US2007747A

US2007747A - Acoustic apparatus

Info

Publication number: US2007747A
Application number: US661237A
Authority: US
Inventors: Ringel Abraham
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1933-03-17
Filing date: 1933-03-17
Publication date: 1935-07-09
Anticipated expiration: 1952-07-09
Also published as: BE402059A; GB439561A; DK50698C; CH179149A; NL40839C; FR770109A; DE680788C; AT143569B

Description

RINGEL TIC APPARATUS Filed March 17, 1933 July ,9, 1935.

3 Sheet s-Shet 1 INVENTOR A Sf. BY #4 ATTORNEY y A. RINGEL Z,O07,747

Acofisnc APPARATUS Filed March 17. 1953 SSheets-Sheet 2 INVENTOR A. 5. fill/6H ATTORNEY 935. v A. RINGEL 2,007,747

ACOUSTIC APPARATUS Filed March 17, 1933 3 Sheets-Sheet 3 INVENTOR A S. fi/NGEL BY vr gw ATTORNEY Patented 9', 1935 Abraham Ringel, Merchantville, N. 1., assignor to Radio Corporation of America, a corporation of Delaware Application March 17.1933. Serial No.661,23'l

21 Claims.

This invention relates to acoustic apparatus. as the frequency increases; At the highest'fre- More particularly, it relates to acoustic appara tus in which one or more parts of the vibratile system (diaphragm and associated parts) is divided into sections interconnected by compliances of such nature that at certain frequencies the.

sections vibrate together and at other frequencies one section vibrates relative to another section. The invention is particularly applicable to e1ec-'- trodynamic loudspeakers.

Electrodynamic loudspeakers are well known in the prior art. v They are used extensively in radio apparatus. The electrodynamic loudspeaker consists essentially of a magnet structure forming an .air gap, a flexibly supported conical dia.-

phragm and a driving coil connected to'the apex portion' of the diaphragm and supported to vibrate within the air gap.

Electrodynamic loudspeakers have proved very satisfactory in reproducing sound over a relatively wide frequency range, but attempts to increase the frequency range, especially at the high frequency end, havenot been entirely successful for several reasons, one of which is the failure of the apparatus to respond at high frequencies due to the high mechanical impedance of the moving parts. At the lower frequencies the impedance of the moving parts is suiiiciently low so that it does not have a material effect on the fidelity of reproduction, but at the higher frequencies, particularly frequencies above 6,000

cycles per second, the mechanical impedance of the moving parts becomes relatively high and seriously affects the fidelity of reproduction.

-It is an object of the invention to provide an improved acoustic device which will: respond with a high degree of fidelity over a broader frequency range'than that covered by electrodynamic loudspeakers of present commercial construction. This object is attained by using an improved diaphragm system, an improved driving system or a combination of both;

In its broadest aspect'the invention consists ofdividing either the diaphragm system or the driving system or both, into a plurality of sections or parts interconnected by compliant couplings. The degree of elasticity of each coupling is made such that different sections of the dia-' phragm system, or of the driving system, or both, vibrate depending on the instantaneous frequency of the sound vibrations. At the lower frequencies the entire diaphragm system and system vibrate substantially as a whole. A smaller area of the diaphragm system and/or a smaller portion of the driving system. vibrates quencies to which the device is adapted to respond, only a small area of the diaphragm system and/or only a small portion of the driving system vibrates. The compliant couplings and 5 the diaphragm and driving system sections are so arranged that the portion of the driving system adapted to respond at the highest frequency is preferably located immediately adjacent 'the section of the diaphragm system which responds 10 at the highest frequency. Thus only the diaphragm and driving system sections havingthe lowest mechanical impedance are set into vibration at the highest frequencies.

Other and more specific objects of the inven- 15 tion will become apparent upon reading the speci- 'flcation and appended claims in connection with the accompanying drawings.

