CA1120580A - Single loudspeaker having a moving coil transducer for feedback purposes - Google Patents
Single loudspeaker having a moving coil transducer for feedback purposesInfo
- Publication number
- CA1120580A CA1120580A CA000280342A CA280342A CA1120580A CA 1120580 A CA1120580 A CA 1120580A CA 000280342 A CA000280342 A CA 000280342A CA 280342 A CA280342 A CA 280342A CA 1120580 A CA1120580 A CA 1120580A
- Authority
- CA
- Canada
- Prior art keywords
- transducer
- loudspeaker
- amplifier
- voice coil
- coil
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
- 230000005291 magnetic effect Effects 0.000 claims description 16
- 230000004907 flux Effects 0.000 claims description 12
- 239000003990 capacitor Substances 0.000 claims description 9
- 230000004044 response Effects 0.000 claims description 9
- 230000008878 coupling Effects 0.000 claims description 6
- 238000010168 coupling process Methods 0.000 claims description 6
- 238000005859 coupling reaction Methods 0.000 claims description 6
- 230000033001 locomotion Effects 0.000 claims description 4
- 239000004020 conductor Substances 0.000 claims 1
- 230000033458 reproduction Effects 0.000 description 4
- 238000013016 damping Methods 0.000 description 3
- 238000000034 method Methods 0.000 description 3
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 2
- 238000010276 construction Methods 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 238000009434 installation Methods 0.000 description 2
- QHGVXILFMXYDRS-UHFFFAOYSA-N pyraclofos Chemical compound C1=C(OP(=O)(OCC)SCCC)C=NN1C1=CC=C(Cl)C=C1 QHGVXILFMXYDRS-UHFFFAOYSA-N 0.000 description 2
- 230000005855 radiation Effects 0.000 description 2
- WWYNJERNGUHSAO-XUDSTZEESA-N (+)-Norgestrel Chemical compound O=C1CC[C@@H]2[C@H]3CC[C@](CC)([C@](CC4)(O)C#C)[C@@H]4[C@@H]3CCC2=C1 WWYNJERNGUHSAO-XUDSTZEESA-N 0.000 description 1
- 241000905957 Channa melasoma Species 0.000 description 1
- 241000820057 Ithone Species 0.000 description 1
- 241000353097 Molva molva Species 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 230000007812 deficiency Effects 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 230000008569 process Effects 0.000 description 1
- 230000008707 rearrangement Effects 0.000 description 1
- 125000006850 spacer group Chemical group 0.000 description 1
- 238000001228 spectrum Methods 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
- H04R3/00—Circuits for transducers, loudspeakers or microphones
- H04R3/002—Damping circuit arrangements for transducers, e.g. motional feedback circuits
Landscapes
- Physics & Mathematics (AREA)
- Engineering & Computer Science (AREA)
- Acoustics & Sound (AREA)
- Signal Processing (AREA)
- Circuit For Audible Band Transducer (AREA)
- Audible-Bandwidth Dynamoelectric Transducers Other Than Pickups (AREA)
Abstract
ABSTRACT
A loudspeaker incorporating a moving coil transducer magnetically and electrically independent of the voice coil, and associated circuitry to feed back the output from the transducer to the amplifier.
A loudspeaker incorporating a moving coil transducer magnetically and electrically independent of the voice coil, and associated circuitry to feed back the output from the transducer to the amplifier.
Description
.. ~ 'L'h-i.s :inverl-L~:ioYI.le~LaL:e~ to :LolA(-lsl?ecl:k(~:K S a YLd associated c:ircuit:ry and has been c'l.~ ised pa:r~icularly thou.yh not solely as a loudspeaker system incorpora-~,incJ
an elec-tro mechanical feedbac:k and the circuitry as;o~
ciated therewi-th.
Using conventioY!al techniques it is diP.ficult -to design a sinyle loudspeaker which will operate satis-eactorily over .the Pull audio .~-`requency spectr-um. For hiyh fidelity sound reproduc-tion it is usual -to c'Lesign loudspeakers to operate over a limite~ frequency 'band, and to achieve reproduction over -the complete a1ldio frequency spectrum multi-speaker systems have been used.
Loudspeakers designed to handle bass fre~uencies have required sophistica-ted mechanical design in order -to reduce non-linearities in the suspensi.on system and maynet:ic circuit and furthermcJre they have been re(.luired to be mounted in carefully designed enclosures of.`ten haviny a considerable volume and t:herefore occUpyiYly a consi.der'ab].e spaee in,orcLer to ensll:re p:roper loa-'L:i.ny and dampin(~.
