[0001] This invention relates to transducers, and more specifically to a tunable response
transducer such as a tunable response variable reluctance speaker.
[0002] Microphones having variable directional characteristics are known. There are, for
example, the devices disclosed in U.S. Patents 3,527,902 and 3,536,862. There are
also the disclosures of
U.S. Patents 3,502,811: 4,327,257; and 4,363,937.
[0003] According to the invention, a transducer comprises a frame for providing first and
second openings, a diaphragm for covering the first opening, a motor, means for coupling
the motor to the diaphragm such that actuation of the motor excites the diaphragm,
the diaphragm defining a chamber within the frame and behind the diaphragm, means
defining a passageway between the chamber and the second opening, and an adjustable
valve for selectively controlling air flow through the second opening to permit tuning
of the diaphragm's frequency response to motor actuation.
[0004] Additionally according to the invention, the transducer comprises a variable reluctance
speaker.
[0005] Further according to the invention, the motor comprises a magnet, means for mounting
the magnet in the frame, a transducer coil, means for reacting to the fields provided
by the magnet and the transducer coil to produce diaphragm movement, and means for
coupling the reacting means to the diaphragm.
[0006] Further according to the invention, the reacting means comprises a reluctor plate,
for example, a disk of ferrous material, and the means for coupling the reacting means
to the diaphragm comprises means for mounting the reluctor plate from the diaphragm.
[0007] In addition, according to an embodiment of the invention, the means for selectively
controlling the flow of air from the second opening comprises a plate covering the
second opening, means for movably mounting the plate relative to the second opening,
and means providing a port in the plate. Alignment of the port with the second opening
optimizes venting of the chamber and movement of the plate into a position in which
the port is less aligned with the second opening reduces the venting of the chamber.
[0008] According to another embodiment of the invention, the means for selectively controlling
the flow of air from the second opening comprises a plate covering the second opening,
means for movably mounting the plate relative to the second opening, and means providing
a port in the plate. A porous compressible material is captured between the frame
and the plate. The means for movably mounting the plate relative to the second opening
includes means for selectively compressing the compressible material between the second
opening and the port in the plate to control selectively the air flow between the
second opening and the port in the plate.
[0009] More specifically, according to an illustrative embodiment, the means for selectively
controlling the flow of air from the second opening comprises a first plate covering
the second opening, means for stationarily mounting the first plate over the opening,
means providing a port in the first plate, a second plate, means for movably mounting
the second plate relative to the first, and means providing a port in the second plate.
Alignment of the port in the first plate with the port in the second plate optimizes
the venting of the chamber. Movement of the second plate into a position in which
the ports in the first and second plates are less aligned reduces the venting of the
chamber.
[0010] Further according to a specific illustrated embodiment, the means for selectively
controlling the flow of air from the second opening comprises a first plate covering
the second opening, means providing a port in the first plate, a second plate, means
for movably mounting the second plate relative to the first, and means for providing
a port in the second plate. A porous compressible material is captured between the
first and second plates. The means for movably mounting the second plate relative
to the first includes means for selectively compressing the compressible material
between the first and second plates to control selectively the air flow between the
port in the first plate and the port in the second plate.
[0011] Additionally according to the invention, a method for tuning the frequency response
of a transducer comprises the steps of providing a transducer frame having first and
second openings, with the first opening covered by a diaphragm to define a cavity
behind the diaphragm and within the frame, providing a passageway between the cavity
and the second opening, providing an adjustable valve for varying selectively the
air flow through the second opening, driving the motor element of the transducer,
testing the response of the transducer, and adjusting the valve to provide the desired
frequency response.
[0012] Additionally, the method comprises the step of testing the response of the transducer
after adjusting the valve.
[0013] According to another aspect of the invention, a tuned transducer is obtained by providing
a transducer frame having first and second openings, with the first opening covered
by a diaphragm to define a cavity within the frame and behind the diaphragm, providing
a passageway between the cavity and the second opening, providing an adjustable valve
for selectively varying the air flow through the second opening, driving the motor
element of the transducer, testing the response of the transducer, and adjusting the
valve to provide the desired transducer response.
