JP2008182583A - Air flow speaker - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an air flow speaker which generates high grade voice. <P>SOLUTION: The air flow speaker 1 concerning the present invention is provided with: an air flow generation means 2 for generating air flow; an air flow passage 3 through which the air flow generated by the air flow generation means 2 passes and a passage cross section changing means 4 for changing cross section of the air flow passage 3. Then, an ultrasonic motor 10 is used as a driving source of the passage cross section changing means 4 and the ultrasonic motor 10 is controlled based on a voice signal. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a speaker, and more particularly to an airflow speaker that generates sound waves by modulating an airflow having a constant flow velocity.

  In the 1930s, an “air flow speaker”, an electroacoustic transducer for the purpose of reproducing large sounds, was proposed. An airflow speaker is a speaker that generates a sound as sound by changing the flow rate of air. A generally known airflow speaker has a configuration in which an airflow having a constant flow velocity is generated by a compressor or the like, and an air valve is controlled to open and close by an electric signal. With this configuration, it is possible to modulate the air flow at a constant flow rate and obtain a desired sound wave. Initially, airflow speakers were used for broadcasting on aircraft carrier decks and sound waves to enemy sites several kilometers away, but now they are used to create a simulated sound field for rocket launch sounds. ing. The airflow speaker can obtain a large acoustic output with a small electric signal input, and is generally said to be highly efficient. Despite this high efficiency, airflow speakers were rarely made for general use due to their size, noise, and difficulty in control. Note that all of the electrodynamic, electromagnetic, capacitor, and piezoelectric direct radiation speakers widely used have a conversion efficiency of about 1%.

  As an air flow speaker, Patent Document 1 proposes an air flow speaker shown in FIG. This air flow speaker 51 includes a positive pressure or negative pressure tank into which positive or negative pressure air is fed from an air pressure source, a fixed plate 52 fixed to one of the tanks and having a number of air circulation holes 53. The movable plate 55 moves along the fixed plate 52 and has an air flow hole 54 at a position overlapping the air flow hole 53 of the fixed plate 52. And actuating means 56 for operating.

Here, in the air flow speaker 51 described in Patent Document 1, a voice coil 57 is used as a component of the operating means 56. The voice coil is a coil used for an electrodynamic speaker and is a main part for operating a cone. In an electromagnetic speaker, a voice coil is placed in an electromagnetic field, a current is passed, and electromagnetic force is generated (Fleming's left hand rule) to actuate the cone. The airflow speaker 51 of Patent Document 1 also uses this principle. Specifically, an electromagnetic field is generated by the electromagnet 58, a voice coil 57 is connected to the moving plate 55, a current is passed in accordance with an audio signal, and the moving plate 55 is vibrated. Since the air circulation hole 54 of the moving plate 55 is provided at a position overlapping with the air circulation hole 53 of the fixed plate 52, the area of the air circulation hole changes and the air flow rate changes by vibrating the moving plate 55. Sound waves can be generated.
Japanese Utility Model Publication No. 62-93898

  However, the voice coil 57 does not operate only by electromagnetic force, but actually requires a configuration for returning the moved voice coil 57 to its original position. In the airflow speaker 51 described in Patent Document 1, the leaf spring 59 plays this role. That is, since the voice coil 57 returns to the original position by the elastic force of the leaf spring 59, the speed at which the voice coil 57 returns depends on the elasticity of the leaf spring 59. Therefore, the responsiveness of the airflow speaker 51 with respect to the signal is never high. In particular, when the diaphragm 55 has a certain amount of mass as in the air flow speaker 51 described in Patent Document 1 and a frictional force with the fixed plate 52 is generated, the tendency becomes remarkable.

  A speaker with low responsiveness causes a large phase shift between input and output due to response delay. This phase shift causes a real time delay that varies depending on the frequency. As a result, the listener can hear the bass sound later than the treble sound. As described above, in the airflow speaker described in Patent Document 1, the difference in how the low sound and high sound are heard is large, and high-quality sound cannot be generated.

