JP4674138B2 - Airflow modulation speaker - Google Patents

Description

  The present invention relates to an airflow modulation speaker that converts an audio signal into an acoustic output by modulating the generated airflow according to an input audio signal.

ただしρａは空気の密度、Ｓは放射体の実効面積、ｒは観測点までの距離、ｋは波定数である。またスピーカは理想的な全指向性と仮定している。 In the conventional dynamic speaker, the lowest reproducible frequency is restricted by the resonance frequency of the vibration system. This point will be explained in detail. The complex effective value of the output sound pressure of the direct radiation type speaker that emits a sine wave signal of the angular frequency ω is converted into the conversion principle when the effective value of the vibration velocity of the radiator is V. Regardless, it is given by the following equation.
(Equation 1)

Where ρa is the air density, S is the effective area of the radiator, r is the distance to the observation point, and k is the wave constant. The speaker is assumed to be ideally omnidirectional.

  From this equation, it can be seen that ωV (vibration acceleration) should be constant regardless of the frequency in order to realize a flat frequency response. Since a normal vibration system is a single resonance system composed of a mass and a spring, this can be achieved by setting the resonance frequency (so-called F-zero) as low as possible and using the mass control region. In particular, for the low frequency range, it is necessary to increase the mass or soften the spring. However, there are limitations in both cases, and there are many advantages if a "low frequency range speaker without F-zero limitation" is realized. Is considered.

  As a method for fundamentally solving this problem, it is desirable to use a radiator that can completely control the vibration characteristics and realize the above characteristics by electrical control. However, since the electrodynamic and electromagnetic transducers used in conventional speakers are driven by a remote operation of electromagnetic force, it is difficult to increase the drive mechanical impedance. On the other hand, a piezoelectric / electrostrictive conversion system using solid deformation has a high mechanical impedance but is difficult to operate with a large amplitude, and is not suitable for a direct radiation type low frequency speaker.

  In other words, all of the electrodynamic, electromagnetic, condenser, and piezoelectric speakers are so-called energy conversion type electroacoustic transducers that convert the input electrical energy into acoustic energy, so the conversion efficiency is 100%. There was no limit, and there was a theoretical upper limit on the conversion efficiency.

  As a means for overcoming the upper limit of the conversion efficiency as described above, there is a converter of a type that modulates the energy flow. That is, the sounding body is an airflow modulation type sounding body in which a direct airflow is prepared and this flow rate is adjusted to emit sound waves. An example of this type of converter is a siren for signal sound emission. The output acoustic energy of a small siren is much higher than that of a large speaker.

An airflow modulation speaker has been used for many years as an airflow modulation type sounding body that outputs a sound wave having an arbitrary waveform (see Patent Document 1). The difference between the airflow modulation speaker and the signal sound emitting siren is the presence of a valve that is electromagnetically driven according to the waveform of the input signal. That is, the air flow generated by the blowing means flows in from the inlet and flows out from the upper right outlet. Due to the vibration of the electromagnetically driven valve, the area of the outlet changes, and the flow rate is modulated by the signal waveform, so that a change in atmospheric pressure occurs with the outflow of the air flow, and as a result, sound waves are emitted from the horn. .
JP-A 62-62700

  By the way, such an airflow modulation type speaker has a very high output volume, such as a sound wave exposure test of a rocket or an aircraft body, a broadcast on the deck of an aircraft carrier, and a sound wave to an enemy military base several kilometers away. However, as you can see from the principle, it started with a constant air flow and required a large compressor and air tank to operate stably. Also, in order to handle such a high-speed fluid, it was easy to carry a wide-range background noise. Therefore, such a conventional airflow modulation speaker is not suitable for practical use.

  The present invention solves the above-described problems, and its object is to realize a radiator whose vibration characteristics are electrically controlled, and to freely set the lower limit of the frequency band regardless of the resonance characteristics of the vibration system. An object of the present invention is to provide a compact and compact airflow modulation speaker that can be controlled.

In order to achieve the above object, the invention of claim 1 includes an ultrasonic motor and a rotor that rotates by driving the ultrasonic motor, and a plurality of fins are provided on an outer periphery or a surface of the rotor. A wind tunnel is provided so as to cover the fins, the wind tunnel covering the fins and having an air flow path formed on the inside, and the coating generated by rotation of the fins accompanying rotation of the ultrasonic motor Two rotors having a discharge port for discharging the airflow in the unit and an inlet for the airflow from the outside and having the fin on the outer periphery are provided in parallel with a common central axis. The fin provided in the child is characterized by being covered with one wind tunnel .