In the accompanying drawings in which I have disclosed apparatus embodying several modiflca- 20 tions of the invention, Fig. 1 is a sectional view illustrating the details of apparatus embodying a form of the invention in which compliant coupling means is used to connect one section of the diaphragm system with the driving system;

Figs. 2, 3 and 4 are sectional views illustrating modifications of the apparatus shown in Fig. 1;

Fig. 5 is a sectional view illustrating a. modification in which the driving system is divided into sections by compliant coupling means; 30

Fig. 6 is a view showing a cross section of apparatussimilar to that shown in Fig. 5, and diagrammatically representing an approved circuit for energizing the apparatus;

Fig. '1 illustrates diagrammatically the electri- 35 cal analog of the apparatus shown in Fig. 5;

Fig. 8 is a sectional view illustrating a modification of the apparatus shown in Fig. 5; and

Figs. 9 to 13 are circuit diagrams illustrating modifications of the circuit arrangements diagrammatically illustrated in Fig. 5.

The apparatus illustrated in Fig. 1 comprises a loudspeaker of the electrodynamic or moving coil type. It consists of a central pole piece l0 and an outer pole piece ll spaced from the central pole piece to form an annular air gap in which the driving system I2 is supported. The driving system l2 consists of a voice coil l3 wound on a suitable cylindrical form 14. The driving system H secured to a diaphragm system in any suitable manner. 'The driving system is supported in strip of flexible material I6 extending between a suitable support I! and a part of the diaphragm system.

The diaphragm system according to one form of the invention, consists of two diaphragms or sound wave producing portions I 8 and I9. The diaphragm or sound wave producing portion I8 is frustum shaped and preferably made of relatively stiff paper. It is connected with the driving system I2 by compliant coupling means 29. The compliant coupling 28 may be formed by providing annular corrugations in the diaphragm l8 adjacent its smaller base, or by treating the portion of the frustum immediately adjacent its smaller base in some other manner to make it more flexible than the main portion of the frustum. The

compliant coupling 20 may also consist of a strip of some material more flexible than the material of the frustum I8.

The coupling 20 is designed to be substantially rigid, i. e., non-absorbent to vibrations, at low frequencies, and relatively absorbent to vibrations at high frequencies. For example, the coupling 20 is sufiiciently rigid so that vibrations of the driving system I2 are transmitted to the frustum I8, at frequencies up to, say, 2,000 cycles per second, Whereas, at frequencies considerably higher than 2,000 cycles per second, e. g., around 6,000 cycles per second, the coupling becomes absorbent to vibrations so that substantially no vibrations are transmitted from the driving system to the frustum l8. This is due to the fact that at high frequencies the inertia of the frustum I8 is so large that the force required to move the frustum is much greater than the force required to deform the coupling. The force exerted by the driving system is, therefore, expended in deforming the compliant coupling. In this operating condition, the compliant coupling absorbs vibrations as distinguished from transmitting them from the driving system to the diaphragm portion I8. At intermediate frequencies, the coupling 20 is semiabsorbent to vibrations and the vibrations of the driving system are transmitted, to some extent. to the frustum I8.

The small diaphragm or sound wave producing portion I9 is preferably made of relatively light material such as aluminum or paper. It is directly connected with the driving system I2. The diaphragm I9 may be an extension of the coil form I i if the material of the coil form is sufficiently light in weight. The diaphragm I9 is substantially conical and has a small opening 2| at its apex for providing access to the screw for securing the centering spider I5 to the central pole piece ID. The opening. 2| will also prevent the formation of an air pocket between the central pole piece and the diaphragm I9.

While the centering spider I5 is shown internally of the coil form It, it is to be understood that a centering member extending outwardly from the coil form and supported by the outer pole piece II, may be used. It may not be neces sary to provide an opening 2i when an outer spider member is used.

