JPS62271527A - Loudspeaker - Google Patents

Abstract

PURPOSE:To obtain a loudspeaker with high accuracy while suppressing howling by using a conventional band limit analog filter, a sampling circuit and D/A, A/D converters so as to apply the operation processing using all digital signals to the frequency transition by the single side band amplitude modulation SSB method through the use of weaver modulation. CONSTITUTION:A microphone input 1 is subjected to sampling 3 through an LPF 2, subjected to A/D conversion 4, processing 5, then D/A conversion 6 and sampling 7 and the result is outputted (9) via an LPF 8. The circuit 5 applies the multiplication of a sinusoidal and a consine wave whose center frequency fB to an input 10, the result is given to an LPF, and the result is multiplied respectively with the sinsoidal and cosine wave whose center frequency is fc and the result is summed and multiplied with 2. In such processing, the signal whose center frequency fB is transited to the signal having center frequency fc. Through the constitution above, since the operation processing is applied to the multiplication of the sinusoidal and cosine wave and definite impulse response type LPFs 13, 14 only with the software change in the conventional processing circuit 5, the hardware for a pitch control means is simplified, the accuracy by a digital filter is improved and an inexpensive loudspeaker is obtained while suppressing the howling.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a public address system used in a place with a large space such as a hall or conference room.

(Prior Art) Conventionally, a pitch controller has been added to this type of public address system to suppress howling. FIG. 1 shows the configuration of a public address system including this pitch controller. In FIG. 1, M is a microphone, and its output is a microphone amplifier M.

It is input to A. The outputs of the microphone amplifiers M, A are input to pitch controllers p, c, and the outputs thereof are input to power amplifiers P, A.

The outputs of the power amplifiers P and A are input to a speaker S. Among the pitch controller methods, single sideband amplitude modulation (hereinafter referred to as SSB) is one in which the amount of frequency transition is constant.
). The most common method for SSB is a method using a balanced modulator.

This circuit configuration is shown in FIG. Furthermore, the relationship between the spectra of the input signal and output signal of this modulator is shown in FIG.

The amount of frequency transition is determined by the difference between one frequency f1 and f2.

Generally, in a public address system, acoustic coupling occurs between a speaker and a microphone, forming an acoustic loop. If the gain of this loop exceeds OdB and the phases are in phase, howling will occur.

The transmission characteristics of the acoustic system from the speaker to the microphone vary depending on the size, shape, sound absorption effect, IJL degree, etc. of the parts, but there are fine peaks and valleys of 8 degrees at a frequency of several Hz to 30 Hz, and these peaks and average The difference in level is about 10 dB. Since the loop gain seen on the frequency axis also has characteristics similar to the frequency characteristics of the first chamber (Fig. 3), as the loop gain is increased, howling begins to occur at the maximum peak frequency. When howling reaches its limit,
In other words, the level at the maximum peak is the loop gain OdB
When set to , the average level is about 1.0 dB lower than the peak, so the sound pressure from the speaker is 1.0 dB lower than the sound pressure at the howling limit assuming that the loop gain characteristics are flat. It will become smaller by about Od mouth.

Next, the operation of the above conventional example will be explained. Pitchcon 1
- When the frequency of the input signal from the microphone is slightly shifted by the roller, for example, the frequency component amplified at the maximum peak of the loop gain will be amplified by the gain at the shifted frequency as it goes around the loop, and then As the peaks and troughs of the gain are offset several times, the gain is gradually amplified to the average level and settles down. The transitioned signal will eventually go out of the high frequency band or out of the low frequency band.

In other words, even in a public address system including a conventional pitch controller, the loop gain can be further adjusted from a state where the maximum peak level is set to the loop gain OdB without causing howling, thereby suppressing howling. Can be done.

(Problems to be Solved by the Invention) However, as shown in FIG.
Since the bands of the input signal and the output signal overlap, it is not possible to directly obtain one sideband, and two-stage modulation is required as shown in FIG. Therefore, after two-stage modulation, it is necessary to limit the other sideband with filters A and B.