In the invention of claim 1 as described above, when the rotor rotates at a constant angular velocity by the rotation of the ultrasonic motor, an air flow is generated by the fins provided on the rotor, and the air inside the covering portion is formed from the inlet of the wind tunnel. Direct airflow is discharged from the outlet through the flow path. When the rotational angular velocity is changed according to the waveform of the acoustic signal, the flow rate of the direct air current is modulated, and sound waves are emitted from the outlet. The ultrasonic motor has less influence of inertia than a general electromagnetic motor, and can accurately control the rotational angular velocity at high speed. By using this, the flow rate can be changed at high speed. As described above, since the ultrasonic motor is used for the airflow modulation speaker, the structure is driven by the solid contact between the piezoelectric vibrator and the metal, so that a sufficiently high mechanical impedance can be expected. In addition, since the basic structure is a motor that rotates infinitely, it is suitable for large amplitude operation.
Further, the fins provided on the two rotors rotate in parallel at the same angular velocity, so that an air flow can be generated efficiently. Further, when the fins of the respective ultrasonic motors are rotated while maintaining a gap, the airflow can flow between the fins, so that the efficiency of airflow generation is reduced and the flow rate can be reduced. In this way, the flow rate can be freely modulated by changing the relative rotational angular velocities of the two ultrasonic motors provided in parallel in accordance with the signal waveform.

According to a second aspect of the present invention, in the first aspect of the present invention, the inflow port is provided with an acoustic resistor that provides resistance to the inflowing airflow.
According to the invention of claim 2 as described above, the relative resistance of the fins provided in the two ultrasonic motors according to claim 1 is provided by providing an acoustic resistor for the air flow at the inlet and providing resistance to the air flow. The flow rate change due to the position change can be further increased.

According to a third aspect of the present invention, in the first aspect of the present invention, the inflow port is provided with a filter including an acoustic circuit in which acoustic resistance, acoustic mass, and acoustic stiffness are controlled.
According to the invention of claim 3 as described above, the output frequency characteristics can be controlled by using, for example, a filter with an acoustic circuit similar to an automobile muffler that controls acoustic resistance, acoustic mass, and acoustic stiffness at the inlet. Can be performed.

According to a fourth aspect of the present invention, in the first aspect of the present invention, the inflow port is provided with airflow generation means for feeding an airflow into the wind tunnel.
According to the invention of claim 4 as described above, the sound output can be increased by installing the airflow generating means such as a fan at the inlet.

According to a fifth aspect of the present invention, in the invention according to any one of the first to fourth aspects, the space between the wind tunnel and the rotor is sealed.
According to the invention of claim 5 as described above, the airflow leaking from between the rotor and the wind tunnel can be reduced by sealing between the wind tunnel and the rotor.

The invention of claim 6 is the invention according to any one of claims 1 to 5 , wherein the inlet and the outlet are equal to or greater than a wavelength of a signal having the lowest frequency to be regenerated. It is cut off by a flat plate or box-shaped baffle having dimensions.
According to the invention of claim 6 as described above, in the airflow modulation speaker of the present invention, sound waves may be emitted not only from the outlet but also from the inlet, but these two sound waves are at a specific frequency. Since the phases may be opposite to each other and interfere with each other in space to deteriorate the radiation efficiency and frequency characteristics, acoustic waves between the inlet and outlet may be acoustically insulated by a baffle plate, etc. Interference can be prevented, and deterioration of radiation efficiency and frequency characteristics can be prevented.

  According to the present invention as described above, a small and compact airflow modulation speaker that realizes a radiator whose vibration characteristics are electrically controlled and can freely control the lower limit of the frequency band regardless of the resonance characteristics of the vibration system. Can be provided.

  Next, the best mode for carrying out the voice console of the present invention (hereinafter referred to as “the present embodiment”) will be described with reference to the drawings. Note that the same preconditions as those already described in the background art and issues are not repeated.

(1) Reference example [configuration]
The airflow modulation speaker of this reference example is configured using an ultrasonic motor. The basic configuration will be described with reference to FIG. 1. The airflow modulation speaker 1 of this reference example is provided with fins 2 for airflow control on the outer periphery of a rotor 5 fixed to the shaft of the ultrasonic motor 4. Is covered by a wind tunnel 3 from both sides.

