JPH0135560B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an acoustic device that cancels Doppler distortion of a speaker.

A speaker simultaneously converts an electrical signal with many frequency components into acoustic energy. Therefore, for example, if a signal with a low frequency component and a signal with a high frequency component are applied at the same time, the sounding position of the signal with a high frequency component will change every moment due to the displacement of the sounding body by the signal with a low frequency component. . As a result, the frequency of a signal with a high frequency component is frequency modulated by a signal with a low frequency component due to the Doppler effect, and acoustic energy containing a frequency component different from that of the input signal is generated. This is called Doppler distortion.

This Doppler distortion occurs even in the case of one signal. Even in the case of one signal, since the sounding position of the speaker changes depending on the signal itself, the arrival time from the sounding position to the listening position changes, resulting in distortion.

Doppler distortion in the case of one signal will be explained using FIG. 1.

In Figure 1, p ₀ is the static position of the speaker's sounding body, Q is the listening position, P ₀ , P ₁ , P ₂ , P ₃ , P ₄ are the positions of the sounding body at each time, and x(t) is the sounding position. body displacement, p(t) is the sound pressure at the sounding position, T ₀ ,
T ₁ , T ₂ , T ₃ , T ₄ are each sound generation position P ₀ , P ₁ , P ₃ , P ₄
The time at which the sound from Q arrives at the listening position Q, q(t)
is the sound pressure at the listening position, P ₁ , P ₃ is the sound production position P ₁ ,
The sound pressure at P ₃ , q ₁ and q ₃ are the time T ₁ at the listening position,
Sound pressure at T ₃ , t is time, l is distance between P ₀ Q,
V is the speed of sound.

First, when a sine wave is applied to a speaker, a sine wave sound pressure p(t) is generated in the piston vibration region.
At this time, the displacement x(t) of the sounding body of the speaker is p
(t) is integrated twice, and x in Figure 1
It becomes a sine wave like (t).

The sound emitted from point P ₀ reaches point Q after a time of T ₀ =l/V. The sound from point P ₁ similarly arrives at time T ₁ . The sound pressure q ₁ at this time is proportional to the sound pressure p ₁ at the point P ₁ . Similarly, points P ₂ , P ₃ , P ₄
The sound emitted from the listening position is at times T ₂ , T ₃ ,
To reach T ₄ , the sound pressure at listening position Q is
The waveform becomes distorted as shown in q(t) in FIG.

The present invention provides an audio device that cancels out this Doppler distortion using a circuit. This distortion occurs because, as explained with reference to FIG. 1, the arrival time from each sounding body position to the listening position changes every moment. The time required for the sound generated at time t to reach the listening point is T(t)
Then, it becomes as follows.

T(t)=l−x(t)/V=T ₀ −1/Vx(t)…
...(1) Therefore, by applying a signal that has been corrected in advance for the change in the required time to the speaker, the arrival time can be made constant and the distortion can be canceled out.

This correction can be performed using a variable delay circuit such as a BBC.

The signal delay due to BBD will be explained using FIG. In Figure 2, C ₁ , C ₂ ...Cn is BBD
represents each stage of , and a(t ₁ ) is BBD at time t ₁
The amplitude of the input signal, b (t ₁ + t _o ) is the input signal a (t ₁ )
The amplitude of the output signal after the required time t _o to pass through the BBD,
The relationship between the amplitude of these input signals and the amplitude of the output signal is a(t ₁ )=b(t ₁ +t _o ).

Now, assuming that the clock frequency of the BBD is sufficiently higher than the frequency of the signal, the clock period τ(t) of the BBD in a certain minute time interval of the signal can be regarded as constant.

Therefore, the BBD transit time t _o (t) of the signal in a certain minute time interval is t _o (t)=nτ(t) (2). Here, n is the number of stages of BBD.

Therefore, the average value of the clock period τ(t) is τ ₀ ,
Letting the change from τ ₀ be Δτ(t), equation (2) becomes t _o (t)=n{τ ₀ +Δτ(t)} =nτ ₀ +nΔτ(t) (3).

