Note: Descriptions are shown in the official language in which they were submitted.
26720-46
Acoustical transducers provide for the conversion of
energy between electrical and mechanical stakes and are
particularly useful as speakers, such as high-frequency speakers,
for converting electrical energy into acoustical energy.
Typically, such speakers have a piezoelectric driving
element acoustically coupled to a cone-type or dome-type diaphragm
(see, for example United Sta-tes Patent 3,548,116, issued
December 15, 1970, and United States Patent 3,786,202, issued
January 15, 1974). Such diaphragms are usually constructed of a
thin, somewhat fragile, compliant material, such as plastic or
paper. The nature of the dome-like or cone-like diaphragm
provides certain structural and geometric effects and constrain-ts
in the design of the speaker and in the use of the speaker in
other devices.
Further, the construction and design of such prior-art
speakers often do not permit the efficient, well-dispersed,
frequency response desired in high-frequency speakers. Prior-art
speakers, employing paper or plastic diaphragms, also have a
reduced ability to dissipate heat, due to the low heat conductivity
of the diaphragm material.
Thus, it is desirable to provide an improved, acoustical
transducer which overcomes or improves on all or some of the
limitations and constraints of prior-art transducers, and
particularly high-~requency speakers.
This invention relates to an acoustic transducer having
a diaphragm composed of a honeycomb material. More particularly,
the invention concerns an acoustic tranducer, such as a high-
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fre~uency speaker, haviny a piezoelec-tric driving element
acoustically coupled to a generally flat, honeyc~omb-type, me-t;ll
diaphragm sheet material.
The acoustic transducer of the invention comprises a
piezoelectric driving element which is acoustically coupled to
a honeycomb-type diaphragm sheet material. The acoustic trans~
ducer so constructed, for example, with a honeycomb aluminum
metal diaphragm material and a thin metal coupler, provides for
an efficient, well-dispersed, fre~uency response without cavity
or geometrical effects which are exhibited by cone-type or dome-
type diaphragm transducer configurations. Further, the acoustic
transducer may be constructed in extremely shallow designs; for
example, in designs of less than 1/4 of an inch. T}~e acoustic
transducer of the invention also provides for improved heat
dissipation due to the high heat conductivity, where the honeycomb
diaphragm material and coupling elements are composed of metal,
such as of thin aluminum.
The acoustic transducer of the invention comprises a
housing or frame element generally of dish-like construction,
within which is disposed a piezoelectric driving element,
~ypically circular or oval in form, a support means to secure one
side of the piezoelectric element to the housing element, and an
acoustical coupler, typically of a thin sheet material, of either
an annular-ring, truncated-cone or other design or construction,
secured to the opposite side of the pie~oelectric driving
element; for example, either peripherally or centrally disposed,
and typically secured by adhesives, and a honeycomb diaphragm
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element characterized by a high stiffness-to-weight ratio, and
generally a flat sheet composed of a heat-conductive metal,
which honeycomb material is acoustically coupled to the opposite
edge of the annular-ring coupler ox ko the larger diameter of the
truncated-cone coupler.
The high-frequency speakers of the invention include a
piezoelectric element which may comprise a monomorph or a wafer
assembly, such as a bimorph, as desired. The piezoelectric
element may be used in various shapes, but usually is employed
in a circular or oval configuration. In one embodiment, the
transducer of the invention provides for an acoustical output of
over 80 decibels or more at over 2.0 kilohertz, such as over the
range of 2.5 to 20 kilohertz.
The means employed to couple the piezoelectric element
to the honeycomb diaphragm generally comprises a thin; for
example, 2 to 40 mils, flat, sheet material preferably of heat-
conductive metal, but which may be other material, such as paper
or plastic material, to act as a coupler between the piezoelec-tric
element and the honeycomb diaphragm. The acoustical coupling
means provides coupling with the honeycomb diaphragm at the one
end and also aids in providing support thereof, while the other
edge receives acoustical signals from the piezoelectric element.
Prefera~ly, the coupling means is composed of the same or similar
material as the honeycomb diaphragm material and preferably
comprises a thin, heat-conductive material, such as brass,
aluminum or other metal, while nonmetal materials include, but
are not limited to: paper and plastic like nylon, polycarbonates,
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polypropylene and other materials used for acoustical coupliny.
The coupling means is secured to and between the honey-
comb diaphragm and the piezoelectric element, and usually such
means to secure includes or comprises the use of resin material,
such as resin adhesive material, such as hardenable epoxy and
other resins.