The diaphragm I9 is shown located-inside the diaphragm I8 as this is the preferred construction. Various other arrangements can be made however, without departing from the spirit of the invention. For example, the diaphragm I9 may be omitted and the coupling moved up the diaphragm I8 to provide a section corresponding to section 22 of Fig. 3. Such a section would function just the same as diaphragm I9 of Fig. 1.

The small diaphragm I9 due to its rigid connection with the driving system I2, is adapted to vibrate at all frequencies at which the driving system l2 vibrates. It is especially adapted to reproduce high frequencies by reason of its small size and light mass. For this reason it will hereinafter be referred to as the high frequency diaphragm. On the other hand the frustum I8 which is relatively large in size and mass compared to the high frequency diaphragm l9, and which is connected with the driving system I2 by a compliant coupling that only transfers low frequency vibrations, is especially adapted to reproduce low frequencies. The frustum I8 will therefore hereinafter be referred to as the low frequency diaphragm. The diaphragm system will vibrate as a whole at the lower frequencies. As the frequency increases diaphragm I8 vibrates to a lesser extent until, at the very high frequencies, there is substantially no vibration of the low frequency diaphragm I8, and the high frequency diaphragm I9 sets up substantially all of the sound waves radiated from the acoustic device.

The apparatus illustrated by Fig. 2 is similar to the apparatus of Fig. 1 except that diaphragm I9 is shown as a separate member from the coil form I4 whereas in Fig. 1 it is shown as a continuation of the coil form. A small horn 23 supported by suitable arms 24 secured to the support IT, is provided for amplifying the high frequency vibrations from the diaphragm l9. The throat of the horn is preferably located adjacent the connection between the'diaphragm I9 and the driving system I2. The horn may be of any desired size, shape or material, but it is preferably designed to give the desired output characteristic.

In the modification illustrated by Fig. 3 the high frequency diaphragm I9 is somewhat larger than in the modification illustrated by Fig. 1. It is connected to a frustum 22 instead of directly to the driving system I2, as in Fig. l. The compliant coupling 20 is located between the frustum 22 and the larger frustum or low frequency diaphragm I8. The low frequency diaphragm I8 is made of relatively stiff material and the high frequency diaphragm I9 is made of comparatively thin, light material as in the modification illustrated by Fig. 1. The frustum 22 which is secured in any suitable manner to the driving system, is also preferably made of thin, light material.

The compliant coupling 20 may be a continuationof the frustum 22 suitably treated such as by being provided with corrugations, to increase its flexibility. The compliant coupling 28 may also be made of a separate piece of material or it may even be a continuation of the frustum I8 suitably treated to increase its flexibility. i

The apparatus illustrated by Fig. 3 may also be provided with a hor'n23 supportedf-by'a'rms '24. The throat of the horn is preferably'located adjacent the connection between'the diaphragm I9 and the frustum 22 to which-the diaphragm I9 is secured. The horn will function in the same manner as the corresponding" horn of Fig. 2.

The modification illustrated by Fig. 4 is similar to the modification illustrated by Fig. 1, except that the low frequency diaphragm I8 is shaped so that it functions as a horn or acoustic diaphragm I3.

In the modification illustrated by Fig. 5 the diaphragm system is vibrated by an improved, driving system 3|. The driving system 3| consists of a coil 32 supported on a coil form 33. The driving system is supported in the usual manner by a spider I3. It is connected with the diaphragm system in any well known manner.

The coil form 33 is divided into two

parts

34 and 35 connected by a compliant coupling 38. The part 34 which is at the end of the. driving system connected with the diaphragm system, may be called the high frequency part of the coil .form. The section 35 which is usually. larger than part 34, may be called the low frequency part of the coil form. The high frequency coil form part 34 supports a winding 31 and the low frequency coil form part 35 supports a winding 38. The winding 31 preferably consists of a small number of turns of a very light conductor such as, for example, aluminum wire. Winding 31 is known as the high frequency winding. Winding 38 which will hereinafter be referred to as the low frequency winding, consists of a largernumber of turns of wire. The wire or conductor forming coil 38, may be of copper or any suitable material as its mass is relatively unimportant compared with the effective mass of the high frequency portions of the vibratilesystem. The coil form part 34 and its associated winding 31 will hereinafter be referred toas the high frequency section ofithedriving system. The coil form part 35 and winding 38 will be referred to as the low frequency section of the driving system.

