JPH08190389A - Muffling sound wavee generating device - Google Patents

Abstract

PURPOSE: To reduce a cost and to make a device compact by nearly equalizing a frequency of a generated sound wave of a sound wave generation means with a resonance frequency of a vibration system nearly equal to the frequency of a basic wave of a noise wave. CONSTITUTION: A flange part 14 of a frame F of a speaker 12 is fixed to an edge part of a central opening of an enclosure 11 with a rectangular shape, and a vibration plate constituted of a paper cone faces to the sealed space 13 of the enclosure 11. Then, an output of a noise detection means 22 of a noise source 21 such as an air conditioner, a compressor, an engine and a vibration parts feeder, etc., is supplied to a muffling signal generation device 23. In such a case, the device is constituted so that the resonance frequency f0c of a vibration system constituted of the speaker 12 and the enclosure 11, etc., is equalized with a muffling sound wave frequency generated by the speaker 12, and in this example, the f0c is decided by its inner capacity. Further, the resonance frequency f0c of the vibration system is set so as to become nearly equal to the frequency of the basic wave of the noise sound wave of the noise source 21.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sound wave generator for silencing.

[0002]

2. Description of the Related Art FIG. 4 shows a sound deadening sound wave generator of a conventional example. In the figure, a circular opening is formed in an upper wall portion of an enclosure 1 having a substantially rectangular shape, and a speaker for an audio device is formed. 2 is fixed at the flange portion 4. The speaker 2 is constructed in a known manner, and a paper cone 5 is vibratably attached to a flange portion 4 via a ring-shaped edge in a frame F, and is not shown in a driving portion 6 including a voice coil. Also, a control circuit for supplying a drive current is connected to this. A closed space 3 is formed in the enclosure 1 and is filled with a sound absorbing material (made of glass wool, for example) 7. This sound absorbing material 7
Is filled in the closed space 3 in an amount for preventing generation of a constant material wave.

FIG. 5 shows a frequency-output sound pressure characteristic of a sound wave generator according to a conventional example. The low resonance frequency f0c (Hz) of the entire vibration system including the enclosure 1 and the speaker 2 which form the closed space 3 is shown. The enclosure 1 has a sufficient volume so that it is sufficiently lower than the frequency of the generated sound wave. That is, the output sound pressure level at the generation frequency of the silencing sound wave is in a flat region as shown on the right side in FIG. 5, and is designed to utilize this flat region. This is the same as how to use audio equipment.

The calculation of the effective internal volume Vc of the enclosure 1 is performed by the following formulas 1 to 3.

[0005]

[Equation 1]

M0: Effective mass (g) of the vibrating body of this vibrating system, S0: Stiffness of this vibrating system (stiffness due to the support member of the cone such as the speaker edge, damper, etc.), or the elastic modulus, Sc: In the enclosure 1. The stiffness of the space (that is, the stiffness including the sound absorbing material 7 and using air as a spring). S0 and Sc are represented by Formulas 2 ... (2) and (3), respectively.

[0007]

[Equation 2]

Where f0 is the lowest resonance frequency (Hz) of the speaker 2, and a is the effective vibration radius (c of this speaker).
m), Vc: Effective internal volume (liter) of the enclosure 1. From the above equations (1) and (3), the following equation is obtained.

[0009]

(Equation 3)

Next, the operation of the conventional sound wave generator will be described.

For example, in the above device, a = 3 cm,
8 cm diameter with m0 = 1.15 g and f0 = 140 Hz
When a sound wave of 300 Hz is generated by using the small speaker 2 of No. 1, if it is set sufficiently far and set to f0c = 200 Hz, Vc = 1.2 liters can be designed.

In designing the drive device for the speaker 2, the nominal value of the speaker 2 is used as the impedance of the sound wave generator.

The sound wave generator of the conventional example is configured as described above and has no problem for Hi-Fi applications such as music reproduction, but when viewed as a sound wave generator for active noise control (ANC), it is as follows. There is a drawback of.

That is, as shown in FIG. 5, a large volume is required in order to set f0c sufficiently lower than the generation frequency of the silencing sound wave. Next, since the region where the output sound pressure level is flat (the region where the impedance is low) is used, a large amount of energy, that is, a current is required to obtain a large sound pressure. In this case, the drive capability of the power amplifier, which is the drive means of the sound wave generating means, and the capacity of the power supply source thereof are increased. This increases the cost and mounting space.

[0015]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and it is an object of the present invention to provide a low-cost compact sound-deadening sound wave generator.

