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An improved machine-acoustic transducer is provided. A mechanical-acoustic transducer
comprises an actuator, which is at least one piezoelectric motor connected generally
perpendicularly to one edge of a diaphragm formed of thin, flexible sheet material. The
diaphragm from the actuator to the support member at a location spaced in the direction of its
movement so that the displacement of the actuator is converted mechanically to the
displacement of the diaphragm, which is typically amplified by 5 to 7 times It is fixed. The
diaphragm is slightly curved in a parabolic manner. The diaphragm can be mounted on the frame
of the display screen if it is formed in an optically transparent state and can be used as a screen
speaker. The actuator is fixed at one end to the frame and the other, movable end is fixed to the
end of the diaphragm in a substantially vertical direction. A gasket is sealed to the edge of the
diaphragm to maintain the pressure gradient of the diaphragm. [Selected figure] Figure 1
Machine-acoustic transducer and multimedia flat film speaker
The present invention relates to a transducer (or transducer) that converts mechanical energy
into acoustic energy. In particular, the invention relates, in one form, to a loudspeaker equipped
with a piezo actuator and, in another form, to a flat film speaker compatible with a display.
All acoustic transducers alternately supply air at positive and negative pressure. In the simplest
form, an electromagnetic, electrostatic or piezoelectric linear motor drives the diaphragm (or
diaphragm). The diaphragm may be configured as part of a motor.
Many (loud) speakers (hereinafter simply referred to as speakers) use an electromagnetic
transducer (or an electromagnetic transducer). As for dynamic speakers, they have not changed
substantially since the 1920s. Electromagnetic motors have (relatively) long linear movements.
This feature is necessary for relatively small and rigid diaphragms (in a "piston-like" manner, as
the term is used in this field) the (relatively) long displacement (or deflection) necessary for the
generation of sound Used to wake up However, this operation has the disadvantage of being
inefficient at relatively long distances.
Electrostatic or piezoelectric devices have excellent electromechanical coupling efficiency for
dynamic speakers. These devices theoretically have high efficiency, but have been limited due to
their relatively short linear transitions, and have been used only in limited areas for a long time.
In the case of electrostatics, structures for very large diaphragms of the order of a few tens of
centimeters (or more than a meter) are required on both sides in order to cause the necessary
acoustical transitions. Alternatively, in order to make them of practical size, their operation must
be limited to the operation of the high frequency part, which does not require a long transition.
Piezoelectrics have the highest efficiency but are considered dedicated to high frequencies due to
their relatively small size and limited displacement.
Accordingly, the object of the present invention is to provide a new class of mechanical-acoustic
transducers. The converter according to the invention can utilize all the actuators described
above, but in particular the high efficiency, short linear displacement of a piezoelectric motor (or
piezo motor), like a piston of a diaphragm (or comparable to that) It is suitable for converting
into a large transition. Another object of the present invention is to provide a flat film type
speaker for a monitor for a television or computer, which can see the display through the
The machine-acoustic transducer according to the invention is preferably a piezomotor (or
piezomotor) coupled to a thin, (relatively) hard and flexible (or flexible) diaphragm. There is at
least one actuator (or actuator). The diaphragm is fixed (to the support member) at a point (or
place) away from the junction point (s) of the diaphragm and the actuator. The diaphragm, when
viewed in cross-section from the vertical direction (i.e. when viewed from the side of the
diaphragm), is the coupling point with the actuator (s) and the fixing point (s) Curved between
and. The diaphragm is formed of thin, flexible sheet material. When used as a screen speaker (ie,
a speaker disposed on the screen), the diaphragm is further formed of a transparent material.
In one form, the actuator is placed on or near a longitudinal centerline that divides the
diaphragm into two sections (to provide substantially two transducers). In order to fix the
diaphragm (whole) against movement, the edges of the diaphragm distal to the actuator are fixed.
The edges on both sides may be fixed to a frame supporting a diaphragm and a piezo bimorph
drive. A gasket (or packing) attached to the edge of the diaphragm is utilized to maintain the
pressure gradient of the device.
