US1895441A - Sound translating device - Google Patents

Sound translating device Download PDF

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Publication number
US1895441A
US1895441A US486381A US48638130A US1895441A US 1895441 A US1895441 A US 1895441A US 486381 A US486381 A US 486381A US 48638130 A US48638130 A US 48638130A US 1895441 A US1895441 A US 1895441A
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United States
Prior art keywords
diaphragm
frequency
mechanical
resistance
vibratory
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
Application number
US486381A
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English (en)
Inventor
Lee G Bostwick
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AT&T Corp
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Bell Telephone Laboratories Inc
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Filing date
Publication date
Application filed by Bell Telephone Laboratories Inc filed Critical Bell Telephone Laboratories Inc
Priority to US486381A priority Critical patent/US1895441A/en
Priority to FR724151D priority patent/FR724151A/fr
Application granted granted Critical
Publication of US1895441A publication Critical patent/US1895441A/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; ELECTRIC HEARING AIDS; PUBLIC ADDRESS SYSTEMS
    • H04R7/00—Diaphragms for electromechanical transducers; Cones
    • H04R7/02—Diaphragms for electromechanical transducers; Cones characterised by the construction
    • H04R7/12—Non-planar diaphragms or cones
    • H04R7/122—Non-planar diaphragms or cones comprising a plurality of sections or layers
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; ELECTRIC HEARING AIDS; PUBLIC ADDRESS SYSTEMS
    • H04R9/00—Transducers of moving-coil, moving-strip, or moving-wire type
    • H04R9/02—Details
    • H04R9/04—Construction, mounting, or centering of coil
    • H04R9/041—Centering
    • H04R9/043—Inner suspension or damper, e.g. spider