: In o:rder to avold. these compl:icati.ons it is known to derive a signal related -to -the.cone movemen-t and -to use this siynal to provide nega-tive Peedback Por -the amplifieY driving the loudspeaker.' In -thi.s ~jlay -the 25 ' amplifier substantially cornpensa-tes Por -the lo~AcLspeaker deficienci.es. ~resen-t feedbaclc arransements have not been found -to be completely satisfactory in.use often givi.ny a non-l.inear response and furthermore -théy are expensive to manuPact-ure and require carePul assembly and alignmen-t of the components within the loudspealcer.
' 5~1~
. .
It is therefore an object of the present invention to provide a loudspeaker and driving circuit therefor, which will obviate or minimise the foregoing disadvantages in a simple yet effective manner or which will at least provide the public with a useful choice.
Accordingly the invention consists in a loudspeaker system comprising a support frame, a first magnet mounted in said frame, a voice coil operable in a driving magnetic flux field from said magnet, a diaphragm or cone suspended in said frame and capable of being driven by said voice coil, a second magnet means for providing a magnetic flux field substantially separate from said driving magnetic field, a moving coil transducer operable by movement of said diaphragm or cone and incorporating a transducer coil operable in said magnetic flux field substantially separate from the driving magnetic flux field, connections coupling the output voltage of said transducer to an input of an amplifier adapted to drive said voice coil in a manner such that the coupling between said transducer and said amplifier does not have any common electrical path with the coupling between said amplifier and said voice coil, the output signal from said transducer being coupled to one end of a first resistor of suitable value and fed through said resistor to said input of said amplifier, a first capacitor of suitable value provided connected between said one end of said first resistor and the earth of the circuitry associated with said amplifier and a second resistor and a second capacitor connected in series between the said inpu~ of said amplifier and earth, the values of said second resistor and said second capacitor being selected to give a 3a flat frequency response from the amplifier at high frequencies.
'rO those skilled in the art to which this inven-tion relates, many changes in construction and widely differing embodiments and applications of the invention will suggest themselves without departing from the scope of the invention as defined in the appended claims. The disclosures and the description herein are purely illustrative and are not intended to be in any sense limiting.
ne preferred form of the invention will now be described with reference to the accompanying drawings in which, Fig. 1 is a cross-sectional view of a loudspeaker incorporating feedback elements according to the invention, Fig. 2 is a block diagram of the amplifier and associated circuitry required to feed back the signal ---3a-~lZ05Bal from the lo-udspeaker sho~/n -ln ~'ig. 1 and l~ig. 3 is a c:ircuit di~g:rarrl of~ the ac~tuclL c~m-ponents used in l:he block diayram oP ~:ig. 2.
The use of Peedback -to control the response of high qual~ty amplifiers and other components in the sound recording and reproduction chain iS well es-ta-blished. Ilhis inven-tion provides means for incor-porating feedback in a loudspeaker system -to con-trol the electro-mechanical conversion process and can be exploited in any of the followiny ways.
1. By application to a single loudspeaker designed as a wide frequency range unit,
an elec-tro mechanical feedbac:k and the circuitry as;o~
ciated therewi-th.
Using conventioY!al techniques it is diP.ficult -to design a sinyle loudspeaker which will operate satis-eactorily over .the Pull audio .~-`requency spectr-um. For hiyh fidelity sound reproduc-tion it is usual -to c'Lesign loudspeakers to operate over a limite~ frequency 'band, and to achieve reproduction over -the complete a1ldio frequency spectrum multi-speaker systems have been used.
Loudspeakers designed to handle bass fre~uencies have required sophistica-ted mechanical design in order -to reduce non-linearities in the suspensi.on system and maynet:ic circuit and furthermcJre they have been re(.luired to be mounted in carefully designed enclosures of.`ten haviny a considerable volume and t:herefore occUpyiYly a consi.der'ab].e spaee in,orcLer to ensll:re p:roper loa-'L:i.ny and dampin(~.
: In o:rder to avold. these compl:icati.ons it is known to derive a signal related -to -the.cone movemen-t and -to use this siynal to provide nega-tive Peedback Por -the amplifieY driving the loudspeaker.' In -thi.s ~jlay -the 25 ' amplifier substantially cornpensa-tes Por -the lo~AcLspeaker deficienci.es. ~resen-t feedbaclc arransements have not been found -to be completely satisfactory in.use often givi.ny a non-l.inear response and furthermore -théy are expensive to manuPact-ure and require carePul assembly and alignmen-t of the components within the loudspealcer.
' 5~1~
. .
It is therefore an object of the present invention to provide a loudspeaker and driving circuit therefor, which will obviate or minimise the foregoing disadvantages in a simple yet effective manner or which will at least provide the public with a useful choice.