The compliant coupling 35 may be formed by suitably corrugating the coil form 33 or by treating a section of the coil form in some other manner so as to increase its flexibility. The coupling may also consist of a connecting member of some material more resilient than that of the

coil form parts

34 and 35. The degree of resiliency of the compliant coupling 33 is made such that the coupling acts as a relatively rigid connecting member at the lower frequencies, e. g., frequencies up to 2,000 cycles per second, and as a relatively flexible connecting member at higher frequencies, e. g. frequencies well above 2,000 cycles per second, for an ordinary eight inch cone. The foregoing frequency values depend on the size of the cone and the frequency range it is desired to cover. They will change to some extent if either the size of the cone or the frequency range is varied materially.

The high frequency and

low frequency windings

31 and 38 may be connected in series or in parallel and energized from a suitable source of energy such as the output of a radio receiver. Means are provided for materially reducing the high frequency component of the energy supplied to the low frequencywinding 33. This also tends' to keep the electrical impedance of the driving system more nearly constant than that of a single voice coil. Several approved ways of connecting the

coils

31 and 33 to the source of energy, through suitable high pass and low pass filters 39 and 40, will be described hereinafter.

' When the energy is supplied to the

windings

31 and 33 the flow of current through the windings causes the device to operate in the manner well known in the art. Whenlow frequency energy is supplied to both windings or to the low frequency winding 38 alone, the driving system 3| moves as a whole and transmits vibrations to the diaphragm system As the frequency increases, less energy is supplied to the low frequency winding 30 until at the very high frequencies, the high frequency winding 31 is the only portion of the driving coil 32 which is energized. When the high frequency winding 31 is energized and vibrated at high frequencies, the

low frequency section

35, 38 remains substantially stationary due to the fact that the transmission of mechanical vibrations through the compliant coupling 36 is materially reduced at high frequencies. This results'in the mass of the effective part of the driving system being materially decreased as the frequency of vibration increases, with a resulting increase in the frequency range over which the loudspeaker will respond. At intermediate frequencies a large portion'of the driving force is derived from the high frequency winding 31, but some driving force is also supplied by the low frequency winding 33 due to the fact that the compliant coupling 36 transmits some energy-to the diaphragm at intermediate frequencies. 1

As shown in Fig. 5, the high frequency diaphragm I9 is directly connected with the

high frequency section

34, 31 of the driving system and the low frequency diaphragm i8 is connected with the driving system through a compliant coupling 20, similar to the compliant couplings illustrated in Figs. 1 to 4. At lowfrequencies the driving system 3| vibrates as a whole and transmits vibrations to both the highfrequency diaphragm l3 and the low frequency diaphragm I8. As the frequency of vibration is increased, less energy is transferred to the low frequency diaphragm I8 because of the energy because of the electric filter circuits hereinafter referred to, and consequently it vibrates to a lesser extent. At high frequencies the high frequency diaphragm l3 and the

high frequency section

34, 31 vibrate substantially as a whole, while the low frequency diaphragm l8 and the

low frequency section

35, 31 either remain substantially stationary or vibrate only to a slight extent.

Fig. 6 illustrates a modification in which a, diaphragm system similar to that shown in Fig. 4 is combined with a driving system similar to that shown "in Fig.5. The high frequency diaphragm I9 is secured to the driving system 3| in any convenient manner.