Each of the two sections of the diaphragm is slightly parabolically curved when viewed from a
plane perpendicular to the longitudinal axis of the diaphragm. When the piezoelectric bimorph
(or bimorph piezoelectric element) is located at the center rest position (or neutral position), one
section is convexly curved and the other section is concavely curved, as a whole, "S" It has the
shape of a mold. A DC potential may be used to minimize the hysteresis present in the
piezoelectric structure. Although hysteresis is also present in linear magnetic motors commonly
used in conventional loudspeakers, this hysteresis can not be dealt with positively (or actively) as
in the case of bimorphs. Placing the actuator at the center point of the "S" curve cancels the
asymmetry between the positive and negative transitions of the diaphragm and responds to the
drive's substantially linear lateral shift. There is a substantially linear effective (longitudinal)
displacement of the diaphragm.
An actuator convenient for use in the speaker of the present invention is an actuator
characterized by a large force (strong) and a short displacement (short displacement). Also, the
diaphragm of the speaker of the present invention is characterized by a piston-like, large
displacement (long displacement). A typical amplification device, or mechanical lever, of the
present invention doubles the transition 5 to 7 times. Also, in one embodiment of the present
invention, a plurality of longitudinally disposed actuators may drive corresponding portions of
the longitudinally disposed diaphragms. In another form, the actuator is fixed to one of the
lateral edges of the diaphragm.
In another form of the invention, the invention uses a thin sheet diaphragm of (relatively) hard,
transparent material mounted on a display such as a television or computer monitor. In the
preferred form, the sheet is formed by two longitudinal sections each having three free ends at
the top, bottom and sides, or a longitudinal centerline or the like, to form "feathers" Along the
vicinity (as preferred, at the upper or lower edge of the sheet), it can be mechanically (pinned etc)
clamped or fixed with an adhesive. Linear actuators are preferred: the lateral ends of both wings
of the diaphragm are operatively enabled by adhering the free end of the actuator to the edge of
the adjacent diaphragm with an adhesive or the like Approximately vertically.
The linear lateral movement of each actuator increases or decreases the slight curvature of the
corresponding wing. Curvature preferably has a parabolic curvature (e.g., when viewed in a plane
perpendicular to a vertical axis, such as a clamped center line). A typical diaphragm of the
present invention has a "radius" of about 1 meter (when the parabola is approximated by a
The actuator is an electro-mechanical type such as an electromagnetic type, a piezoelectric type,
or an electrostatic type. The use of a piezoelectric actuator is particularly preferred as it does not
generate a magnetic field that would interfere with the image of the display. For loudspeaker
applications, the actuators are usually of the type of high power (strong), short displacement
(short displacement). The loudspeaker of the invention converts this movement of the actuator
into a movement of a diaphragm with low pressure and increased displacement (long
displacement). A layer of polarizing material may be bonded to the sheet to control the glare of
the screen, or other well known processes on the surface of the diaphragm to produce an optical
effect to reduce glare. May be applied or shaped.
These and other features and objects of the present invention will be understood by reference to
the following detailed description in conjunction with the accompanying drawings.
Figures 1-6 show an embodiment of a first type of a mechanical-acoustic transducer 10
according to the invention, which is particularly suitable for loudspeaker applications.
The transducer 10 has a large force (hereinafter referred to as strong) and a short linear
transition (hereinafter referred to as short transition) driving mechanism of the actuator 12 and
an increased large displacement of the diaphragm 14 (hereinafter referred to as , Called longdisplacement), has the ability to convert into piston-like motion. As used herein, the term "strong"
means being at least an order of magnitude more powerful than the driving force of a
conventional speaker. The difference in force is typically on the order of 40: 1. The typical
motion amplifier (or vibration amplifier) provided by the present invention increases the
displacement by a factor of 5 to 7.
The drive mechanism or actuator 12 suitable for the present invention is a piezoelectric bimorph
(or bimorph piezoelectric). For the loudspeaker of FIGS. 1-6, the presently preferred piezoelectric
bimorph drive is the piezoelectric bimorph drive sold by Piezo Systems Inc (Cambridge Mass.)
Under Part No. # 58-S4-ENH. As shown in FIG. 1, the drive 12 is coupled to both sides of a
central substrate 28 of brass, kevlar, or other material, with conductive coatings 20, 22, 24, 26
on both sides. Is a substantially seven-layer device consisting of layers of "wafer (or flakes)" 16,
18 of piezoelectric material with. The substrate has a certain degree of elasticity. The substrate
can also be used as a buffer and, when in an isolated state, as a capacitive insert material, whose
properties can be used to adjust the frequency response of the drive.
