Electrodynamic acoustic transducer

1. An acoustic transducer, comprising:

a pole piece comprising a first end;

a voice coil comprising wire windings configured to receive electrical current, the voice coil being configured to move along the first end of the pole piece;

a magnetic structure comprising parts defining an air gap, wherein the voice coil on the first end of the pole piece is disposed in the air gap so that the magnetic structure creates a magnetic field in which the voice coil is configured to move along the first end of the pole piece;

a diaphragm comprising an inner periphery defining a central opening and an outer periphery, the inner periphery of the diaphragm being attached to the voice coil to move with the voice coil; wherein said diaphragm is configured to move as a piston;

a waveguide extension structure attached to the first end of the pole piece; and

an inner flexible roll seal coupled to the diaphragm and to the waveguide extension structure, wherein the inner flexible roll seal seals a gap between the voice coil and the first end of the pole piece.

2. An acoustic transducer according to claim 1 , wherein the inner flexible roll seal includes non-porous material.

3. An acoustic transducer according to claim 2 , wherein the inner flexible roll seal comprises an elastic damping material that dampens sound waves within frequency range of the acoustic transducer to a substantially greater degree than degree of damping of the sound waves by the diaphragm.

4. An acoustic transducer according to claim 2 , wherein the inner flexible roll seal is substantially arch-shaped in cross-section.

5. An acoustic transducer according to claim 2 , wherein the inner flexible roll seal is substantially semicircular in cross-section.

6. An acoustic transducer according to claim 2 , wherein decrease in effective piston area of the transducer caused by the inner flexible roll seal and the waveguide extension structure is less than about ten percent as compared to a transducer with identical components but without the inner flexible roll seal and without the waveguide extension structure.

7. An acoustic transducer according to claim 2 , wherein decrease in efficiency of the transducer caused by the inner flexible roll seal and the waveguide extension structure is less than about ten percent as compared to a transducer with identical components but without the inner flexible roll seal and without the waveguide extension structure.

8. An acoustic transducer according to claim 2 , wherein increase in moving mass of the transducer caused by the inner flexible roll seal and the waveguide extension structure is less than about ten percent as compared to a transducer with identical components but without the inner flexible roll seal and without the waveguide extension structure.

9. An acoustic transducer according to claim 1 , wherein the inner flexible roll seal comprises a ring of elastometric non-porous material.

10. An acoustic transducer according to claim 9 , wherein the inner flexible roll seal is substantially arch-shaped in cross-section.

11. An acoustic transducer according to claim 10 , wherein decrease in piston area of the transducer caused by the inner flexible roll seal and the waveguide extension structure is less than about ten percent as compared to a transducer with identical components but without the inner flexible roll seal and without the waveguide extension structure.

12. An acoustic transducer according to claim 10 , wherein decrease in efficiency of the transducer caused by the inner flexible roll seal and the waveguide extension structure is less than about ten percent as compared to a transducer with identical components but without the inner flexible roll seal and without the waveguide extension structure.

13. An acoustic transducer according to claim 9 , further comprising: a frame attached to the magnetic structure; and an outer roll seal attaching the outer periphery of the diaphragm to the frame; wherein: the magnetic structure comprises a permanent magnet and a front plate comprising portions defining an annular opening; and the voice coil and the first end of the pole piece are disposed in the opening of the front plate.

14. An acoustic transducer according to claim 13 , further comprising a spider attached to the frame and to the voice coil, wherein the spider aligns and centers the voice coil.

15. An acoustic transducer according to claim 13 , wherein the outer roll seal is made from substantially the same material as the inner flexible roll seal.

16. An acoustic transducer according to claim 15 , wherein the outer roll seal has substantially the same working geometry and excursion capability as the inner flexible roll seal.

17. An acoustic transducer according to claim 13 , wherein the waveguide extension structure extends substantially to a plane defined by the outer periphery of the diaphragm when the voice coil is at rest.

18. An acoustic transducer according to claim 13 , wherein the waveguide extension structure extends not substantially farther than a plane defined by the outer periphery of the diaphragm when the voice coil is at maximum forward excursion.