  Therefore, an object of the present invention is to provide an airflow speaker that generates high-quality sound.

  In order to solve the above problems, an airflow speaker according to the present invention includes an airflow generation unit that generates an airflow, an airflow passage through which the airflow generated by the airflow generation unit passes, and a passage break that changes a cross-sectional area of the airflow passage. An area changing unit, and a drive source of the passage cross-sectional area changing unit is an ultrasonic motor, and the ultrasonic motor is controlled based on an audio signal.

  Here, the ultrasonic motor is mainly composed of a stator and a rotor (in the case of a linear type, a stator and a slider). When a predetermined alternating voltage is applied to the stator, a traveling wave in the circumferential direction is generated on the surface of the stator. It is a motor that can generate and rotate the rotor (slider slider). In an ultrasonic motor, the rotor (slider) is strongly pressed against the stator, so when a voltage is applied that reverses the traveling direction of the traveling wave, the rotor (slider) responds quickly and rotates in the opposite direction ( Slide).

  According to said structure, the responsiveness of a drive system can be made high. Therefore, the cross-sectional area of the airflow passage can be instantaneously changed based on the audio signal, and the delay of the sound wave phase due to the delay of the cross-sectional area change of the airflow passage hardly occurs.

  Further, in the airflow speaker, the passage cross-sectional area modulating means includes a fixed plate and a slide plate, and the slide plate is provided so as to overlap the fixed plate, and the fixed plate and the slide Each of the plates is provided with an opening, and an overlapping portion of the opening of the fixed plate and the opening of the slide plate forms the air flow passage. The slide plate uses the ultrasonic motor as a drive source. The sectional area of the airflow passage may be changed by sliding with respect to the fixed plate and sliding the slide plate.

  According to this configuration, the cross-sectional area of the airflow passage can be changed in proportion to the sliding amount of the slide plate. Therefore, it is possible to obtain an air flow speaker in which the control of the cross-sectional area of the air flow passage is relatively simple.

  In the airflow speaker, the flow velocity of the airflow generated by the airflow generating means may be equal to or lower than the subsonic speed. In an airflow speaker, when the airflow exceeds the speed of sound, it is known that large noise unrelated to the audio signal is generated. Therefore, as in the above configuration, such noise is not generated if the speed is lower than the subsonic speed.

  The air flow speaker may further include a horn, and the horn may be disposed downstream of the passage cross-sectional area modulating means. According to such a configuration, sound is radiated in a state close to a plane wave at the horn opening, so that directivity becomes strong and the sound does not spread like a spherical wave, and the efficiency can be increased.

  The air flow speaker may further include a sound absorbing material, and the sound absorbing material may be disposed downstream and / or upstream of the passage cross-sectional area modulating means (claim 5). According to this configuration, since the sound absorbing material functions as a filter for medium and high sounds, it is possible to reduce medium and high sound noises that are unrelated to the sound signal that is likely to be generated in the airflow speaker.

  In the air flow speaker, the ultrasonic motor may be disposed in the air flow passage. According to this configuration, heat generated from the ultrasonic motor can be effectively released.

  In the air flow speaker, the ultrasonic motor may be disposed through a vibration isolating material (claim 7). According to this configuration, it is possible to reduce the influence of vibration generated by the ultrasonic motor.

  According to this invention, it can be set as a highly responsive air flow speaker. Therefore, there is almost no delay in the phase of the sound wave due to the delay in the change in the cross-sectional area of the airflow passage. Therefore, it is possible to provide an airflow speaker that generates high-quality sound with high efficiency.

  The best mode for carrying out the air flow speaker according to the present invention will be described below with reference to FIGS. In the present embodiment, a general airflow speaker is assumed. As described above, the air flow speaker can obtain a large output sound volume and has high conversion efficiency. In this embodiment, it pays attention to the high conversion efficiency among these. And it is set as the structure which reduces the noise which generate | occur | produced as a price of a high output sound volume.