The piezoelectric wafers 16, 18 expand or contract in the X-axis direction (generally aligned or
generally parallel to the vertical axis 30 and the planar direction of the wafer), as best seen in
FIG. The coatings 20, 22, 24, 26 are wired out of phase with one another so that the polarity is
reversed for any voltage. As a result, one of the wafers 16, 18 expands and the other contracts.
Therefore, the final bending motion D is much larger than that of the piezoelectric wafer alone.
At 60 volts, the bimorph described above has a displacement of 0.3 mm, corresponding to 1.09
watts at 500 Hz.
The piezoelectric bimorph 12 undergoing electrical stimulation (or excitation) causes positive
and negative motion along the X-axis direction, and the curvature and return of the diaphragm
14 causes positive and negative along the Y-axis. Resulting in a piston-like transition (see Figures
1 and 5). FIG. 2 shows the half cycle operation of the rightward shift. Because the actuator 12 is
fixed at one end, movement along this X axis produces mechanical leverage when it is driven.
The diaphragm is a thin, flexible sheet formed in a parabolic curved section. The diaphragm may
be a Young's modulus material (including plastics such as Kapton (polyamide-imide),
polycarbonate, polyvinylidene fluoride (PVDF), polypropylene, or blends of similar polymers (ie,
mixtures and compounds) Young's Modulus material) materials with optical properties such as
triacetate and tempered glass; titanium, or other flexible metals; fibers containing resins, or any
other compound or compound Good.
The relationships described below affect the efficiency and frequency response of the converter.
The displacement (efficiency) for any input is proportional to the radius of curvature of the
diaphragm. The asymmetry between positive and negative transitions is proportional to the
radius of curvature of the diaphragm. The resonance of the high frequency (maximum value of
the acoustic output) is inversely proportional to the radius of curvature of the diaphragm. The
resonance of high frequency is proportional to the Young's modulus of the material of the
diaphragm. The high frequency resonance is inversely proportional to the weight (or size) of the
The asymmetry between positive and negative transitions is canceled by driving the two
diaphragms 14a, 14b by a single piezoelectric bimorph actuator disposed between them, and the
output of acoustic energy is doubled. As shown in FIG. 3, one diaphragm 14a is in a convexly
curved state, and the other is in a concave state. This is substantially the same as one diaphragm
having an "S" -shaped cross section in which the actuator 12 is mounted at the center of the
diaphragm. However, the diaphragm 14 may be formed as two separate portions 14a, 14b, with
the edge of each side adjacent to each other being coupled to one actuator 12 and driven by the
actuator 12.
A single (relatively) large bimorph 12 extending in the "height" (or "longitudinal") direction of the
diaphragm may be used to drive the loudspeakers, as shown in FIG. As such, a plurality of
actuators 12a, 12b, 12c, each driven by a frequency response with different contours, may be
utilized to form a three dimensional output of the speaker 10. For example, a high frequency
signal may be supplied exclusively to one or more actuators. The regions of the diaphragm
coupled to these actuators control the acoustic output and radiation pattern (or directivity)
assigned for the high frequency region.
An audio amplifier driving a step-up transformer may be used to drive the speaker 10 at an
appropriate voltage for the piezo crystal, or a system-specific amplifier may be designed .
Piezoelectric motors require maximum drive voltages in the range of 30 to 120 volts, depending
on the chosen piezoelectric material and wiring method. FIG. 18 shows a speaker drive circuit 70
utilizing a conventional notch filter 73 operatively connected to an audio amplifier 72. The
output of the audio amplifier 72 is connected in series to a step-up transformer 74 which drives
the speaker 10 via a resistor 76.
The resistor 76 may be connected to the “front” of the transformer 74 or may be connected to
the “rear”. The resistance controls the roll off of the audio response. By increasing the
resistance, the frequency at which roll-off occurs is reduced. The active filter is a conventional,
first order band rejection "notch" filter. When used for the test converter described below, the
filter has a Q value of 2.8 to 3.0 and a down dB of 13. As shown in FIG. 18, a resistor 76 is placed
in front of the converter. An alternative arrangement after the converter is shown in dotted lines.
