A speaker comprises a permanent magnet ( 2 ) and a coil ( 8 ) positioned around the permanent magnet ( 2 ) and attached to a membrane ( 10 ), wherein the membrane comprises an elastomer of thickness less than 0.3 mm and with a Young's modulus below 100 MPa.
1. A speaker comprising a permanent magnet, and a coil positioned around the permanent magnet and attached to a membrane, wherein the membrane is a single layer monolithic structure formed from an elastomer of thickness less than 0.3 mm and with a Young's modulus below 100 MPa.
2. A speaker as claimed in claim 1 , wherein the elastomer comprises a silicone.
3. A speaker as claimed in claim 1 , wherein the membrane is injection moulded.
4. A speaker as claimed in claim 1 , wherein the membrane comprises a flat central region and a supporting edge region, and wherein the speaker further comprises a stiffening element on the flat central region on the opposite side of the membrane to the coil.
5. A speaker as claimed in claim 1 , further comprising a support structure which defines a back volume, wherein the back volume is less than 1 cm 3 .
6. A speaker as claimed in claim 5 , wherein the back volume is less than 0.5 cm 3 .
7. A speaker as claimed in claim 1 , wherein the resonant frequency is below 300 Hz.
8. A speaker as claimed in claim 7 , wherein the resonant frequency is below 250 Hz.
9. The speaker of claim 1 , wherein the membrane is formed from an elastomer having a Young's modulus below 50 MPa.
10. The speaker of claim 1 , wherein the membrane is formed from an elastomer having a Young's modulus below 12 MPa.
11. The speaker of claim 1 , wherein the membrane is formed from an elastomer having a Young's modulus below 10 MPa.
12. A method of manufacturing a speaker, comprising:
forming a membrane from an elastomer, wherein the membrane is a single layer monolithic structure and has thickness less than 0.3 mm and a Young's modulus below 100 MPa;
attaching a coil to the membrane; and
assembling the speaker by suspending the membrane, such that the coil is positioned around a permanent magnet.
13. A method as claimed in claim 12 , wherein the elastomer comprises silicone.
14. A method as claimed in claim 12 , wherein the membrane is formed using injection moulding.
15. A method as claimed in claim 12 , wherein the membrane is formed with a flat central region and a supporting edge region, and wherein the method further comprises providing a stiffening element on the flat central region on the opposite side of the membrane to the coil.
16. A micro speaker comprising:
a body portion comprising a frame and a lid, the lid having an opening;
a magnetic circuit comprising a yoke, a permanent magnet contained within the yoke, and an upper plate attached to an upper surface of the permanent magnet; and
a vibration system, comprising:
a voice coil fitted into a gap between the permanent magnet and an inner surface of the yoke; and
a speaker membrane attached to the voice coil and affixed to the frame, the speaker membrane formed from a single layer elastomer having a thickness less than 0.3 mm and a Young's modulus below 100 MPa.