt~ ~he aanaellation . .. . .
4. output ~or each ahann~l into t~o aom~o~a~t~ that drive ~aah ~5 of th~ ported ~peaker ~ectio~
~- 16 .
. 17 Whll~ a~ lllu~tr~tiva embodim~3nt o~ t~ yantlon ha~ P~3~n ;!~
... .. . .
lB da~arlbed above, it i~, o~ cour~e~ under~ood that various 19 modl~laations ~ill be appar~nt to tho~ ordl~ary ~kill 20 in the art ? Such modi~laatian~ ~r~ Wit~i~ the ~pirlt and . 21 ~aope o~ the inyentlo~ whioh 1~ limite~ ~nd de~lned only : 22 by thq appended alaim~.

:,,~i,, , "~ , . , . ~ .

Claims (3)

1. A noise cancellation system, comprising:
(a) a symmetrical assembly of microphone inputs;
(b) a controller for receiving the output of said microphone assembly and generating an electrical cancellation signal having a polarity opposite the polarity of a portion of a noise to be cancelled and a magnitude equal to the magnitude of said portion of said noise to be cancelled; and (c) an actuator for receiving said electrical cancellation signal and outputing an audio cancellation signal.

2. A noise cancellation system as in Claim 1, wherein said actuator has a theoretical equivalent point source position and said actuator is positioned with said point source position inside a cylinder defined by said symmetrical assembly.

3. A noise cancellation system as in Claim 2, wherein said symmetrical assembly is symmetrical about an axis substantially perpendicular to a plane defined by said symmetrical assembly and said point source position is substantially located on said axis and a zone of maximum cancellation is defined by a portion of a spherical surface substantially centered on said point source position and substantially including said symmetrical assembly of microphone inputs.