HK1118415B - Electro-acoustic transducer - Google Patents

Description

Electroacoustic transducer

The present invention relates to an electroacoustic transducer, and in particular to such a transducer for a loudspeaker. The invention relates in particular to a dome-shaped transducer, such as a high frequency transducer commonly referred to as a "tweeter".

Rigid ("stiff") dome shaped electroacoustic transducers arranged to be able to transmit sound waves at high frequencies, e.g. more than about 15kHz, have been used in loudspeakers for many years. Their ideal function is based on the fact that such stiff dome transducers are substantially rigid (so that they exhibit minimal flexibility during use) and are relatively lightweight (so that the input energy can be converted to acoustic output energy at a maximum rate). This pair of goals has been achieved by combining the inherent structural rigidity of the dome shape with the use of low density materials, including plastic materials, low density metals and metal alloys, ceramic materials, and composite materials.

A number of specific examples of known dome-shaped electroacoustic transducers include those disclosed in (among numerous other examples) us patents 4531608 and 6757404B 2.

The present invention seeks to provide an improved electroacoustic transducer which is able to combine the characteristics of high stiffness and low mass (low mass) with less constraints on shape than prior art transducers.

Accordingly, a first aspect of the present invention provides an electroacoustic transducer comprising a front part having an acoustic propagation surface, a support part supporting the front part and extending from a peripheral region of the front part in a direction away from the acoustic propagation surface, and a stiffening part providing rigidity to the transducer. Wherein the reinforcement member extends from the support member to the front member such that a portion of the reinforcement member is spaced from the front member and/or the support member.

The invention has the advantage that the transducer can be made with high rigidity and low mass while having a large free space in the design of the sound propagation surface by providing the transducer with a stiffening member extending between the support member and the front member, but spaced from the front member and/or the support member. The invention thus substantially differs from known dome transducers in that it substantially avoids the need to provide the required rigidity of the sound-propagating part of the transducer by design in its shape. Instead, the determination of the shape of the acoustically propagating portion of the transducer according to the invention may be considered primarily or (preferably) substantially entirely from an acoustic point of view rather than a mechanical point of view.

In a preferred embodiment of the invention, a portion of the reinforcing member is spaced from both the front member and the support member. The stiffening member is located behind the front member of the transducer.

Preferably, the support member extends substantially from the periphery of the front member. Preferably, the periphery of the front part is substantially circular. Advantageously, the support member may be substantially cylindrical.

Preferably, at least that part of the reinforcing member which is spaced from the front member and/or the support member is substantially dome-shaped or frusto-dome-shaped. Advantageously, the dome or truncated dome of the reinforcing member may have a substantially spherical or substantially ellipsoidal curvature. Alternatively, at least a portion of the reinforcing member spaced from the front member and/or the support member may be substantially conical or frusto-conical, for example. The stiffening member may be substantially continuous, for example, about the axis of the transducer. Alternatively, the reinforcing component may comprise a plurality of sections (sections), which are, for example, spaced apart from one another. For example, such a section may include a reinforcing strut. For example, the reinforcing member may be perforated or porous.

Preferably, the stiffening member and/or the support member and/or the front member are formed from one or more sheets of material.

In a preferred embodiment of the invention, the front part of the transducer is dome-shaped. Preferably, the sound propagation surface of the front element is dome-shaped, and most preferably, its shape is substantially a segment (segment) of a sphere.

Preferably, the radius or smallest radius of the sound propagation surface of the front member is larger than the radius or largest radius of at least a part of the stiffening member spaced from the front member and/or the support member.

In at least some preferred embodiments of the invention, the stiffening members of the transducer are spaced from the front member and/or the support member by a distance of at most 5 mm, more preferably at most 3 mm, still more preferably at most 1 mm, especially preferably at most 0.5 mm, for example at most 0.3 mm.

Preferably, the sound propagation surface of the transducer according to the invention has a diameter of at least 10 mm, more preferably at least 15 mm, for example close to 19 mm. Preferably, the sound propagation surface of the transducer has a diameter of no more than 120 mm, preferably no more than 100 mm, more preferably no more than 80 mm, still more preferably no more than 60 mm, especially no more than 40 mm.