The honeycomb diaphragm employed in the transducer of
the invention comprises a thin material, particularly of metal,
formed into a honeycomb-type structure, such as forming a
plurality of adjacent thin~wall cells, particularly of a defined
polygonical structure, such as of a hexagonal or octagonal
nature. The honeycomb material should be characteriæed by a high
stiffness-to-weight ratio, so that it enhances the acoustical
eneryy from the coupling means. Typically, the honeycomb
material is composed of a plurality of polygonal-shaped material
having thin walls and covered by and secured to one or more
layers of sheet material of the same or different material than
the material forming the honeycomb structureO
Thus, in one embodiment, the honeycomb diaphragm may
comprise a thin-wall, honeycomb structure secured, such as by an
adhesive, to a single, flat, sheet material, or be secured to
upper and lower, flat, sheet materials, par-ticularly where the
material is a thin, heat-conductive material, such as aluminum
or an a:Luminum~alloy material. T~le honeycomb diaphragm is
typically a flat diaphragm material; for example, less than about
1 inch in thickness; for eYample, less than 1/4 of an inch in
thickness, which permits the construction of hlgh-fre~uency
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speakers of very shallow design, without sacrifice of acoustical
output. The honeycomb material is used in a flat sheet form,
but other forms may be used, such as dome or cone form, althouyh
such ~orms do not provide the advantage o~ shallow designO Ik
is particularly preferred that the honeycomb diaphragm be
composed of a flat sheet material of a thin upper and lower layer
oE aluminum, with an aluminum, polygonal, honeycomb structure
therebetween, the honeycomb being substantially perpendicular to
the thin layer material, to provide a light-weight structure o~
high strength and stiffness.
In summary, according to a broad aspect o~ the present
invention, there is provided an acoustic transducer which
comprises: a) a piezoelectric element to convert stimuli between
electrical and acoustical energy states, the piezoelectr~c
element characterized by a major surface on one or the other side
of the piezoelectric e].ement; b) means to support the piezo-
electric element; c) conductive means to provide or receive
electrical stimuli to or from the piezoel.ectric element; d) a
coupling means which comprise~ a sheet material peripherally
secured at the one edge thereof to the one major surface of the
piezoelectric element in an acoustically coupled relationship
with the major surface of the piezoelectric element; and e) a
generally honeycomb sheet diaphragm material having a one and
another side, the diaphragm material having a high stiffness-to-
weight ratio and capable of acoustical vibration generally in a
piston-type mode, the one side of the diaphragm material secured
to the other peripheral edge of the sheet material o~ the coupli.ng
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means, the honeycomb diaphragm material spaced apart from the
piezoelectric element by the coupling means and acoustically
coupled thereto by the other edge of the coupling means.
The invention will now be described in greater dekail
with reference to the accompanying drawings, in which:
Figure 1 is a schematic cross-sectional vlew of an
acoustic transducer of the invention;
:Figure 2 is a schematic cross-sectional view of another
embodiment of an acoustic transducer of the invention;
Figure 3 is a fragmentary, enlarged, partially cutaway,
perspective view of the honeycomb material used in the acoustic
transducer of the invention; and
Figure 4 is a graphical representation of the sound
output in decibels versus the frequency response in hertz of an
acoustic transducer of Figure 1.
Figure 1 shows a high-frequency speaker 10 of the
invention having a dish-like, stamped, metal frame 12 and contain-
ing a monomorph or blmorph piezoelectric element 14 having a
generally flat surface and being ganerally circular in shape. The
piezoelectric element 14 is supported in a fixed position by a
rigi~, central, support post 16 centra].ly positioned in -the
interior of the dish-like frame 120 The support post is
adhesively fixed to the bottom dish of the frame 12 and to the
cenkral area on one side of the piezoelectric element 14.