Definitions

  • This invention relates to sound translating devices and more particularly to loud speakers employing a moving coil actuated, direct acting diaphragm.
  • the diaphragm in loud speakers of this type is usually designed to vibrate substantially as a piston over the lower portion of the frequency range, say below 800 cycles, and as a wave type radiator in the upper frequency range.
  • Such aloud speaker has two distinct disadvantages.
  • the efficiency must inherently be low because most ofthe actuating force is expended in accelerating the vibratory system and but little is useful in producing sound radiation; secondly, the dissipation or resistance must be so small that the diaphragm vibration poorly damped resulting in either an undesirable resonance period and a poor reproduction of transient sounds or the necessity of locating the resonance period outside the translated frequency range.
  • An object of this invention is to improve the efliciency of loud speakers and to translate sound uniformly over a wide frequency range.
  • the mechanical impedance of the vi bratory system and the mechanical motional resistance at the driving coil associated with the diaphragm are so related that the diaphragm is substantially resistance controlled instead of mass controlled below a certain frequency well within the frequency range it is desired to translate. This results in an improved efficiency over a desired frequency range and makes possible a mechanical motional resistance of suiiicient magnitude to critically damp the vibrating system and to completely suppress the main dia phragm resonance.
  • a loud speaker diaphragm is forms of some plasticv material, such as cellulose acetate or phenol condensate, so that it will have a continuously curved radiating surface and is further so proportioned that it may be vibrated as a whole with substantially uniform elliciency and response over a desired portion of the audio frequency spectrum.
  • the vibratory element in a loud speaker of the moving coil type is so mount ed that substantially no restraint is ofiered to true linear displacement of an edge of the diaphragm and an annular drivingcoil affined thereto.
  • FIG. 1 is an elevational view mainly in cross-section of a loud speaker made in accordance with this invention
  • Fig. 2 is an enlarged detail view in perspective of the spider for carrying the actuating coil and supporting the diaphragm as shown in Fi 'fl;
  • Fig. 3 is a dimensioned cross-sectional view of a preferred form of a diaphragm proportioned in accordance with this invention
  • Fig. 4 is an elevational view of an alterna tive form of diaphragm
  • FIG. 5 is an enlarged fragmentaryview in cross-section of the spider shown in Fig. 2, illustrating the method of mounting the actuating coil and the leading-in wires therefor; p i
  • Fig. 6 shows diagrammatically an electrical circuit analogous to or equivalent to the mechanical vibratory portion of a moving coil loud speaker of the typeshown in Fig. 1;
  • 7 shows characteristic output curves for mass controlled and a resistance controlled loud speaker, and a characteristic output curve for a combined mass and resistance controlled loud speaker in accordance with this invention.
  • the loud speaker of this invention comprises a frusto-conoidal diaphragm 10 preferably of some plastic material, such as cellulose acetate or phenol condensate, which may be easily molded and formed to desired dimensions, and which in its final state possesses appreciable inherent stiffness and rigidity.
  • the diaphragm 10 is adapted to vibrate substantially as a whole over a substantial range of frequencies, say up to the point where the radiation resistance thereof approaches a constant, and it has been found that the response characteristic of the loud speak-er may be improved by forming the diaphragm as a frustum of a surface of revolution, the diameter of which varies non-linearly between the two bases of the diaphragm.
  • the diaphragm as shown in Fig. 3 is frustoconoidal and has a continuously curved substantially hyperboloidal or paraboloidal surface.
  • the ratio of the diameters of the bases is substantially, and preferably, three to one. It is to be understood that although specific dimensions of a diaphragm are shown in Fig. 3, the invention is not limited thereto and any diaphragm proportioned similarly to that shown in Fig. 3 is contemplated within the scope of this invention.
  • the diaphragm in another embodiment, in accordance with this invention, comprises a plurality of frustoconical sections 11 and 12 of lightweight material such as cellulose acetate or phenol condensate, the larger base of one section being joined to the smaller base of the other section.
  • the junction of the two sections is reinforced by a ring 13, cemented or otherwise suitably attached to each of the sections, so that the rigidity of the diaphragm is increased and the diaphragm will vibrate as a piston throughout the desired portion of the audio frequency spectrum.
  • the diaphragm shown in- Fig. 4t comprises but two frusto-conical sections, it is to be understood that any number of joined sections may be used without departing from the scope of this invention.
  • the larger base of the diaphragm 10 is connected to a supporting frame by a thin annulus 14 of flexible material such as limp leather, silk or the like which is cemented or otherwise suitably attached to the edge of the diaphragm 10 and is clamped between two flanged ring members 15 held together by bolts 16.
  • the smaller base of the diaphragm 10 is suitably affixed to the flange 17 of a spider 18.
  • the spider 18, as shown more clearly in Fig. 2, comprises a thin metallic stamping of lightweight non-magnetic material such as duralumin or aluminum, having an annular flanged portion 17, a central hub portion .19, and three equally spaced annular arms 20 joining the flange 17 and the hub 19.
  • annular driving coil 21 consisting of a flat ribbon conductor wound edgewise and having an insulatory coating of lacquer, varnish or the like is set in the recessed portion and fastened therein by a suitable adhesive or cement.
  • Leading-in wires for the driving coil 21 are cemented or otherwise suitably aiiixed to the inner surface of the flange 17 and may be sin'iilarly attached along arms 20 of the spider 18.
  • the spider 18 is mounted on a central pole piece 23 by a bolt 24 passing through a central opening 25 in the hub 19 and through two non-metallic washers 26.
  • the pole piece 23 is of slightly smaller diameter than the flange 17 so'that the driving coil 21 is reciprocally disposed in a narrow annular air gap formed by the pole piece 23 and an outer pole piece 27 lVhen the driving coil 21. oscillates in the air gap, it is desirable that it move with true linear displacement and at all times be out of contact with the pole pieces 23 and 27.
  • the pole piece 27 is mounted on an outer pole 28 of a rectangular shaped magnetic structure 9 having a circular core or inner pole 30, by bolts 29 and the pole piece 23 is mounted on the inner pole 3O by bolts 31.
  • An energizing winding 32 encircles the inner pole and is provided with leading-in wires 33 which extend through bores in the outer pole piece 28 and are connected to the terminals 34 mounted on an insulating terminal block 35, positioned in a recessed portion in the pole 28.
  • a sheet metal cap member 36 is affixed to the pole 28 by bolts 37, only one of which is shown, and closes the recess in which the terminal block is mounted.
  • a plurality of angular supports 39 are bolted or otherwise secured to the outer pole 28 and are likewise bolted to the rings 15.
  • leading-in wires 22 for the driving coil 21 extend through an opening 40 in the pole piece 23, pass through a recessed portion 41 in said pole piece and are connected to terminals, not shown, mounted on the terminal block 35.
  • the mechanical motional resistance at the driving coil 21 is made substantially equal to the mechanical impedance of the vibratory element, comprising the diaphragm 10, the spider 18, the driving coil 21 and the annulus 14., at some frequency within the lower portion of the audio spectrum and above the lowest frequency it is desired to translate.
