US3057961A - Self-correcting, high fidelity, sound reproducing apparatus - Google Patents

Description

Oct. 9, 1962 w. M. TURNER' 3,057,961

SELF-CORRECTING, HIGH FIDELITY, SOUND REPRODUCING APPARATUS Filed Jan. 8, 1959 2 Sheets-Sheet l 60 54F f mmuz/vcr MHDULATED mm'M/MTfiWL/HER war s/slv/u man/25p INVENTOR. WHEELER M: TURNER Oct. 9, 1962 w. M. TURNER 3,057,961

SELF-CORRECTING, HIGH FIDELITY, SOUND REPRODUCING APPARATUS Filed Jan. 8, 1959 2 Sheets-Sheet 2 FEEDBACK ANPL IF IE1? aq vsaucfk L a /s f 20 FEEDBACK TRANSDUCER INVENTOR. /ac WHEELER M.TURNER United States Patent 3,057,961 SELF-CURREQTENG, HEGH FIDELITY, SOUND REPRGDUQING AEPARATUS Wheeler M. Turner, Santa Barbara, Calif, assignor to Security First National flank, Los Angeles County,

Calif a national banking association Filed .ian. S, 1959, Ser. No. 735,733 6 Claims. (Cl. 1791) The present invention consists of self-correcting, high fidelity, sound reproducing apparatus of a type comprising electroacoustic sound-producing transducer means including a mechanically vibratable output element effectively coupled to ambient atmosphere, including electrical input circuit means, and including electro-mechanical translating motor means effectively electrically energizably coupled to the electrical input circuit means and effectively drivingly coupled to the mechanically vibratable output element for vibrating same in a manner corresponding to a variable electric input signal fed into the electrical input circuit means, and further including capacitive mechano-electrical feedback transducer means including a vibratable input element and a second element in capacitive relationship to each other, with the vibratable input element of the feed back transducer means being eifectively coincident with the vibratable output element of the sound-producing transducer means, and with said two elements of said feedback transducer means being eifectively electrically coupled, in negative feedback relationship, with respect to the electrical input circuit means, which in one preferred form may include amplifier means.

It should be noted that in one preferred form of the present invention, the vibratable input element of the capacitive negative feedback transducer means. comprises an electrically conductive thin-sheet member coextensive with a substantial portion of the surface area (usually substantially the entire surface area) of the vibratable output element of the sound-producing transducer means whereby to eifectively integrate and sum vibratory variations in different portions of the vibratable output element.

It should be noted that in one preferred specific form of the invention, the electro-mechanical translating motor means of the electroacoustic sound-producing transducer means may take the form of electromagnetic motor means consisting of a voice coil and a permanent magnet providing a magnetic field encompassing said voice coil, with said voice coil being effectively electrically energizably coupled to the electrical input circuit means, which in one preferred form includes amplifier means.

It should also be noted that, in one preferred specific form of the invention, the mechanically vibratable output element of the electroacoustic sound-producing transducer means may include a conical member having its interior conical surface coupled to ambient atmosphere.

It should also be noted that in one preferred form of the invention, the vibratable input element of the capacitive negative feedback transducer means may comprise a conical electrically conductive thin-sheet member coextensive with substantially the entire conical surface area of at least one side of (preferably the front side of) the conical vibratable output element of the soundproducing transducer means, while the second element of the feedback transducer means may comprise an electrically conductive frame means mounting the conical mechanically vibratable output element of the sound-producing transducer means.

In other words, one preferred form of the invention may comprise a conventional type loudspeaker wherein the loudspeaker cone carries on either the front or rear ice surface thereof an electrically conductive coating, such as conductive silver paint or the like, adapted to be mechanically vibrated by the loudspeaker cone in capacitive relationship with respect to the electrically conductive metallic frame mounting the entire loudspeaker, and with said electrically conductive coating and said electrically conductive frame together comprising the abovementioned capacitive negative feedback transducer means and being effectively connected, in a negative feedback sense, to amplifier means in the electrical input circuit means eifectively driving the voice coil of the conventional loudspeaker.