In order to improve the transfer characteristics of this filter, not only was it difficult to design analog elements, but adjustments were also required. Furthermore, two sets of balanced modulators and oscillators are required, and if these were designed using analog elements, the scale of the hardware would be large and expensive, but the precision would be low.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a public address system in which howling is suppressed and whose pitch controller means is simple in design and does not require adjustment.

Another object of the present invention is to provide a loudspeaker system that suppresses howling with high precision despite having small hardware and low cost.

Another object of the present invention is to provide a loudspeaker that suppresses howling at low cost and with high accuracy by simply using general-purpose circuits and software.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides a general-purpose band-limiting analog filter and a sampling circuit.

D/A and A/D converters are used. Also, SS
The frequency transition according to the B method is performed in the form of arithmetic processing of digital signals, including the digital filter, by using Weiber modulation.

To this end, the loudspeaker of the present invention includes: low-pass filter means for limiting the band of the input signal from the microphone; means for sampling the signal that has passed through the filter; and means for converting the sampling signal into a digital signal. digital signal processing means comprising a Wiver modulator, which is one of the single-sideband amplitude modulations for processing the digital signal; means for converting the output signal of the digital signal processing means into an analog signal; A low-pass filter means for smoothing the signal waveform is provided to suppress howling.

(Function) Therefore, according to the present invention, there are provided a low-pass filter means for limiting the band of an input signal from a microphone, a low-pass filter means for smoothing an analog signal waveform, and a low-pass filter means for smoothing an analog signal waveform. The filter means can be installed with a circuit configuration with a small number of parts, and the sampling means.

Since general-purpose A/D and D/A converters can be used, the design of the loudspeaker is simple and inexpensive.

Furthermore, according to the present invention, the Weiber modulator performs signal processing as shown in FIG. That is, the audio signal input from the input signal terminal 10 is multiplied by a cosine wave and a sine wave, respectively, at the center frequency f of the band of the signal. next,
Each produces two sidebands, but in order to capture only the lower sideband, it is passed through a low-pass filter with a stopband fl. The result is further multiplied by a cosine wave and a sine wave of center frequency f. Finally, by adding these two and multiplying by 2, the signal with the center frequency f11 can be transitioned to the signal with the center frequency fc.

Therefore, the present invention combines cosine and sine waves with center frequencies f, , fc, and a low-pass filter (finite impulse response) with stopband fB.
response) type filters) can perform arithmetic processing simply by changing the software of the general-purpose digital signal processing circuit, so the hardware for the pitch controller means is not only simple and inexpensive, but also This has the excellent effect of easily increasing accuracy.

(Embodiment) FIG. 5 shows an embodiment of the pitch controller of the present invention.

After the input signal from the microphone enters the input signal terminal 1-, only the low frequency of the signal is passed through the low-pass filter 2, and this signal is sent to the sample-and-hold circuit 3.
The A/D converter 4 converts the sampled analog signal into a digital signal. This digital signal is subjected to arithmetic processing in the digital signal processing circuit 5 shown in FIG.
The discrete digital signal is converted into a continuous analog signal by converting the discrete digital signal into an analog signal, inputting this output to the sample-and-hold circuit 7, and passing it through the low-pass filter 8.

-7= Next, one embodiment of the digital signal processing circuit 5 is a Wiver modulator, which is one type of single sideband amplitude modulation, as shown in FIG.

A digital signal encoded into 16 bits 1- by the A/D converter 4 enters from the input signal terminal 10 and has a center frequency f.
Multiply the values (16 bits) of the cosine wave and sine wave of B.

Since the digital signal processing circuit 5 is a type of computer with a single function, a table is provided inside it.
Perform calculations by referring to this table. Then, in order to obtain only the low frequency range, a finite impulse response (F I R
) type low-pass filter. That is, the necessary signal is obtained by convolving the audio signal with the filter coefficients (16 bits) 120 times. Furthermore, each output has a center frequency f.

