US3482062A - Damped electro-acoustic high frequency transducer - Google Patents

Description

Dec. 2, 1969 w. HECHT 3,482,062

DAMPED ELECTRO-ACOUSTIC HIGH FREQUENCY TRANSDUCER Filed April 18, 1967 20 Q I 9 fizz-a" gzzzzesz g J k\\\\\\\\\\\\\\ INVENTOR. HECHT ATTORNEYS WILLIAM United States Patent 3,482,062 DAMPED ELECTRO-ACOUSTIC HIGH FREQUENCY TRANSDUCER William Hecht, 80 Norfolk St., Bergenfield, NJ. 07621 Filed Apr. 18, 1967, Ser. No. 631,732 Int. Cl. H04r 9/00, 9/06, 9/10 U.S. Cl. 179-115.5 6 Claims ABSTRACT OF THE DISCLOSURE A damped electro-acoustic high frequency transducer which provides a chamber filled with a viscous substance which is relatively incompressible, which chamber is defined by the inner wall of a voice coil form, the end of a pole piece, and an elastomeric cap affixed to the voice coil form; movement of the voice coil form with respect to the pole piece varies the volumetric capacity of the chamber, causing the viscous material to move the elastic cap and exert thereby a damping effect upon the excursions of the voice coil form, and the diaphragm connected to it.

In the reproduction of musical sounds with a high degree of fidelity, loud speaker systems usually utilize a variety of transducers with appropriate crossover networks. It is common practice to use, in addition to a low frequency transducer, a mid-range transducer for reproducing the frequencies from 200 to 2,000 Hz. and a high range transducer for reproducing the frequencies from the vicinity of 1,000 to 20,000 Hz. Such transducers have a diaphragm, which may be of various shapes, but which is usually conical, made of an air impenetrable material and, consequently, capable of moving air. The diaphragm is attached to a voice coil form and the voice coil form is disposed with respect to a magnet to which it moves axially. Since the diaphragm is made of somewhat resilient material, it will assume a normal position. Signals applied to the voice coil wound on the form will cause it to move with respect to the magnet and to operate the diaphragm in correspondence with the signal. By reason of the natural resonance of the transducer, it is normal for such transducers to resonate in the area of 200 to 2,000 Hz. This introduced distortions into the sounds reproduced which were not present in the original signal. The ideal transducer is one which gives a flat response with respect to the signal applied to the voice coil.

In order to achieve such a response, efforts are made to dampen the response sufficiently to nullify the natural resonance of the transducer. Such efforts frequently require substantial modification of the transducer system which adds to the complexity, invites additional wear and breakdown, and may introduce other additional resonances and distortions. It has been found that it is possible to make a very simple addition to a transducer that will have the effect of establishing a substantially linear relationship between the reproduced and the applied signal. This is accomplished by forming a chamber, the side wall of which is defined by the inner wall of the voice coil form, one end wall by the pole piece, and the other end wall by an elastomeric cap aifixed to the other end of the voice coil form. In this chamber, a relatively thick viscous material is positioned. Thus, when the voice coil form moves,the volumetric capacity of the chamber is either increased or decreased. Since the viscous material in the chamber is relatively incompressible, the movement of the voice coil form will cause this viscous material to either distend or suck in the elastomeric material that caps the chamber. The force required to move the elastomeric cap is sufficient to exert a damping effect upon the excursions of the diaphragm and, in this manner, produces a linear response.

This object and advantage may be attained, as well as other objects and advantages, by the device shown by way of illustration in the drawings in which FIGURE 1 is a vertical, sectional view of the transducer.