  FIG. 1 is a schematic vertical cross-sectional view of an airflow speaker 1 according to the present embodiment. The airflow speaker 1 includes an airflow generation unit 2, an airflow passage 3, a passage cross-sectional area changing unit 4, a horn 5, and a sound absorbing material 6. First, the components 2 to 6 will be described, and then the passage sectional area changing means 4 will be described in more detail.

  The airflow generation means 2 has a role of generating an airflow in the airflow speaker 1. In the present embodiment, the fan 2 is used as the airflow generation means 2. As shown in FIG. 1, the fan 2 is disposed at the inlet of the airflow speaker 1, and rotates the rotor blade to take in air from the outside and generate an airflow in the airflow speaker 1. By controlling the rotational speed of the fan 1, the airflow is made constant and the airflow is free from pressure fluctuation (this airflow is referred to as “DC airflow”). The fan 1 is an existing fan and a small fan is used. Thereby, manufacturing cost can be suppressed and it can install also in a comparatively narrow place. Also, the flow velocity of the air current is set to be equal to or lower than the subsonic speed. This is to prevent noise that increases significantly when the flow velocity exceeds or exceeds the sound velocity. From this point of view, the fan need not be large. In this embodiment, the fan 2 is used as the airflow generation means 2, but a pump may be used instead.

  The airflow passage 3 is a passage for the airflow generated by the airflow generation means 2. As shown in FIG. 1, the airflow generated by the airflow generation means 2 passes through the inside of the airflow passage tube 7, and the inside of the airflow passage tube 7 constitutes a part of the airflow passage 3. In the present embodiment, the airflow passage tube 7 is linear, but the shape of the airflow passage tube 7 may be curved in consideration of the position on the inlet side and the sound generation direction. However, the airflow passage pipe 7 is configured so as not to disturb the direct current airflow generated from the airflow generation means 2 in order to prevent unnecessary sound generation unrelated to the audio signal. In this embodiment, an air tank (buffer tank) is not provided for space saving. However, if the air flow becomes a pulsating flow due to the configuration of the air flow generating means 2, the air tank is used to correct this. It may be provided. In that case, the size of the air tank should be the minimum necessary.

  The passage sectional area changing means 4 plays a role of changing the sectional area of the airflow passage 3. As shown in FIG. 1, the passage sectional area changing means 4 is located on the downstream side of the airflow passage pipe 7. The passage cross-section changing means 4 includes a fixed plate 8 and a slide plate 9 each having openings 13 and 14 (see FIGS. 2 and 3), and a portion where both the openings 13 and 14 overlap is a part of the airflow passage 3. Part. The drive source of the passage cross-sectional area changing means 4 is an ultrasonic motor 7, and the ultrasonic motor 7 is controlled based on an audio signal. The details of the passage cross-sectional area changing means 4 will be described later.

  The horn 5 has a role of radiating sound generated inside the airflow speaker 1 to the outside. As shown in FIG. 1, the horn 5 is disposed downstream of the passage cross-sectional area changing means 4 and forms an outlet portion of the airflow speaker 1. The sound radiation efficiency is enhanced by the action of the horn 5.

  The sound absorbing material 6 has a role of absorbing sound in a part of the frequency region, and is disposed downstream of the passage cross-sectional area changing unit 4. In the present embodiment, glass wool 6 having a thickness of 50 to 100 mm is used as the sound absorbing material 6. As shown in FIG. 1, the glass wool 6 is disposed so as to block the inside of the horn 5. When the glass wool 6 is made to have a certain thickness and the sound passes therethrough, a phenomenon occurs in which only middle and high sounds are reduced. Therefore, the glass wool 6 having a predetermined thickness is disposed in the downstream portion of the airflow speaker 1 to play a role as a filter for medium and high sounds that cuts medium and high sounds. As a result, it is possible to reduce middle and high-pitched noises that are likely to occur in the airflow speaker 1 regardless of the audio signal. In the present embodiment, glass wool 6 is used as the sound absorbing material 6, but other fiber shapes may be used instead, or a continuous air flow type soft foamed resin may be used. Even with this configuration, the same effect can be obtained. The continuous air flow type soft foamed resin refers to, for example, an open-cell foamed polyurethane resin. The sound absorbing material 6 may be disposed only downstream of the passage cross-sectional area changing means 4 as in the present embodiment, but may be disposed only upstream, or both downstream and upstream. It may be arranged. By disposing the sound absorbing material 6 upstream of the passage cross-sectional area changing means 4, noise released to the upstream side can be reduced and dust can be prevented from flowing into the passage cross-sectional area changing means 4. A dustproof effect can be obtained.