[0014] Additionally, the transducer response is again tested after adjustment of the valve.
[0015] The invention may best be understood by referring to the following description and
accompanying drawings which illustrate the invention. In the drawings:
Fig. 1 is a rear elevational view of a device constructed according to the present
invention;
Fig. 2 is a sectional side elevational view of the device of Fig. 1, taken generally
along section lines 2-2 thereof;
Fig. 3 is a rear elevational view of a device constructed according to the present
invention;
Fig. 4 is a sectional side elevational view of the device of Fig. 3, taken generally
along section lines 4-4 thereof; and
Fig. 5 illustrates in dotted line the frequency response characteristic of an untuned
transducer immediately after manufacture, and in solid line the frequency response
characteristic of the same transducer after tuning according to the method of the
present invention.
[0016] Turning now to Figs. 1 and 2, a tunable response transducer 20 includes a frame,
or basket, 22, illustratively molded from a resin. The basket 22 is generally right
circular cylindrical in configuration, and provides a front opening 24 and a rear
opening 26. Basket 22 is provided with radially outwardly extending ears 28 disposed
generally diametrically from each other. Each of ears 28 is provided with an eyelet
30 for mechanical mounting purposes, as well as to provide electrical terminations
to the components inside the basket 22.
[0017] An annular lip 32 is provided around the perimeter of rear opening 26. As best seen
in Fig. 2, the annular lip includes a rearward radially inner step 34 and a forward
radially outer step 36. Step 36 steps out to the dimension of the generally right
circular cylindrical inner wall 38 of basket 22. The rear opening 26 is covered by
two generally circular flat plates 40, 42. The diameter of plate 42 is such that it
fits within the diameter of step 34 with sufficient clearance to be rotated when force
is applied to rotate it. When no force is applied to plate 42, however, the frictional
engagement between plate 42 and step 34 is sufficient to hold plate 42 in its adjusted
position. The diameter of plate 40 is sufficient that it is stationary within the
inner wall 38.
[0018] Plate 40 serves as the pole plate for the transducer 20. Plate 40 is provided with
a plurality of ports 44, illustratively four. Plate 42 is provided with a plurality
of ports 46, also illustratively four in number. The ports 44, 46 are spaced sufficiently
close together that they all lie within the diameter of the center opening 48 provided
in a right circular cylindrical magnet 50 positioned within the inner wall 38 against
plate 40. Magnet 50 may be mounted in the basket 22 by the use of an adhesive. Plate
40 is provided with a pole piece 52 which extends generally coaxially within the center
opening 48. Pole piece 52 is generally right circular cylindrical in configuration.
A stationary coil 54 surrounds pole piece 52, and includes leads 56 which extend through
the side wall 58 of basket 22 and terminate at respective eyelets 30.
[0019] The front opening 24 is closed by a phenolic, or the like, film diaphragm 60 which
is glued or otherwise attached to the basket 22 edge surrounding the front opening
24. Although not illustrated, the diaphragm may be formed with concentric compliances
in it. A reluctor plate 62 is glued or otherwise attached to the outside surface 64
of diaphragm 60. The reluctor plate is typically constructed from a ferromagnetic
stainless steel.
[0020] Application of audio frequency voltage across eyelets 30 results in the passage of
current through the coil 54 and variation of the reluctance in the center opening
48. This results in the application of force to the reluctor plate 62, causing the
plate 62 and the diaphragm 60 to which it is coupled to react, converting the audio
frequency electrical voltage applied across eyelets 30 to acoustical energy. The cavity
66 formed behind diaphragm 60 is vented through the region of the center opening 48
radially outside the coil 54 and the ports 44, 46 to atmosphere. As best illustrated
in Fig. 1, plate 42 is provided with spanner wrench holes 68 which can be engaged
by a spanner wrench to rotate plate 42 to vary the alignment between ports 44, 46.
Alignment of the ports 44, 46 in the first and second plates 40, 42, respectively,
optimizes the venting of the cavity 66. Rotation of plate 42 into a position in which
the ports 44, 46 are less aligned reduces the venting of the cavity 66 and dampens
the response of the transducer 20 in the vicinity of the principal resonant frequency
of the moving system. A layer 70 of woven material is inserted between plates 40,
42 to enhance the tuning effect of this adjustment.