Therefore, if n and Δτ(t) in equation (3) are set and controlled so that nΔτ(t)=1/Vx(t)...(4), the signal
The BBD transit time t _o (t) is t _o (t)=nτ ₀ +1/Vx(t) (5).

When a signal controlled in this manner is applied to a speaker, the time it takes for each phase to reach the listening point is as follows.

t _o (t)+T(t)=nτ ₀ +1/Vx(t) +T ₀ −1/Vx(t) =T ₀ +nτ ₀ (6) In other words, it becomes constant and the distortion is corrected.

As mentioned above, x(t) is the signal integrated twice. FIG. 3 shows a specific example of a circuit that delays a signal as shown in equation (5).

In FIG. 3, 1 is an input terminal, 2 is a BBD for signal delay, 3 is a clock oscillator for BBD, 4 is an integrating circuit, 5 is an amplifier, and 6 is a speaker.

In the example shown in Fig. 3, the signal is first integrated twice by the integrating circuit 4, and the oscillation period of the clock oscillator 3 is controlled by the integrated output, and the BBD 2 is clocked by the oscillation output. Controls the delay time of the signal applied to the input. Then, the BBD output is amplified by an amplifier 5 to drive a speaker 6.
In this case, the extent to which the clock period is controlled by the integral output, that is, the degree of modulation, is determined by BBD2 so that it satisfies equation (4).
It is determined from the number of stages and the speed of sound.

The integrating circuit 4 in FIG. 3 can be realized, for example, by a circuit as shown in FIG. 4. In Figure 4, 7, 8
is an operational amplifier, 9 and 10 are input resistors, 11 and 12
is a feedback capacitor, and 13 is an integrating circuit output.

Further, the clock oscillator 3 in FIG. 3 is, for example,
This can be realized with a circuit as shown in FIG. In Fig. 5, 14 is a transistor, 15 is an emitter resistor, 16 is a capacitor, 17 is a trigger diode, 18 is a resistor, 19 is a 1/2 frequency divider, 20, 21
is the oscillator output.

The operation of the oscillator shown in FIG. 5 will be explained using the waveforms shown in FIG. 6.

First, a current is generated in the collector of the transistor 14 according to the voltage applied to the terminal 13. The capacitor 16 is charged with the current. When the charging voltage of the capacitor 16 reaches the trigger voltage of the trigger diode 17, the trigger diode 17 becomes conductive and the capacitor 16 is discharged. When the battery finishes discharging, charging begins again. Therefore, a waveform as shown in FIG. 6a appears at both ends of the capacitor 16. A voltage corresponding to the discharge current as shown in FIG. 6b appears across the resistor 18. This is frequency divider 19
The waveform shown in FIG. 6c and its opposite phase waveform (FIG. 6d) are obtained. The BBD2 is clocked by the waveforms shown in FIG. 6c and d.

Currently available BBDs do not have sufficient S/N performance, and if used as is, they will pose a problem when used in high-fidelity devices.

An example of solving this problem is shown in FIG. This example is
This is a multi-amplifier system in which two or more amplifier systems are used and each amplifier drives a speaker, and the above-mentioned method is applied only to the bass speaker 6 where Doppler distortion becomes large because the amplitude of the speaker generator is large.
A Doppler distortion correction circuit manufactured by BBC is used, and the correction circuits 2, 3, and 4 are inserted between the input terminal 1 and the low-pass filter 22. Note that 23 is a high-pass filter, 24 is a treble amplifier, and 25 is a treble speaker.

With this configuration, the high-frequency portion of noise generated from the BBD is filtered out by the low-pass filter 22. Since this cutoff frequency is usually set in the middle of the audible frequency range, the S/N improvement effect is quite large. Also, this low-pass filter 22
has the effect of carrier suppression of BBD output.

In the examples shown in Figures 3 and 7, the amplifier, speaker, filter, correction circuit, etc. are integrated, but for example, there may be cases where the speaker is separate, a speaker and amplifier are separate, or a correction circuit. In the case where only the amplifiers and speakers are independent, it is necessary to adjust the amount of correction depending on the characteristics of the amplifier and speaker to be combined, so it is desirable to have such an adjustment function.