Accordingly the invention consists in a loudspeaker system comprising a support frame, a first magnet mounted in said frame, a voice coil operable in a driving magnetic flux field from said magnet, a diaphragm or cone suspended in said frame and capable of being driven by said voice coil, a second magnet means for providing a magnetic flux field substantially separate from said driving magnetic field, a moving coil transducer operable by movement of said diaphragm or cone and incorporating a transducer coil operable in said magnetic flux field substantially separate from the driving magnetic flux field, connections coupling the output voltage of said transducer to an input of an amplifier adapted to drive said voice coil in a manner such that the coupling between said transducer and said amplifier does not have any common electrical path with the coupling between said amplifier and said voice coil, the output signal from said transducer being coupled to one end of a first resistor of suitable value and fed through said resistor to said input of said amplifier, a first capacitor of suitable value provided connected between said one end of said first resistor and the earth of the circuitry associated with said amplifier and a second resistor and a second capacitor connected in series between the said inpu~ of said amplifier and earth, the values of said second resistor and said second capacitor being selected to give a 3a flat frequency response from the amplifier at high frequencies.
'rO those skilled in the art to which this inven-tion relates, many changes in construction and widely differing embodiments and applications of the invention will suggest themselves without departing from the scope of the invention as defined in the appended claims. The disclosures and the description herein are purely illustrative and are not intended to be in any sense limiting.
ne preferred form of the invention will now be described with reference to the accompanying drawings in which, Fig. 1 is a cross-sectional view of a loudspeaker incorporating feedback elements according to the invention, Fig. 2 is a block diagram of the amplifier and associated circuitry required to feed back the signal ---3a-~lZ05Bal from the lo-udspeaker sho~/n -ln ~'ig. 1 and l~ig. 3 is a c:ircuit di~g:rarrl of~ the ac~tuclL c~m-ponents used in l:he block diayram oP ~:ig. 2.
The use of Peedback -to control the response of high qual~ty amplifiers and other components in the sound recording and reproduction chain iS well es-ta-blished. Ilhis inven-tion provides means for incor-porating feedback in a loudspeaker system -to con-trol the electro-mechanical conversion process and can be exploited in any of the followiny ways.
1. By application to a single loudspeaker designed as a wide frequency range unit,
2, By applicatlon to the bass driver of a two (or more) way speaker system~ all speakers being driven from the same amplifier.
3. By applica-tion to the bass driver of a two (or more) way sys-tem where the bass driver is driven from a separate ampliPier to tha-t oP -the high ~requency speakers.
4. By application to speakers other than the bass driver and not necessarily o~ the rnoving coil type.
One particular form of the inven-tion will be described in which -the feedbaclc is applied to the bass driver of a -Lwo or more way speaker system, all speakers ~ -being driven from~the same amplifier as described in paragraph 2 above. The degree of feedback applied can be varied by changing the ~ of the electronic B componen-ts in -the system to any degree cLesired to give a usePul result.
~z~s~ ~
. A loud.spealcer is px ovided hav-Lny a frame 1 i.n which are mounted the ma:in loudspeaker magnet 2 arranged -to provide a driviny magnet.ic flux fiéld across gap 30 in which the voice coil 3 oP -the loudspeaker is restrained to move. The voice coil is connec ted to a cone 'or diaphragm 4 suspended around the periphery by way of a resillent mounting 5 to the ~rame of: the loudspeaker .in the form well lcnown in loudspeaker construction.
10~ Attached to the voice coil 3 oP -the loudspeaker a ~:~
tube 6 is provided,~ for ~example, formed or rolled of ~ -laminated paper or ~cardboard~ or any o-ther suitable material so ~ -that ln use :the~ tube will move relative .
:
to the frame o the loudspeaker: in the same manner ,-as the voice coil 3. The ~roice 'coil could oP course : ~ : :
be wound onto one~end of the tube 6. A moving coil transducer :7 is provided which may for example, be'.
;: arranged so: that the coil 8 is ~tound about the other end :of -the tube 6 and the transducer magnet g :is ~:~ 2 0 a-t-tached to the rame oP the loudspeaker. For examp:Le, :::
'~ " the magnet may be attache~d to the'.Prame by way o.~ amounting bar (not shown ) extendiny across the .eace oP
the speaker .erom the circurnPeren tial mounting f lange 11 or alternatively the magnet~ 9 may be directly mounted~, 25~ to -the magnet ~2 o the volce coil by way of a rod or ; bolt 10 pa~ssing through the magnet 2, the centre of -the tube 6 and the magnet: 9. q~he bolt is secured by a nut 25.