  • the mechanical impedance of the vibratory element throughout that portion of the audio frequency spectrum in which the diaphragm acts as a piston may be expressed algebraically as In mass controlled'loud speakers, the mass is so large with respect to the compliance, the mechanical motional resistance, and the radiation resistance that for all frequencies below that at which the diaphragm breaks up, the mass reactance is the dominating and substantially the sole factor determining the acoustic output of the loud speaker
  • the output characteristic is similar in form to that indicated by the line B in Fig. 7. Although such a characteristic is desirable in view of the uniformity of the output with respect to frequency, the efficiency of the loud speaker is inherently low since most of the actuating force is expended in accelerating the vibratory mass. Furthermore, the vibratory system may have an undesirable resonance at some frequency f in the lower portion of the frequency spectrum.
  • the desirable properties of a mass controlled and a resistance controlled loud speaker may be combined. If the mechanical motional resistance at the driving coil and the mechanical impedance of the vibratory system are made substantially equal at some frequency between the lowest frequency f it is desired to translate and the frequency f at which the diaphragm breaks up, the acoustic power will vary somewhat as indicated by curve D in Fig. 7. The specific magnitude and form of the acoustic power characteristic will of course, be dependent upon the magnitude of the physical constants involved and the particular frequency at which the mechanical motional resistance and the mechanical impedance of the vibratory system are made substantially equal. It has been found desirable to select this frequency between and 400 cycles.
  • the mechanical motional resistance at the driving coil can be made approximately the same magnitude as the critical damping resistance which results in the compl te suppression of the main diaphragm resonance. In order that this may be the case, it is necessary that the frequency at which the mechanical moample. a
  • tional resistance at the driving Coil and the mechanical impedance of the vibratory sys tem are made substantially equal be greater than twice apparent resonance frequency of the diaphragm as determined algebrarcal- In the partic Jar embooiment of my in vention il ustrated in the drawings, for e itii-cfactory einciency and response may be obtained with a diaphragm proportioned as shown in Fig. 3, a driving coil having a diameter of substantially l and comprising 50 turns of copper wire ribbon .002 by .02 and a flux density of approximately 15,000 gausses. In this particular embodiment the diaphr 'n breaks up between 600 and 1.000 cycles '2. l the lowest frequency it is desired to translate is about 60 cycles.
  • the loud speaker of this invention may be used in conjunction with a battle board or a short horn which may be so designed as to its loading characteristic as to compensate for the drooping of the mass-resistance controlled curve at low frequencies as intricated by curve D in Fig. 7.
  • a sound translating device comprising a vibratory element adapted to vibrate as awhole over the lower portion of the audiofrequency spectrum, and electro-dynamic means for actuating said vibratory element, the mechanical motional resistance of said means and the mechanical impedance of said vibratory element being substantially equal at a frequency between the lowest frequency it desired to translate and the approximate frequency at which the vibratory element ceases to vibrate as a whole.
  • a sound translating device comprising a vibratory element, and electro-dynamic means for actuating said vibrator 1 element, the mechanical motional resistance of said means being substantially equal to the mechanical impedance of the vibratory element at a frequency between 100 and 400 cycles.
  • a sound translating device comprising a vibratory element, and means for actuating said vibratory element.
  • the mechanical motional resistance of said means and the mechanical impedance of said vibratory element being substantially equal at a frequency such that said mechanical motional resistance wil be approximately of the same magnitude as the critical damping resistance of said vibratory element.
  • a sound translating device comprising a vibratory element, and means for actuating said vibratory elementythe mechanical motional resistance of said means and the mechanical impedance of said vibratory element being substantially equal at a frequency greater than twice the apparent resonance frequency of said vibratory element.
  • a sound translating device comprising vibratory element, and means for actuating said vibratory element, the mechanical motional resistance of said means and the mechanical impedance of said element being substantially equal at a frequency such that the vibratory element will be'substantially resistance controlled up to said frequency and will be substantially mass controlled between said frequency and the frequency at which the vibratory system ceases to vibrate as a whole.
  • a sound translating device comprising a vibratory element including a frusto-con0idal diaphragm, and means including a driving coil associated with said vibratory element for actuat-ng it, the mechanical motional resistance of said means and the mechanical impedance of said element being substantially equal at a frequency between 100 and 400 cycles.
  • a sound translating device comprising a vibratory element includ ng a diaphragm of plastic material, said diaphragm being formed so that it willvibrate as a whole over asubstantial por'tion'of the lower audiofrequency spectrum, and means for actuating said vibratory element.
  • the mechanical motional resistance of said means and the mechanical impedance of said vibratory element being substantially equal at a frequency between the lowest frequency it is desired to translate and the frequency at which the diaphragm ceases to vibrate as a whole.
  • a sound translating device comprising a support, a vibratory element including a diaphragm, flexible means connecting said diaphragmto said support,.and means for actuating said vibratory element, the mechanical motional resistance of said means and the mechanical impedance of said vibratory element being substantially equal at a frequency between 100 and 400 cycles.
  • a sound translating device comprising a support, a magnet having concentric pole pieces forming an annular air gap, a vibratory element including a diaphragm, flexible means connect ng said diaphragm and said support, flexible means conn cting said dia-, phragm and one of said pole pieces, and an annular coil disposed in said air gap and associated with said diaphragm for driving it, the mechanical motional resistance at said coil being substantially equal to the mechanical impedance of said vibratory element between and 400 cycles.
  • a sound translating device comprising a support, a magnet having concentric pole pieces forming an annular air gap, a vibratory element including a frusto-conoidal diaphragm of plastic material adapted to vibrate as a whole over a substantial portion of the lower audio-frequency spectrum, flexible means connecting the end of said diaphragm and said support, a spider member mounted on the inner of said pole pieces and connected to the smaller end of said diaphragm, and a coil mounted on said spider member and disposed in said annular air gap, the mechanical motional resistance at said coil being substantially equal to the mechanical impedance of said vibratory element at a frequency above the lowest frequency it is desired to translate and below the frequency at which the diaphragm ceases to vibrate as a whole.
  • a sound translating device in accordance with claim 10 in which the mechanical motional resistance at the driving coil and the mechancal impedance of the vibratory element are substantially equal at afrequency greater than twice the apparent resonance frequency of said vibratory element.
  • a sound translating device in accordance with claim 10 in which the mechanical motional resistance of the coil and the mechanical impedance of the vibratory element are substantially equal at a frequency such that the vibratory element will be substantially resistance controlled up to said frequency and will be substantially mass controlled between said frequency and the frequency at which the diaphragm ceases to vibrate as a whole.