The transducers 10, 10 ', 10' 'are shown together with a capacitor C. That is, C indicates that the
piezoelectric actuator actually has a capacitance and exhibits a capacitive impedance as a load to
the drive circuit. As will be described in detail later, the transducer also exhibits substantially
acoustic "capacitance" and exhibits acoustic "inductance" when used with the enclosure (or in a
container). Boost transformers for acoustic systems are well known and relatively inexpensive.
However, the characteristics can also be further improved by connecting a dedicated amplifier
with an output adjusted to the load to the input of the speaker without using a separate
Low density expanded closed closed cell foam rubber or similar material gasket (or packing)
along the perimeter of the side of the diaphragm to maintain the integrity of the pressure
gradient of the system 35, 35 are inserted (see FIG. 3). In an alternative embodiment, as shown in
FIG. 17, this edge seal is a very thin, very flexible, closed-cell foam tape (with an adhesive layer
on the outside) Alternatively, it may be a piece. The tape (or strips) may extend along the slightly
curved edges of the diaphragm or may be affixed to all four sides of the diaphragm.
A DC bias may be provided to the piezoelectric bimorph to reduce hysteresis at low signal levels.
Providing a bias to a magnetic speaker is quite difficult. Also, all electrostatic speakers are
designed in this manner.
An actuator 12 made by the method described in conjunction with FIGS. 1-6, for example (but
not limited to) 5 cm high, 13 cm long (along the "longitudinal" axis 30), and 0.5 cm The actuator
with a curved diaphragm of height (FIG. 5) has an output of 105 dB at 1 m, 450 Hz, 1 watt. This
is very effective. The average coil mobile speaker has an efficiency in the range of 85 to 95 dB at
1 W / 1 m.
Figures 7-8 illustrate an alternative form of the present invention. The loudspeaker 10 'is shown
as a loudspeaker with a single curved diaphragm, with a single drive at each end for a specific
purpose. (In the embodiment of FIGS. 7-8, elements similar to the components of FIGS. 1-6 are
indicated by the same reference numerals with '. The converter 10 'is configured to be mounted
on a display screen, such as a television or computer monitor.
In the embodiment of FIGS. 7-8, the speaker diaphragm 14 'is comprised of a slightly curved
sheet of optically clear plastic. The plastic sheet 14 'is supported on a thin frame disposed on the
front of the display screen (not shown). The frame may be removably mounted on the screen,
may be semi-permanently retrofitted to an existing display (eg, a computer monitor, etc.), or may
be semi-permanently incorporated into the display . For permanent installation, a conventional
monitor may be provided with an integrally molded peripheral flange (or rim) for mounting the
transducer 10 ', which protrudes forward from the screen.
The visual display on the screen can be viewed through the speakers. Furthermore, in the case of
a diaphragm configuration with two sections, which will be described in detail later, the sounds
may be output independently of each other from the left and right of the "speaker-screen". Thus,
they can essentially comprise two transducers and two speakers in one frame and can carry
stereo or multi-channel audio. The sound seems to be emitted directly from the visual sound
The transducer 10 'of the present invention operates substantially in the frequency range of
human voice and beyond (100-20 KHz). The heavy low band may be added by an independent
subwoofer (or a speaker dedicated to low band) as implemented in common audio systems. The
transducer 10 'emits speech as a linear or planar sound source. This directly conveys the sound
to the user in a controlled manner, suppressing reflections from the desktop and nearby walls,
and virtually eliminating reflections from the screen since the speaker is the screen. The reflected
acoustic energy degrades the characteristics of the speaker system and perplexes and perturbs
human hearing. The present invention eliminates the desktop speakers (boxes) of the computer
system, reduces the desktop and increases the available desktop space. Also, the transducer 10
'is a substantially invisible speaker.
Describing in detail with respect to the operation and structure of the converter 10 ', the
diaphragm 14' is thin and rigid, such as a sheet of tempered glass bonded to a polarizing film
made of polycarbonate, triacetate, or plastic. It may be a flexible, optical sheet with plastic
properties and a combination of speakers and computer screen filters. As an example (although it
is not a limitation), the diaphragm may be about 300 mm × 400 mm, or may have the same size
as the corresponding display screen. The diaphragm has a slightly curved shape (or parallel to
the parabola) that is vertically aligned (or parallel to the parabola) with a "radius" of
approximately 1 meter (when approximated as a circle) It may be formed.
