JP2000115877A - Output sound source - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an output sound source from which large acoustic power is obtained regardless of its small size. SOLUTION: A support plate 3 supports an actuator 2 in an enclosure 4. The actuator 2 generates vibration. The vibration of the actuator 2 vibrates a diaphragm 1. The diaphragm 1 that is vibrated propagates a sound wave in front of the diaphragm 1 and in the inside of the enclosure 4. A length L of the enclosure 4 is decided so that an anti-resonance frequency of the enclosure 4 is in matching with a frequency desired of enhancing an electroacoustic transduction efficiency. An acoustic impedance at the frequency in the enclosure 4 is much increased to enhance the electroacoustic transduction efficiency.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an ANC (Active N
oise Control), which relates to an output sound source such as a secondary sound source applied to a technology or the like. Here, the ANC is a method of reducing noise by artificially adding a sound wave having the same amplitude and the opposite phase to the waveform of the noise from a secondary sound source in a sound field where the noise exists and causing the two (sound waves) to interfere with each other. And is particularly excellent in noise reduction in a low frequency region.

[0002]

2. Description of the Related Art FIG. 4 shows a structural example of an electrodynamic actuator 11 as an example of a sound source. In conventional sound sources,
As shown in the figure, the magnetic flux density of the permanent magnet 12 and the coil 1
The required acoustic power is obtained by adjusting the electro-acoustic conversion efficiency of the sound source by the length of 3.

[0003]

In such a sound source, it is necessary to increase the magnetic flux density of the permanent magnet 12 or the length of the coil 13 in order to increase the sound power (sound output W). However, when a magnetic flux density higher than the residual magnetic flux density is required, the size of the permanent magnet 12 becomes very large, and the cost increases. The present invention has been made in view of such circumstances, and has as its object to provide an output sound source that is small and can obtain large acoustic power.

[0004]

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and utilizes acoustic impedance at an anti-resonance frequency of an enclosure.
Increase the electro-acoustic conversion efficiency of a specific frequency.

Further, the present invention utilizes the acoustic impedance of a plurality of enclosures at anti-resonance frequencies to increase the electro-acoustic conversion efficiency at a plurality of specific frequencies.
That is, the anti-resonance frequencies of a plurality of enclosures are used.

In addition, the present invention can freely change the length of the enclosure, thereby increasing the electro-acoustic conversion efficiency at an arbitrary frequency by utilizing the acoustic impedance at the anti-resonant frequency of the enclosure. That is, the length of the enclosure can be freely changed, and the electro-acoustic conversion efficiency at a specific frequency can be easily increased.

That is, if the length of the enclosure is determined so that the anti-resonance frequency determined by the length of the enclosure becomes a frequency at which the electro-acoustic conversion efficiency is desired to be increased, the specific frequency becomes Increase.

[0008]

Next, an embodiment of an output sound source according to the present invention will be described with reference to the drawings. First, first
The output sound source according to the embodiment will be described. As shown in FIG. 1, the enclosure 4 has an equal cross section in the length direction.
The length is formed with a predetermined dimension L, and there is a predetermined value (known) of an anti-resonance frequency. Note that the anti-resonance frequency is a frequency at which the response does not increase even if the excitation frequency slightly changes in any direction in the forced vibration system, and is determined by the length L of the enclosure 4. The actuator 2 is supported in the enclosure 4 by a support plate 3. Actuator 2
Can generate vibration of any frequency. The diaphragm 1 is provided in the enclosure 4. The diaphragm 1 is a part of the mechanical vibration system of the electroacoustic transducer, and is a part that converts mechanical vibration into sound waves or sound waves into mechanical vibrations. The diaphragm 1, the actuator 2, the support plate 3
The shape and material of the enclosure 4 are arbitrarily set according to the purpose of use of the high-output sound source. The large output sound source referred to here is a sound source with high electroacoustic conversion efficiency.
As the material of the diaphragm 1, for example, any of paper, metal, wood, plastic, rubber, boron, diamond, or a composite material thereof may be used. Further, as the actuator 2, in addition to the electrodynamic type, for example, any one of an electromagnetic type, an electrostatic type, a piezoelectric type and the like may be used. Further, as the type of the enclosure 4, for example, any one of a flat baffle, a rear open box back load horn, a front load horn, a resonance tube, a bass reflex, a seal, and an air suspension may be used.