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  • Engineering & Computer Science (AREA)
  • Multimedia (AREA)
  • Physics & Mathematics (AREA)
  • Acoustics & Sound (AREA)
  • Signal Processing (AREA)
  • Audible-Bandwidth Dynamoelectric Transducers Other Than Pickups (AREA)
US486381A 1930-10-04 1930-10-04 Sound translating device Expired - Lifetime US1895441A (en)

Priority Applications (2)

Application Number Priority Date Filing Date Title
US486381A US1895441A (en) 1930-10-04 1930-10-04 Sound translating device
FR724151D FR724151A (fr) 1930-10-04 1931-10-01 Perfectionnements aux dispositifs traducteurs du son

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US486381A US1895441A (en) 1930-10-04 1930-10-04 Sound translating device

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE969535C (de) * 1942-04-14 1958-06-12 Siemens Ag Schwingsystem mit aus Polyvinylchloridfolie bestehender Membran
US3935402A (en) * 1973-07-25 1976-01-27 Ohm Acoustics Corporation Loudspeaker voice coil arrangement

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE969535C (de) * 1942-04-14 1958-06-12 Siemens Ag Schwingsystem mit aus Polyvinylchloridfolie bestehender Membran
US3935402A (en) * 1973-07-25 1976-01-27 Ohm Acoustics Corporation Loudspeaker voice coil arrangement

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Publication number Publication date
FR724151A (fr) 1932-04-22

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