The diaphragm 14 'made of a plastic sheet may be mechanically fastened (by pins or the like)
along the upper and lower portions of the diaphragm on the "longitudinal" center line of the
speaker frame, or it may be bonded It may be done. (The term "longitudinal centerline" as used
herein does not necessarily mean exactly at the center, but at or near the center, and in certain
applications, the left and right sections of the diaphragm may be of different sizes. In some cases,
the center line may be a line off center. The fixation of this central part forms two independent
"feathers" of the diaphragm 14 ', which can move independently, forming the left and right
sections 14a' of the loudspeaker. The longitudinally extending free ends of the sides of these
diaphragm sections 14a 'are longitudinally disposed (or longitudinally extending) on the left and
right longitudinally extending members of the speaker frame Attached to one or more
electromechanical actuators 12 '.
Because the actuators 12 'move (or shift) laterally and are connected to the section 14a' of the
diaphragm, they increase and decrease the curvature of the diaphragm, and the diaphragm
section 14a ' Increase and decrease the (longitudinal) displacement. A small rightward movement
of the actuator 12 'on the left speaker panel causes the diaphragm to bulge forward and a
positive pressure from the speaker; a leftward movement of the actuator produces a negative
pressure. The actuator may be of any type of electro-mechanical, including, for example,
electromagnetic, piezoelectric, electrostatic and the like. However, in this application,
piezoelectric is preferred because it does not generate a magnetic field that distorts the display
screen. Bonding of the diaphragm and the actuator is preferably a method of adhering the edge
of the diaphragm adjacent to the end face of the actuator substantially perpendicularly (with
respect to the actuator) by means of an adhesive.
Figures 9-9B and 13-17 illustrate another preferred embodiment of the present invention. The
screen speaker (or screen speaker) 10 'or 10' 'is FACE International Corp. Use a piezoelectric
motor 12 '' of the type sold under the name "Thunder" actuator. (Similar elements to those in
FIGS. 1-8 are indicated by the same reference numerals with '. ) As shown in FIG. 9, this motor
uses a single layer 16 '' of piezoelectric material sandwiched by two thin metal strips 28a '', 28b
'', 'bender (or Act as The larger layer 28b ′ ′ is preferably a thin sheet of stainless steel and the
smaller layer 28a ′ ′ is a sheet of aluminum.
As can be seen from the side view of FIG. 9B, the stainless steel 28b ′ ′, ie, the actuator, is
slightly concave. The structure is bonded in a slightly curved, pre-stressed state by means of two
adhesive layers 27 (see FIG. 9B). The "Thunder" actuator has the same degree of displacement
capability as the bimorph actuator described in conjunction with FIGS. 1-5.
This actuator also has characteristics that make it suitable for this application that is not present
in bimorphs. First, since the piezoelectric wafer 16 '' is surrounded on both sides by metal (layers
28a '', 28b ''), the overall structure is very robust and may break during use or micro cracks Less
likely to occur. In addition, the fundamental resonance frequency of the actuator itself is very
high, usually 3,000 Hz or more. While the conventional piezoelectric devices operate near the
resonant frequency, this preferred form of the invention mainly operates at frequencies lower
than this resonant frequency. This brings great advantages, as described below.
In the motor structure 12 ′ ′, there is no resonance or harmonic vibration between about
3,000 Hz and direct current (0 Hz). In this range, the device is completely controlled and
operates by its compliance, as in the "exemplary" monotonic transducer, since there are no
resonant modes. Mechanically, it resembles a diving board. The compliance is "low", ie, so low
that it produces a resonance of about 3,000 Hz when connected to the weight of the diaphragm
being driven.
When the frequency advances to the high frequency side, resonance occurs at about 3,000 Hz
with a Q factor of about 3 and exhibits a narrow and high peak of about 15 dB. This resonance is
audible enough that it needs to be equalized (or corrected) to the point that the system operates
satisfactorily. The equivalent (or correction) may be achieved by an active drive circuit or by
passive elements. Besides this resonant frequency, there may be a fractional or integral (or
fractional or integral multiple), spurious resonance (or quasi-resonance) of the fundamental
resonance of about 3,000 Hz. These resonances are also characterized as high Q resonances that
affect only a narrow band of frequencies, and may be mechanically damped in a manner well
known in the art.