Preferably, the dome transducer is formed from a substantially rigid, low density material, such as a metallic or metal alloy material, a composite material, a carbon fibre material, a plastics material or a ceramic material. Some preferred metals for forming suitable metallic or alloy materials include: titanium, aluminum, and beryllium. The sound propagation surface of the dome transducer may be formed of a special material, such as diamond (especially chemically deposited diamond).

A second aspect of the invention provides a loudspeaker comprising at least one transducer according to the first aspect of the invention. For example, the loudspeaker may comprise one or more further transducers and/or one or more acoustically propagating diaphragms.

A third aspect of the invention provides a loudspeaker system comprising a plurality of loudspeakers according to the second aspect of the invention.

Other preferred and optional features of the invention are set out below and in the dependent claims.

Examples of preferred embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

figure 1 shows schematically a cross-sectional view of a part of a loudspeaker incorporating a transducer according to the invention;

FIG. 2 shows a detail of FIG. 1, particularly illustrating an electroacoustic transducer according to the present invention; and is

Fig. 3 shows the sound pressure level (in dB) as a function of sound frequency (in Hz) for an enhanced transducer model according to the present invention, and the sound pressure level (in dB) as a function of sound frequency (in Hz) for a transducer model having the same shaped sound propagation surface but without enhancement (and therefore outside the scope of the present invention), and compares the two.

Fig. 1 and 2 schematically show a cross-sectional view of a part of a loudspeaker 1 according to the invention. (both figures show only half of the loudspeaker on one side of the longitudinal axis 12. the loudspeaker is symmetrical about this axis.) the loudspeaker 1 comprises a horn waveguide (horn waveguide)3 having a waveguide surface 5 and a convex dome transducer 7 according to the invention located generally within the throat 9 of the horn waveguide. The convex dome-shaped transducer 7 has a substantially rigid sound propagation surface 11, which is preferably shaped substantially like a segment of a sphere. (i.e. the curvature of the surface 11 is substantially spherical) the transducer 7 comprises a stiffening member 6, which is shown in fig. 2 but is not shown in fig. 1 for clarity. Horn waveguide 3 is a generally frusto-conical, flared, stationary waveguide having a longitudinal axis 12. The surround 13 of the dome transducer 7 is attached to the waveguide 3 behind the throat 9.

The drive unit 15 of the dome transducer 7 comprises a housing (pot)17, a disc-shaped magnet 19 and a disc-shaped inner pole (pole) 21. The housing 17 is substantially cylindrical and has an opening 23 to accommodate the disc-shaped magnet 19 and the disc-shaped inner pole 21. The opening 23 is defined by a radially inwardly extending lip 25, the lip 25 forming an outer pole of the drive unit 15. A substantially cylindrical support member (or former) 27 of the dome transducer 7 carries an electrical conductor (e.g. wire) coil 29 surrounding the support member 27. The coil 29 and the shaped body 27 extend between the inner pole 21 and the outer pole 25 of the drive unit. The dome transducer 7 is driven substantially along an axis 12 by a drive unit and is stabilized by a surround 13. The flexible web member (or sealing member) 31 of the surround allows axial movement of the transducer 7. Preferably, at least 50% of the outer surface of the web member 31 of the surround 13 over the radial width overlaps the horn waveguide throat 9.

Fig. 2 shows in detail a part of an electrical transducer 7, the transducer 7 comprising a front part 2 having an acoustic propagation surface 11, a support part (or form) 27 supporting the front part and extending from a peripheral region 4 of the front part in a direction away from the acoustic propagation surface, and a stiffening part 6 providing rigidity to the transducer. The reinforcement member 6 extends from the support member 27 to the front member 2 such that a portion of the reinforcement member is separated from the front member and/or the support member by a gap 8. The rigidity provided by the stiffening component 6 to the transducer 7 provides a large degree of design freedom in the shape of the sound propagation surface 11, so that the surface can be designed substantially entirely according to acoustic criteria rather than mechanical criteria. Also, the fact that a portion of the reinforcing member is spaced from the front member 2 and the support member 27 means that the reinforcing member can have a lighter mass and therefore only the lightest inertial mass for the transducer. (this is advantageous because the lighter the mass of the transducer 7, the higher the rate at which the applied electrical energy is converted into acoustic energy.)