[0021] Turning now to the embodiment of Figs. 3 and 4, a tunable response transducer 120
includes a frame, or basket, 122. The basket 122 is generally right circular cylindrical
in configuration, and is provided with a front opening 124 and a rear opening 126.
Basket 122 is provided with generally diametrically disposed, radially outwardly extending
ears 128. Each of ears 128 is provided with an eyelet 130 for mechanical mounting
purposes and electrical termination.
[0022] An annular lip 132 is provided around the perimeter of rear opening 126. As best
seen in Fig. 4, the annular lip includes a rearward radially inner step 134 and a
forward radially outer step 136. Step 136 steps out to the dimension of the generally
right circular cylindrical inner wall 138 of basket 122. The rear opening 126 is covered
by two generally circular flat plates 140, 142. The diameter of plate 142 is such
that it fits within the diameter of step 134 with sufficient clearance to be moved
axially of inner wall 138 relative to plate 140. The diameter of plate 140 is sufficient
that it is maintained stationary within the inner wall 138. A screw-threaded opening
141 is provided at the center of plate 140. An unthreaded opening 143 is provided
at the center of plate 142. A layer 147 of a woven material is inserted between plates
140, 142. A screw 145 is passed through opening 143 and cloth 147, and is threaded
into opening 141.
[0023] Plate 140 serves as the pole plate for the transducer 120. Plate 140 is provided
with a plurality of ports 144, illustratively four. Plate 142 is provided with a plurality
of ports 146, also illustratively four. The ports 144, 146 are spaced sufficiently
close together that they all lie within the diameter of the center opening 148 provided
in a right circular cylindrical magnet 150 positioned within the inner wall 138 against
plate 140. Magnet 150 may be mounted in the basket 122 by the use of an adhesive.
Plate 140 is provided with a pole piece 152 which extends generally coaxially within
the center opening 148. Pole piece 152 is generally right circular cylindrical in
configuration. A stationary coil 154 surrounds pole piece 152, and includes leads
156 which extend through the side wall 158 of basket 122 and terminate at respective
eyelets 130.
[0024] The front opening 124 is closed by a phenolic, or the like, film diaphragm 160 which
is glued or otherwise attached to the basket 122 edge surrounding the front opening
124. A reluctor plate 162, typically constructed from a ferromagnetic stainless steel,
is glued or otherwise attached to the outside surface 164 of diaphragm 160.
[0025] Application of audio frequency voltage across eyelets 130, the input terminals, results
in the passage of current through the coil 154 and variation of the reluctance in
the center opening 148. This results in the application of force to the reluctor plate
162, causing the plate 162 and the diaphragm 160 to which it is coupled to react,
converting the audio frequency electrical voltage applied across eyelets 130 to acoustical
energy. The cavity 166 behind diaphragm 160 is vented through the region of the center
opening 148 radially outside the coil 154 and the ports 144, 146 to atmosphere. As
best illustrated in Fig. 4, tightening of screw 145 compresses the woven material
147. The venting of cavity 166 through ports 144, woven material 147, and ports 146
can be controlled by controlling this compression of the layer of woven material.
This permits selective tuning of the dampening of the response of transducer 120 in
the vicinity of its principal resonant frequency. Other techniques which can be used
to tune the stiffness of the transducer include, without limitation, the use of screw-adjustable
valves, and combined rotary plate port-alignment and woven layer-compression techniques.
Of course, the configuration of the ports and the types of woven materials are also
variable to achieve desired damping and tuning effects.
[0026] Referring now to Fig. 5, immediately after assembly, a device of the type illustrated
in Figs. 1-4 can have a frequency response characteristic like that illustrated in
dotted line. Testing of the frequency response of the device immediately after manufacture
yields this frequency response characteristic. The device is then tuned, illustratively
by rotation of the plate 42 with a spanner wrench (Figs. 1-2), or by loosening or
tightening of the screw 145 to reduce or increase, respectively, the compression of
the layer 147 of woven material (Figs. 3-4) until the frequency response characteristic
is "flattened" somewhat in the operative range of the transducer, to achieve a characteristic
such as that illustrated in solid line in Fig. 5. Typically, after tuning, the transducer
is tested again to ensure that its frequency response is satisfactorily flattened.