In the preferred form described herein, this applies precisely (or carefully) to the edge of the
motor structure or the diaphragm driven by the motor a member of various viscosities or rubber
like Is achieved by It should be noted here that the explanation for the resonance is mainly given
for the motor structure. All loudspeakers, like the present invention, have resonance and
response variations related to the diaphragm moving air. The following description is directed to
a diaphragm for moving air, which also affects the present invention. In particular, the motion of
the diaphragm in the enclosed state is compared to the motion with free air and the motion of a
typical speaker.
The majority of conventional speakers operate with some type of enclosure. Otherwise, the
backward acoustic radiation is added to the forward radiation (with out of phase) to cancel the
acoustic output. The acoustic radiation in the enclosure is sealed and only energy from the front
of the diaphragm is emitted. (Various bass reflex systems, etc., where the low frequency is
increased by the pressure in the enclosure are an exception. The air in the enclosure acts as
acoustical compliance, a spring, and is similar to an electrical capacitor (or a capacitor) in series
with the drive of the speaker.
In contrast to the present invention, conventional speakers operate mainly in the upper region
above their resonant frequency, which is controlled as mass. This mass is similar to the inductor
of the electrical circuit. The combination of the acoustical inductance represented by the moving
mass of the system and the "capacitive" compliance on the acoustics of the loudspeaker
combined with the capacitance corresponding to the air in the enclosure is a second-order
highpass electronic filter Generate the acoustic equivalent of In fact, the smaller the enclosure,
the weaker the low-pass; the smaller the enclosure, the higher the "Q" value of the second-order
high pass filter, and the system response will peak before low frequency roll-off.
In the present invention, the acoustic and electrical loads are both capacitive. The present
invention takes advantage of the low compliance of the motor to control its operation. This
compliance is the mechanical equivalent of a capacitor in an electrical circuit. The driving of the
capacitive load in series with the capacitance of the air in the enclosure is the acoustic equivalent
of a simple voltage divider in an electrical analog circuit. The overall power level of all
frequencies is reduced. The final result, in practice, means that the dimensions of the box that the
speaker 10 'encloses is not substantially influenced. This simple fact is of commercial importance
in terms of space, utilization, miniaturization, adaptation of screen speakers to existing products,
and frequency response and driving stability of the acoustic system. The latter two points are
described in detail below.
Care must be taken to drive capacitive loads. However, on the other hand, the converter /
speaker of the present invention is a general characterization method for ordinary loudspeakers
to match the drive to the load and obtain optimal It is not possible to categorize by an input
impedance such as 8 ohms or 4 ohms which is a common value.
The pilot converter (hereinafter referred to as the test converter) is formed of a 14 cm by 17 cm
polycarbonate sheet with a radius of 120 cm and a thickness of 0.25 mm (or 10 mils). And a
single FACE piezoelectric actuator 12 '' operatively connected thereto. The test actuator 12 has
an electrical capacitance of 9 × 10 <−9> farads. Drive circuit 70 (FIG. 18) used a 1: 19.5 stepup transformer 74 with a 6 watt output. The impedance of the lower end of the actuator (alone)
was about 156 ohms when driven at 300 Hz.
The test converter exhibited free air operation as shown in FIG. The on-axis acoustic output by
the transducer is plotted as a function of the frequency (Hz) of the drive signal. FIG. 11 actively
uses the normal first-order band-stop 'notch' filter 73 with an actuator input drive signal with a Q
value of 2.8 to 3.0 and 13 down dB Figure 11 shows the same transducer frequency response as
in Figure 10 in the filtered state; Figure 12 uses the same filter and also has a small painted
"MDF" with dimensions of about 33 cm (length) x 25 cm (width) x 2.5 cm (height) or 2100 cm
<3> Figure 11 shows the same transducer frequency response as in Figures 10 and 11 as
mounted within a (medium density fiberboard wood) enclosure.
At the top of the speaker's frequency spectrum, eg, at 20 KHz, the impedance of the test actuator
alone drops to about 2.5 ohms, making it somewhat less likely to destabilize or damage many
amplifiers. In the present invention, this problem is not particularly problematic by operating
below the resonance of the converter. Frequency response, alteration, and drive stabilization are
achieved together.
