RU2116632C1 - Method of directed measurement of acoustic signals of sound source ( versions ) - Google Patents

Abstract

FIELD: acoustic measurements. SUBSTANCE: n sound detectors are arranged in agreement with method equidistantly on one measurement axis. Sound pressures are measured simultaneously in points of location of detectors and certain operations are carried out in correspondence with newly established mathematical laws relating signals measured by sound detectors to sound pressure, rate of oscillation of particles, active and reactive parts of acoustic intensity of radiation of sound source in direction of measurement axis at known distance from it. Radiation patterns of proposed method of directed measurement of acoustic signals of sound source by pressure, rate of oscillation of particles and intensity are presented by mathematical expressions given below depending on number of sound detectors

, where R_p2(α) is radiation pattern of known end-difference method of measurement of pressure for two sound detectors, 2β₀= 2KΔxcosα is phase incursion over field of method of measurement, n is number of sound detectors employed for measurement, h = 1/KΔx is frequency-dependent coefficient. EFFECT: increased selective capability of measurement of sound pressure and provision for directed measurement of rate of oscillation of particles and intensity of acoustic radiation of sound source. 3 cl, 3 dwg

Description

 The invention relates to techniques for acoustic measurements and can be used to determine the sound-absorbing properties of materials and structures, in systems for actively suppressing and localizing sound sources, when measuring the acoustic characteristics of a sound source under acoustic noise conditions, and also for diagnosing the technical condition of machines and units whose work accompanied by sound generation.

, интегрирование результата деления и умножение на параметры окружающей среды ρc (блоки вычитания "-", умножения "X" и интегрирования "∫" );
суммирование результатов второй и третьей операций для измерения параметров падающей волны и вычитание результатов второй и третьей операций для измерения отраженной волны (блок суммы, разности "+").Closest to the proposed technical essence is a method of directional measurements of the reflection coefficient of sound in acoustic pipes using unidirectional reception systems [1], which consists in separating the incident and reflected waves. This method, selected as a prototype, is based on finite-difference conversion of the signals of two sound receivers closely located compared to the wavelength and consists of the following operations (Fig. 2):
simultaneous measurement of sound pressures at two points of the acoustic field P ₁ (t), P ₂ (t);
determination of the half-sum of these pressures (summation block "+");
determination of the difference of these pressures, its division by the distance between the receivers and the air density

, integration of the result of division and multiplication by environmental parameters ρc (blocks of subtraction "-", multiplication "X" and integration "∫");
summing up the results of the second and third operations for measuring the incident wave parameters and subtracting the results of the second and third operations for measuring the reflected wave (sum block, difference "+").

 However, this method does not always provide the required sharpness of the radiation pattern and does not have selective selectivity for measuring the acoustic velocity of the particles and the radiation intensity of the sound source in the direction of measurement.

 The technical result of the proposed method is to increase the selectivity of the directional measurement of sound pressure and the possibility of directional measurement of the velocity of the particles and the intensity of the acoustic radiation of the sound source.

, результат которого дает звуковое давление источника звука по направлению измерительной оси приемников звука. Акустическую скорость колебания частиц по тому же направлению определяют путем вычитания результата преобразования с номером

из результата преобразования с номером

, делят эту разность на расстояние между соседними приемниками и плотность воздуха

, интегрируют результат деления. Активную часть акустической интенсивности в заданном направлении определяют как среднее значение произведения звукового давления и скорости колебаний частиц, а реактивную часть акустической интенсивности - как среднее значение произведения звукового давления и результата преобразования Гильберта скорости колебаний частиц.The indicated technical result is achieved by the fact that n sound receivers are located equidistantly on the same measuring axis, at the same time sound pressure is measured at the receiver location points, pairwise finite-difference transformations of the signals of neighboring receivers are performed, the results of the transforms are again converted in pairs until the conversion with the number

, the result of which gives the sound pressure of the sound source in the direction of the measuring axis of the sound receivers. The acoustic velocity of particles in the same direction is determined by subtracting the result of the transformation with the number

from conversion result with number

divide this difference by the distance between adjacent receivers and the air density

integrate the result of division. The active part of the acoustic intensity in a given direction is defined as the average value of the product of sound pressure and particle velocity, and the reactive part of the acoustic intensity is the average value of the product of sound pressure and the result of the Hilbert transform of the particle velocity.

