SU726676A1 - Method of measuring electroacoustic transducers characteristics - Google Patents

Description

I

The invention relates to the field of instrumentation and can be used for testing electroacoustic transducers.

A known method for measuring the characteristics of electroacoustic transducers over a traveling wave field in the presence of reflected waves is based on a preliminary measurement of the impulse response by digitally accumulating discrete voltage samples at the output of the measuring path when the path input is excited by a sequence of short square pulses 1.

However, this method does not provide the required accuracy of measurements due to the influence of the fluctuations of the speed of sound on the measurement results.

-: A method of measuring the characteristics of electroacoustic transducers is also known, based on a preliminary determination of the impulse transient response of the electroacoustic path when rectangular impulses are fed to its input and the subsequent Fourier transform of the first nonzero transient response 2.

However, this method also does not provide the required accuracy and noise immunity of measurements due to the effect of fluctuations in the speed of sound.

The aim of the invention is to improve the accuracy and noise immunity of measurements of the characteristics of electroacoustic transducers.

The task is achieved due to the fact that at the same time a frequency-stabilized reference harmonic signal is fed to the input of the electro-acoustic path, which is extracted at the output of the electro-acoustic path, converted into a series of square pulses, which are then used as clock pulses for analog-digital conversion of the main measuring circuit. signal, and the frequency of the reference signal is chosen in the frequency range above the doubled upper frequency of the main measuring signal and so that the sound pressure level -THR mogosignala at the reference frequency, however, ten times, higher than the level of sound pressure of the reflected signals.

The drawing shows a block diagram of a device for implementing the method.

The device contains a frequency generator 1, a counter-key circuit 2, a generator of 3 single rectangular pulses, a power amplifier 4, an emitter 5, a receiver

6 radiators, band-pass filter 7, 8 low-pass filter, converter 9 of harmonic signals into square pulses, analog-to-digital converter (ADC) 10 and computing device 11.

When the device is operated in the counting-key circuit 2, periodically repeating segments of the reference frequency fo supplied from generator 1 and synchronizing pulses to start generator 3 are delayed by 4-8 periods of frequency f о relative to the beginning of each segment. The duration of each signal segment of the frequency fo certainly exceeds the duration of the impulse transition characteristic of the path under study, and the period of their repetition certainly exceeds the reverberation time. The segments of the reference signal through the amplifier 4 and the emitter 5 emit to

in the receiving part of the path, the signal of frequency f о is passed through a bandpass filter

7i are converted into a sequence of pulses in converter 9, therefore, after the beginning of the cutoff of the signal fo arrives at the receiver 6 at the converter 9, the beginning of the sequence (“packs) of pulses is formed, which automatically start the ADC 10 and the computing device 11 and prepare them for the arrival of the main pulse from the generator 3. The latter is fed to the input of the ADC 10 through the filter 8.

The voltage samples from the output of the ADC 10 are fed to the input of the device 11 and stored in it. The arrival times of these samples are synchronized with the beginning of the reference signal segment and strictly correspond to equidistant moments of time at the input of the radiator 5, regardless of the value of the speed of sound at these points in time. After the end of the reference signal section, the supply of clock pulses to the A / D converter 10 and the computing device 11 is stopped, which serves as a signal to the end of this measurement cycle.

With the beginning of the next segment of the reference signal, the measurement cycle is repeated as described above, while the samples at the output of the A / D converter 10 are summed with the corresponding samples obtained in the first measurement cycle and stored in the memory of the device 11 (or with the sum of the samples accumulated on all previous measurement cycles). So

as samples taken at each measurement cycle are synchronized with the beginning of the corresponding reference signal segment and do not depend on the instantaneous speed of sound, the memory of the computing device 11 accumulates the sum of samples of the true values of the impulse response characteristic corresponding to the time points ito y- (where i - reference number; to 4- - reference signal period).

The accumulated amount of samples in memory

does not depend on fluctuations of the speed of sound, nor on random changes in the distance between the emitter and receiver in the measurement process.

Thus, the described method provides the required accuracy and noise immunity of measurements of electroacoustic transducers.

Claims (2)

1.Vegtap J.M. The Application of the Digital Technignes to the Measurement of  Zondspeakers. Zonrual of the Audio Engineering Society. V. 25, No. 6, 1977, p. 537. 2. USSR author's certificate No. 449455, cl. H 04 R 29/00, 1974 (prototype).