  Here, the principle and configuration of the ultrasonic motor will be described. As shown in FIG. 2A, the ultrasonic motor 4 includes a circular rotor 4a made of a hard material such as metal, and a circular rotor 4a made of a piezoelectric ceramic material and in contact with the rotor 4a with an appropriate pressing force. And a stator 4b. The stator 4b is provided with a number of grooves in a direction perpendicular to the circumference as shown in the figure, and the stator 4b is in contact with the rotor 4a at the convex portions of the grooves. When an AC electric signal having an appropriate frequency and voltage is applied to the stator 4b, a bending vibration wave as shown in FIG. 5B is generated and propagates along the circumference. At this time, since the convex portion of the stator performs a minute circular motion, the rotor in contact therewith rotates in the circumferential direction. The angular velocity of this rotation is controlled by changing the voltage and frequency of the input electrical signal.

  A plurality of fins 2 (14 in the drawing) are provided in a square shape around the rotor 5 and radially about the axis of the rotor 5. The wind tunnel 3 includes a covering portion 3a that covers the periphery of the fin 2 and an inflow port 3c and an outflow port 3d through which air flows into or out of the covering portion 3a. The inflow port 3c and the outflow port 3d are cylindrical and are provided so as to protrude in parallel from the covering portion 3a.

  The covering portion 3a has a donut shape and forms an air flow path 3b formed of a concave groove on the side where the rotor 5 is accommodated. As shown in FIG. 3B, the gap between the inner wall of the air flow path 3b and the fins 2 accommodated in the air flow path 3b is formed to be as small as manufacturing accuracy permits. In the figure, for convenience of explanation, the wind tunnel 3 is represented by the minimum necessary size, but it is also possible to cover the fins 2 and the rotor 5 with the structure of the wind tunnel 3 to reduce airflow leakage. It is. Details will be described later.

[Function and effect]
The operation of the airflow modulation speaker of the present reference example configured as described above will be described with reference to FIG. When the rotor 5 fixed to the shaft of the ultrasonic motor 4 rotates at a constant angular velocity, an air flow is generated by the fins 2 provided on the rotor 5 and passes through the air flow path 3 of the covering portion 3a from the inlet 3c. Then, the direct airflow is discharged from the outlet 3d.

  When the rotational angular velocity is changed according to the waveform of the acoustic signal, the flow rate of the direct air current is modulated, and sound waves are emitted from the outlet 3d. As described above, the characteristic of the ultrasonic motor 4 is, for example, a general electromagnetic motor as shown in FIG. 4 that shows the relationship between the DC voltage measured in the ultrasonic motor of a commercial product (USR60E3 manufactured by Shinsei Kogyo Co., Ltd.) Compared to the above, the influence of inertia is small and the rotational angular velocity can be controlled accurately at high speed, and this can be used to change the flow rate at high speed.

  Here, the major feature of ultrasonic motors is that the mechanical impedance of the drive part is extremely large compared to the mechanical impedance of the mass of the rotor compared to a general electromagnetic motor because the rotation is driven by deformation of a solid solid. Therefore, since there is little free rotation due to inertia, the rotational speed can be accurately controlled by changing the electric input. A drawback of the early ultrasonic motors was that noise was generated with the rotation, but the noise was greatly reduced by recent technological advances, and it became applicable to acoustic equipment.

  By using an ultrasonic motor having such a characteristic for an airflow modulation speaker, a structure that is driven by a solid contact between a piezoelectric vibrating body and a metal can be used, and a sufficiently high mechanical impedance can be expected. In addition, since the basic structure is a motor that rotates infinitely, it is considered suitable for large amplitude operation.

  In general, the most conceivable configuration for an acoustic device using an ultrasonic motor is to connect a rod to the outer periphery of the ultrasonic motor or a position close to it, and connect the other end of the rod to a diaphragm such as a cone. Is reciprocally rotated to emit sound waves from the diaphragm. However, with this structure, the ultrasonic motor repeats the operations of forward rotation, stationary, reverse rotation, and stationary at an early cycle. Since the dynamic friction force when the rotor is moving and the static friction force when the rotor is stationary are different in magnitude, this structure is inherently susceptible to distortion of the vibration waveform. Ingenuity is needed.

(2) First embodiment
The airflow modulation speaker 10 according to the first embodiment is obtained by improving the configuration of the reference example . As shown in FIG. 5, the rotor 13 provided with the fins 11 and the rotor 14 provided with the fins 12 are arranged in parallel, sharing the central axis.