The specific negative feedback loudspeaker arrangement just described has several distinct and very important advantages over prior art loudspeaker systems. For example, any distortion or production of spurious sound occurring as a result of imperfect action of the loudspeaker conein other words, action of the loudspeaker cone in a manner other than as the perfect piston which it is supposed to simulate-such as cone breakup, standing waves, and the like, will be corrected and compensated for by the improved apparatus of the present invention because the capacitive mechano-electrical negative feedback transducer, consisting of the electrically conductive coating carried by the loudspeaker cone and the closely adjacent metallic loudspeaker frame in association with the electrical circuit components connected thereto, causes an error signal to be produced by portions of the cone having spurious vibrations not corresponding to the correct signal fed to the voice coil and occurring as a result of cone break-up, standing waves, and the like, which error signal is fed to the driving amplifier in a negative feedback sense in a manner which will cause mechanical movement of the voice coil and cone in exact opposition to the spurious vibrations of the cone, to a degree such as to effectively completely cancel them out, leaving only the proper or correct vibratory mechanical output of the cone corresponding to the correct electrical signal fed to the voice coil. In other Words, the apparatus of the present invention virtually completely corrects and compensates for the distortion normally present in virtually all loudspeaker systems and occurring as a result of cone break-up, standing waves, and the like.

It should be noted that the integrating and summing feature of the capacitive mechano-electrical negative feedback transducer means, which effectively integrates and sums the vibrations of virtually the complete surface area of the loudspeaker cone, is an extremely important aspect of the present invention, since this is the feature which results in virtually complete correction of and compensation for all spurious output from. the loudspeaker cone, which normally occurs as a result of cone break-up, standing waves, and the like. i

It should further be noted that the arrangement just described also has the effect of extending the frequency response characteristics. of the system as compared to conventional loudspeaker sound reproducing systems. This is particularly true at the low frequency end of the sound spectrum, since the very substantial attenuation which normally occurs at the low frequency end of the sound spectrum is substantially modified by the negative feed back feature of the above-described arrangement of the present invention to an extent such as to provide a considerable extension of and flattening of the low frequency response curve or characteristic of such a sound reproducing system.

It should also be noted that the sound reproducing apparatus of the present invention additionally provides a substantial degree of self-correction and compensation for acoustic variations affecting the reproduction of sound and occurring as a result of changed environmental conditionsfor example, enclosure resonance, room resonance, or other conditions of the enclosure or room in which the sound reproducing apparatus of the present invention is placed. These conditions frequently may cause undesirable peaks and/or valleys to occur at certain locations in the sound frequency spectrum of the radiated audio energy. However, the self-correcting summing and integrating negative feedback arrangement of the present invention provides a very substantial degree of correction and compensation for such peaks and valleys arising from special acoustic conditions of the region in which the sound reproducing apparatus is to operate, whereby to greatly flatten the frequency response curve by substantially eliminating such peaks and/or valleys therein.

With the above points in mind, it is an object of the present invention to provide an improved self-correcting, high fidelity, sound reproducing apparatus wherein a mechanically vibratable output element coupled to ambient atmosphere carries an electrically conductive thinsheet member or coating comprising one plate of a capacitive mechanoelectrical negative feedback transducer means having what amounts to a second usually fixed plate closely spaced and in capacitive relationship with respect thereto, and wherein said capactive mechano-electrical negative feedback transducer means is connected, in a negative feedback sense, to an electrical input circuit means driving the mechanically vibratable output element by electro-mechanical translating motor means (usually of the electromagnetic type).

It is a further object of the present invention to provide self-correcting, high fidelity, sound reproducing apparatus of the character set forth in the preceding object, wherein said second plate of the capacitive mechano-electrical negative feedback transducer means comprises the electrically conductive frame means of a loudspeaker, wherein the mechanically vibratable output element consists of the conventional loudspeaker cone, and wherein the effectively vibratable plate of the capacitive mechano-electrical negative feedback transducer means comprises a thin metallic coating, such as silver paint, or the like, coextensive with substantially the entire surface area of (usually of one side of) the loudspeaker cone to provide the effective integration and summing of all spurious error signals produced by the cone, for self-correcting application in a negative feedback sense to the speaker cone-driving amplifier. It is a further object of the present invention to provide a self-correcting, high fidelity, sound reproducing apparatus of the character set forth in any of the preceding objects, wherein the electrical input circuit means includes amplifier means having a control electrode, and wherein said control electrode is effectively coupled, in a negative feedback sense, to said capacitive mechano-electrical negative feedback transducer means.