A thin-wall; for example 2 to 5 mils, hollow cylinder
of an aluminum, acoustical, coupling material 18 is employed as
an acoustical coupling means, with one edge of the coupling
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material 18 adhesively secured, for example by an epoxy resin,
about the ou-ter periphery of the upper major surface of the
piezoelectric element 14. A flat sheet of about 1/~ of an inch
thickness, for example 1/8 to 1/2 of an inch, of honeycomb
material 22 is employed as a flat diaphragm, the honeycomb
material composed of aluminum metal, which material is shown more
particularly in Figure 3. The honeycomb diaphragm 22 is generally
circular in configuration and is of larger diameter than and
acoustically positioned and coupled with the piezoelectric element
14 through being adhesively secured to the other upper edge of the
coupling material 18. The honeycomb diaphragm 22 is surrounded,
and the interior of the frame 12 is sealed from outside contamina-
tion, by the use of a flexible surrounding material 20, such as
paper or aluminum, about and secured to the peripheral edges of
the honeycomb diaphragm 220 The exterior of the frame 12
includes a flat, electric, insulating board 24 with electrical
terminals 26, which terminals are electrically connected by
electrical wires 28 to the piezoelectric element 14, so that
electrical energy may be imported to or received from the piezo-
electric element 14.
Figure 2 shows another embodiment of an acoustictransducer 30 of similar construction as the speaker of Figure 1,
except that the coupling means comprises a truncated, conical
element 38, and the piezoelectric element 34 is flexibly
supported at its outer peripheral edges by a surrounding,
flexible, support materia] 3~. The truncated, conical coupler
is adhesively secured at the smaller diameter edge to one surface
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807
of the piezoelectric element 34, while the other edge is
adhesively secured to the honeycomb diaphragm ~2. The honeycomb
diaphragm 42 is secured to and surrounded by a flexible surround-
ing material 40 to the frame 32. The piezoelectric element 34,
rather than being centrally and rigidly supported, is
peripherally supported and spaced apart from -the interior back
surface of the :Erame 32 by the flexible surrounding material 36
adhesively secured at its outer edges to the interior of the
frame 32 and the piezoelectric element 34. The transducer 30
includes an insulating board 44, electrical terminals 46 and
electrical wires 48. Optionally, the devices 10 and 30 may be
enhanced in output by coupling acoustically by adhesives the
exterior edges of the other exterior surface of the honeycomb
diaphragm 22 or 42 with an acoustical horn 56, such as a
truncated cone or parabolic horn, to enhance the sound output.
Figure 3 shows a preferred honeycomb material useful as
the honeycomb diaphragm in Figures 1 and 2, wherein the honeycomb
material comprises a thin upper 52 and thin lower 50 layer of
aluminum metal laminated to a plurality of honeycomb-like cells
54 of hexagonal shape made of thin aluminum, with all the thin
walls being disposed generally perpendicular to the upper and
lower layers 52 and 50. The material 22 may vary in thickness,
but typically ranges from about 1/16 of an inch to 1 inch, for
examp].e 1/8 of an inch to 1/2 of an inch in thickness. The size
and shape of the open cells which make up the honeycomb may vary,
but typically are polygonal and range in width and lenyth from
1/8 of an inch to 1 inch, for example 1/4 to 1/2 of an inch. The
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honeycomb material has a high stiffness-to-weight ratio. One
form of hone~comb mater;a:L suitable for use in the invention
comprises honeycomb manufacturecl by Hexcel Corporation of Dublin,
CaliEornia, with the cell of about 3/16 inches in size and the
honeycomb material having a 0.9 mil~ aluminum upper and lower
skin layer and the hexagonal cell formed of 0.7 milO aluminum
with an overall plate or honeycomb thickness of 0.062 inches.
The honeycomb material had a stiffness such that in a 4-inch span
with a 0.07 psi load, the deflection of the material was 0.012
inches.
Figure 4 shows a graphical representation of a
frequency-response curve employing the transducer illustrated in
Figure 1. The first peak is relatively insignificant in sound
output and arises from resonance of the honeycomb material, which
peak if desired can be removed, modulated or dampened by dampening
the honeycomb material preferably, for cosmetic reason, by a
dampening material on the interior side of the honeycomb
material. The second peak is significant and shows an average
sound decibel of 95. over the range of about 8.5 KH to 16 KH
while exhibiting a flat response over the 0.2 to 2.2 KH range.
~he responsive curve is based on the Figure 1 device wherein the
flexible surrounding material comprises Mylar, a polyester film,
and the coupling means is a 3 mil. aluminum cylinder of 44 mm.
diameter and 2 mm. height, the piezoelectric element is a bimorph
TDK Corporation of Japan element with a diameter of 21 mm. The
input was 2.83 volts with the microphone at 0O~ meter distance.
The aluminum honeycomb diaphragm was 23 mm in diameter with a
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thickness of about .062 inches.
The transducer so described provides for a sh~llow
design, good heat dissipation and good sound v. Erequency
response.
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