1. A transducer comprising a frame for providing first and second openings (24,26;
124,126), a diaphragm (60; 160) for covering the first opening (24; 124), a motor
(50,52,54; 150,152,154), means for coupling the motor to the diaphragm such that actuation
of the motor excites the diaphragm, the diaphragm defining a chamber (66;166) within
the frame and behind the diaphragm, characterised by means defining a passageway (48;148)
between the chamber and the second opening, and an adjustable valve (40,42,44, 46;140,142,144,146)
for selectively controlling air flow through the second opening (126).
2. A transducer according to claim 1, characterised in that the transducer comprises
a variable reluctance speaker.
3. A transducer according to claim 1 or 2, characterised in that the motor comprises
a magnet (50;150), means for mounting the magnet in the frame, a transducer coil (54;154),
means for reacting to the fields provided by the magnet and the transducer coil to
produce diaphragm movement, and means for coupling the reacting means to the diaphragm.
4. A transducer according to claim 3, characterised in that the reacting means comprises
a reluctor plate (62;162) and the means for coupling the reacting means to the diaphragm
comprises means for mounting the reluctor plate on the diaphragm.
5. A transducer according to claim 3 or 4, and further characterised by means for
mounting the transducer coil (54;154) stationarily with respect to the magnet (50;150).
6. A transducer according to any one of the preceding claims, characterised in that
the valve comprises a plate (42;142) covering the second opening, means (32;132) for
movably mounting the plate relative to the second opening and a port (46;146) in the
plate.
7. A transducer according to any one of claims 1 to 5, characterised in that the valve
comprises: a plate (142) covering the second opening; means for movably mounting the
plate relative to the second opening; a port (146) in the plate; and a porous compressible
material (147) captured between the frame and the plate (142), the means for movably
mounting the plate relative to the second opening including means (145) for selectively
compressing the compressible material (147) between the second opening and the port
(146) in the plate.
8. A transducer according to any one of claims 1 to 5, characterised in that the valve
comprises a first plate (40;140) covering the second opening, means for stationarily
mounting the first plate over the opening, means providing a port(44;144) in the first
plate, a second plate (42;l42), means (32;132) for movably mounting the second plate
relative to the first, and a port (46;146) in the second plate.
9. A transducer according to any one of claims 1 to 5, characterised in that the valve
comprises a first plate (140) covering the second opening, a port (144) in the first
plate, a second plate (142), means (143) for movably mounting the second plate (42;142)
relative to the first, a port in the second plate, a porous compressible material
captured between the first and second plates, the means (145) for movably mounting
the second plate (142) relative to the first (140) including means (145) for selectively
compressing the compressible material between the first and second plates (140,142).
10. A method for tuning the frequency response of a transducer comprising the steps
of providing a transducer frame having first and second openings (24,26; 124,126),
with the first opening (24;124) covered by a diaphragm (64;164) to define a cavity
(66;166) behind the diaphragm and within the frame, and with a passageway between
the cavity and the second opening, characterised in that an adjustable valve is provided
for varying selectively the air flow through the second opening (26;126), and further
characterised by the steps of driving the motor element (50,52,54;150,152,154) of
the transducer, testing the response of the transducer, and adjusting the valve (40,42,44,46;140,142,144,146).
11. A method according to claim 10, and further characterised by the step of again
testing the response of the transducer after adjusting the valve.
12. A tuned transducer obtained by providing a transducer frame having first and second
openings (24,26; 124,126), the first opening (24;124) covered by a diaphragm (64:164)
to define a cavity (66:166) within the frame and behind the diaphragm, providing a
passageway (48:148) between the cavity and the second opening, providing an adjustable
valve (40,42,44,46;140,142,144,146) for selectively varying the air flow through the
second opening, driving the motor element (50,52,54;150,152,154) of the transducer,
testing the response of the transducer, and adjusting the valve.