A vibration of a predetermined frequency is generated by the actuator 2, and the vibration causes the diaphragm 1 to vibrate. When the diaphragm 1 vibrates, the air before and after the diaphragm is pressurized or decompressed, and a compression wave of air is generated, and a sound wave propagates in front of the diaphragm 1 and in the enclosure 4. At a frequency that matches the anti-resonance frequency of the enclosure 4, the acoustic impedance inside the enclosure 4 becomes very large within the enclosure 4. Here, the acoustic impedance Z _A is represented by the sound pressure p at one point in the sound field and the particle velocity u
And the volume velocity Su which is the product of the micro area S perpendicular to the particle velocity
And the complex impedance (Z _A = R _A + j
X _A , R _A : acoustic resistance, X _A : acoustic reactance). Sound waves, the acoustic impedance Z _A rebounds at the boundaries of different media. If the difference between the acoustic impedances Z _A of the respective media is extremely large, no sound is absorbed or transmitted to the enclosure 4 and all of the sound waves are reflected. Thus, a specific frequency that matches the anti-resonance frequency of the enclosure 4 has a high electro-acoustic conversion efficiency. That is, the vibration of the sound source is efficiently converted into sound.

Next, an output sound source according to a second embodiment will be described. As shown in FIG. 2, the provision of the vibration plate 1, the actuator 2, and the support plate 3 is the same as that of the first embodiment (see FIG. 1), and redundant description will be omitted. The enclosure 5a has a length L1 and the enclosure 5
b is a length L2, in this case a different length L1,
L2. Therefore, in this case, the length L
1 and the anti-resonance frequency of the enclosure 5b determined by the length L2. Thus, two specific frequencies (anti-resonant frequencies)
With regard to the above, the electro-acoustic conversion efficiency can be increased.
Similarly, a plurality of different lengths L1, L2,.
By providing n in the enclosure, it is possible to improve the electro-acoustic conversion efficiency of many specific frequencies.

Next, an output sound source according to a third embodiment will be described. As shown in FIG. 3, the enclosure 6 includes a length variable unit 7 that makes the length variable.
The length Lx of the enclosure 6 can be freely adjusted by lengthening or shortening the variable length section 7. In this manner, the length of the enclosure 6 is adjusted by the variable length section 7, whereby the enclosure 6 is adjusted.
The anti-resonance frequency of the specific frequency changes, and the electro-acoustic conversion efficiency at a specific frequency can be easily increased. In the variable length section 7,
A drive unit controlled by the control unit may be provided so that the length of the enclosure changes to a desired value.
The enclosure 6 shown in FIG. 3 can be assumed to be an acoustic tube with one end open (speaker side) and the other end closed. In this case, the acoustic impedance Z _A of the enclosure 6 is such that the area of the tube is S and the density of the medium in the tube is S. Assuming that ρ, the sound velocity in the pipe is C, the wave number is k, and the length of the pipe is 1 (lowercase letter L), Z _A = −j (ρC / S) cot (kl), and the acoustic impedance Z _A There resonance frequency a frequency having a minimum, the frequency at which the acoustic impedance Z _a is the largest is anti-resonant frequency. As in the other embodiments, the diaphragm 1, the actuator 2, and the support plate 3
(See FIG. 1 and FIG. 2), and redundant description will be omitted.

[0012]

According to the present invention, since the acoustic impedance at the anti-resonance frequency of the enclosure is used,
Electro-acoustic conversion efficiency of a specific frequency can be increased,
It is small and can easily obtain a large acoustic power for a predetermined frequency.

Further, since the acoustic impedance of the plurality of enclosures at the anti-resonance frequency is used, the electro-acoustic conversion efficiency of a plurality of specific frequencies can be increased, and a small and large acoustic power can be easily obtained for a plurality of predetermined frequencies. Obtainable.

Further, the length of the enclosure can be freely changed, and the acoustic impedance at the anti-resonance frequency of the enclosure is used to increase the electro-acoustic conversion efficiency at an arbitrary frequency. Sound power can be easily obtained.

[Brief description of the drawings]

FIG. 1 is a perspective view schematically showing a configuration of an output sound source according to a first embodiment.

FIG. 2 is a perspective view schematically showing a configuration of an output sound source according to a second embodiment.

FIG. 3 is a perspective view schematically showing a configuration of an output sound source according to a third embodiment.

FIG. 4 is a cross-sectional view schematically illustrating a structural example of an electrodynamic actuator.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Diaphragm 2 Actuator 3 Support plate 4, 5a, 5b, 6 Enclosure 7 Variable length part L, L1, L2, Ln, Lx Length of enclosure

Claims (3)

[Claims] 1. An output sound source utilizing acoustic impedance at an anti-resonant frequency of an enclosure. 2. An output sound source characterized by utilizing acoustic impedances at anti-resonance frequencies of a plurality of enclosures. 3. An output sound source characterized in that the length of the enclosure can be freely changed, thereby increasing the electro-acoustic conversion efficiency at an arbitrary frequency by utilizing the acoustic impedance at the anti-resonance frequency of the enclosure.