- блок усреднения; X - блок перемножения; "-" - блок вычитания. На входы M₁, M₂, . . ., M_n функциональной схемы подают сигналы приемников звука, а на ее выходе снимают сигналы, пропорциональные звуковому давлению

, акустической скорости колебаний частиц

, активной

и реактивной

частям акустической интенсивности звука по направлению измерений, которые являются функциями времени. Координату x точки измерений определяют как полусумму расстояний от излучателя звука до первого и последнего приемников звука.In FIG. 1 is a functional diagram of a device that implements the proposed method, where the following notation is adopted: 1 — finite-difference driver of a signal for directional measurement of sound pressure [1]; PG - Hilbert Converter; ∫ - integrating block, ρc - weight coefficient;

- averaging block; X - block multiplication; "-" is a subtraction block. To the inputs M ₁ , M ₂ ,. . ., M _{n of the} functional circuit supplies signals from sound receivers, and signals proportional to sound pressure are taken at its output

acoustic velocity of particle oscillations

active

and reactive

parts of the acoustic sound intensity in the direction of measurements, which are functions of time. The x-coordinate of the measurement point is defined as the half-sum of the distances from the sound emitter to the first and last sound receivers.

по направлению измерений.The spectral processing of these signals based on the Fourier transform 1 (FFT block, Fig. 1) gives a frequency representation of the results of measurements of sound pressure, particle velocity, active and reactive parts of acoustic intensity

in the direction of measurements.

можно получить выполнив сначала комплексные Фурье преобразования звуковых давлений, измеряемых приемниками звука, а затем преобразовать результаты в соответствии с выражениями.The same result -

can be obtained by first performing complex Fourier transforms of sound pressures measured by sound receivers, and then transforming the results in accordance with the expressions.

Для скорости колебаний частиц

где m=n-1.For pressure

For particle velocity

where m = n-1.

Для реактивной части интенсивности

В выражениях (1-4) приняты обозначения: P_i(ω) - комплексный спектр сигнала i-го микрофона цепочки; Ai=(m-1)!/{(i-1)!(m-i)!} - действительный коэффициент; ΔP_i(ω) = P_i+1(ω) - P_i(ω); Z = jkΔx - частотно зависимый коэффициент: k - волновое число; 2Δx - расстояние между соседними приемниками; ρc - постоянная окружающей среды, ρ - плотность воздуха, c - скорость звука в воздухе; реальная Re{S_pνn(ω)} и мнимая Im{S_pνn(ω)} части взаимного спектра давления - скорости, полученные для группы из n приемников. Следует отметить, что смена знаков в выражениях (1) и (2) у сомножителей в скобках, под знаком суммы, приводит к смене направления измерений, соответствующего наибольшей чувствительности приема, на противоположное.For the active part of the intensity

For the reactive part of the intensity

In the expressions (1-4), the following notations are used: P _i (ω) is the complex spectrum of the signal of the ith microphone of the chain; Ai = (m-1)! / {(I-1)! (Mi)!} Is the real coefficient; ΔP _i (ω) = P _{i + 1} (ω) - P _i (ω); Z = jkΔx - frequency-dependent coefficient: k - wave number; 2Δx is the distance between adjacent receivers; ρc is the constant of the environment, ρ is the density of air, c is the speed of sound in air; the real Re {S _pνn (ω)} and imaginary Im {S _pνn (ω)} parts of the mutual pressure spectrum are the velocities obtained for a group of n receivers. It should be noted that the change of signs in expressions (1) and (2) in the factors in brackets, under the sign of the sum, leads to a change in the direction of measurements corresponding to the highest sensitivity of reception, to the opposite.