It is a further object of the present invention to provide self-correcting high fidelity sound reproducing apparatus of the character set forth in any of the preceding objects including polarizing means for applying a potential of the proper polarity to the capacitive mechano-electrical negative feedback transducer means and also including capacitive-discharge-restricting circuit means connected thereto to provide a conventional type electrostatic transducer.

It is a further object to provide a self-correcting high fidelity sound reproducing apparatus of the character set forth in the preceding object, wherein the polarizing means and the capacitive-discharge-restricting circuit means are connected between the capacitive mechanoelectrical negative feedback transducer means and an amplifier means, and comprise a cathode follower electron tube and associated circuitry.

It is a further object to provide a modified form of the invention wherein the capacitive mechano-electrical negative feedback transducer means is not of the elecill) trostatic type but is of a type wherein the resonant frequency of a tuned circuit is varied by the capacitive variations, is amplified, and is subsequently discriminated to provide corresponding amplitude variations which are then fed into the voice coil driving amplifier in a negative feedback sense.

It is a further object of the present invention to provide self-correcting, high fidelity, sound reproducing apparatus of the character set forth in any of the preceding objects, which is adapted to very effectively compensate and correct for spurious audio output produced by speaker cone break-up, standing waves, and other types of distortion not corresponding to the correct electrical signal fed into a loudspeaker voice coil; the self-correction and compensation being such as to oppose all such spurious audio output in a manner effectively cancelling and nulling out same.

It is a further object of the present invention to provide a self-correcting, high fidelity, sound reproducing apparatus of the character set forth in any of the preceding objects, adapted to correct for distorted audio output occurring as a result of peculiar surrounding environmental conditions, by decreasing the audio output in those regions of the frequency response curve where said peculiar environmental conditions tend to increase the audio output, and by increasing the audio output in those regions of the frequency response curve where said peculiar environmental conditions tend to decrease the audio output.

It is a further object of the present invention to provide self-correcting, high fidelity, sound reproducing apparatus of the character set forth in any of the preceding objects, which by reason of the integrating and negative feedback feature of the invention, provides extended frequency response. This is particularly evident at the low frequency end of the sound spectrum where the audio output is greatly attenuated in conventional sound reproducing systems.

It is a further object of the present invention to provide a self-correcting high fidelity sound reproducing apparatus including a plurality of loudspeakers each having a capacitive mechano-electrical negative feedback transducer means connected to a single driving amplifier means or to a single cathode follower circuit connected to a driving amplifier means, whereby the combination system will provide a very efficient and self-correcting sound reproducing system capable of radiating a very large audio output, self-corrected as hereinbefore described.

It is a further object of the present invention to provide apparatus for measuring the characteristics of loudspeaker systems and the like and including the mechanoelectrical transducer means, which produces a voltage which may be directly measured and which is indicative of the total sound generated by the loudspeaker cone regardless of directivity patterns.

Further objects will be apparent to persons skilled in the art after a careful study hereof.

For the purpose of clarifying the nature of my invention, several exemplary embodiments are illustrated in the hereinbelow-described figures of the accompanying drawings and are described in detail hereinafter.

FIG. 1 is a schematic diagrammatic view illustrating one embodiment of the present invention.

FIG. 2 is a schematic diagrammatic view illustrating a second embodiment of the present invention including an additional stage of amplification between the feedback transducer and the voice-coil-driving amplifier.

FIG. 3 is a schematic diagrammatic view generally similar to FIG. 2 but slightly more specific in nature and showing considerably more detail of one specific form of loudspeaker and capacitive feedback transducer.

FIG. 4 is a schematic diagrammatic view very similar to FIG. 3 but includes an additional stage of amplification between the capacitive feedback transducer and the voicecoil-driving amplifier.

FIG. is a larger-scale fragmentary view, partly in vertical section, showing a small portion of the capacitive feedback transducer and the connection of leads to the metallic loudspeaker frame and the conductive coating carried by the speaker cone.

FIG. 6 is another and more detailed electrical schematic view showing one specific embodiment of the present invention corresponding to the version shown in FIG. 4. This view shows the loudspeaker in diagrammatic form but shows the electrical components of the capacitive feedback transducer and the feedback amplifier in detail.