Preferably, as illustrated, the stiffening member (or at least that portion spaced from the backing member and/or the front member of the transducer) comprises a thin sheet of material. Preferably, the stiffening member comprises a sheet material having a thickness substantially the same as the material preferably forming the transducer front face member and/or the backing member. Alternatively, however, the stiffening member may be thicker or thinner than the material forming the transducer front face member and/or the backing member. Also, the material forming the stiffening member may be the same as or different from the material forming the transducer front face member and/or the backing member. For example, the reinforcing member may be formed of a carbon fiber material. As illustrated, the stiffening member preferably comprises a truncated dome extending between the support member and the front member of the transducer. Advantageously, the stiffening member transmits forces between the backing member and the front member of the transducer in a progressive manner.

Fig. 3 shows the sound pressure level (in dB) and sound frequency (in Hz) as a function of an enhanced transducer model according to the invention and the sound pressure level (in dB) and sound frequency (in Hz) as a function of a transducer model having the same shaped sound propagation surface but without enhancement (and therefore departing from the scope of the invention) and compares the two. Wherein the model is modeled on a computer by means of finite element analysis. The structure of a computer-modeled transducer according to the invention is shown in fig. 2. A computer modeled unenhanced transducer is also shown in fig. 2, except that the stiffening member 6 is absent.

As is known to the skilled person, for the transducer to function adequately, it is necessary that the sound pressure of the sound emitted by the transducer is as constant as possible (for a given input power) over substantially the entire acoustic frequency operating range of the transducer. For preferred transducers according to the invention the operating frequency range is typically from about 5kHz to about 20kHz (or possibly higher; for example for a Super Audio Compact Disc (SACD) system the operating frequency range exceeds 20 kHz). Thus, for the transducer according to the invention it is required to have a (flat) sound pressure level response that is as constant as possible over this frequency range.

Figure 3 clearly shows that the modeled reinforced transducer according to the invention exhibits a significantly flatter sound pressure level response than the non-reinforced transducer, especially over the frequency range from 10kHz to 20kHz (which is the most important range for high frequency transducers, i.e. "tweeters"). Thus, the stiffened transducer according to the present invention demonstrates a significant acoustic advantage over an un-stiffened transducer.

Claims (20)

1. An electro-acoustic transducer comprising a front member having an acoustic propagation surface, a support member supporting the front member and extending from a peripheral region of the front member in a direction away from the acoustic propagation surface, and a stiffening member providing rigidity to the transducer, wherein the stiffening member extends from the support member to the front member such that a portion of the stiffening member is spaced from the front member and/or the support member, and at least the portion of the stiffening member spaced from the front member and/or the support member is frusto-dome shaped.

2. The transducer of claim 1, wherein the support member extends from a periphery of the front member.

3. The transducer of any preceding claim, wherein the periphery of the front member is circular.

4. The transducer of claim 1, wherein the support member is cylindrical.

5. The transducer of claim 1, wherein the truncated dome shape of the stiffening member has a spherical curvature.

6. The transducer of claim 1, wherein at least the portion of the stiffening member spaced from the front member and/or the backing member is continuous.

7. The transducer of claim 1, wherein the stiffening member and/or the backing member and/or the front member are formed from one or more pieces of material.

8. The transducer of claim 1, wherein at least the portion of the stiffening member spaced from the front member and/or the backing member comprises a plurality of segments.

9. The transducer of claim 8, wherein at least some of the sections are spaced apart from one another.

10. The transducer of claim 8, wherein the section comprises a stiffening strut.

11. The transducer of claim 1, wherein the stiffening member is perforated.

12. The transducer of claim 1, wherein the front face member is dome-shaped.

13. The transducer of claim 1, wherein the sound propagation surface of the front member is dome shaped.

14. The transducer of claim 1, wherein the shape of the sound propagation surface of the front member is a segment of a sphere.

15. The transducer of claim 13 or 14, wherein the radius or minimum radius of the sound propagation surface of the front member is greater than the radius or maximum radius of at least the portion of the stiffening member spaced from the front member and/or the support member.

16. The transducer of claim 1, further comprising an electrical conductor coil carried by the support member.

17. The transducer according to claim 1, characterized in that the transducer further comprises a component formed by a magnet for a drive unit of the transducer.

18. A loudspeaker comprising at least one transducer according to any preceding claim.

19. A loudspeaker according to claim 18, wherein the loudspeaker comprises one or more further transducers and/or one or more acoustically propagating diaphragms.

20. A speaker system comprising a plurality of speakers according to claim 18 or 19.