The driving system 3| contains a compliant coupling 36, but in this modification it consists of a corrugation extending inwardly whereas in Fig. 5 the corrugation extends outwardly. The inner pole piece to is cut away as at 4| to prevent frictional engagement between the compliant coupling 36 and the pole piece. The outer pole piece may also be cut away as at 42. An object of cutting away portions of the pole pieces as at 4| and 42, is to produce two regions having uniform magnetic fields. Oneregion of uniform magnetic field extends between the upper portion 43 of the central pole piece and the upper portion 44 of the outer pole piece. The other region of uniform magnetic field extends between windings 3'! and 38, so that the windings extend into the non-uniform fields at the ends of the gaps, the flux traversing the windings is constant and distortion at large amplitudes of movement is avoided.

The high frequency winding 31 and the low frequency winding 38 are similar to the windings nected in the leads extending to the low frequency winding 38.

The high pass filter 39 consists of a typical constant K high pass filter of the 1r section type such as is well known in the art. It consists of a capacitive reactance element connected in one of the leads and inductive reactance elements connected across the leads on both sides of the capacitor. The values of the elements are so chosen that low frequency energy does not reach the high frequency coil 31.

The low pass filter 40 is a typical constant K low pass filter, of the 1r section type. It consists of an inductive reactance element connected in one of the leads between two shunting capacitive reactance elements. The values of the elements are so chosen that high frequency energy does not reach the winding 38. I

When the

windings

31 and 38 are connected in the manner shown in Fig. 6, and provided with proper filters, the winding 38 is the only portion of the driving coil energized at low frequencies and the winding '31 is the only portion of the driving coil energized at high frequencies. At low frequencies the vibrations of the

low frequency sections

35, 38 are transferred through the compliant coupling 36, and the

high frequency section

34, 31 to the diaphragm system. The low frequency diaphragm l8 and the high frequency diaphragm l9 are both vibrated at low frequencies due to the fact that the compliant coupling 20 transmits mechanical vibrations at these frequencies. At the high frequencies the vibrations of the

high frequency section

34, 31 are transferred to the high frequency diaphragm l9 but not to the low frequency diaphragm I8 because of the compliant coupling 20. Moreover, due to the compliant coupling 36, the vibrations of the

high frequency section

34, 31 are not transferred to the

low frequency section

35, 38 at high frequencies. At' intermediate frequencies both windings are energized to some extent and energy is transferred to both diaphragms. The compliant coupling 20 transfers some, but not all of the energy from the driving system to the low frequency diaphragm l8 at intermediate frequencies. I r

Fig. '7 illustrates diagrammatically a circuit which is the electrical analog of the devices illustrated in Figs. and 6. Reference character F1 indicates the force driving the low frequency coil 38, inductance 50 represents the mass of the low frequency driving coil 38, capacity 5| represents the compliance 36 between the low frequency and high frequency coils, F2 represents the force driving the high frequency coil 37, inductance 52 represents the mass of the high frequency coil 31, inductance 53 and resistance represent the added mass .and resistance due to radiation from the smaller diaphragm, inductance couplings.

55 represents the 'mass of the smaller diaphragm, capacity 66 represents the compliance between the diaphragms, inductance 51 represents the mass of the large diaphragm, and inductance 66 and resistance 59 represent the added mass and resistance due to radiation from the large diaphragm 16. When low frequency forces are applied at F1, the current in the circuits II and III will not be widely difierent from that in circuit I, since the impedance of the capacities BI and 66 is suiiiciently high so that their shunt effect is negligible. Thus low frequency currents or velocities are transmitted undiminished to all parts of the diaphragm structure which move in unison and at the same amplitude. There are no high frequency forces applied at F1. All high frequency forces are applied at F2. At high frequencies the capacities 6| and 56 have sufliciently low reactances so that they successfully shunt or short circuit 50 and .51, 58 and 59 respectively. Thus high frequency currents circulate substantially only in circuit II, where relatively small impedances for the high frequencies only are involved. All the large masses and resultant high impedances for high frequencies are, in effect, short circuited by the compliances. Thus much greater high frequency currents are set up in circuit II than if the other impedances had been attached, with resultant increased sound output for these frequencies.