FIG. 7 is a view very similar to FIG. 5 but shows a slight modification of the invention wherein the conductive coating carried by the cone is on the rear surface thereof rather than on the front surface thereof.

FIG. 8 is a schematic view generally similar to FIG. 2 but illustrates a slightly modified form having a capacitive feedback transducer of the frequency modulation type including an intermediate amplification stage and a frequency discrimination stage coupled to the voice-coildriving amplifier.

The self-correcting, high fidelity, sound reproducing apparatus of the present invention, broadly speaking, includes eleetroacoustic sound-producing transducer means having a mechanically vibratable output element effectively coupled to ambient atmosphere, having electrical input circuit means and electromechanical translating motor means effectively electrically energizably coupled to the electrical input circuit means and effectively drivingly coupled to the mechanically vibratable output element for vibrating same in a manner corresponding to a variable electric input signal fed into the electrical input circuit means. it also includes capacitive mechano-electrical negative feedback transducer means having a vibratable input element and a second element in capacitive relationship to each other, with the vibratable input element of the feedback transducer means being effectively coincident with the vibratable output element of the soundproducing transducer means, and with the two elements of the feedback transducer means being effectively electrically coupled, in negative feedback relationship, with respect to the electrical input circuit means.

In the specific example illustrated in FIG. 1 in schematic diagrammatic form, the electroacoustic soundproducing transducer means is indicated generally at It) and is shown as comprising a conventional type loudspeaker, although it is not so limited. The mechanically vibratable element of the sound-producing transducer means indicated generally at 10 is designated in schematic diagrammatic form by the arrow 11 in FIG. 1, and in the loudspeaker form of the sound-producing transducer means 10 shown in FIG. 1, this would comprise a conventional loudspeaker cone, such as is shown in greater detail at 26 in FIG. 3, for example. In the specific example of the invention shown in diagrammatic form in FIG. 1, the electrical input circuit means referred to above is indicated generally at 12 and includes the input leads 13 and 14, the driving amplifier 15 connected thereto, and the leads 16 and 17 connected from the driving amplifier to the above-mentioned electro-mechanical translating motor means, which is indicated diagrammatically at 18 in FIG. 1 and, in the loudspeaker form of sound-producing transducer means. shown in FIG. 1, comprises electromagnetic motor means of a type such as is shown in greater detail in certain of the other figures, and which is drivingly coupled to the mechanically vibratable element or loudspeaker cone diagrammatically indicated by the arrow 11 in FIG. 10 and of a type such as is shown at 26 in FIG. 3, for example.

In the specific example illustrated in FIG. 1, the capacitive mechano-electrical negative feedback transducer means is indicated in diagrammatic form at 20 and is shown as being directly operated or vibrated by the mechanically vibratable output element or loudspeaker cone of the loudspeaker 10, as indicated by the arrow 11 extending from the loudspeaker 10 to the feedback transducer 20. It should be understood that the feedback transducer 20 is merely shown in diagrammatic form and, in one preferred form which comprises a capacitive transducer, the variable capacitor thereof is actually carried by and effectively comprises a part of the loudspeaker 10, in a manner which will be shown in greater detail in certain of the other figures and described in greater detail hereinafter. In the specific example illustrated in FIG. 1, the feedback transducer indicated generally at 20 is connected by leads 21 and 22 to the driving amplifier 15; this connection being in a negative feedback sense such that the error signal fed from the feedback transducer 20 to the driving amplifier 15 causes the electromechanical motor means 18 of the sound-producing transducer means 10 to be moved in a direction opposite to the movement causing the error signal in the feedback transducer 20.

FIG. 2 is very similar to FIG. 1 and similar parts will be indicated by the same reference numerals followed by the letter A. However, in this modification, an additional feedback amplifier, indicated at 23, is connected between the feedback transducer 20A and the driving amplifier 15A. Otherwise, this modification is substantially the same as the first form illustrated in FIG. 1 and, therefore, requires no further explanation.

