U.S. patent number 3,660,602 [Application Number 05/042,378] was granted by the patent office on 1972-05-02 for microphone cartridge with amplifier.
This patent grant is currently assigned to Conrac Corporation. Invention is credited to Paul Thompson.
United States Patent |
3,660,602 |
Thompson |
May 2, 1972 |
MICROPHONE CARTRIDGE WITH AMPLIFIER
Abstract
The microphone of the invention obtains damping from a
perforated baffle closely adjacent the diaphragm with fabric
covering the perforations, and from resistive structures behind the
baffle. The piezoelectric transducer element is mounted directly on
a circuit board which also carries all electronic components of a
preamplifier circuit.
Inventors: |
Thompson; Paul (Cedar Rapids,
IA) |
Assignee: |
Conrac Corporation (New York,
NY)
|
Family
ID: |
21921598 |
Appl.
No.: |
05/042,378 |
Filed: |
June 1, 1970 |
Current U.S.
Class: |
381/114; 310/326;
310/330; 381/173 |
Current CPC
Class: |
H04R
17/02 (20130101) |
Current International
Class: |
H04R
17/02 (20060101); H04c 017/02 () |
Field of
Search: |
;179/11A,180 ;317/235M
;310/8.2,8.5 ;340/10 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
Carlson, A Wideband Miniature Microphone, Journal of the Audio
Engineering Society, p. 631-635..
|
Primary Examiner: Claffy; Kathleen H.
Assistant Examiner: Leaheey; Jon Bradford
Claims
I claim:
1. A microphone and amplifier unit, comprising in combination
a generally cylindrical housing, open at one end to receive sound
energy,
a circuit board mounted transversely of the housing and having an
outwardly opening central cavity,
an elongated piezoelectric element responsive to bending stresses
and having two opposite conductive longitudinal output faces,
a conductive mounting surface on the outer face of the circuit
board adjacent the cavity,
an electrically conductive spring clip having one portion rigidly
mounted on the board and another portion resiliently engaging one
face of the element to clamp the element with its other face
engaging the mounting surface and with a free end extending
unsupported over the cavity,
a sound responsive diaphragm peripherally mounted in spaced
relation outward of the circuit board,
structure mechanically coupling the diaphragm to the free end of
the element for driving the same,
and an amplifying circuit including circuit components mounted on
the circuit board and printed circuit connections on at least one
board face interconnecting the components with said mounting
surface and spring clip to supply the output of the element as
input to the amplifying circuit.
2. A microphone and amplifier unit as defined in claim 1, and
including also
a substantially rigid perforated baffle plate peripherally mounted
on the housing between the diaphragm and circuit board with a
central clearance aperture for said coupling structure,
and air pervious fabric covering the perforations of the baffle
plate for damping the diaphragm movement.
3. A microphone and amplifier unit, comprising in combination
a generally cylindrical housing, open at one end to receive sound
energy,
a circuit board mounted transversely of the housing and having an
outwardly opening central cavity,
an elongated piezoelectric element responsive to bending stresses
and having two opposite conductive output faces,
structure mounting the element on the circuit board with a free end
extending unsupported over the cavity,
a sound responsive diaphragm peripherally mounted in spaced
relation outward of the circuit board,
a substantially rigid perforated baffle plate peripherally mounted
between the diaphragm and the circuit board and having a central
clearance aperture,
structure extending in spaced relation through said clearance
aperture for mechanically coupling the diaphragm to the free end of
the element to drive the same,
and an amplifying circuit including circuit components mounted on
the circuit board and printed circuit connections on at least one
board face interconnecting the components and cooperating with the
element mounting structure to supply the output of the element as
input to the amplifying circuit.
Description
This invention has to do with microphone cartridges, and relates
more particularly to improved structure for incorporating
amplification circuitry within a microphone cartridge.
A primary object of the invention is to permit essentially unitary
mounting of the amplifying circuitry as a part of the microphone
structure, thereby reducing the required number of parts,
simplifying assembly, and improving both performance and
reliability.
The microphone structure of the invention further provides
particularly effective and economical damping of the diaphragm
movement, and facilitates effective protection of the entire
microphone structure from external conditions such as dampness.