  The above is description of each component 2-6 of the airflow speaker 1. FIG. Next, the passage sectional area changing means 4 will be described in more detail. FIG. 2 is an enlarged view near the passage cross-sectional area changing means 4. As shown in FIG. 2, the passage cross-sectional area changing unit 4 includes a fixed plate 8, a slide plate 9, an ultrasonic motor 10, and a digital control unit 12 (see FIG. 7). Each configuration will be described below.

  The fixed plate 8 is a flat plate fixed to the airflow passage tube 7. As shown in FIG. 2, the fixing plate 8 is installed perpendicular to the axial direction of the airflow passage tube 7. FIG. 3 is a perspective view of the fixed plate 8 and the slide plate 9. As shown in FIG. 3, the fixing plate 8 is provided with a plurality of openings 13. The openings 13 are regularly arranged vertically and horizontally, and the shape thereof is a rectangle.

  The slide plate 9 is a flat plate that slides with respect to the fixed plate 8. As shown in FIG. 2, the slide plate 9 is provided below the fixed plate 8 so as to overlap the fixed plate 8. Guides 15 extending in the left-right direction are provided on the front side and the back side below the fixed plate 8. The slide plate 9 can slide along the guide 15. As shown in FIG. 3, the slide plate 9 has a smaller left and right width than the fixed plate 8 in consideration of the slide amount. The slide plate 9 is also provided with a plurality of openings 14 at positions corresponding to the openings 13 of the fixed plate 8 and has a rectangular shape. A portion where the opening 13 of the fixed plate 8 and the opening 14 of the slide plate 9 overlap forms a part of the airflow passage 3. That is, the cross-sectional area of the airflow passage 3 can be changed by sliding the slide plate 9.

  The ultrasonic motor 10 serves as a drive source for sliding the slide plate 9 with respect to the fixed plate 8. As shown in FIG. 2, the ultrasonic motor 10 is attached to the outside of the airflow passage tube 7 and in the vicinity of the slide plate 9. A connecting member 16 that is perpendicular to the rotating shaft and extends substantially parallel to the airflow is attached to the rotating shaft of the ultrasonic motor 10, and the tip of the connecting member 16 and the slide plate 9 are connected via a plate spring 24. Are connected. The ultrasonic motor 10 reciprocates within a predetermined angle range based on a drive signal described later. With this reciprocation, the connecting member 16 also reciprocates, and the slide plate 9 connected to the connecting member 16 via the leaf spring 24 also slides. Since the reciprocating motion of the connecting member 16 is a circular motion around the rotation axis of the ultrasonic motor 10, the positional relationship between the tip of the connecting member 16 and the slide plate 9 changes. Absorbed by 24 bends.

