GB2070389A - Electroacoustic transducer - Google Patents

Abstract

The invention relates to an electroacoustic transducer, the diaphragm of which is of the hemispherical cap type and which comprises an annular portion (4) resiliently supported at its external periphery and enclosed at the internal periphery (6) between two adjacent damping discs (7), coupled to an equalizing element (9), for example, through a pressure washer (14) and clamping device (12, 13). The diaphragm thus formed has its active or radiating part between the attachment of the external periphery to the supporting resilient structure (5) and the internal periphery (6) confined between the two damping discs (7). <IMAGE>

Description

SPECIFICATION Electroacoustic transducer This invention relates to an electroacoustical transducer which is particularly applicable to industrial types of high fidelity systems such as used in, for example, cinemas, record libraries, stadiums, public squares etc, and which comprise compression units for horn loud-speakers and the like.

As well known, in compression units for loudspeakers and the like, the air pressure generated by the convex or concave part of a hemispherical cap type of diaphragm is utilized for converting electrical signals into acoustical signals. It is also known that hemispherical cap diaphragms exploiting air pressure generation by the convex part thereof suffer from the disadvantage of providing, particularly in the average to high range of the sound spectrum, a barely linear response. This is due to the fact that the acoustical signals generated by the diaphragm, as coupled by means of an equalizer at the output of any compression unit, are devoid of phase coherence or are increasingly delayed with respect to one another depending on the distance between the signal emission location on the diaphragm and the output from said unit.

This occurs in spite of the provision of the equalizerwhich, as well known, performs the function of equalizer as far as possible the output, particularly at high frequencies. The differential lengths of the signal paths causes considerable changes and voids in response curves.

This disadvantage could be overcome by using the hemispherical cap diaphragms so that the electrical signals are converted into acoustical signals by using the air pressure generated by the concave part, rather than by the convex part thereof. Thus, all of the signals are of the same length and are directed to a single location, represented by the ideal center of the hemispherical cap diaphragm, corresponding to the output of the pressure unit.

However, particular equalizers are required for this purpose which, in addition to necessitating an increase in volume of the pressure chamber, are provided with pluralities of radial and concentric slits having said output signals passing therethrough.

The working or machining of such equalizers is at present extremely difficult because the slits have to be made using specialised techniques and instruments.

It is an object of the present invention to provide an electroacoustic transducer which mitigates the above mentioned disadvantages, that is to provide a transducer having response curves of improved linearity, while using the technique of acoustic signals generated by the convex part of the diaphragm.

It is another object of the present invention to provide an electroacoustic transducer having relative ease of manufacture, good characteristics and acceptable or reduced cost compared with those using the concave part of the diaphragm for acoustic signal generation.

According to a first aspect of the present invention there is provided an electroacoustictransducer having a diaphragm of the hemispherical cap type comprising an annular portion resiliently supported at its external periphery by a resilient supporting structure, carrying a coil, and enclosed at its internal periphery between two adjacent damping discs which are coupled to an equalizer element.

Preferably, the damping discs are coupled to the equalizing element by a pressure washer and a clamping device, the action of which is adjusted by a spacer.

According to a second aspect of the present invention there is provided an electroacoustic transducer having a diaphragm of the hemispherical cap type comprising an annular portion resiliently supported at its external periphery, carrying a coil and resiliently coupled at its internal periphery to an equalizing element.

In order that the present invention be more clearly understood, a detailed description thereof will now be given by way of example and with reference to the accompanying drawing, in which: Figure 1 is a cross-sectional view of an electroacoustic transducer as used in a compression unit; Figure 2 is a fragmentary cross-sectional view showing a second embodiment of the hemispherical cap diaphragm having an annular portion, and Figure 3 is a graph showing the comparison of the pattern of the frequency response curves on the emission axis between a conventional transducer and a transducer of the same characteristics, but implemented according to the present invention.

Referring to Figure 1 of the accompanying drawings, a compression unit 1 is shown as comprising a conventional type of magnetic assembly or permanent magnet 2.

In the air gap between the poles of magnet 2 a moving coil 3 is located and connected at one end to the external peripheral part of diaphragm 4. The diaphragm 4 is of the hemispherical cap type and comprises an annular portion connected, at its external periphery, to a resilient structure 5 and to the circular moving coil 3. The internal periphery 6 of the diaphragm 4 is located between two damping discs 7 which, in addition to completely enclosing the internal periphery 6, will occlude the central hole 8 of the annular portion.

In Figure 1, the upper damping disc is adjacent to the equalizer 9 which in turn is retained on the diffuser body 10 which together with the diaphragm 4, defines the compression chamber 11.

The damping discs 7 and equalizer 9 are coupled to one another by means of screw 12, spacer 13 and pressure washer 14.

The elements 12, 13 and 14 comprise the adjusting or calibrating deviceforthe pressure being exerted by the discs 7 on the internal periphery 6 of diaphragm 4. However, it is also envisaged, as shown by dashed line in Figure 1, that the equalizer 9 and damping discs 7 can be retained by a pin 16 to the central pole 15 of the permanent magnet 2, instead of being rigidly retained on the diffuser body 10.