The transducer màgnet 9~ is arranged to provide a -trans~
ducer magne-tic Plux fleld across gap 31 and is spaced Prom the main magnet by a spacer 26.
z~s~ ~
Connections to the ~oice coil and ~eedba~k co-Ll are made in the usual manner.
In this manner a loudspealcer is provided with a transducer 7 which ~y vlrtue of -the fact that the coil ;
of the transducer ls substan-tially rigidly connec-ted to -the voice coil of the loudsp~aker will faithfully ~; produce a vol-tage propo:rtional to -the veloci-ty of ~he speaker cone. Because the driving magnetic ~lux field i~
, . ~
across gap 30 is separated from the transducer magnetic ~lux field across gap 31 and because the transducer coil 8 is separte~from~the~voice coil 3 (i.e. is not co-axial : ~ :
~ with or adjacent to the voice coil),~the signal derived .
from the transducer is substantially free of inter-ference from the operation of -the voice coil. The driving magnetic flux field and the -transducer magnetic flux field may be provided~by the same magne-t ( by : : .
suitable rearrangement of components) as long as the fields are kept separate and do not magnetically ~:
interfere~ith one another. rrhe leng~h o~ the trans-ducer coil 8 should be su~eeicient to preven~ a non-; linear response at extremes o~ movement Oe the voice coil i.e.~ the transducer coil should never move out o~
the transducer magnetic flux eield.
; In use the loudspeaker as described may be connected into the circuit of an associated driving amplifier as :~ :
~ shown in block diagram form in Fig. 2.
~ .
The preferred form oP thé invention uses an amplif-ier 12 havlng differen-tial inpu-ts. The output of the pre-amplLfier is fed -to one amplifier input and the amplifier output is fed through -two leads of a four core - .~ cable 11 to a conventicnal two-way cross-over networ:lc 13 in the ].oudspealcer enclosu:re . rL~he c:ro~s-over frequenc~
is such that the bass driver 14 recelves all frequenci.es where it is desired to utilis~ spea1ce.-r f`eedbaclc, and higher frequencies a.re recei~ed b~ the high ~requency ' ' speaker 15.
The signal ~from the transducer 7 is L`ed back to the ampli~ier~through the remainlng leads o.e 'the four core : cable. Frequencies above approximately~1cHz are 11tèred , ,1a ou-t.of tl1e feedback slgnal by a capaci-tor 16 which orms : a -time constant with the inherent resistance of -thej~ .
feedback coil 8. The feedback signal is then fed through ~ ~ .
resistor 17:as~shown to~the ampl~ifier feedback pointO
In this manner the feedback vol-tage from thé -transducer 8 ~ is fed into the.amplifier as parallel feedback to control the output from~-the ampli.Pier and thus ensure that the ~' ; loudspea1cer diaphragm veloci~y closely follows -the input signal -to the amplifier.
The~ampli.eier output is also fed back vla resistor ' and capacitor 20 to the ~eed'baclc point so I,hat the :::
: ampli.eier ope:rates ln the conventlonal manner at high ~requencies where the L`eed'back signal is not applicable.
llhe series resi~tor and capacitor 18 are required to ~: ~ ensure a::flat frequency response output at high: ~;
Prequencles. :
' one of the leads from the feedback transducer 8 is ::
earthed at point:19 in the:amplifier. This lead canno-t be used b~ the s'ame lead that earths the loudspeaker voice CDil since high currents'are present in the voice .coil earth lead and potenti.als developed across the lead .
., ; , .
~z~
._ ~ will interfere with the feedback siyn~
The sys-tem describe.d above does not allow for the characterlstic variation of radlation resistance wi-th erequency below a frequency determined by the loud-: ~5 spealcer diaphragm area. Thls charac-teristic requires . that below this critical erequency the dlaphragm velocity should vary in inverse p-roportion to the frequency if:a flat acoustic Prequency respanse is to be maintained. The applica-~ion o feedback arcund the loud- ,~
spealcer -takes advantaye of the inverse relationship ,~ , which is already:provided by the loudspeaker resonance~
Feedbaclc~ac-ts to damp this resonance, and in fact the correct degree of feedbaclc is applied when there i5 just enough damping to ensure a Çlat frequency relationship between voltage input to the power amplifier and the . diaphragm~veloclty~over the resion of varying radiation resistance. ~:
The lnverse relationship required -to counteract -the varying radiation resistance rnust be restored .: .
~ 20 ~ elect~onically. This may be done by adding an acti.ve ; ~ilter 21 :in the pre-amplifier. The filter response fa:l.ls at 6d:B pe:r octave between 20Hz and the p.revi.ously ..