  Here, the principle of the ultrasonic motor 10 will be described. The ultrasonic motor 10 is mainly composed of a rotor 17 and a stator 18. FIG. 4 is a perspective sectional view of the rotor 17 and the stator 18. As shown in FIG. 4, both the rotor 17 and the stator 18 have a ring shape. Actually, the rotor 17 is strongly pressed against the stator 18. The upper surface of the stator 18 is provided with a groove 19 extending in the radial direction, so that the stator 19 is easily bent and deformed. A piezoelectric ceramic plate 20 is bonded to the lower surface of the stator 18. When a voltage is applied to the piezoelectric ceramic plate 20 at an ultrasonic frequency (20 kHz or higher), a standing wave (a wave repeated at the same amplitude) is generated in the stator 18 and the stator 18 is deformed as shown in FIG. . If this standing wave can be a traveling wave, the rotor 17 can be rotated. In order to make the standing wave a traveling wave, the voltage ceramic 20 is polarized up and down, and the polarization direction is reversed between positive and negative every half of the standing wave. A voltage is applied for each polarization direction. At this time, as shown in FIG. 6, if each applied voltage is shifted by 90 ° (a relation between sin and cos), a traveling wave is generated. Thereby, the rotor 17 rotates in the direction (left direction in FIG. 6) opposite to the traveling direction of the traveling wave (right direction in FIG. 6). Further, if the applied voltage is shifted by 270 °, the rotor 17 can be rotated in the reverse direction (rightward in FIG. 6). By repeating this forward and reverse rotation, the ultrasonic motor 10 can be reciprocated. In addition, since the rotor of the ultrasonic motor 10 is pressed against the stator 18, the rotor 17 can be reversed with a high torque at the time of reversal. Therefore, in the ultrasonic motor 10, there is almost no delay in response to the drive signal.

  The digital control means 12 plays a role of controlling the movement of the ultrasonic motor 10. FIG. 7 is a diagram showing a signal flow in the passage cross-sectional area changing means 4. As shown in FIG. 7, the digital control means 12 receives the audio signal 22 sent from the audio amplifier 21 and generates a drive signal 23 by performing predetermined modulation on the audio signal 22, and this drive signal 23 is sent to the ultrasonic motor 10. As shown in FIG. 3, since the opening 13 of the fixed plate 8 and the opening 14 of the slide plate 9 are both rectangular, the airflow passage 3 is proportional to the slide amount of the slide plate 9. The cross-sectional area can be changed. Therefore, the cross-sectional area of the airflow passage 3 can be controlled relatively easily. Further, when backlash occurs during reversal in the reciprocating motion of the ultrasonic motor 10, the digital control means 12 performs correction processing so as not to affect the sound quality.

  The above is the configuration of the airflow speaker 1 according to the present embodiment. With this configuration, it is possible to change the cross-sectional area of the airflow passage 3 based on the audio signal 22 from the audio amplifier 21 and modulate the DC airflow to generate sound waves. Further, since the ultrasonic motor 10 is used as the drive source of the passage cross-sectional area changing means 4, the responsiveness of the drive system can be increased. Therefore, the air flow speaker 1 having high responsiveness to the audio signal is obtained.

  The best mode for carrying out the airflow speaker 1 according to the present invention has been described above.

  In addition, although the structure which slides the slide plate 9 which has the opening part 13 and changes the cross-sectional area of the airflow path 3 as the path | route cross-section change means 4 was demonstrated above, it replaced with this in FIG. As shown, the cross-sectional area may be changed by changing the diameter of the airflow passage 3a by changing the positions of the plurality of overlapped blades as in the case of the diaphragm of the camera. Further, as shown in FIG. 8B, a fixed plate 31 having a plurality of radially extending openings and a rotating plate 32 having blades arranged at positions corresponding to the openings are provided, and the rotating plate 32 rotates. By doing so, it is good also as a structure which changes the opening area of an opening part and changes the cross-sectional area of the airflow path 3b. In any configuration, since the cross-sectional area of the airflow passages 3a and 3b can be changed, the DC airflow can be converted into a modulated airflow based on the audio signal.

  Moreover, FIG. 9 is the figure which showed other embodiment of the airflow speaker concerning this invention, Comprising: FIG. 9 (a) is an enlarged front view inside the direct current | flow airflow pipe 7, FIG.9 (b) is a side view. FIG. 9C is a top view. In the best embodiment, the case where the ultrasonic motor 10 is disposed outside the direct current airflow tube 7 has been described. Instead, as shown in FIG. You may arrange | position inside. According to such a configuration, the direct current airflow is effective for releasing the heat generated from the ultrasonic motor 10, and also has an effect of reducing the emission of the driving sound of the ultrasonic motor 10 that is slightly generated. When the ultrasonic motor 10 is disposed inside the direct current airflow tube 7, the same effect as that of the best embodiment can be obtained by making the fixed plate 8A and the slide plate 9A into an arc shape. Furthermore, the ultrasonic motor 10 can be arranged in the direct current airflow pipe 7 via the vibration isolator 35, so that vibration transmitted from the ultrasonic motor 10 to the direct current airflow pipe 7 and the like can be reduced. The anti-vibration material 35 can be used not only when the ultrasonic motor 10 is disposed inside the direct current airflow pipe 7 but also when disposed outside the direct current airflow pipe 7.