Furthermore, below the low resonant frequency of the speaker, the frequency characteristics of the speaker decrease with respect to the input signal, and the phase characteristics change. Therefore, the above-mentioned Doppler distortion correction circuit cannot effectively correct below the reduced resonance frequency. FIG. 8 shows an example in which the correctable frequency range of the Doppler distortion correction circuit is expanded by correcting the frequency characteristics and phase characteristics circuit-wise.

In FIG. 8, 26 is a reduction correction circuit for this speaker. Since this reduction correction circuit corrects the characteristics of the speaker, it is provided closer to the speaker than the Doppler distortion correction circuits 2 to 4.

Note that the present invention is equally effective for single-signal Doppler distortion and multi-signal Doppler distortion.
As described above, according to the present invention, (1) Doppler distortion of a speaker can be corrected using a circuit.

(2) When combined with multi-thump method, BBD
The S/N ratio of variable delay circuits such as the above is improved.

(3) When combined with a speaker low frequency characteristic correction circuit, the range in which Doppler distortion can be corrected can be expanded.

This excellent effect can be obtained.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of the principle of Doppler distortion generation, Fig. 2 is an explanatory diagram of BBD, Fig. 3 is a block diagram of the first embodiment of the present invention, and Fig. 4 is an example of an integrating circuit used in the present invention. FIG. 5 is a diagram showing an example of a clock oscillator used in the present invention, FIGS. 6 a to d are waveform diagrams for explaining FIG. 5, and FIG. Block Diagram FIG. 8 is a block diagram of a third embodiment of the present invention. 2...BBD, 3...Clock oscillator, 4...
Integrating circuit, 5...Amplifier, 6...Speaker, 14
~18... Sawtooth oscillator, 19... Frequency divider,
22...Low pass filter, 23...High pass filter, 24...Second amplifier, 25...Second speaker, 26...Speaker low frequency characteristic correction circuit.

Claims (1)

[Scope of Claims] 1. A speaker having a sounding body, an amplifier, a variable delay circuit, a clock oscillator for the variable delay circuit, an integrating circuit that performs two-time integration, and an input signal input to the variable delay circuit. means for injecting the same into the input of the integrating circuit; means for modulating the period of the clock oscillator with the output of the integrating circuit; and means for variably controlling the delay time of the variable delay circuit using the oscillation output of the clock oscillator; means for coupling the output of the variable delay circuit to the input of the amplifier; and means for coupling the output of the amplifier to the speaker; An acoustic device characterized in that the Doppler distortion of the speaker is canceled by using the time displacement as the displacement of the sounding body of the speaker. 2. The acoustic device according to claim 1, wherein the clock oscillator is composed of a constant amplitude sawtooth wave oscillator with variable slope and a frequency divider. 3. The acoustic device according to claim 1, wherein the means for coupling the output of the variable delay circuit to the input of the amplifier includes a low frequency characteristic correction circuit of the speaker. 4. First and second speakers having a sounding body, first and second amplifiers that drive the first and second speakers, a variable delay circuit, a clock oscillator for the variable delay circuit, and two-time integration. a low-pass filter connected to the input side of the first amplifier; a high-pass or bandpass filter connected to the input side of the second amplifier; means for injecting the input of the integrating circuit into the high-pass or band-pass filter; means for modulating the period of the clock oscillator with the output of the integrating circuit; and means for modulating the period of the clock oscillator with the output of the integrating circuit; and controlling the delay time of the variable delay circuit with the oscillation output of the clock oscillator. and means for coupling the output of the variable delay circuit to the input of the low-pass filter, for setting the degree of modulation of the period of the clock oscillator, and adjusting the variation of the delay time of the variable delay circuit. An acoustic device characterized in that the Doppler distortion of the first speaker is canceled by the displacement of the sounding body of the speaker. 5. The acoustic device according to claim 4, wherein the clock oscillator is comprised of a constant amplitude sawtooth wave oscillator with variable slope and a frequency divider.