[0016]

DISCLOSURE OF THE INVENTION The above object is to generate a sound wave propagating from the front side of a sound wave generating means attached to the enclosure, with the back side facing the closed space formed by the enclosure, and the noise source. In a sound deadening sound wave generator configured to eliminate the noise wave by interference with a noise wave propagating from the sound wave generator, the frequency of the sound wave generated by the sound wave generator is set to the resonance frequency of a vibration system including the sound wave generator and the enclosure. And the resonance frequency is set to be substantially equal to the frequency of the fundamental wave of the noise wave of the noise source.

[0017]

The resonance frequency of the vibration system including the sound wave generating means and the enclosure is increased from the conventional one, that is, the frequency of the sound wave to be generated and the frequency of the fundamental wave of the noise source are matched, so that the peak of the output sound pressure level becomes large. Become. That is, since the frequency of the silencing sound wave is made to substantially match the resonance frequency of this vibration system, a large output sound pressure level can be obtained with small energy. Also, as is clear from the above formula, the volume of the enclosure can be reduced,
When a sound absorbing material is put in this, the volume can be further reduced. Since the frequency of the fundamental wave of the noise wave to be silenced is substantially equal to the resonance frequency of the vibration system, the noise can be silenced efficiently.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A sound deadening sound wave generator according to an embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a sound deadening sound wave generator according to an embodiment of the present invention. In this embodiment, the sound deadening sound wave generator Q is attached to a duct 20 extending one-dimensionally to the left and right, A noise source 2 is provided on the closed end side of the duct 20.
1 is provided, and the noise detector 22 is provided in the vicinity thereof.
The output of this (which may be a microphone or a vibration detector) is supplied to the muffling signal generator 23, from which the speaker drive current is supplied to the drive 16 of the speaker 12. The speaker 12 has a configuration similar to that of the above-mentioned conventional example, and the flange portion 14 of the frame F is
A diaphragm 15 made of a paper cone is fixed to the edge of the central opening of the rectangular enclosure 11, and faces the closed space 13 of the enclosure 11. Further, the sound absorbing material 17 is filled in the enclosure 11.

The noise source 21 may be, for example, an air conditioner, a compressor, an engine, a vibrating parts feeder, etc. In short, this embodiment is applied to a noise source having a single frequency or its harmonics. The output of the noise detecting means 22 of the noise source 21 is supplied to the muffling signal generating device 23. In this embodiment, the resonance frequency f0c of the vibration system including the speaker 12, the enclosure 11 and the like is the speaker 1.
2 is equal to the sound deadening sound wave frequency generated, and is determined by the internal volume of the enclosure 11 in this embodiment. The calculation of the internal volume of the enclosure 11 is performed in the following procedure.

When the low frequency resonance frequency f0 of the speaker 12 is sufficiently lower than the frequency of the sound wave to be generated and the closed space 13 has an extremely small volume, Sc becomes dominant, and the above equation (1) is expressed by Equation 4 can be approximated by (5).

[0022]

[Equation 4]

The following equations are obtained from the above equations (3) and (5).

[0024]

(Equation 5)

Resonance sharpness Q0c at frequency f0c
Can be expressed by the following equations 6 ... (7).

[0026]

(Equation 6)

Here, Q0 is the resonance sharpness at f0 of the speaker 12 alone.

Next, referring to FIG. 2, the silence signal generator 23
Will be described in detail. The analog output of the vibration detector 22 is amplified by the amplifier 36, and the A / D converter 3
7, where the analog value is converted to a digital value and the result is supplied to the adaptive algorithm 39 and the adaptive filter 40. The adaptive algorithm 39 changes the constant and transfer function of the adaptive filter 40 in accordance with parameters that change with time in an actual noise environment, such as atmospheric pressure, temperature, humidity, sound pressure and frequency components. A sound wave signal is generated such that a sound wave having the same level as the sound wave as noise detected by the microphone 32 provided in the vicinity of the opening end of the duct 20 but having the opposite density is obtained at the position of the microphone 32. In the D / A converter 42, the digital input is converted into an analog force output, which is the amplifier 43.
Is amplified and supplied to the speaker 12. As a result, the sound wave transmitted from the noise source 21 is transmitted to the mute deviation microphone 32.
However, the analog output detected by the microphone 32 is amplified by the amplifier 45, and this is converted into a digital value by the A / D converter 44 and the adaptive algorithm 39 described above is used. It is supplied and a predetermined calculation is performed here. That is, if it is not zero at the position of the microphone 32, this is corrected.

The present embodiment is constructed as described above. Next, this operation will be described.

The muffling signal generator 23 receives the output of the noise detector 22 and generates a muffling signal that has the same amplitude as the noise and the phase is inverted by 180 degrees at the opening 20a of the duct 20. Therefore, noise reduction at the opening 20a of the duct 20 is the same as the conventional silencing action.

In this embodiment, for example, as described in the conventional example, a small speaker 12 having a diameter of 8 cm is used and 300 Hz.
Volume of the enclosure 11 when generating sound waves
c = 0.28 liters are obtained.

