Acoustic transducer including piezoelectric driving element

Claim 2

Apparatus providing conversions between electrical and mechanical stimuli comprising: a. a piezoelectric element having a generally flat major surface, electrodes attached to said element for driving said element in A planar bending mode when said electrodes are properly energized, and first overtone nodal lines present on said major surface during planar bending mode operation of said element; b. a generally conically shaped diaphragm having a truncated apex defining a generally circular area with a diameter larger than a point and sufficiently less than the distance between nodes of the first overtone to reduce the amplitude of the output of the first overtone to approximately the amplitude of the output of the fundamental; and c. means fixedly attaching the truncated apex of said diaphragm to said piezoelectric element with the circular area defined by said apex generally encircled by and substantially centered within the first overtone nodal lines.

Claim 3

Apparatus as set forth in claim 1 wherein the piezoelectric element is generally disk shaped and the nodal line for the first overtone defines a generally circular area concentric with the truncated apex of the diaphragm.

Claim 4

Apparatus as set forth in claim 1 wherein the piezoelectric element includes two piezoelectric wafers affixed together in parallel contiguous relationship with electrodes on each side of each wafer.

Claim 5

Apparatus as set forth in claim 1 having in addition a resilient damping member affixed to the piezoelectric element on the side opposite the diaphragm for lowering the fundamental resonance frequency and damping the resonance peak thereof to extend the range of the speaker to lower frequencies and to provide a relative flat response over the entire range.

Claim 6

Apparatus as set forth in claim 4 wherein the damping member is formed from a material including rubber.

Claim 7

Apparatus as set forth in claim 5 wherein the rubber has a glass transition region approximately including the frequency of the first overtone.

Claim 8

Apparatus as set forth in claim 5 wherein the rubber includes neoprene.

Claim 9

Apparatus as set forth in claim 5 wherein the damping member includes particles of a relatively heavy material intermixed with the rubber for providing frictional damping at the higher frequencies of operation.

Claim 10

Apparatus as set forth in claim 8 wherein the particles include lead of approximately 100 mesh size and three parts by weight of lead to one part by weight of rubber.

Claim 11

Apparatus as set forth in claim 8 wherein the damping member further includes particles of dry lubricant intermixed with the particles of relatively heavy material for increasing relative motion between the particles of relatively heavy material and the rubber at the higher frequencies of operation.

Claim 12

Apparatus as set forth in claim 4 wherein the damping member extends outwardly beyond the edges of the piezoelectric element for further damping the lower frequencies of operation.

Claim 13

Apparatus as set forth in claim 4 wherein the combined mass of the piezoelectric element and the damping member is substantially heavier than the mass of the diaphragm.

Claim 14

An improved acoustic transducer comprising: a. a housing defining a cavity therein; b. a generally disk shaped piezoelectric element having opposed generally flat major surfaces and defining thereon a nodal ring for a first overtone frequency, said element having electrodes attached thereto for driving said element in a planar bending mode when said electrodes are properly energized; c. a generally conically shaped diaphragm having a truncated apex defining a generally circular area with a diameter larger than a point and sufficiently different from the diameter of the first overtone nodal ring to reduce the amplitude of the output of the first overtone to approximately the amplitude of the output of the fundamental; d. means fixedly attaching the truncated apex of said diaphragm to one of said major surfaces of said piezoelectric element with the circular area defined by said apex generally concentric with the first overtone nodal ring; and e. means operatively mounting said diaphragm within the cavity of said housing.

Claim 15

An improved acoustic transducer comprising: a. a housing defining a cavity therein; b. a generally disk shaped piezoelectric element having opposed generally flat major surfaces and defining thereon a nodal ring for a first overtone frequency, said element having electrodes attached thereto for driving said element in a planar bending mode when said electrodes are properly energized; c. a generally conically shaped diaphragm having a truncated apex defining a generally circular area with a diameter larger than a point and sufficiently different from the diameter of the first overtone nodal ring to reduce the amplitude of the output of the first overtone to approximately the amplitude of the output of the fundamental; d. means fixedly attaching the truncated apex of said diaphragm to one of said major surfaces of said piezoelectric element with the circular area defined by said apex generally concentric with the first overtone nodal ring; and e. means operatively mounting said diaphragm within the cavity of said housing.

Claim 16

An improved acOustic transducer as set forth in claim 13 having in addition a generally disk shaped resilient damping member affixed to the major surface of said piezoelectric element opposite the major surface having the diaphragm affixed thereto.

Claim 17

An improved acoustic transducer as set forth in claim 14 having in addition acoustic absorbing material positioned in the cavity of said housing generally between said housing and said diaphragm.