  FIG. 10 is a view showing still another embodiment of the air flow speaker according to the present invention. In the best embodiment, the rotary ultrasonic motor 10 has been described, but instead, a linear ultrasonic motor 10A may be used as shown in FIG. In this case, the stator 20 has a linear portion, and a slider 17A is used instead of the rotor 17. Since the slider 17A moves linearly, the rigid link 3 can be used instead of the leaf spring 24 which is an elastic body.

  According to the present invention, it is possible to provide an airflow speaker that generates high-quality sound. Therefore, it is useful in the technical field of speakers, particularly in the technical field of airflow speakers.

It is a longitudinal section schematic diagram showing one embodiment of an air current speaker of the present invention. It is an enlarged view of the passage cross-sectional area changing means and the vicinity shown in FIG. FIG. 3 is a perspective view of a fixed plate and a slide plate shown in FIG. 2. FIG. 3 is a perspective sectional view of a rotor and a stator that are components of the ultrasonic motor shown in FIG. 2. It is the figure which showed the deformation | transformation of the stator of the ultrasonic motor shown in FIG. It is the figure which showed the principle which the traveling wave of the ultrasonic motor shown in FIG. 2 generate | occur | produces. It is the figure which showed the flow of the signal in the channel | path cross-sectional area change means shown in FIG. It is the figure which showed other embodiment of the channel | path cross-sectional area change means of this invention. It is the figure which showed other embodiment of this invention, Comprising: (a) is a front view, (b) is a side view, (c) is a top view. It is the figure which showed other embodiment of this invention. It is the figure which showed the conventional airflow speaker.

Explanation of symbols

1, 1A, 1B Airflow speaker 2 Airflow generating means (fan)
3 Airflow passage 4 Passage cross-sectional area changing means 5 Horn 6 Sound absorbing material 8, 8A Fixed plate 9, 9A Slide plate 10 Ultrasonic motor 10A Ultrasonic motor (linear type)
22 Audio signal 35 Anti-vibration material

Claims (7)

An airflow generating means for generating an airflow;
An airflow passage through which the airflow generated by the airflow generating means passes;
Passage cross-sectional area changing means for changing the cross-sectional area of the air flow passage,
The drive source of the passage cross-sectional area changing means is an ultrasonic motor,
The air flow speaker, wherein the ultrasonic motor is controlled based on an audio signal. The passage cross-sectional area changing means has a fixed plate and a slide plate,
The slide plate is provided so as to overlap the fixed plate,
The fixing plate and the slide plate are each provided with an opening,
The overlapping portion of the opening of the fixed plate and the opening of the slide plate forms the air flow passage,
The slide plate slides with respect to the fixed plate using the ultrasonic motor as a drive source,
When the slide plate slides, the cross-sectional area of the airflow passage changes.
The airflow speaker according to claim 1.   The airflow speaker according to claim 1 or 2, wherein a flow velocity of the airflow generated by the airflow generating means is equal to or lower than subsonic speed.   The air flow speaker according to any one of claims 1 to 3, further comprising a horn, wherein the horn is disposed downstream of the passage cross-sectional area changing unit.   The airflow speaker according to any one of claims 1 to 4, further comprising a sound absorbing material, wherein the sound absorbing material is disposed downstream and / or upstream of the passage cross-sectional area changing means.   The airflow speaker according to any one of claims 1 to 5, wherein the ultrasonic motor is disposed in the airflow passage.   The airflow speaker according to any one of claims 1 to 6, wherein the ultrasonic motor is disposed via a vibration-proof material.

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