:: mentione~d frequency determined by loudspeaker area. .
bove this.frequency the filter has a flat response.
2~5 The system;as descrlbed above has been found -to be .
particularly effective in providing a clear un-coloured .( , .
: sound over a wide range of~frequencies even with -the : use of a relativèly:simple and cheap conventional loud-: speaker~basis in a small enclosure. It is a feature of the sys-tem tha-t the voice coil and feedback coil are , , *Z05iBO
- ' electro maynetically inclependen-t mlni,mis:ing incLu.ct~ve coupllng between t.he .~eedback and voic~ co.il sys tems and allowiYly residual hi~h-frequency signals in the feedback to be simply fi.ltered out, . 5 The advantages to ~e gained from using'the system are ~ that a flat acoustic frequency response can be extended below the~speakerrs bass resonance even in a small speaker enclosure oP 'infinite ba~fle' ~esign. ~ low ;, cost bass~speaker can be used to provide sound quality ' ' ~: 10 , exceediny that provided by most conventional domestic :
sound reproduction~systems. Improvement in quality is brought abou-t~through the increased damping of:the . speaker diaphragm as a result o~ feedback. ~ con- -' ventional high quality speaker can be improved by the 15~ a.dditional damping~ provided b~ the eedbaclc system and conven-tiorlal loudspealcer ma~nufac-turing techniques can be used in the production of speakers adap-ted ~or this :, feedbaclc syStem. This enables a high ~i.cl.elity sound system to be manu~actured at a very eheap and com~etit:ive eost.
~ Modi~i.catlons required to the ampli~ier des:ign are also si.mple and lo~ ln cost.
'rrhe feedback signal deriv,ed ~rom the tra~sdu.cer i is proportional to -the velocity of the spealcer diaphragm which is the parameter of motion direcl.~.y related to .
acoustic power (power lS proportional to velocity ' squared).
' The feedbaclc system used is also particularly -:
: suitable for use in multi-spealcer installations where it is only clesired to provide feedbaclc control over the ~ 3~ bass driver. In a multl-speaker installation -the .. . ' :
:
~`
l~h~5~30 .. . .
Peedback dampirlg is res~xicted -to a ~acl:or; of~ to allow the hi~h Prequency units to be properly c~r.iverl withou~
signiPic~ant interPerence ~rom the Peecl'~fack sys tem.
, :
; : :: : , ~, . .
:: : : : :.
f ~: : ' ' ' i ' :
': , ~: ~ ' ~ ' ' ,"~
?.
- 10 _ '~ ' .
~ ' ' ' .
One particular form of the inven-tion will be described in which -the feedbaclc is applied to the bass driver of a -Lwo or more way speaker system, all speakers ~ -being driven from~the same amplifier as described in paragraph 2 above. The degree of feedback applied can be varied by changing the ~ of the electronic B componen-ts in -the system to any degree cLesired to give a usePul result.
~z~s~ ~
. A loud.spealcer is px ovided hav-Lny a frame 1 i.n which are mounted the ma:in loudspeaker magnet 2 arranged -to provide a driviny magnet.ic flux fiéld across gap 30 in which the voice coil 3 oP -the loudspeaker is restrained to move. The voice coil is connec ted to a cone 'or diaphragm 4 suspended around the periphery by way of a resillent mounting 5 to the ~rame of: the loudspeaker .in the form well lcnown in loudspeaker construction.
10~ Attached to the voice coil 3 oP -the loudspeaker a ~:~
tube 6 is provided,~ for ~example, formed or rolled of ~ -laminated paper or ~cardboard~ or any o-ther suitable material so ~ -that ln use :the~ tube will move relative .
:
to the frame o the loudspeaker: in the same manner ,-as the voice coil 3. The ~roice 'coil could oP course : ~ : :
be wound onto one~end of the tube 6. A moving coil transducer :7 is provided which may for example, be'.
;: arranged so: that the coil 8 is ~tound about the other end :of -the tube 6 and the transducer magnet g :is ~:~ 2 0 a-t-tached to the rame oP the loudspeaker. For examp:Le, :::
'~ " the magnet may be attache~d to the'.Prame by way o.~ amounting bar (not shown ) extendiny across the .eace oP
the speaker .erom the circurnPeren tial mounting f lange 11 or alternatively the magnet~ 9 may be directly mounted~, 25~ to -the magnet ~2 o the volce coil by way of a rod or ; bolt 10 pa~ssing through the magnet 2, the centre of -the tube 6 and the magnet: 9. q~he bolt is secured by a nut 25.
