Loudspeaker diaphragm
A loudspeaker diaphragm ( 12 ) comprising a woven fibre body supports damping material ( 25 ), for example PVA polymer, on a rearward-facing surface ( 24 ). The woven fibre body may be formed of lengths ( 14 ) non-metallic fibre material (for example glass fibre) coating with a thin metal coating ( 32 ). The mass of the layer of damping material ( 25 ) may be less than the mass of the woven fibre body. An attractive sparkly looking loudspeaker diaphragm ( 12 ) may thus be provided which damps undesirable vibration whilst providing a flatter frequency-response curve ( 50 ).
1. A loudspeaker diaphragm configured to have a range of operation over a band of frequencies that makes the diaphragm suitable for use in a midrange drive unit for a hi-fi loudspeaker, comprising:
a woven fibre body; and
a layer of damping material, wherein the woven fibre body is configured to act as a skeleton structure that supports the damping material,
wherein the diaphragm has a stiffness such that without the damping material the diaphragm would not exhibit break-up behaviour at frequencies below 500 Hz, but would exhibit break-up behaviour at certain frequencies above 500 Hz but still within the band of frequencies of the range of operation, and
wherein the damping material is configured to damp the break-up behaviour at the certain frequencies; and
a mass per unit area of damping material on the diaphragm is in the range of 100 to 500 g/m 2 .
2. The loudspeaker diaphragm of claim 1 , wherein the diaphragm is configured to behave as a rigid piston up to 1,000 Hz.
3. The loudspeaker diaphragm of claim 1 , wherein the band of frequencies of the range of operation comprises 200 Hz to 5,000 Hz.
4. The loudspeaker diaphragm of claim 3 , wherein the band of frequencies of the range of operation comprises 20 Hz to 6,000 Hz.
5. The loudspeaker diaphragm of claim 1 , wherein the frequency response curve is substantially flat over a 200 Hz to 6,000 Hz range.
6. The loudspeaker diaphragm of claim 1 , wherein the loudspeaker diaphragm has a stiffness corresponding to a first frequency at which break-up behaviour first occurs.
7. The loudspeaker diaphragm of claim 6 , wherein the stiffness corresponds to Young's modulus of 20-140 GPa.
8. The loudspeaker diaphragm of claim 1 , wherein the woven fibre body comprises a metal-coated non-metallic fibre material.
9. The loudspeaker diaphragm of claim 1 , wherein the mass of the layer of damping material is more than the mass of the woven fibre body.
10. The loudspeaker diaphragm of claim 1 , wherein the damping material has a mechanical loss factor of at least 0.25 at a frequency between 1,000 Hz and 8,000 Hz.
11. The loudspeaker diaphragm according to claim 10 , wherein the damping material comprises a synthetic resin elastomeric material.
12. A loudspeaker diaphragm for a midrange drive unit for a hi-fi loudspeaker, wherein the diaphragm has a forward-facing sound-radiating surface and a rearward-facing surface, and wherein the diaphragm comprises:
a woven fibre body comprising metal-coated glass fibre material; and
damping material disposed on the rearward-facing surface of the diaphragm, wherein the damping material has a mechanical loss factor of at least 0.25 at a frequency between 1,000 Hz and 8,000 Hz,
wherein a stiffness of the glass fibre material of the diaphragm results in a cone structure that is compliant that it behaves as a rigid piston at frequencies less than 1,000 Hz, and break-up modes, which occur at frequencies extending up to 6,000 Hz, are damped by the damping material.
13. The loudspeaker diaphragm of claim 12 , wherein the stiffness corresponds to Young's modulus of 20-140 GPa.
14. The loudspeaker diaphragm of claim 12 , wherein a mass of a layer of the damping material is between 100 and 500 g/m 2 and the mass of the layer of damping material is more than a mass of the woven fibre body.
15. The loudspeaker diaphragm according to claim 12 , wherein the damping material comprises polyvinyl-acetate (PVA).
16. A loudspeaker diaphragm configured to have a range of operation over a band of frequencies that makes the diaphragm suitable for use in a midrange drive unit for a hi-fi loudspeaker, comprising:
a woven fibre body; and
a damping material, wherein the woven fibre body is configured to act as a skeleton structure that supports the damping material,
wherein the diaphragm has a stiffness such that without the damping material the diaphragm would not exhibit break-up behaviour at frequencies below 500 Hz, but would exhibit break-up behaviour at certain frequencies above 500 Hz but still within the band of frequencies of the range of operation, and
wherein the damping material is configured to damp the break-up behaviour at the certain frequencies; and
the damping material has a mechanical loss factor of at least 0.25 at a frequency between 1,000 Hz and 8,000 Hz.
17. A loudspeaker drive unit comprising a loudspeaker diaphragm according to claim 1 .
18. A loudspeaker drive unit comprising a loudspeaker diaphragm according to claim 12 .
19. A loudspeaker drive unit comprising a loudspeaker diaphragm according to claim 16 .