  In the air flow modulation speaker 10 of this embodiment configured as described above, the fins 11 and 12 provided on the two rotors 13 and 14 rotate in parallel at the same angular velocity as shown in FIG. 6 (a). As a result, airflow can be generated efficiently. Further, when the fins 11 and 12 of the respective ultrasonic motors rotate while maintaining a gap as shown in FIG. 6B, the air flow can flow between the fins 11 and 12, so the generation efficiency of the air flow is reduced. The flow rate decreases.

  Thus, if the relative rotational angular velocities of the two rotors 13 and 14 provided in parallel are changed in accordance with the signal waveform, the flow rate can be freely modulated.

(2-1) Modification 1
As a modification of the airflow modulation speaker 10 of the first embodiment as described above, an acoustic resistor 15 against the airflow is installed at the inlet 3c as shown in FIG. 7 to give resistance to the airflow. Thereby, the flow volume change by the relative position change of said fin can be increased.

  Further, instead of this acoustic resistor, it is possible to control the output frequency characteristics by using, for example, a filter by an acoustic circuit similar to an automobile muffler that controls acoustic resistance, acoustic mass, and acoustic stiffness.

(2-2) Modification 2
As another modification, as shown in FIG. 8, when an airflow generating means 16 for generating an airflow such as a fan is installed at the inlet 3c, contrary to the above description, compared to the case where fins are arranged in parallel. The flow rate increases when the fins maintain a gap. In this configuration, instead of requiring an additional device, the rotational angular velocity of the ultrasonic motor may be small. When the airflow generating means is strengthened, there is an effect of increasing the sound output.

(3) Second embodiment
The airflow modulation speaker 20 according to the second embodiment is an improvement of the wind tunnel of the first embodiment , and the wind tunnel is configured to cover the entire fins 2 and the rotor 5. The space between the wind tunnel is sealed.

More specifically, as shown in FIG. 9, the air channel 21, like the air channel 3 of the first embodiment, the left and right side air channel 21a made of the covering portion and the air flow path, the ultrasonic motor 4 It consists of a surface wind tunnel 21b covering the upper surface side and the bottom surface side.

  Thus, by covering and sealing the fins 2 and the entire rotor 5 with the wind tunnel 31, it is possible to reduce the airflow leaking from between the rotor 5 and the wind tunnel 21.

(4) Other Embodiments The present invention is not limited to the above-described embodiment, and includes other embodiments as exemplified below. In the airflow modulation speaker in the above-described embodiment, sound waves may be emitted not only from the outlet 3d but also from the inlet 3c. These two sound waves have mutually opposite phases at a specific frequency, and may interfere with each other in space to deteriorate radiation efficiency and frequency characteristics. Therefore, when the speaker of the present invention is put into practical use, it is preferable that the inlet 3c and the outlet 3d are acoustically insulated by the baffle plate 17 as shown in FIG.

  The design method of the baffle plate 17 is the same as that of a general speaker, and a flat plate having a size equivalent to or larger than the wavelength of the lowest frequency signal to be reproduced may be used. A box-shaped baffle can also be used. However, the use of an airtight box is not appropriate because of the inflow of airflow.

  Moreover, in the said embodiment, although the wind tunnel was comprised so that the inflow or outflow port of air might protrude from the coating | coated part which covers a fin in the rotation direction of a fin, this invention is not limited to such a structure. That is, as shown in FIG. 11, the wind tunnel 30 is constituted by a side wind tunnel 31 and a surface wind tunnel 32, and a notch portion is provided in a part of the front side of the side wind tunnel 31 in the figure, whereby the inlet 33, You may comprise the outflow port 34 so that it may be pinched | interposed by the surface wind tunnels 32a and 32b. By comprising in this way, the airflow modulation speaker using an ultrasonic motor can be created more simply.

  Further, in the above embodiment, the fins are all square, but if the inner wall shape of the wind tunnel covering portion is circular or polygonal, for example, the fin shape can be configured as circular or polygonal, Regardless of the shape of the inner wall of the wind tunnel, the shape is arbitrary as long as the air flow is sufficiently generated.

  Furthermore, in the said embodiment, it was set as the structure which provides a fin on the outer periphery of a rotor, However, This invention is not limited to such embodiment, The position which provides a fin with respect to a rotor can be changed arbitrarily. It is.