Referring now to the drawings in detail, there is provlded a pole plate 9, a pole piece 10, a yoke 11, and a magnet 12. A dust cap 13 is attached to the pole plate 9 and surrounds the magnet 12. A voice coil form 14 surrounds the pole piece 10 and has its internal diameter disposed extremely closely to the pole piece 12 without coming into contact with it. A voice coil 7 is wound on the voice coil form 14; the voice coil form is positioned by the support or spider 8. The end 15 of the voice coil form 14 extends above the top of the pole piece 10 to define a chamber. To the end 15, a truncated conical diaphragm 17 is attached at its inner portion. A basket 18 is attached to the pole plate 9. The outer end 19 of the diaphragm is secured to the basket 18 and a retainer 20 which is rigid in character is secured to the marginal flange or outer end 19 of the diaphragm 17. A cap 21 is adhesively secured to the open end of the voice coil form 14, thereby enclosing the chamber 22 defined by the inner wall of the voice coil form 14 and the top 16 of the pole piece 10. In this chamber, a viscous, self-sustaining material 23 is deposited so as to fill the chamber at its normal volumetric capacity. This material 23 must have such a consistency that it will not normally enter the interstitial spacebetween the inside of the voice coil form 14 and the outside of the pole piece 10 during excursions of the voice coil form 14. High viscosity oils are not considered too satisfactory because they tend to flow and enter into the interstitial space. It has been found that high temperature silicone greases, which are self-sustaining, are quite satisfactory for this purpose. A high temperature silicone lubricant 23 is deposited in the chamber 22. It will be seen that as the voice coil form 14 moves with respect to the top 16 of the pole piece 10, in response to the signal applied, the volumetric capacity of the chamber 22 will change. If the excursion of the voice coil form 14 is such as to make the chamber 22 smaller, the grease or viscous material 23 will exert pressure on the cap 21 and tend to cause it to assume an externally convex position. on the other hand, if the excursion of the voice coil 14 is such as to enlarge the capacity of the chamber'22, the grease or lubricant 23 will tend to cause the cap 21 to assume an externally concave configuration. The force required to deform the cap 21 is sufficient to dampen the excursions of the diaphragm 17 and to produce the desired flat response corresponding substantially to the applied signal. The damping effect achieved is most marked in the range of 200 to 2,000 Hz., where the natural resonance of the normal transducer frequently introduces undesirable distortions. It has been observed that the mass of viscous material functions as a heat sink, and permits the application of substantially greater power inputs to the voice coil of the transducer, beyond those normally applied. In spite of this, voice coil failures from overheating that might normally occur due to higher input levels, do not occur under these increased load conditions. Voice coil burn-out under higher input levels is reduced.

A speaker resonance peak of perhaps 9 to 12 decibels beyond that which might have been anticipated from the applied signal, in this manner is avoided.

The foregoing description is merely intended to illustrate an embodiment of the invention. The component parts have been shown and described. They each may have substitutes which may perform a substantially similar function; such substitutes may be known as proper substitutes for the said components and may have actually been known or invented before the present invention; these substitutes are contemplated as being within the scope of the appended claims, although they are not specifically catalogued herein.

What is claimed:

-1. A damped electro-acoustic high frequency transducer comprising (a) a pole piece,

(b) a voice coil form closely embracing the pole piece, and extending beyond it to define an open chamber with the end of the pole piece,

(c) the chamber filled with a self-sustaining viscous material,

((1) an elastomeric seal on the open end of the voice coil form to enclose the chamber and to contain the viscous mass,

(e) the volumetric capacity of the chamber varying with the movement of the voice coil,

(f) the seal normally tending to yield to the movement of the viscous material in the chamber upon changes in the volumetric capacity of the chamber.

2. A damped electro-acoustic high frequency transducer comprising (a) the device according to claim 1, and

(b) the viscous material in the chamber being a silicone grease.

3. A damped electro-acoustic high frequency transducer comprising (a) the device according to claim 1, and

(b) a spacing spider attached to the voice coil, to position it in surrounding and spaced relation to the pole p1ece.

4. A damped electro-acoustic high frequency transducer comprising (a) the device according to claim 1, and (b) the elastomeric material having suflicient tensile strength to exert a damping influence on the excursions of the voice coil. 5. A damped electro-acoustic high frequency transducer comprising (a) the device according to claim 1, and (b) the elastomeric material having sufiicient tensile strength to exert a damping influence on the excursions of the voice coil in the frequency range of 200 to 2,000 Hz. 6. A damped electro-acoustic high frequency transducer comprising (a) the device according to claim 1, and (b) the viscous material defining a heat sink, for maintaining the voice coil temperature at a safe level, under high power input conditions.

References Cited UNITED STATES PATENTS 2,563,452 8/1951 Bozak 179-1155 2,655,566 10/1953 Pittinger 179--115.5 2,910,546 10/1959 Swanson 179115.5 2,993,961 7/1961 Blake 179-180 X RALPH D. BLAKESLEE, Primary Examiner U.S. Cl. X.R.

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