FIG. 3 is a view effectively illustrating one specific embodiment of the form of the invention shown broadly in diagrammatic form in FIG. 1, and corresponding por tions are indicated by similar reference numerals, fol lowed by the letter B. In this modification, the electromechanical translating motor means 18B of the soundproducing transducer means indicated generally at 16B comprises an electromagnetic motor which consists of a voice coil 24 Wound on a hollow tubular member 25 carried at the inner end of a conical mechanically vibratable output element comprising a loudspeaker cone 26, said electromagnetic motor means also including a conventional loudspeaker permanent magnet indicated at 27 having pole portions positioned so as to cause magnetic flux to pass directly across the voice coil 24 whereby variations in electric current from the voice coil-driving amplifier 15B will cause longitudinal vibratory movement of the voice coil toward the right and left as viewed in FIG. 3 and thus will effectively vibrate the loudspeaker cone 26 in a similar manner, since the voice coil 24 is firmly effectively fastened to the tubular portion 25 carried at the inner end of the loudspeaker cone 26. In this connection, it should be noted that the inner end of the loudspeaker cone 26 and the tubular portion 25 carried thereby are resiliently centered and mounted for axial piston-like vibratory motion by means of a conventional resilient mounting spider 28 at the inner end of the cone 26 and also by a similar annular corrugated mounting portion 29 at the outer edge of the cone 26. Thus, it can be seen that electrical current from the voice-coildriving amplifier 1513 will effectively cause vibration of the loudspeaker cone 26. In this modification, the feedback transducer is of the capacitive type and includes the portion shown diagrammatically at 205 and the two effective plates of the variable capacitor, which are comprised in effect by an electrically conductive thin-sheet mem'ber carried by the face of the loudspeaker cone 26, as best seen at 30 in FIG. 5, to which the lead 223 is connected as indicated at 31, and the electrically conductive frame means 32 mounting the entire loudspeaker, to which the lead 21B is connected as indicated at 33. It should be understood that the electrically conductive thin-sheet member 34 may comprise a coating of conductive paint, such as silver paint, or the like, carried by the material of which the cone 26 is made and that this comprises the variable plate or vibratable input element of the capacitive means of the capacitive feedback transducer while the electrically conductive frame 32 comprises the fixed capacitive plate or second element thereof. It should further be noted that the capacitive feedback transducer, indicated in diagrammatic form at 203 in FIG. 3, includes means, when coupled with the elements 30, 31, 32, and the leads 21B and 22B, to comprise a complete capacitive transducer. This may be of either the electrostatic type including polarizing means for applying a polarized potential to the frame 32 and the conductive coating 30 and capacitivedischarge-restricting circuit means in association therewith whereby to provide an output voltage from the capacitive feedback transducer 203 having an amplitude corresponding to the excursion of the conductive coating 30 carried by the cone 26; or the capacitive feedback transducer may be of a type such as is indicated more specifically in FIG. 8, including a first frequency modulation step, an intermediate amplification step, and a discrimination step, so as to provide an output voltage corresponding to the excursion of the conductive coating carried by the loudspeaker cone. This will be described hereinafter in connection with FIG. 8.

It should be noted that FIG. 3 shows only one soundproducing transducer means as exemplified by the loudspeaker indicated generally at 108. However, it should be clearly understood that the present invention may include a plurality of such loudspeakers connected in parallel with respect to a single voice'coil-driving amplifier such as is shown at 153 and with respect to a single capacitive feedback transducer (exclusive of the elements such as the coating 30 and the frame 32) as indicated at 20B in FIG. 3. The parallel connection points in the circuitry for this purpose are indicated respectively at 61 and 62. In this kind of arrangement, with a plurality of such loudspeakers connected in parallel, all loudspeakers will carry part of the load of correcting error sounds being generated by all of the other speakers. In such an arrangement, it should be noted that each of the capacitors effectively provided by the conductive coatings 30 and the loudspeaker frames 32 (of the type shown in FIG. would be connected together before connecting same to the single electronic portions of the capacitive feedback transducer 20B. Various connection arrangements for such multiple loudspeaker systems may be employed.

FIG. 4 is a schematic diagrammatic view illustrating a slight modification of the form of the invention illustrated in FIG. 3 and similar part will be indicated by the same reference numerals, followed by the letter C. However, in this modification, a feedback amplifier, indicated generally at 34, is connected between the capacitive feedback transducer 20C and the amplifier C. Otherwise, this modification is substantially the same as the form illustrated in FIG. 3 and, therefore, requires no further explanation.