  For example, as shown in the airflow modulation speaker 40 of FIG. 12A, a plurality of fins 42 can be formed on the surface side of the rotor 41. In such an embodiment, when the rotor 41 is rotated by driving the ultrasonic motor 4, as shown in FIGS. 12 (a) and 12 (b), air flows from the outer peripheral portion provided with the fins 42. Direct airflow is discharged toward the outlet 43 at the bottom of the figure. At this time, by changing the rotational angular velocity of the ultrasonic motor 4 according to the waveform of the acoustic signal, the flow rate of the direct air current is modulated, and sound waves are emitted from the outlet 43.

  Moreover, in the said embodiment, although it is supposed that a fin is provided in the rotor comprised separately from the ultrasonic motor, in the airflow modulation speaker of this invention, an ultrasonic motor main body is regarded as a rotor, and a fin is provided in this. It is also possible to configure. That is, by providing fins on the outer periphery of the cylindrical portion of the ultrasonic motor 4 shown in FIG. 1 and rotating the motor while the shaft of the ultrasonic motor 4 is fixed, the motor body rotates to rotate the fins. It is also possible to make it.

The perspective view which shows the whole structure of the airflow modulation speaker of the reference example of this invention. The figure which shows the structure of the ultrasonic motor of the reference example of this invention. The top view (a) and sectional drawing (b) which show the internal structure of the fin and wind tunnel of the airflow modulation speaker of the reference example of this invention. The graph which shows the rotation speed characteristic of the ultrasonic motor of the reference example of this invention. The perspective view which shows the whole structure of the airflow modulation | alteration speaker of the 1st Embodiment of this invention. The conceptual diagram which shows the effect | action of the fin of the airflow modulation speaker of the 1st Embodiment of this invention. The figure which shows the modification 1 of the airflow modulation | alteration speaker of the 1st Embodiment of this invention. The figure which shows the modification 2 of the airflow modulation | alteration speaker of the 1st Embodiment of this invention. The perspective view which shows the whole structure of the airflow modulation | alteration speaker of the 2nd Embodiment of this invention. The figure which shows the structure of the airflow modulation | alteration speaker of other embodiment of this invention. The perspective view which shows the structure of the airflow modulation | alteration speaker of other embodiment of this invention. The side view (a), top view (b), and perspective view (c) which show the structure of the airflow modulation | alteration speaker of other embodiment of this invention.

Explanation of symbols

1, 10, 20, 40 ... Airflow modulation speakers 2, 11, 12, 42 ... Fins 3, 21, 30 ... Wind tunnel 3a ... Cover 3b ... Air flow path 3c, 33 ... Inlet 3d, 34, 43 ... Outlet 4 ... Ultrasonic motor 4a ... Rotor 4b ... Stator 5, 13, 14, 41 ... Rotor 15 ... Acoustic resistor 16 ... Airflow generating means 17 ... Baffle plates 21a, 31 ... Side wind tunnels 21b, 32, 32a, 32b ... surface Wind tunnel

Claims (6)

An ultrasonic motor, and a rotor that rotates by driving the ultrasonic motor,
A plurality of fins are provided on the outer periphery or surface of the rotor,
A wind tunnel is provided to cover the fin,
The wind tunnel includes a covering portion that covers the fin and has an air flow path formed inside, a discharge port that discharges an airflow in the covering portion that is generated by rotation of the fin accompanying rotation of the ultrasonic motor, and an external And an inflow port through which airflow flows ,
Two rotors having the fins on the outer periphery are provided in parallel with a common central axis, and the fins provided on the two rotors are covered by one wind tunnel. Modulation speaker. The airflow modulation speaker according to claim 1 , wherein an acoustic resistor that provides resistance to the inflowing airflow is provided at the inlet . The airflow modulation speaker according to claim 1 , wherein a filter including an acoustic circuit that controls acoustic resistance, acoustic mass, and acoustic stiffness is provided at the inlet . The airflow modulation speaker according to claim 1 , wherein airflow generating means for supplying airflow into the wind tunnel is provided at the inlet . The airflow modulation speaker according to any one of claims 1 to 4 , wherein a space between the wind tunnel and the rotor is sealed. Wherein A flow inlet and the outlet, claim 1, characterized in that the flat or box-shaped baffle consisting of wavelength equal to or greater size than the wavelength of the signal of the lowest frequency to be reproduced, have been cut off 6. The airflow modulation speaker according to any one of items 1 to 5 .

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