A full understanding of the invention, and of its further objects
and advantages, will be had from the following description of an
illustrative structure for carrying it out. The particulars of that
description, and of the accompanying drawings which form part of
it, are intended only as illustration and not as a limitation upon
the scope of the invention, which is defined in the appended
claims.
In the drawings:
FIG. 1 is a front elevation of a microphone unit illustrating the
invention;
FIG. 2 is a section at enlarged scale on line 2--2 of FIG. 1;
FIG. 3 is a detail section on line 3--3 of FIG. 2;
FIG. 4 is a rear elevation, partially broken away;
FIG. 5 is a fragmentary section on line 5--5 of FIG. 2, at an
intermediate scale; and
FIG. 6 is a schematic diagram representing illustrative
circuitry.
The illustrative microphone unit shown in the drawings comprises a
housing 10 of generally cylindrical form, closed at its rear end by
the wall 12 and open at its front end at the circular edge 13. The
housing wall is deformed inwardly at two diametrically opposite
sectors, forming internal shelf structures 14 which face toward the
open end of the housing, and also forming the external recesses 16.
The disk 20 of dielectric material is mounted on the two shelf
formations 14 by the eyelets 22 and 23, which also serve to mount
external terminal lugs 24 and 25 in the respective recesses 16 and
to connect them electrically to internal circuit structure to be
more fully described. The plastic bushings 27 insulate eyelets 22
from the housing, which is typically a unitary metal die casting.
Disk 20 is thick enough to be substantially rigid, and forms with
housing end wall 12 a chamber 26. The central apertures 18 and 28
in housing wall 12 and disk 20, respectively, are covered by the
pads 19 and 29 which breathe sufficiently to equalize atmospheric
pressure, while sealing chamber 26 acoustically and against foreign
matter. In addition, aperture 28 and pad 29, form an acoustic
resistance, and are of utility in shaping and controlling frequency
response of the microphone. A suitable material for those pads is
the synthetic unwoven fabric sold under the tradename Viskon.
The sound responsive diaphragm 30 is slightly conical and is
mounted against the front edge of the housing and is cemented
thereto with a suitable adhesive. The diaphragm and forward portion
of the housing are covered by the thin flexible membrane 32, formed
of a suitable plastic, which provides a substantially moisture
impermeable barrier for the protection of the entire internal
structure of the microphone. The diaphragm and moisture barrier are
clamped firmly in place by the gasket 34 and the metal grille 36,
the periphery of which is of cup form and grips the external
housing flange 35.
The rigid metal baffle 40 is of shallow conical form, closely
matching the shape of the diaphragm, and is mounted inward of the
diaphragm in parallel and closely spaced relation. Baffle 40 is
seated on the internal housing flange 41 and is retained by
adhesive 43. It is generously perforated as indicated at 42. An air
pervious fabric 44, such as light silk cloth, is adhered to a face
of the baffle, covering perforations 42 and offering a selected
degree of friction to air passage through those perforations.
Diaphragm vibration in response to sound is damped by the energy
loss that accompanies air movement through the fabric. The degree
of that damping action is readily controllable by suitable
selection of such factors as the ratio of baffle perforations to
solid area, the baffle spacing from the diaphragm and the
permeability of the fabric.
The transducer proper comprises a piezoelectric ceramic element 50
of bar form with its two active longitudinal faces coated with
silver to render them conductive. Piezoelectric element 50 is of a
type that generates an electrical potential between its conductive
faces when stressed by bending. Element 50 is mounted on the front
face of disk 20, one end of the element being held effectively
rigidly and the other end projecting freely and essentially
radially into the central clearance aperture 28 of the disk. That
free end of element 50 is coupled to the center of diaphragm 30 by
the drive pin 54, which projects in spaced relation through the
central clearance aperture 46 in baffle 40. One end of pin 54 is
mounted semi-rigidly at the diaphragm apex by a drop of suitable
adhesive 55. The other end of the pin has an aperture which is
pressed with a force fit over the free end of element 50, which it
grips firmly.