The transducer màgnet 9~ is arranged to provide a -trans~
ducer magne-tic Plux fleld across gap 31 and is spaced Prom the main magnet by a spacer 26.
z~s~ ~
Connections to the ~oice coil and ~eedba~k co-Ll are made in the usual manner.
In this manner a loudspealcer is provided with a transducer 7 which ~y vlrtue of -the fact that the coil ;
of the transducer ls substan-tially rigidly connec-ted to -the voice coil of the loudsp~aker will faithfully ~; produce a vol-tage propo:rtional to -the veloci-ty of ~he speaker cone. Because the driving magnetic ~lux field i~
, . ~
across gap 30 is separated from the transducer magnetic ~lux field across gap 31 and because the transducer coil 8 is separte~from~the~voice coil 3 (i.e. is not co-axial : ~ :
~ with or adjacent to the voice coil),~the signal derived .
from the transducer is substantially free of inter-ference from the operation of -the voice coil. The driving magnetic flux field and the -transducer magnetic flux field may be provided~by the same magne-t ( by : : .
suitable rearrangement of components) as long as the fields are kept separate and do not magnetically ~:
interfere~ith one another. rrhe leng~h o~ the trans-ducer coil 8 should be su~eeicient to preven~ a non-; linear response at extremes o~ movement Oe the voice coil i.e.~ the transducer coil should never move out o~
the transducer magnetic flux eield.
; In use the loudspeaker as described may be connected into the circuit of an associated driving amplifier as :~ :
~ shown in block diagram form in Fig. 2.
~ .
The preferred form oP thé invention uses an amplif-ier 12 havlng differen-tial inpu-ts. The output of the pre-amplLfier is fed -to one amplifier input and the amplifier output is fed through -two leads of a four core - .~ cable 11 to a conventicnal two-way cross-over networ:lc 13 in the ].oudspealcer enclosu:re . rL~he c:ro~s-over frequenc~
is such that the bass driver 14 recelves all frequenci.es where it is desired to utilis~ spea1ce.-r f`eedbaclc, and higher frequencies a.re recei~ed b~ the high ~requency ' ' speaker 15.
The signal ~from the transducer 7 is L`ed back to the ampli~ier~through the remainlng leads o.e 'the four core : cable. Frequencies above approximately~1cHz are 11tèred , ,1a ou-t.of tl1e feedback slgnal by a capaci-tor 16 which orms : a -time constant with the inherent resistance of -thej~ .
feedback coil 8. The feedback signal is then fed through ~ ~ .
resistor 17:as~shown to~the ampl~ifier feedback pointO
In this manner the feedback vol-tage from thé -transducer 8 ~ is fed into the.amplifier as parallel feedback to control the output from~-the ampli.Pier and thus ensure that the ~' ; loudspea1cer diaphragm veloci~y closely follows -the input signal -to the amplifier.
The~ampli.eier output is also fed back vla resistor ' and capacitor 20 to the ~eed'baclc point so I,hat the :::
: ampli.eier ope:rates ln the conventlonal manner at high ~requencies where the L`eed'back signal is not applicable.
llhe series resi~tor and capacitor 18 are required to ~: ~ ensure a::flat frequency response output at high: ~;
Prequencles. :
' one of the leads from the feedback transducer 8 is ::
earthed at point:19 in the:amplifier. This lead canno-t be used b~ the s'ame lead that earths the loudspeaker voice CDil since high currents'are present in the voice .coil earth lead and potenti.als developed across the lead .
., ; , .
~z~
._ ~ will interfere with the feedback siyn~
The sys-tem describe.d above does not allow for the characterlstic variation of radlation resistance wi-th erequency below a frequency determined by the loud-: ~5 spealcer diaphragm area. Thls charac-teristic requires . that below this critical erequency the dlaphragm velocity should vary in inverse p-roportion to the frequency if:a flat acoustic Prequency respanse is to be maintained. The applica-~ion o feedback arcund the loud- ,~
spealcer -takes advantaye of the inverse relationship ,~ , which is already:provided by the loudspeaker resonance~
Feedbaclc~ac-ts to damp this resonance, and in fact the correct degree of feedbaclc is applied when there i5 just enough damping to ensure a Çlat frequency relationship between voltage input to the power amplifier and the . diaphragm~veloclty~over the resion of varying radiation resistance. ~:
The lnverse relationship required -to counteract -the varying radiation resistance rnust be restored .: .
~ 20 ~ elect~onically. This may be done by adding an acti.ve ; ~ilter 21 :in the pre-amplifier. The filter response fa:l.ls at 6d:B pe:r octave between 20Hz and the p.revi.ously ..
:: mentione~d frequency determined by loudspeaker area. .
bove this.frequency the filter has a flat response.