Multiply the values of the cosine wave and sine wave, add these two, and finally multiply by 2.

These processes are performed in real time because high-speed calculations are performed by the software of the digital signal processing circuit 5.

Furthermore, let's confirm the above process using a mathematical formula.

When a sine wave with a frequency f within the band is input as a signal.

x (nT)=sin2πfnT x, (nT)=sin2πfnTXcos2πfBnT
='(sin2π(4+fB)nT+sj,n2z(f
-fn)nT>0-pass filter a! −5in2π(ff,,)nT x2(nT)=sin2πfnTXsj, n2z f
BnT=4(cos2πcf+1n)nT−coS2π
(f-fn)nT) Pass through a low-pass filter a'coq2π(ff,,)nT yl(nT)=-! -5in2s(f-fe)nTXc
os2πfcnT=↓(sj, n2π(f+4cmf,
,)nT+5in2π(ffc-fn)nT)y2(n
T)=-! ”cos2π(f −f ,,)nTXsi
n2πf cnT-↓(sin2π(f+4cmf,)
nT-sjn2π(f fc-fe)nT)y (nT
)=y1(nT)+yz(nT)=-'5jn2π(f
+fc 7a) nTy (nT) is a sine wave x (nT) of frequency f shifted by frequency f, -fI].

All of the above calculations are processed at high speed by software in the digital signal processing circuit 5.

(Effects of the Invention) Since the present invention uses a simple low-pass filter, a general-purpose sampling circuit, and an A/D and D/A converter, the hardware is small and inexpensive, and the amplification system suppresses howling. It can be a device.

Furthermore, instead of configuring the conventional single sideband amplitude modulation circuit using analog elements, the present invention uses a digital processing circuit configuring Wiver modulation that performs multiplication and digital filter calculations, etc. entirely by software. ,
Not only is the design simple, the hardware is small, and an inexpensive loudspeaker system that suppresses howling can be achieved.

Furthermore, the present invention provides software that allows filters that are difficult to design and adjust using analog elements to perform a finite number of calculations.
By assembling hardware, it is possible to create a public address system that suppresses howling, which not only makes designing and adjusting the digital filter simple and inexpensive, but also makes it easy to improve accuracy.

[Brief explanation of drawings]

Figure 1 is a block diagram of a public address system including a pitch controller that has the effect of suppressing howling, Figure 2 is a block diagram of an SSB modulator that has the function of a conventional pitch controller, and Figure 3 is a block diagram of an SSB modulator that has the function of a conventional pitch controller. 4 is a diagram of the loop gain of the loudspeaker system, and FIG. 5 is a circuit configuration diagram for realizing the present invention.
FIG. 6 is a diagram of signal processing of Wiver modulation performed by software of a digital signal processing circuit, and FIG. 7 is a power spectrum diagram of an input signal and an output signal of the pitch controller (Wiver modulation) of the present invention. M...Microphone, M, A...Mic amplifier, p,
c,... Pitch controller, P, A,... Power amplifier, S... Speaker, 1... Input signal end, 2... Low pass filter, 3... Sample hold circuit, 4...・A/D converter,
5...Digital signal processing circuit. 6...D/A converter, 7...Hold circuit, 8...Low pass filter, 9...Output signal end, 10...Input signal end, 11. , 12.15
゜16, 18... Multiplier, 13.14... Low pass filter, 17. Adder, 19... Output signal end. Patent Applicant: Matsushita Electric Industrial Co., Ltd. Figure 3 Figure 5 Figure 6 Figure 7 Retrofit δ No.

Claims (1)

[Claims] Low-pass filter means for limiting the band of an input signal from a microphone, means for sampling the signal passed through the filter, means for converting the sampling signal into a digital signal, and a single side wave for processing the digital signal. Digital signal processing means consisting of a weaver modulator, which is one type of band amplitude modulation; means for converting the output signal of the digital signal processing means into an analog signal; A loudspeaker system for suppressing howling, which comprises a range filter means.