The electrical output signal from transducer element 50 is
amplified by a suitable solid state amplification circuit
incorporated in the microphone cartridge. An illustrative circuit
for that purpose is shown in schematic form at 60 in FIG. 6,
comprising the two transistors Q1 and Q2, directly coupled via the
resistance R3. The amplified microphone output at terminals 24 and
25 is shunted by capacitance C1, to bypass unwanted radio frequency
energy often present when the microphone is used to modulate radio
transmitters. The dashed lines 72 in FIG. 6 represent a flexible
cable connecting the microphone cartridge output terminals 24 and
25 to the remainder of the electrical system. That system includes
a power supply, indicated in schematic and illustrative form at 70.
A direct current power source is indicated at B, with the
resistance R6, which acts as load impedance for transistor Q2. The
terminals 74 and 75 supply the microphone output to further
amplification circuitry, forming part of the system remote from the
microphone cartridge and typically of conventional design.
In accordance with one aspect of the present invention,
amplification circuitry 60 is constructed as a self-contained unit
mounted on disk 20, already described, and including printed
circuit connective elements formed directly on that disk as a
circuit board. Disk 20 thus serves not only as mechanical support
and electrical means of connection for transducer element 50, but
also as mounting support and essentially an integral part of the
circuitry for amplifying the output from that transducer.
In accordance with the present invention, the various circuit
components are mounted on the rear face of circuit board 20, so
that in the assembled cartridge they are contained within chamber
26. Those components are connected to form an amplifying circuit
primarily by means of a conductive coating deposited in definitely
predetermined configuration on the front face of circuit board 20,
typically utilizing known printed circuit techniques. The wire
leads originally provided on each circuit component typically
project through small holes 82 in the circuit board and are
connected to the printed circuit coating by solder. The detailed
arrangement of the components, and the exact configuration of
printed circuit elements will depend, of course, upon the selected
amplifying circuit.
An illustrative circuit arrangement is shown in somewhat
fragmentary form in FIGS. 2 and 5, where the circuit components
that are mounted behind circuit board 20 are represented in FIG. 2
by R3 and Q2, and in FIG. 5 by R2, R3, Q1 and Q2 (shown in dotted
lines), other components being omitted for clarity of illustration.
Thus, as shown in FIG. 5, for example, transistor Q1 has its
respective terminals connected to printed elements 80a, 80b and
80c, while resistor R2 is connected between elements 80c and 80e.
Printed elements 80d and 80e surround the holes in which mounting
eyelets 22 and 23 are secured, and form electrical output
connections via those eyelets to the respective output terminals 24
and 25, already described.
A particular feature of the present invention concerns the manner
of mounting ceramic piezoelectric transducer element 50. That
element is coated on its two working side faces in conventional
manner with a conductive metal film. The mounted end of element 50
rests directly on printed circuit element 80a, with one of its
coated faces making direct electrical contact with that element.
The transducer is held effectively rigidly in that position by a
spring which also makes electrical connection with the opposite
coated face of the ceramic element. As shown, that spring 90
includes two spring arms 91 which are anchored at one end and have
their opposite ends joined by the elongated bar portion 92. That
bar is longitudinally corrugated to make it effectively rigid. The
center of the corrugation rests on the ceramic element, securely
clamping it to the circuit board and in reliable electrical contact
with printed surface element 80a. The two anchored spring ends 91
rest directly on printed circuit element 80b and are secured by the
eyelets 94, maintaining reliable electrical contact between the
ceramic element and the circuit component Q1, for example.
In assembling the described structure, the entire amplifying
circuit 60 is mounted on circuit board 20 together with transducer
element 50, clamping spring 90 and driving pin 54. The electrical
system can then be tested as a unit to any desired extent before
mounting the circuit board in the housing. The circuit board
assembly is mounted in the housing, secured by eyelets 22 and 23
and sealed around its periphery with suitable sealant 93.
Baffle 40 is then installed and diaphragm 30 is added, with pin 54
projecting through a small clearance hole at the center of the
diaphragm. Only then is the pin coupled to the diaphragm by
adhesive 55. That procedure relieves axial tolerances and insures
unstrained equilibrium position of the moving parts.
* * * * *