FIG. 6 is a view illustrating one specific form of electrical portions of the apparatus in a version such as is shown in FIG. 4, showing said electrical portions in greater detail, and similar parts will be indicated by the same reference numerals, following by the letter D. In this modification, the capacitive feedback transducer indicated generally at D includes the electron tube 35 connected in a cathode follower circuit and having the lead 22D, which is connected to the conductive coating (not shown in FIG. 6) carried by the loudspeaker cone 26, to the grid 36 of the electron tube 35; said lead 22D also being connected through a load resistor 37 to a terminal 38 between two cathode resistors 39 and 40 connected between the cathode 41 of electron tube 35 and ground, as indicated at 42. The anode 43 of the electron tube 35 is connected to a terminal 44, which is adapted to be connected to a suitable source of positive potential, which is adapted to have its negative terminal grounded. Said potential source is not shown, since such is well known in the art and does not comprise my real invention.

It will be noted that the cathode follower circuit, just described and associated with the electron tube 35, provides means for applying a positive polarizing voltage through the lead 22D to the conductive coating (not shown in detail in FIG. 6, but indicated at 30 in FIG. 5) carried by the loudspeaker cone 26D, it being noted that the frame 32D of the loudspeaker is at ground potential by reason of connection of the lead 21D to ground as indicated at 45. The circuit components associated with the electron tube 35 provide, in effect, a capacitive-discharge-restricting circuit means adapted to prevent rapid discharge of electrons from the capacitor formed by the conductive coating carried by the loudspeaker cone 26D, such as is indicated at 30 in FIG. 5, and the frame 32D. Therefore, vibratory movement of the loudspeaker cone 26D will be transformed by the polarizing voltage provided by the cathode follower circuit associated with the electron tube 35, into an error signal potential applied in an electron-fiow-controlling manner with respect to the control grid 36 and the cathode 41 of the electron tube 35, whereby current flow through the electron tube 35 will correspondingly vary and will be coupled through capacitor 46 and the cathode resistor 47 to the control grid 48 and cathode 49, respectively, of a second electron tube 50, which comprises an amplifier, whereby the amplified current flow through said amplifying electron tube 50 will be fed through an output circuit to a voice-coildriving amplifier 15D where it joins the normal variable electrical input signal fed to the voice-coil-driving amplifier 15D through an input terminal 51 of input circuit means indicated generally at 12D. It should be noted that the lead 17D connected to the voice coil 24D corresponds to the lead 17C shown in FIG. 4. However, in this modification, the other lead 161) is grounded as indicated at 52, since the other end of the voice coil 24D is also grounded as indicated at 53. However, it will be noted that the circuit continuity remains the same.

For the purpose of providing a full and complete disclosure, representative values of certain of the components shown in FIG. 6 will be listed. However, it should be understood that they are not to be construed as limiting the invention but are set forth merely to exemplify one working embodiment of the invention. Such representative values are as follows:

Resistor 37 may have a value of 150,000 ohms Resistor 39 may have a value of 3,900 ohms Resistor 40 may have a value of 47,000 ohms Resistor 54 may have a value of 220,000 ohms Resistor 47 may have a value of 5,000 ohms Resistor 55 may have a value of 100,000 ohms Resistor 56 may have a value of 220,000 ohms Resistor 57 may have a value of 390,000 ohms Capacitor 46 may have a value of 0.1 microfarad Capacitor 58 may have a value of 0.1 microfarad, and Capacitor 59 may have a value of 470 micromicrofarads.

Each of the electron tubes 35 and 50 may be l2AX7 tubes.

FIG. 7 is a view similar to FIG. 5 but illustrates a slightly modified form of the invention wherein the conductive coating 30E is carried by the rear surface of the loudspeaker cone 26E. Similar parts are indicated by similar reference numerals followed by the letter B and since this is the only difference, no further explanation is thought necessary.

FIG. 8 is a view similar to FIG. 4 except that the capacitive feedback transducer shown at 20C in FIG. 4 is no longer of the electrostatic type in the modification illustrated in FIG. 8. In the form illustrated in FIG. 8, said capacitive feedback transducer includes a first portion indicated in diagrammatic form at 20F as comprising a frequency modulated error signal producer, which is connected to the variable capacitor indicated at connection points 31F and 33E; said transducer 20F being of the frequency modulation type adapted to be connected to a tuned circuit associated with an oscillation generator for effectively varying the frequency of output oscillations therefrom which are then fed to an amplifier such as is indicated diagrammatically at MP in FIG. 8, and which are then fed to a frequency discriminator, such as is indicated diagrammatically at 61) in FIG. 8, and which is adapted to convert the amplified frequency modulated error signal into a corresponding variable potential error signal which is fed into the voice-coil-amplifier F in the same manner as described hereinbefore. In other words, in the modification of the invention illustrated in FIG. 8, the only difference is that a frequency modulation and discrimination type of capacitive transducer is substituted for the electrostatic type of capacitive transducer shown in FIG. 6 in detail.

It should be noted that the apparatus of the present invention is readily adapted for use with more complex speaker systems, including what are known in the art as tweeters, woofers, crossover networks, and the like.

It should be understood that the figures and the specific description thereof set forth in this application are for the purpose of illustrating the present invention and are not to be construed as limiting the present invention to the precise and detailed specific structure shown in the figures and specifically described hereinbefore. Rather, the real invention is intended to include substantially equivalent constructions embodying the basic teachings and inventive concept of the present invention.

I claim:

1. Self-correcting high fidelity sound reproducing apparatus, comprising: electroacoustic sound-producing transducer means including a mechanically vibratable output element effectively coupleable to ambient atmosphere, including electrical input circuit means, and including electromechanical translating motor means effectively electrically energizably coupled to said electrical input circuit means and effectively drivingly coupled to said mechanically vibratable output element for vibrating same in a manner corresponding to a variable electric input signal fed into said electrical input circuit means; and capacitive mechano-electrical feedback transducer means including a vibratable input element and a second element in capacitive relationship to each other, said vibratable input element of said capacitive mechano-electrical feedback transducer means comprising an electrically conductive thinsheet member co-extensive with substantially the entire surface area of at least one side of said vibratable output element of said sound-producing transducer means and physically carried by said vibratable output element in integrating and summing relationship with respect to said vibratable output element whereby to effectively integrate and sum vibratory variations in different portions of said vibratable output element, and said feedback transducer means being effectively electrically coupled, in negative feedback relationship, with respect to said electrical input circuit means.

2. Self-correcting high fidelity sound reproducing apparatus, comprising: electroacoustic sound-producing transducer means including a mechanically vibratable output element consisting of a conical member having its interior conical surface coupled to ambient atmosphere, including electrical input circuit means, and including electromagnetic motor means effectively electrically energizably coupled to said electrical input circuit means and effectively drivingly coupled to said conical mechanically vibratable output element for vibrating same in a manner corresponding to a variable electric input signal fed into said electrical input circuit means; and capacitive mechanoelectrical feedback transducer means including a vibratable input element and a second element in capacitive relationship to each other, said vibratable input element of said capacitive mechano-electrical feedback transducer means comprising a conical electrically conductive thinsheet member coextensive with substantially the entire conical surface area of at least one side of said conical vibratable output element of said sound-producing transducer means and physically carried by said conical vibratable output element in integrating and summing relationship with respect to said conical vibratable output element whereby to effectively integrate and sum vibratory variations in different portions of said conical vibratable output element, and said two elements of said feedback transducer means being effectively electrically coupled, in negative feedback relationship, with respect to said electrical input circuit means.

3. Self-correcting high fidelity sound reproducing apparatus, comprising: electromagnetic sound-producing transducer means including a mechanically vibratable output element consisting of a conical member having its interior conical surface coupled to ambient atmosphere, including electrical input circuit means, and including electromagnetic motor means provided with a voice coil and also including a magnet providing a magnetic field encompassing said voice coil, said voice coil being effectively electrically energizably coupled to said electrical input circuit means and effectively drivingly coupled to said conical mechanically vibratable output element for vibrating same in a manner corresponding to a variable electric input signal fed into said electrical input circuit means; and capacitive mechano-electrical feed-back transducer means including a vibratable input element and a second element in capacitive relationship to each other, said vibratable input element of said capacitive mechano-electrical feedback transducer means comprising a conical electrically conductive thin-sheet member coextensive with substantially the entire conical surface area of at least one side of said conical vibratable output element of said sound-producing transducer means and physically carried by said conical vibratable output element in integrating and summing relationship with respect to said conical vibratable output element whereby to effectively integrate and sum vibratory variations in different portions of said conical vibratable output element, and said two elements of said feedback transducer means being effectively electrically coupled, in negative feedback relationship, with respect to said electrical input circuit means.

4. Self-correcting high fidelity sound reproducing apparatus, comprising: electromagnetic sound-producing transducer means including a mechanically vibratable output element consisting of a conical member having its interior conical surface coupled to ambient atmosphere, including electrical input circuit means, and including electromagnetic motor means provided with a voice coil and also including a magnet providing a magnetic field encompassing said voice coil, said voice coil being effectively electrically energizably coupled to said electrical input circuit means and effectively drivingly coupled to said conical mechanically vibratable output element for vibrating same in a manner corresponding to a variable electric input signal fed into said electrical input circuit means; said electrical input circuit means including amplifier means; and capacitive mechano-electrical feedback transducer means including a vibratable input element and a second element in capacitive relationship to each other, said Vibratable input element of said capacitive mechano-electrical feedback transducer means comprising a conical electrically conductive thin-sheet member coextensive with substantially the entire conical surface area of at least one side of said conical vibratable output element of said sound-producing transducer means and physically carried by said conical vibratable output element in integrating and summing relationship with respect to said conical vibratable output element whereby to effectively integrate and sum vibratory variations in different portions of said conical vibratable output element, and said two elements of said feedback transducer means being effectively electrically coupled, in negative feedback relationship, with respect to said amplifier means of said electrical input circuit means.

5. Self-correcting high fidelity sound reproducing apparatus, comprising: electromagnetic sound-producing transducer means including a mechanically vibratable output element consisting of a conical member having its interior conical surface coupled to ambient atmosphere, including electrical input circuit means, and including electromagnetic motor means provided with a voice coil and also including a magnet providing a magnetic field encompassing said voice coil, said voice being eifectively electrically energizably coupled to said electrical input circuit means and effectively drivingly coupled to said conical mechanically vibratable output element for vibrating same in a manner corresponding to a variable electric input signal fed into said electrical input circuit means; said electrical input circuit means including amplifier means provided with a control electrode; and capacitive mechanoelectrical feedback transducer means including a vibratable input element and a second element in capacitive relationship to each other, said vibratable input element of said capacitive mechano-electrical feedback transducer means comprising a conical electrically conductive thinsheet member coextensive with substantially the entire conical surface area of at least one side of said conical vibratable output element of said sound-producing transducer means and physically carried by said conical vibratable output element in integrating and summing relationship with respect to said conical vibratable output element 'whereby to effectively integrate and sum vibratory variations in different portions of said conical vibratable output element, and said two elements of said feedback transducer means being effectively electrically coupled, in negative feedback relationship, with respect to said control electrode of said amplifier means of said electrical input circuit means.

6. Self-correcting high fidelity sound reproducing apparatus, comprising: electromagnetic sound-producing transducer means including a mechanically vibratable output element consisting of a conical member having its interior conical surface coupled to ambient atmosphere, including electrical input circuit means, and including electromagnetic motor means provided with a voice coil and also including a magnet providing a magnetic field encompassing said voice coil, said voice coil being effectively electrically energizably coupled to said electrical input circuit means and eifectively drivingly coupled to said conical mechanically vibratable output element for vibrating same in a manner corresponding to a variable electric input signal fed into said electrical input circuit means; said electrical input circuit means including amplifier means provided with a control electrode; and capacitive mechano-electrical feedback transducer means including a vibratable input element and a second element in capacitive relationship to each other, said vibratable input element of said capacitive mechano-electrical feedback transducer means comprising a conical electrically conductive thin-sheet member coextensive with substantially the entire conical surface area of at least one side of said conical vibratable output element of said sound-producing transducer means and physically carried by said conical vibratable output element in integrating and summing relationship with respect to said conical vibratable output element whereby to eifectively integrate and sum vibratory variations in different portions of said conical vibratable output element, and said two elements of said feedback transducer means being effectively electrically coupled, in negative feedback relationship, with respect to said control electrode of said amplifier means of said electrical input circuit means, said second element of said feedback transducer means comprising an electrically conductive frame means vibratably mounting said conical mechanically vibratable output element of said sound-producing transducer means.

References Cited in the file of this patent UNITED STATES PATENTS

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