Fig. 8 illustrates a modification in which the diaphragm system and the driving system are both broken up intothree sections by compliant The diaphragm system includes a high frequency diaphragm |9,.a low frequency diaphragm l8 and an additional diaphragm 6i interposed between the low frequency diaphragm l8 and the driving system. The diaphragm 61 is adapted to reproduce intermediate frequencies. A compliant coupling 62 is arranged between the driving system 31 and the intermediate frequency diaphragm 6|. A second compliant coupling 63 is arranged between the intermediate frequency diaphragm 6| and the low frequency diaphragm 18. The compliant coupling 63 is made more flexible than the compliant coupling 62. By suitably designing the compliant couplings they are made such that 1) both couplings will transfervibrations at low frequencies, e. g. up to say 1,000 cycles; (2) compliant couplings 62 will be sufiiciently rigid to transfer vibrations at intermediate frequencies e. g., from say, 1,000 cycles to 5,000 cycles per second; (3) compliant coupling 63 will not transfer vibrations readily as the frequency is increased over 1,000 cycles per second, and (4) compliant coupling 62 will not transfer vibrations as the frequency is increased over some predetermined frequency such as say, 6,000 cycles per second. As a result, diaphragms l8, l9 and 61 will vibrate as a whole at the lower frequencies, diaphragms l3 and 61 will vibrate substantially as'a whole at intermediate frequencies and diaphragm ill will vibrate at high frequencies. The frequency values given will, of course, vary with the cone size, frequency range to be covered etc.

The driving system 31 of Fig. 8, consists of a

high frequency section

34, 31, a

low frequency section

35, 38 and an intermediate frequency section consisting of a coil form part 64 and an intermediate frequency winding 65. A compliant coupling 66 is provided between

sections

35, 38 and 64, 65. The compliant coupling 66 is designed so that it does not transmit mechanical vibrations materially at frequencies higher than, say 1,000 cycles per second. At higher frequencies the coupling 66 does not transfer vibrations between

sections

35, 38 and 64, 85.

Sections

64, and 38, 31 are joined by a compliant coupling 81 which is so designed as to transfer vibrations up to some intermediate frequency e. g. say, 6,000 cycles per second. Thus, vibrations will be transferred between sections 64, G5 and 34, 31 up to a predetermined intermediate frequency and to a decreasingly lesser extent as the frequency increases above the intermediate frequency.

Windings 31, Hand 38 may be connected in series or in parallel, or in a series-parallel combination. Filter circuits are associated with one or more of the windings so as to insure that high frequency energy is not supplied to windings 38 or 65, and that intermediate frequency energy is not supplied to winding 38.

At low frequencies the entire driving system 3| and the three portiofis of; the diaphragm system vibrate as a whoiiei At intermediate frequencies sections-34, 31 and 64,55, of the driving system 3| andlsections i9 and-5839f the diaphragm system vibrate snbstantialiy as a whole. The compliant coup'ling53 does'not transfer vibrations to a material extent to the-low frequency diaphragm portion [8 at intermediate frequencies. Likewise, the compliant coupling 66 is such that at intermediate frequencies vibrations are not transferred to the low frequency section' 35, 33 which is not energized at intermediate frequencies. At high frequencies the high frequency section 34, 31v and the high frequency diaphragm l8 vibrate as a whole. The compliant coupling 82 is such that at high frequencies the vibrations are not transferred to section 6] and likewise compliant coupling 81 such that vibrations are not transferred to

sections

68, 85 and 35, 38 which are not energized at intermediate frequencies.