Additionally, the screw 12 may be replaced by a rivet or any other clamping element provided that the anchorage of the pressure washer 14, as provided through the spacer 13, would ensure a constant pressure on the damping discs 7, independent of the force exerted on the clamping element.

From the foregoing it will be seen that the active part of the diaphragm 4 is only that annular zone from the attachment of the resilient structure 5 to the external edge of the damping discs 7. Thus, all of the sound waves generated by diaphragm 4 have to travel nearly the same path in compression chamber 11 and are consequently presented in phase coherence at the output 17 of unit 1.

It should also be noted that the sizes of damping discs 7 and hole 8 of diaphragm 4 are dimensioned in accordance with; the range of operating frequencies, diameter of diaphragm 4 and moving coil 3, and system power to be employed.

In Figure 2 there is shown a second embodiment of diaphragm 4, in which the internal periphery is provided with a second resilient structure 5' which is directly secured to equalizer 9. In this embodiment, the active part of the diaphragm is between the two resilient structures 5 and 5', so that the path length of all the sound waves within the compression chamber 11 are nearly equal and consequently coherent in phase.

The frequency response curves, taken on the axis of a compression unit provided with an electroacoustic transducer according to the present invention have considerably more linearity than the conventional units. A comparative example of response curves is shown in Figure 3, wherein the dashed curve 18 is the response curve for conventional transducers, and the full line curve 19 is the curve forthetransducer herein shown and de- scribed.

For example, and using a unit having substantially unaltered characteristics except for the different diaphragms, the dashed curve 18 is linear from about 600 Hzto 5 KHz, while the full curve 19 is linear from 600 Hzto 16 KHz.

As can be seen, the construction characteristics of the present electroacoustic transducer are extremely simple and thus economical, whilst ensuring high characteristics of linearity for the frequency response curve.

The efficiency is slightly reduced owing to the use of a diaphragm having a reduced active area com pared with the complete hemisphere used in the known conventional diaphragms.

However, the efficiency is higher than that of most cone type loud-speakers.

The diaphragm can be made by using different materials, such as aluminium, bakelized cloth, plastic films, fiberglass, carbon fibers and the like, whereas the damping discs 7 may be made of felt, foamed polystyrene and the like, provided they allow a suitable limitation of the diaphragm emis sion zone.

While the present invention has been shown and described in connection with some embodiments thereof, it will be evident to those skilled in the art that various modifications can be made to the structure and details without departing from the scope of the invention.

Claims (15)

1. An electroacoustic transducer having a diaphragm of the hemispherical cap type comprising an annular portion resiliently supported at its external periphery, by a resilient supporting structure, carrying a coil, and enclosed at its internal periphery between two adjacent damping discs which are coupled to an equalizing element.

2. An electroacoustic transducer as claimed in Claim 1 wherein the damping discs are coupled to the equalizing element by a pressure washer and a clamping device.

3. An electroacoustic transducer as claimed in Claim 2, wherein the action of the clamping device is adjusted by a spacer.

4. An electroacoustic transducer as claimed in any preceding claim, wherein the active or radiating part of the diaphragm is defined by resilient supporting structure and the edge enclosed between the two damping discs.

5. An electroacoustic transducer as claimed in any preceding claim, wherein the two damping discs are made of felt or the like material.

6. An electroacoustic transducer as claimed in any preceding claim, wherein the diaphragm and the equalizing element are coupled by the two damping discs.

7. An electroacoustic transducer as claimed in Claim 2 or any Claim dependent thereon, wherein the pressure washer is anchored to the equalizing element through a spacerforforming an information device of the pressure of the damping discs on the internal edge of the diaphragm.

8. An electroacoustic transducer as claimed in any preceding claim, wherein the equalizing element is secured to the diffuser body.

9. An electroacoustic transducer as claimed in any of Claims 1 to 7, wherein the equalizing element is secured to the central pole of the magnet of the transducer.

10. An electroacoustictransducer as claimed in any preceding claim, wherein the sizes of the damping discs and the central hole of the annular portion of the diaphragm are selected in dependence upon the range of operating frequencies, diameter of the diaphragm, diameter of the coil and system power.

11. An electroacoustic transducer having a diaphragm of the hemispherical cap type comprising an annular portion resiliently supported at its external periphery, carrying a coil and resiliently coupled at its internal periphery to an equalizing element.

12. An electroacoustic transducer as claimed in any preceding Claim wherein the diaphragm is made either of aluminum, or bakelized cloth, or plastic films, or fiberglass and carbon fibers or the like materials.

13. An electroacoustic transducer comprising adjacent a diffuser body a diaphragm associated with an equalizing element and a coil placed close to a magnet, characterised in that said diaphragm comprises an annular portion of substantially hemis pherical cap connected at its external periphery to a resilient supporting structure and said coil and confirmed at its internal periphery between two adjacent damping discs, the latter being coupled to said equalizing element through a pressure washer and a clamping device.

14. An electroacoustictransducer as claimed in Claim 13, wherein the diaphragm comprises an annular portion of hemispherical cap defined by two resilient structures provided along the external peripheral edge and the edge of the central hole.

15. An electroacoustic transducer substantially as hereinbefore described with reference to and as shown in the accompanying drawings.