19. An acoustic transducer according to claim 1 , wherein the waveguide extension structure occupies more than one half of a cavity formed by projecting the first end of the pole piece to a plane defined by the outer periphery of the diaphragm.

20. An acoustic transducer according to claim 1 , wherein the inner flexible roll seal comprises synthetic rubber.

21. An acoustic transducer according to claim 1 , wherein the inner flexible roll seal comprises synthetic rubber and plasticizer.

22. An acoustic transducer, comprising:

a cylindrical pole piece comprising a first end; a voice coil comprising wire windings for receiving electrical current, the voice coil being configured to move along the first end of the cylindrical pole piece;

a magnetic structure means for immersing the voice coil in magnetic flux interacting with the electrical current in the wire windings to apply a force to the voice coil to cause the voice coil to move along the cylindrical pole piece;

a diaphragm comprising an inner periphery defining a central opening and an outer periphery, the inner periphery of the diaphragm being attached to the voice coil to move with the voice coil; wherein said diaphragm is configured to move as a piston;

a waveguide means for reducing high frequency distortions of the acoustic transducer, the waveguide means being attached to the first end of the pole piece;

a frame for mounting the diaphragm, and the magnetic structure; and a flexible inner seal means for isolating air mass in front of the diaphragm from air mass behind the diaphragm.

23. An acoustic transducer according to claim 22 , wherein the flexible inner seal means comprises means for damping acoustic vibrations of the diaphragm.

24. An electro-acoustic transducer comprising:

a frame;

a pole;

a diaphragm comprising an outer periphery, an inner periphery defining an opening in the diaphragm, and a neck area proximate the inner periphery; wherein said diaphragm is configured to move as a piston;

an outer flexible roll seal connecting the outer periphery of the diaphragm to the frame;

a waveguide extension of the pole that substantially fills cavity in front of the pole;

a voice coil moveable along the pole and connected to the neck area of said diaphragm;

and an inner flexible roll seal connecting said waveguide extension of the pole to the neck area of said diaphragm, wherein the inner flexible roll seal and the outer flexible roll seal are configured such that there is substantially no air leakage between the diaphragm and the waveguide extension of the pole, such that the normal operational movement of the diaphragm is substantially unchanged, and such that resonances in the diaphragm are terminated by the combination of the inner and outer flexible roll seals.

25. The electro-acoustic transducer of claim 24 , wherein the diaphragm is shaped substantially as a straight-sided cone.

26. The electro-acoustic transducer of claim 24 , wherein the diaphragm is shaped substantially as an exponentially curved flare.

27. The electro-acoustic transducer of claim 24 , wherein the waveguide extension of the pole is integral with the pole.

28. The electro-acoustic transducer of claim 24 , wherein the waveguide extension of the pole comprises a portion that reduces in diameter in a smooth arc.

29. The electro-acoustic transducer of claim 24 , wherein the waveguide extension of the pole expands in front of the inner roll seal to a diameter greater than diameter of the pole at a junction of the pole and the waveguide extension of the pole.

30. The electro-acoustic transducer of claim 24 , wherein the waveguide extension of the pole ascends to a height substantially no less than height of the diaphragm with the voice coil at rest, and substantially no more than height of the diaphragm at maximum excursion.

31. The electro-acoustic transducer of claim 24 , wherein the inner flexible roll seal is substantially semi-circular in cross-section.

32. The electro-acoustic transducer of claim 24 , wherein the inner flexible roll seal has substantially the same geometry and excursion capability as the outer flexible roll seal.

33. The electro-acoustic transducer of claim 24 , wherein the inner and outer flexible roll seals function to extend the diaphragm from the frame to the waveguide extension of the pole, thereby effectively separating and sealing the air at the front of the diaphragm from the air at the back of the diaphragm.

34. The electro-acoustic transducer of claim 24 , wherein the inner flexible roll seal has a thickened inner foot ring providing rigidity in area of attachment of the inner flexible roll seal to the waveguide extension of the pole.