2~5 The system;as descrlbed above has been found -to be .
particularly effective in providing a clear un-coloured .( , .
: sound over a wide range of~frequencies even with -the : use of a relativèly:simple and cheap conventional loud-: speaker~basis in a small enclosure. It is a feature of the sys-tem tha-t the voice coil and feedback coil are , , *Z05iBO
- ' electro maynetically inclependen-t mlni,mis:ing incLu.ct~ve coupllng between t.he .~eedback and voic~ co.il sys tems and allowiYly residual hi~h-frequency signals in the feedback to be simply fi.ltered out, . 5 The advantages to ~e gained from using'the system are ~ that a flat acoustic frequency response can be extended below the~speakerrs bass resonance even in a small speaker enclosure oP 'infinite ba~fle' ~esign. ~ low ;, cost bass~speaker can be used to provide sound quality ' ' ~: 10 , exceediny that provided by most conventional domestic :
sound reproduction~systems. Improvement in quality is brought abou-t~through the increased damping of:the . speaker diaphragm as a result o~ feedback. ~ con- -' ventional high quality speaker can be improved by the 15~ a.dditional damping~ provided b~ the eedbaclc system and conven-tiorlal loudspealcer ma~nufac-turing techniques can be used in the production of speakers adap-ted ~or this :, feedbaclc syStem. This enables a high ~i.cl.elity sound system to be manu~actured at a very eheap and com~etit:ive eost.
~ Modi~i.catlons required to the ampli~ier des:ign are also si.mple and lo~ ln cost.
'rrhe feedback signal deriv,ed ~rom the tra~sdu.cer i is proportional to -the velocity of the spealcer diaphragm which is the parameter of motion direcl.~.y related to .
acoustic power (power lS proportional to velocity ' squared).
' The feedbaclc system used is also particularly -:
: suitable for use in multi-spealcer installations where it is only clesired to provide feedbaclc control over the ~ 3~ bass driver. In a multl-speaker installation -the .. . ' :
:
~`
l~h~5~30 .. . .
Peedback dampirlg is res~xicted -to a ~acl:or; of~ to allow the hi~h Prequency units to be properly c~r.iverl withou~
signiPic~ant interPerence ~rom the Peecl'~fack sys tem.
, :
; : :: : , ~, . .
:: : : : :.
f ~: : ' ' ' i ' :
': , ~: ~ ' ~ ' ' ,"~
?.
- 10 _ '~ ' .
~ ' ' ' .
Claims (13)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A loudspeaker system comprising a support frame, a first magnet mounted in said frame, a voice coil operable in a driving magnetic flux field from said magnet, a diaphragm or cone suspended in said frame and capable of being driven by said voice coil, a second magnet means for providing a magnetic flux field substantially separate from said driving magnetic field, a moving coil transducer operable by movement of said diaphragm or cone and incorporating a transducer coil operable in said magnetic flux field substantially separate from the driving magnetic flux field, connections coupling the output voltage of said transducer to an input of an amplifier adapted to drive said voice coil in a manner such that the coupling between said transducer and said amplifier does not have any common electrical path with the coupling between said amplifier and said voice coil, the output signal from said transducer being coupled to one end of a first resistor of suitable value and fed through said resistor to said input of said amplifier, a first capacitor of suitable value provided connected between said one end of said first resistor and the earth of the circuitry associated with said amplifier and a second resistor and a second capacitor connected in series between the said input of said amplifier and earth, the values of said second resistor and said second capacitor being selected to give a flat frequency response from the amplifier at high frequencies.
2. A loudspeaker system as claimed in Claim 1 wherein said voice coil and said transducer coil are arranged so that the conductor fields from each are substantially separate.
3. A loudspeaker system as claimed in Claim 2 wherein said voice coil and said transducer coil are restrained to move
3. A loudspeaker system as claimed in Claim 2 wherein said voice coil and said transducer coil are restrained to move
Claim 3 continued ...
along a common axis but are longitudinally separated along that axis.
along a common axis but are longitudinally separated along that axis.
4. A loudspeaker system as claimed in claim 1 wherein the transducer is mounted on the opposite side of diaphragm or cone from said voice coil and magnet.
5. A loudspeaker as claimed in claim 4 wherein said voice coil and said transducer coil are wound onto a common mounting core and said second magnet is supported by a support rod from said frame passing through said core.
6. A loudspeaker system as claimed in claim 5 wherein the signal from said transducer is fed back as parallel feed back to said input of said amplifier.
7. A loudspeaker system as claimed in claim 6 wherein at least one further loudspeaker and a cross-over network are pro-vided, said cross-over network being arranged to direct high frequency signals to said further loudspeaker or loudspeakers and low frequency signals to said loudspeaker incorporating said transducer.