Figs. 9 to 13 illustrate diagrammatically various types of filters for supplying energy to the high frequency and

low frequency windings

31 and 38. In Fig. 9 the windings are energized from separate secondary windings on the transformer 81. The leads to the windingscontain high pass and low pass filters 39 and 40. In this modification the high pass filter 39 consists of a pair of capacitive reactance elements connected in series in one of the leads and an inductive reactance element connected across the leads from a point between the two 2 capacitive'reactors. The'low pass filter 40 consists of a pair of inductive reactance elements connected in series in one of the leads and a capacitive reactance element connected across the leads from a point between the two inductive reactors. Instead of connecting the windings with two separate transformers the leads can be connected in parallel to a single secondary winding as indicated diagrammatically in Fig. 10. I

Fig. 11 illustrates still another manner of connecting the

windings

31 and 38 with a source of energy. In this modification the windingsare connected in series and a low pass filter 40 similar to the low pass filter of Fig. 6, is connected so as to prevent high frequency energy from reaching the winding 38. Low frequency energy, however, is supplied to both windings.

Fig. 12 illustrates a modification in-'- which coils 31 and 38 are connected in parallel to the same secondary winding and in which the only react-' ance element provided for filtering purposes consists of a capacitor connected in series with the high frequency winding 31., In Fig. 13 the windings are connected in series and the capacitor is shunted-across the low frequency winding 38.

By dividing the voice coil into sections and only energizing one of the sections (the smallersection) at high frequencies, the impedance of the voice coil can be made to more nearly match the impedance of the source of voice currents. In this way a higher efllciency of transfer of energy is obtained.

The foregoing principles and constructions, especially as to the driving system as distinguished from the diaphragm system, may be adapted to microphones of the electrodynamic type and to other types of apparatus in which a moving coil is vibrated ina magnetic field. It is therefore to be understood that while several modifications embodying approved forms of the invention are illustrated and described in the foregoing specification', various modifications and changes may be made thereto without departing from the spirit of the invention. The invention is not to be limited to the specific arrangements shown and described hereinbefcre, but only by the scope of the appended claims.

What I claim is:

- 1. A transducer system for acoustic apparatus of the electrodynamic type, comprising a plurality of windings and compliant coupling means interconnecting said windings.

2. A transducer system for acoustic apparatus comprising a coil form divided into a plurality of sections by compliant means and a winding on each section.

3. A transducer system for acoustic apparatus comprising a coil form divided into a pair of sections, flexible means connecting said sections, and a winding on each section. I

4. A transducer system for acoustic apparatus of the moving coil type comprising a cylindrical coil form provided with an annular corrugation dividing the coil form into a pair of sections, and a winding on each section.

5; A transducer system for acoustic apparatus of the moving coil type comprising a coil form, compliant coupling means dividing said form into a pair of sections, a high frequency winding on one section, and a low frequency winding on the other. a

6. A vibratile system for acoustic apparatus comprising a coil system portion and a. sound wave producing portion, and compliant coupling means for dividing both portions into sections.

7. A vibratile system for acoustic apparatus comprising a coil system portion, compliant means dividing said coil system portion into sections, and a sound wave producing portion including a. pair of diaphragm, said sound wave producing portion being connected with said coil system portion, at least one of said diaphragm portions being connected with said coil system portion by a compliant coupling.

8. A vibratile system for acoustic apparatus Jen. rem-'4 viding a magnetic field for coacting with said windings during operation of said apparatus.

10. A vibratile system for acoustic apparatus comprising a coil form, compliant means dividing said coil form into a pair of sections, a high frequency winding on one section, a low frequency winding on the other section, and a diaphragm connected to said coil form at the end bearing said high frequency winding.

11. Apparatus for reproducing sound comprising a diaphragm, a coil form secured thereto, compliant means dividing said coil form into sec- .tions, at high frequency winding on one section, a low frequency winding on another section, conductors extending from said windings, and means associated with said conductors for keeping high frequency energy out of said low frequency windmg.