Above the piston area, normal or "exemplary" speakers exhibit an on-axis audio pressure
response that reaches 6 dB / octave. (The piston region is a region where the wavelength of the
sound generated on the air is about the size of the diaphragm as measured as the diameter of the
circular diaphragm. In the case of the test converter as an example of the present invention, a
response of 2,000 Hz or more reached 6 dB / octave. The diaphragm and its curvature were
chosen such that the main resonance was outside the audible area. By driving the speaker in
series with the 6 ohm resistor 76, the frequency response is corrected and the safe operating
impedance and on-axis audio pressure response shown in FIGS. 11 and 12 are obtained.
characteristic) was obtained. It should be noted that the peaks of the response at about 2,000 Hz
present in FIG. 10 are not present in FIGS.
All in all, the device of the invention acts as a transformer (or transducer) and converts the
motion of a strong, short-shift, generally linear actuator into a long-shift, low-pressure diaphragm
motion . This implies a new class or type of acoustic transducer. At long displacements of the
diaphragm, positive pressure shifts will be smaller than negative ones. That is, the system is
inherently non-linear in a strict sense. The transfer function (or transformation function) can be
calculated from the radius of curvature. A mirror transfer function can be applied to the drive
electronics at the expense of control over non-linearity.
Figures 13-17 show a frame 50 for mounting the diaphragm 14 ''. The frame can be formed from
any suitable material, such as wood used as a speaker enclosure or "MDF" (medium density
fiberboard wood). The frame may be provided with a back plate 50a forming a speaker
enclosure, or alternatively (as shown by the dotted line 50a in FIG. 15), for example a CRT such
as a computer monitor or television screen The screen may be used as a back plate and mounted
on a CRT screen. The enclosure separates the acoustical radiation to the back of the diaphragm
and acts such that only the reflection from the front of the diaphragm is emitted to the user.
When the frame is used on a CRT screen, the screen-to-diaphragm spacing is typically in the
range of about 19 to 32 mm. The diaphragm is generally planar in view, but it should be noted
that it is not completely "flat". However, the overall shape of the converter is "flat" when used as a
term for "flat" or "wall mounted" television displays and laptop computer displays used for CRT
and TV monitors using CRTs. Or “plane”.
The frame supports, at each of the side edges, two actuators 12 "which operate in the same
manner as the actuators 12" described in conjunction with FIGS. As shown, the diaphragm is
slightly curved and is supported by the support members 52 at a central point in the lateral
direction between the actuators. The support 52 is attached to the frame 50 by clamping,
adhesive, or otherwise. And, the diaphragm 14 '' is attached to the rigid (or rigid) vibration
damping layer 54 on the support 52 by a clamp or an adhesive.
The diaphragm 14 '' is preferably glued to the upper free end of the actuator. This attachment is
preferably with a notch (or notch) 90 cut into the edge of the diaphragm so that the edge of the
diaphragm is adjacent to the surface of the stainless steel strip 28b '' at the free end of the
actuator Is done. Adhesives such as cyanoacrylate glue, which are commonly used in acoustic
related applications, could be used. The attached diaphragm 14 '' operates in the manner which
has been described in conjunction with FIGS.
FIG. 17 shows a very thin, very flexible, gasket 35 ′ ′ in the form of a sticky tape or piece
formed of a closed cell foam material. The tape is placed at the edge of the diaphragm and glued
to the diaphragm and the frame to prevent acoustic energy from being emitted from the back to
the front of the diaphragm. Other sealing members, such as semi-circular foam pieces, may be
fixed or glued to the edge of the diaphragm. In theory (or ideally), the gasket 35 ′ ′ attenuates
spurious resonances from about 6 KHz or more, regardless of what shape it is.
Although the present invention has been described in conjunction with the preferred
embodiments, various changes and modifications will be apparent to those skilled in the art. For
example, as shown in the embodiment of FIG. 4, the diaphragm is separated into a plurality of
physically separated longitudinal sections, dedicated to different output bandwidths, or bands
corresponding to each section. It may be driven by a dedicated, different actuator. As noted
above, non-piezoelectric actuators could also be used, although some of the strengths described
herein may be sacrificed.