8. A loudspeaker system as claimed in claim 2 or 3 wherein the transducer is mounted on the opposite side of diaphragm or cone from said voice coil and magnet.
9, A loudspeaker as claimed in claim 1, 2 or 3 wherein said voice coil and said transducer coil are wound onto a common mounting core and said second magnet is supported by a support rod from said frame passing through said core.
10. A loudspeaker system as claimed in claim 1, 2 or 3 wherein the signal from said transducer is fed back as parallel feed back to said input of said amplifier.
11. A loudspeaker system as claimed in claim 4 wherein the signal from said transducer is fed back as parallel feed back to said input of said amplifier.
12. A loudspeaker system as claimed in claim 1, 2 or 3 wherein at least one further loudspeaker and a cross-over net-work are provided, said cross-over network being arranged to direct high frequency signals to said further loudspeaker or loudspeakers and low frequency signals to said loudspeaker incorporating said transducer.
13. A loudspeaker system as claimed in claim 4 or 5 wherein at least one further loudspeaker and a cross-over network are provided, said cross-over network being arranged to direct high frequency signals to said further loudspeaker or loudspeakers and low frequency signals to said loudspeaker incorporating said transducer.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| NZ18112776A NZ181127A (en) | 1976-06-01 | 1976-06-01 | Loudspeaker with motional feedback |
| NZ181127 | 1976-06-11 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1120580A true CA1120580A (en) | 1982-03-23 |
Family
ID=19917758
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000280342A Expired CA1120580A (en) | 1976-06-01 | 1977-06-10 | Single loudspeaker having a moving coil transducer for feedback purposes |
Country Status (7)
| Country | Link |
|---|---|
| JP (1) | JPS5319823A (en) |
| AU (1) | AU512135B2 (en) |
| CA (1) | CA1120580A (en) |
| DE (1) | DE2726184A1 (en) |
| GB (1) | GB1534842A (en) |
| NL (1) | NL7706404A (en) |
| NZ (1) | NZ181127A (en) |
Families Citing this family (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS53108420A (en) * | 1977-03-03 | 1978-09-21 | Victor Co Of Japan Ltd | Speaker driving system |
| JPS5936845U (en) * | 1982-08-26 | 1984-03-08 | 三菱重工業株式会社 | electrostatic precipitator |
| GB8321810D0 (en) * | 1983-08-12 | 1983-09-14 | Linn Prod Ltd | Loudspeaker with notional feedback |
| NO172469C (en) * | 1984-01-25 | 1993-07-21 | Per Kirksaeter | SOUND REPLACEMENT SYSTEM |
| GB2201318B (en) * | 1987-02-12 | 1990-10-24 | Udi Group Ltd | Electromechanical transducer |
| GB8918975D0 (en) * | 1989-08-21 | 1989-10-04 | Birt David R | Improvements in moving coil loudspeakers |
| DE4225854A1 (en) * | 1992-08-05 | 1994-02-10 | Nokia Deutschland Gmbh | Low depth medium or woofer loudspeaker - has magnetic system fitted in acoustic funnel of diaphragm |
| GB201712391D0 (en) | 2017-08-01 | 2017-09-13 | Turner Michael James | Controller for an electromechanical transducer |
| CN110996235B (en) * | 2019-12-24 | 2025-03-28 | 深圳市睿德龙科技有限公司 | Bone conduction speakers for ultrasonic and electroacoustic systems |
| GB2620787A (en) * | 2022-07-22 | 2024-01-24 | Gp Acoustics Uk Ltd | Loudspeakers |
-
1976
- 1976-06-01 NZ NZ18112776A patent/NZ181127A/en unknown
-
1977
- 1977-06-08 AU AU25943/77A patent/AU512135B2/en not_active Expired
- 1977-06-10 DE DE19772726184 patent/DE2726184A1/en active Pending
- 1977-06-10 NL NL7706404A patent/NL7706404A/en not_active Application Discontinuation
- 1977-06-10 JP JP6873377A patent/JPS5319823A/en active Pending
- 1977-06-10 CA CA000280342A patent/CA1120580A/en not_active Expired
- 1977-06-13 GB GB2457577A patent/GB1534842A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| NZ181127A (en) | 1981-04-24 |
| AU512135B2 (en) | 1980-09-25 |
| JPS5319823A (en) | 1978-02-23 |
| GB1534842A (en) | 1978-12-06 |
| AU2594377A (en) | 1978-12-14 |
| DE2726184A1 (en) | 1977-12-22 |
| NL7706404A (en) | 1977-12-13 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |