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US2971597A - Electro-acoustic devices - Google Patents

Electro-acoustic devices Download PDF

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Publication number
US2971597A
US2971597A US409712A US40971241A US2971597A US 2971597 A US2971597 A US 2971597A US 409712 A US409712 A US 409712A US 40971241 A US40971241 A US 40971241A US 2971597 A US2971597 A US 2971597A
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United States
Prior art keywords
diaphragm
frequency
acoustic
air
impedance
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 - Lifetime
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US409712A
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English (en)
Inventor
Gorike Rudolf
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Henry Heinrich & Co
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Henry Heinrich & Co
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Filing date
Publication date
Priority to BE441671D priority Critical patent/BE441671A/xx
Application filed by Henry Heinrich & Co filed Critical Henry Heinrich & Co
Priority to US409712A priority patent/US2971597A/en
Application granted granted Critical
Publication of US2971597A publication Critical patent/US2971597A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R1/00—Details of transducers, loudspeakers or microphones
    • H04R1/20—Arrangements for obtaining desired frequency or directional characteristics
    • H04R1/22—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired frequency characteristic only 

Definitions

  • the present invention relates to eiectro-acoustic devices and particularly to such devices for receiving and transmitting sound. More specifically, the invention relates to electro-acoustic devices the operative elements of which consist of a piston type diaphragm and an electro-mechanical system especially of the electrodynamic type connected with said diaphragm and either actuated thereby for receiving sound or itself actuating the diaphragm for transmitting sound.
  • An object of the present invention is to affect the resonance frequency of a piston type diaphragm so that all distorting reactions of the mechanical porperties of such diaphragm upon the reception or transmission of vibrations within the acoustical range will be suppressed or avoided.
  • piston type diaphragms that is, diaphragms having a stiff active surface which are elastically suspended merely along their edge so as to vibrate as a unit similar to a piston.
  • Another method known as such for obtaining a flat topped frequency curve by means of an electro-acoustic device having a piston type diaphragm and an air cushion consists in coupling the mentioned cushion chamber with a highly damped resonance chamber the resonance frequency of which corresponds to the natural frequency resulting for the piston diaphragm from its mechanical impedance in cooperation with the stiffness of its suspending means and the elastic effect of the mentioned cushioning volume.
  • the present invention relates to an improvement of electro-acoustic devices having a piston type diaphragm, which improvement can be applied in accordance with the known proposals mentioned above both to sound transmitters as well as sound receivers, and which makes it possible for the first time to provide piston type diaphragms of low weight which in accordance with the requirements of transportation are equipped with sufficient mechanical stiffness, with a natural frequency which lies at, or even below, the lowest frequency of the acoustic frequency band to be governed.
  • Another object of the present invention is to apply the known phenomena of acoustic transformation of velocity in diaphragm chambers having connected thereto a narrow sound guide in combination with the laws applicable to air columns vibrating in a longitudinal direction, in order to increase the mechanical impedance of the piston diaphragm by the acoustic impedance of an air column covibrating cophasely in longitudinal direction, in such a manner that the natural vibration of the system thus formed is decreased down to the lower limit of the practicalacoustic range, that is, to about 50 to 30 Hertz. Since covibrating air columns obviously do not aifect the mechanical resistance of a diaphragm toward shocks, the desired object will be obtained in this manner without affecting in any way the security against shocks.
  • Fig. 1 is a diagrammatic view of one form of the invention
  • Fig. 2 shows diagrammatically an electric transmission circuit constituting an equivalent to the acoustical system shown in Fig. 1;
  • Fig. 3 shows in cross section another embodiment of.
  • Fig. 4 is an electric circuit diagram equivalent to the device shown in Fig. 3;
  • Fig. 5 shows the frequency curve obtained with the device according to Fig. 3;
  • Fig. 6 shows in cross section another embodiment of the invention
  • Fig. 7 is an electric circuit diagram equivalent to the device shown in Fig. 6;
  • Fig. 8 shows the frequency curve obtained with the device according to Fig. 6;
  • Fig. 9 shows in cross section still another embodiment of the invention.
  • Fig. 10 is an electric circuit diagram equivalent to the device shown in Fig. 9.
  • a loudspeaker having a pistonshaped diaphragm M is provided with a funnel K the opening of which is smaller than the surface of the diaphragm M, at the opening 0 because of the transformation of velocity arising, variations of velocity 1; occur which are considerably higher than the variations p occurring at the diaphragm surface.
  • F is the vibrating surface of the piston type diaphragm M and F is thespeaker opening 0, the relation of these velocities is determined by the equation:
  • the acoustic impedance M of this air column covibrating in longitudinal direction is determined by the specific weight s of the air, and the length l and the cross sectional area f of the tube R M according to the formula:
  • the impedance M of the piston diaphragm first forms together with the stiffness C of its suspending means and the stiifnessC of the air cushion behind the diaphragm an oscillatory operating circuit which is shown in the diagram according to Fig. 2 as an oscillatory circuit C, M, C E.
  • the mentioned oscil latory circuit is operatively connected through a resistance R indicating the frictional resistance of the air Within the tube R M with the impedance M of the air column longitudinally vibrating within the tube, whereby said impedance is to be considered according to the Equation 2.
  • a second oscillatory operating circuit C, M, R M E is formed.
  • the capacity C according to Fig. 2 that is, the air cushion C behind the diaphragm M according to Fig. 1, will be made sufficiently small so as not to act as a capacity short circuit which would decouple the impedance M; from the oscillatory system C, M, C E.
  • the easiest way of obtaining this is by making C so shallow that the natural frequency of the oscillatory circuit M, C, C E is placed at the upper region of the frequency range to be governed, that is, for example, within the region of 8,000 to 10,000 Hertz.
  • the velocity transforming chamber in front of the diaphragm M and the funnel K are removed, the resulting arrangement, similar to every rearwardly open system, forms a pressure gradient receiver or transmitter, respectively, which acts similar to a band microphone or band loudspeaker, but can be equipped with a normal magnetic, dynamic or capacitative driving system so that it does not require any special adapter transformer in order to combine this system with an. acoustic pressure receiver or transmitter of the usual kind or of the kind according to the invention, for obtaining receiving or transmitting characteristics of any special type. If, on the other hand, the side of thetube R M,
  • this tube may also be given the shape of, for example, an annular slot which may at the same time be utilized for accommodating the vibrating coil of the dynamic driving system.
  • annular slot for coupling a further stiffness element to the system and hereby to form still another suitably tuned oscillatory operative circuit. It has been found that in such a manner further surprising ajcflvantages may be obtained, as will be described herea ter.
  • FIG. 2 A close study of the diagram according to Fig. 2 shows that aside from the two oscillatory circuits C, M, C E and C, M, C R M E which directly include the source of alternating current E and which may therefore be called operative circuits, it also contains the resonance circuit C R M which is coupled to the source of alternating current B through the alternating current resistance M, C and therefore acts as an energy dissipating circuit as it destroys the energy which it withdraws from the driving system.
  • the resonance frequency of this coupled energy dissipating circuit can be held above the frequency range to be reproduced, that is, for example, at 10,000 Hertz.
  • a further stiffness element is coupled to the system by means of the annular slot provided for accommodating the vibrating coil, such saddles may be avoided by coup ing a further operative resonance circuit to the cushion chamber.
  • the impedance M can then safely be given the value which mechanically is the most suitable. Since piston type diaphragms with an attached vibrating coil are made with the least difliculty and with the most favorable combination of shock resistance and electro-mechanical efliciency for a mechanical natural vibration of about 400 to 500 Hertz, this value of M is about a hundred to four hundred that of M, that is, a value which according to the invention resu ts in lowering the acoustically active natural vibration ten to twenty times relative to the original mechanical natural vibration.
  • FIG. 3 An embodiment of a pressure receiver constructed in such a manner according to the invention is shown in Fig. 3.
  • the diaphragm M having the usual dome shape, carries at its edge the vibration coil S within the ring shaped elastic suspension Zone C.
  • the vibrating coil S enters into an annular s ot R behind which a volume of air C is provided in a known manner.
  • the relation of the acoustically active impedanceM to the impedance M is made so extremely large that the natural frequency of the oscillatory system which is formed by the cushioning volume C and the covibrating volume R M enters into the range of the frequency band to be governed.
  • the natural frequency of the oscillatory system which is formed by the impedance M of the diaphragm, the stiffness C of the diaphragm suspension, the stitfness of the air space C behind the annular slot R and the impedance M is tuned approximately to this same frequency, the impedance-M which may sometimes be negligible being calculated for the volume of air covibrating in longitudinal direction in the annular slot R in consideration of the transformation of velocity arising.
  • FIG. 4 showing the theoretically equivalent electrical diagram for the system according to Fig. 3.
  • This diagram generally shows three operative circuits directly supplied by the source of alternating current E, and two energy dissipating circuits coupled thereto, namely:
  • the energy dissipating circuit R M C C the natural frequency of which should lie either above the upper region of the range of frequency to be governed or which may be placed at any region of the range of the frequency to be governed if it is made substantially equal to the natural frequency of-- (IV) the operative circuit C, M, R M C E which, with suitable damping 2), then overcomes the detrimental effects of the energy dissipating circuit mentioned under (III);
  • An electro-acoustic sound transducing device for transmitting a predetermined frequency range, compris-- ing a diaphragm of the piston type, wall means cooperat-- ing with the rear side of said diaphragm to define an air cushion in back of the latter, wall means defining an air channel communicating, at one end, with said air cushion and opening, at the other end, into a relatively large volume of air, the air'in saidohannel being directly coupled to said diaphragm by Way of said air cushion to vibrate in phase with said diaphragm, the length of said channel being less than one half the wavelength of the highest frequency of said range and being sufficiently large in relation to the cross-sectional area of the channel as to cause a longitudinal vibration of the air in said channel in response to vibration of said diaphragm, said channel being dimensioned to contain a mass of air defining an acoustic impedance which is at least ten times as large as the mechanical impedance of said diaphragm so that said mass of air and
  • An electro-acoustic sound transducing device as in claim 1; wherein said relatively large volume of air is contained in means defining a. first chamber communicating with said air cushion by way of said channel; and further comprising means defining a second chamber, and frictional resistance means through which said second chamber is coupled to said air cushion to damp the resonance of said vibrating system, said mass of air in said channel defining an acoustic impedance having a value approximately one hundred to four hundred times as large as the mechanical impedance of said diaphragm.
  • An electro-acoustic sound transducing device as in claim 4; wherein said diaphragm has a weight of 0.1 gram and an effective surface area of 7 cm. said air cushion has a volume of 0.35 cm. said channel has a length of 1.3 cm. and a cross-sectional area of 0.01 0111. said first and second chambers have volumes of 250 cm. and 30.6 cm. respectively, and said frictional resistance means have a value of 2000 ohms.

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  • Health & Medical Sciences (AREA)
  • Otolaryngology (AREA)
  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Acoustics & Sound (AREA)
  • Signal Processing (AREA)
  • Piezo-Electric Transducers For Audible Bands (AREA)
US409712A 1941-09-05 1941-09-05 Electro-acoustic devices Expired - Lifetime US2971597A (en)

Priority Applications (2)

Application Number Priority Date Filing Date Title
BE441671D BE441671A (fi) 1941-09-05
US409712A US2971597A (en) 1941-09-05 1941-09-05 Electro-acoustic devices

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Application Number Priority Date Filing Date Title
US409712A US2971597A (en) 1941-09-05 1941-09-05 Electro-acoustic devices

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Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3079471A (en) * 1961-03-01 1963-02-26 Ampex Loudspeaker
US3198890A (en) * 1961-06-14 1965-08-03 Rosen Alfred H High fidelity sound reproducer
US3632902A (en) * 1969-02-24 1972-01-04 John J Wahler Sound reflector-modifier for hearing aid microphones
US20060159275A1 (en) * 2004-12-15 2006-07-20 Sony Corporation Loudspeaker apparatus
US20090323995A1 (en) * 2005-05-21 2009-12-31 Alastair Sibbald Miniature Planar Acoustic Networks

Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1841101A (en) * 1930-03-06 1932-01-12 Bell Telephone Labor Inc Loud speaker
US1869178A (en) * 1930-08-15 1932-07-26 Bell Telephone Labor Inc Sound translating device
US1901388A (en) * 1930-04-18 1933-03-14 Rca Corp Method and apparatus for eliminating the effect of cabinet resonance
US1969704A (en) * 1932-06-03 1934-08-07 D Alton Andre Acoustic device
US2065751A (en) * 1935-12-31 1936-12-29 Rca Corp Acoustic resistance device
US2097289A (en) * 1934-12-20 1937-10-26 Rca Corp Acoustic apparatus
US2224919A (en) * 1937-03-31 1940-12-17 Rca Corp Loud-speaker
US2252846A (en) * 1938-09-30 1941-08-19 Associated Electric Lab Inc Acoustic device

Patent Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1841101A (en) * 1930-03-06 1932-01-12 Bell Telephone Labor Inc Loud speaker
US1901388A (en) * 1930-04-18 1933-03-14 Rca Corp Method and apparatus for eliminating the effect of cabinet resonance
US1869178A (en) * 1930-08-15 1932-07-26 Bell Telephone Labor Inc Sound translating device
US1969704A (en) * 1932-06-03 1934-08-07 D Alton Andre Acoustic device
US2097289A (en) * 1934-12-20 1937-10-26 Rca Corp Acoustic apparatus
US2065751A (en) * 1935-12-31 1936-12-29 Rca Corp Acoustic resistance device
US2224919A (en) * 1937-03-31 1940-12-17 Rca Corp Loud-speaker
US2252846A (en) * 1938-09-30 1941-08-19 Associated Electric Lab Inc Acoustic device

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3079471A (en) * 1961-03-01 1963-02-26 Ampex Loudspeaker
US3198890A (en) * 1961-06-14 1965-08-03 Rosen Alfred H High fidelity sound reproducer
US3632902A (en) * 1969-02-24 1972-01-04 John J Wahler Sound reflector-modifier for hearing aid microphones
US20060159275A1 (en) * 2004-12-15 2006-07-20 Sony Corporation Loudspeaker apparatus
US7751576B2 (en) * 2004-12-15 2010-07-06 Sony Corporation Loudspeaker apparatus
US20090323995A1 (en) * 2005-05-21 2009-12-31 Alastair Sibbald Miniature Planar Acoustic Networks

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Publication number Publication date
BE441671A (fi)

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