The output sound pressure level of this system is shown in FIG. 3, and as is clear from this, the resonance frequency f0c of this vibration system is raised more than before, that is, the frequency of the generated sound wave and the noise of the noise source 21. By matching the frequency of the fundamental wave, the resonance sharpness is increased and the output sound pressure level is increased. This can be understood from the above equation (7). Further, at the frequency f0c, the impedance of the speaker 12 is more than doubled, so that the flowing current can be reduced accordingly.

In this embodiment, the volume of the enclosure 11 is determined so that the frequency f0c becomes equal to the frequency of the fundamental wave of the noise sound wave generated. , At least one-third or less. Since the output sound pressure level and the impedance are both high at the frequency f0c and used in this region, the energy (current) required to obtain the same sound pressure as in the conventional case can be made much smaller than in the conventional case.

Therefore, the speaker 12 which is the sound wave generating means.
Power amplifier which is a driving means of the amplifier (the amplifier 4 in FIG.
3) (corresponding to 3), and the capacity of the power supply of this power amplifier is also small, that is, the cost and the mounting space relating to these can be made significantly smaller than the conventional one.

When the noise to be silenced contains harmonics, the output sound pressure level is lowered at a frequency higher than the resonance frequency f0c as shown in FIG. 3, but the sound pressure of the harmonics is generally the fundamental wave. Since it is smaller than, it can be applied without problems. Further, when this harmonic is to be silenced, conventionally, the dynamic range was dominated by the magnitude of the fundamental wave f0c, and the S / N ratio of the harmonic component was deteriorated. However, in this embodiment, the output sound pressure is reduced. Since the characteristic is large for the fundamental wave as shown in FIG. 3, the signal component of the fundamental wave to be applied can be made smaller than the conventional one. Therefore, the gain of the signal can be increased accordingly, so that the S / N ratio of the harmonic component is improved, and a sufficient noise reduction effect can be obtained for the harmonic component.

Although the embodiment of the present invention has been described above, the present invention is not limited to this, and various modifications can be made based on the technical idea of the present invention.

For example, in the above embodiment, the sound-deadening sound wave generator Q was attached to the duct 20 and used to eliminate the noise of the noise source 21 from the noise source 21 arranged inside the duct 20. A vibrating parts feeder may be used as a source, and in this case, an annular sound path is formed on the side circumference of the vibrating parts feeder, and a base block below the vibrating parts feeder is formed so as to propagate a sound deadening sound wave to this. You may make it arrange | position a speaker below. Duct 2 in Figure 1
0 is just an example of the sound path.

In the above embodiments, the sound absorbing material 17 is filled in the enclosure 11. However, of course, the sound absorbing material 17 may be omitted. The volume, that is, the volume of the enclosure 11 can be small. In some cases, the resonance frequency f of the vibration system is changed by changing the filling amount of the sound absorbing material 17.
Fine adjustment of 0c may be performed.

In the above embodiments, the so-called speaker 12 of an acoustic device is used as the sound wave generating means, but instead of this, a diaphragm connected to an actuator, for example, a piezoelectric element by applying a voltage thereto. May be vibrated and a sound wave generated by this vibration may be used.

[0040]

As described above, according to the sound deadening sound wave generator of the present invention, the volume of the enclosure can be made much smaller than the conventional one, and the electric power for driving the sound wave generator is small. Then, the supply source for supplying this, for example, the power amplifier can be made small to significantly reduce the cost.

[Brief description of drawings]

FIG. 1 is a sectional view of a sound deadening sound wave generator according to an embodiment of the present invention.

FIG. 2 is a circuit diagram of a silence signal generation device in the same device.

FIG. 3 is a chart showing characteristics of the device.

FIG. 4 is a sectional view of a conventional sound deadening sound wave generator.

FIG. 5 is a chart showing characteristics of the device.

[Description of sign]

 11 Enclosure 12 Speaker 13 Enclosed Space 21 Noise Source 23 Silent Signal Generator Q Sound Absorbing Sound Generator

Claims (2)

[Claims] 1. An interference between a sound wave generated from a front surface side of a sound wave generating means attached to the enclosure and a noise wave propagated from a noise source, with the back side facing the closed space formed by the enclosure, In a sound deadening sound wave generation device adapted to eliminate the noise wave, the frequency of the sound wave generated by the sound wave generation means is made substantially equal to the resonance frequency of a vibration system including the sound wave generation means and the enclosure, and the resonance frequency is A sound deadening sound wave generator, which is set to be substantially equal to the frequency of the fundamental wave of the noise wave of the noise source. 2. The sound deadening sound wave generator according to claim 1, wherein the sound wave generator is a speaker, and the closed space is at least partially filled with a sound absorbing material.