12. Apparatus for reproducing sound comprising sound wave producing means, a coil form secured thereto, compliant means dividing said coil form into a plurality of sections, a winding on each section, and a filter circuit associated with each winding for assuring that eachwinding is supplied primarily with a different band of frequencies.

, 13. Acoustic apparatus comprising sound wave producing means, a cylindrical coil form secured at one end to said sound wave producing means, an annular, flexible area separating said coil form into cylindrical sections, said annular flexible area being effective to transmit frequencies low in the audible range to said sound wave producing means and substantially ineffective in transmitting higher frequencies in the audible range to the sound wave producing means, a winding on each cylindrical section, a magnet system having an annular air gap, means supporting said sound wave producing means and said coil form so that the windings on said cylindrical sections lie within the magnetic field extending across said annular air gap, and means substantially preventing the flow of high frequency energy through the winding on the cylindrical section which is separated from said sound wave producing means by said annular flexible area.

14. Acoustic apparatus comprising a diaphragm, a coil form joined with said diaphragm, means dividing said coil form into sections, said means being effective to transfer vibrations at frequencies low in the audible range and substantially inefiective in transferring vibrations at frequencies high in the audible range, a winding on each of said sections, and a single means providing a magnetic field for coacting with said windings.

15. Acoustic apparatus comprising sound wave producing means, driving means connected therewith, compliances dividing said driving means into a plurality of sections, a high frequency winding on the section adjacent said sound wave producing means, a low frequency winding on the section farthest from said sound wave producing means, and means providing a single magnetic field for coacting with said windings.

16. The method of reproducing sound by means of an acoustic device of the type having a diaphragm and a plurality ofturns of conductive material operatively associated therewith for vibrating the diaphragm, which consists of energizing a greater number of the turns of conductive material at low frequencies than at high frequencies, and compliantly coupling the conductive turns energized at the low frequencies with the diaphragm.

17. The method of reproducing sound by means of an acoustic device of the type having a diaphragm and a plurality of turns of conductive material operatively associated therewith for vibrating the diaphragm, which consists of energizing a greater number of the turns of conductive material at low frequencies than 'at high frequencies.

18. An electrodynamic loudspeaker comprising a diaphragm, a voice coil connected to said diaphragm, said voice coil being adapted to be energized from a source of energy, means for supplying energy to said voice coil from said source at certain frequencies, and means for energizing a portion only of said voice coil at other frequencies, said portion having an electrical .impedance that more nearly matches the electrical impedance of said source at said other frequencies than the electrical impedance of the entire voice coil.

1Q; An electrodynamic loudspeaker comprising a diaphragm, a driving system for said diaphragm, said driving system including a coil form divided into a pair of sections by a compliant coupling and a winding on each section, an inner magnetic. pole positioned within said coil form, an outer magnetic pole positioned to surround said coil form to form an air gap with said inner pole, and recesses in said poles adja, cent said compliant coupling to provide a pair of uniform magnetic fields each having at each end thereof a non-uniform magnetic field, each of said windings being so large that it extends in both directions past its associated uniform magnetic field into said non-uniform magnetic fields.

20. A vibratile system for acoustic apparatus comprising a driving portion and a sound wave producing portion, said driving portion including a voice coil and a coil form, said sound wave producing portion including a pair of diaphragm surfaces, 9. coupling which is effective to transmit vibrations at low frequencies and which is ineffective in transmitting vibrations at high frequencies connecting one of said diaphragm surfaces with said driving portion, a direct connection between the other diaphragm surface and said driving portion, a compliant coupling separating said coil form into two sections one of which is adjacent the diaphragm surfaces and the other of which is spaced therefrom by the first section and coupling, said voice coil including a high frequency winding on the coil form section adjacent the diaphragm surfaces for driving only the diaphragm surface which is directly connected to the driving portion and a low frequency winding on the other coil form section for driving the other diaphragm surface. I

RINGEL.