A variety of mechanical attachment mechanisms could be employed to secure the diaphragm to
the actuator and support member, including mechanical clamping, clips (or fasteners), and snap
retention devices, etc. . Furthermore, although the invention has been described with a frame
provided with fixed fasteners, it is spaced from the movement of the actuator and holds a portion
of the diaphragm statically at a point "against" to the actuator If possible, the support member
may be of any configuration or shape.
For example, the support member or the point (or location) of the fastener may be part of the
housing of a CRT display or a liquid crystal display. Although the diaphragms 14, 14 ', 14' 'have
been described in the shape of a rectangle, they may be of other shapes. However, they must
have the functional features mentioned above, and as they are mentioned above, by the action of
the actuators, when they are clamped from the actuator at a point spaced in the direction of its
movement It must be driven and mounted so that the diaphragm itself flexes and produces an
audio waveform. For most applications, the diaphragm should only be slightly curved. However,
the diaphragms could operate even though they are more curved. The above and other changes
and modifications will be apparent to those skilled in the art and will also fall within the scope of
the appended claims.
FIG. 1 is a longitudinal cross-sectional view of a strong, short-displacement piezoelectric bimorph
actuator used in the present invention. FIG. 2 is a schematic view of a converter according to the
invention connected to drive an S-shaped diaphragm using the piezoelectric bimorph shown in
FIG. 1, with the diaphragm at rest position (solid line) and to the right The curved state (dotted
line) is shown. FIG. 3 is a perspective view of the converter shown in FIG. 2 attached to a support
frame. FIG. 5 is a perspective view corresponding to FIG. 3 of an alternative embodiment. FIG. 2
is a perspective view showing a stationary position of the piezoelectric bimorph actuator shown
in FIG. 1 and a state of being curved to the left and right. Shown as a function of the linear and
lateral displacement of the actuator, the concave and convex portions of the diaphragm shown in
FIG. 2-4 and the net acoustic displacement due to their combination, substantially linear It is a
graph. FIG. 6 is a simplified schematic diagram of another embodiment of a flat screen converter
in accordance with the present invention suitable for use in combination with a display screen.
FIG. 8 is a side view of the flat screen converter shown in FIG. 7; FIG. 2 is an exploded perspective
view of each layer of a single-layer piezoelectric actuator used in the present invention. FIG. 10 is
a top view of the piezoelectric actuator shown in FIG. 9; FIG. 10 is a side view of the piezoelectric
actuator shown in FIGS. 9 and 9A. Acoustic on-axis pressure for a transducer according to the
invention using an actuator of the type shown in FIG. 9 as a function of frequency and operating
in free air It is a graph of a response. FIG. 11 is a graph corresponding to FIG. 10 of the same
transducer of FIG. 10 operated using an active electronic filter to smooth the resonance of the
system to an acoustic output. 12 is a graph corresponding to FIGS. 10 and 11 when the same
converter as in FIGS. 10 and 11 is operated in a sealed state. FIG. 1 is a perspective view of a
frame with a diaphragm attachment according to the invention. FIG. 16 is a view corresponding
to FIG. 13 showing the diaphragm shown attached to the frame shown in FIG. 13 to form a flat
screen speaker in accordance with the present invention. 15 is a detailed view of a longitudinal
cross-section taken along the line 15-15 of FIG. 14 showing the support at the center of the
diaphragm; FIG. FIG. 16 is a top view of the flat screen speaker of FIGS. 14 and 15; FIG. 17 is a
detailed view of one corner of the speaker shown in FIG. 16;
Fig. 2 is a simplified circuit diagram of a drive circuit of a loudspeaker according to the invention;
Explanation of sign
DESCRIPTION OF SYMBOLS 10 sound transducer 12 piezoelectric bimorph (bimorph
piezoelectric element) 14 diaphragm 16, 18 piezoelectric wafer 20-26 conductive coating 20
drive circuit 27 bonding layer 28 board 28a metal piece (aluminum) 28b metal piece (stainless
steel) 35 gasket Reference Signs List 50 frame 50a back plate 52 support member 54 vibration
damping layer 70 drive circuit for speaker 72 audio amplifier 73 notch filter 74 step-up
transformer 76 resistance C capacitor (capacitance exhibited by piezoelectric actuator) D
operation of piezoelectric bimorph
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