где

- диаграмма направленности конечно-разностного метода измерения звукового давления для двух приемников; 2β₀= 2kΔxcosα - фазовый набег по полю метода измерений; n - количество приемников используемых в измерениях; h = 1/kΔx .In FIG. 3, the radiation patterns of the proposed method for measuring acoustic signals by pressure (a), particle velocity (b) and intensity (c), respectively, which are defined for a different number of sound receivers in accordance with the expressions:

Where

- radiation pattern of the finite-difference method for measuring sound pressure for two receivers; 2β ₀ = 2kΔxcosα - phase incursion along the field of the measurement method; n is the number of receivers used in measurements; h = 1 / kΔx.

 As can be seen from expressions (5) and the dependences of FIG. 3, an increase in the number of receivers leads to a sharp increase in selectivity in the direction of measurements, and with the number of receivers n≥3, in contrast to the well-known [1], the proposed method provides selectivity of measurements for both the particle velocity and the sound source intensity.

где λ - длина звуковой волны, излучаемой источником; 2Δx ≅ 0,1λ .For the correct implementation of the proposed measurement method, the number of sound receivers n should be selected from the condition

where λ is the length of the sound wave emitted by the source; 2Δx ≅ 0.1λ.

Sources of information
1. Pisarevsky N. N. The use of analog intensimetric and correlation equipment and phased two-layer gratings for direct measurements of the complex reflection coefficient by unidirectional reception. Abstracts of the 9th scientific and technical conference on aviation acoustics. TsAGI Publishing Department, 1989.

 2. Pascal J. C., Carles C. Systematic measurements errors whith two-microphone sound intensity meters. J. Sound and Vibr., 1982, v. 83, N 1, 53-65.

Claims (3)

1. The method of directional measurement of acoustic signals of a sound source, which consists in finite-difference conversion, which consists in simultaneously measuring sound pressures by sound receivers at two points of the acoustic field, determining the half-sum of pressures and their difference, dividing the difference by the distance between the measurement points and density air ρ, integrate the result of the division, multiply by the environmental parameters ρc and algebraically sum the result with half the pressure, characterized in that they introduce additional methods sound nicknames and arrange them equidistantly on the same measuring axis, simultaneously measure sound pressures at the points where the receivers are located, perform pairwise finite-difference conversions of the signals of adjacent receivers, the results of the transforms are again converted in pairs until the conversion with the number

determine the acoustic velocity of the particles

in the direction of measurements by subtracting from the result of the transformation with the number

conversion result with number

dividing this difference by the distance between adjacent receivers and air density

integrating the result of division, determine the active part of the acoustic intensity

in the direction of measurements as the average value of the product of sound pressure and particle velocity, and the reactive part of the acoustic intensity

as the average value of the product of sound pressure and the result of the Hilbert transform of the particle vibration velocity, where ρ is the air density, c is the speed of sound in air, n is the number of sound receivers, i is the current microphone number, t is the current time, x is the coordinate of the signal measurement point sound emitter, it is defined as half the distance from the sound emitter to the first and last sound receivers.  2. The method according to claim 1, characterized in that they perform the Fourier transform. 3. The method of directional measurement of acoustic signals of a sound source, which consists in the fact that simultaneously measure sound pressure by sound receivers at two points and determine the acoustic characteristics of the source in the direction of measurement by converting these pressures, characterized in that the additional sound receivers are introduced and placed equidistantly on one measuring axis, simultaneously measure sound pressures at the points of the receivers, perform complex Fourier transforms for each signal ia, and then receive complex spectra of acoustic pressure, particle velocity, active and reactive parts of the intensity, performing the transformations in accordance with the following expressions:

where n is the number of sound receivers, n ≤ n _max = λ / 2Δx;
λ is the sound wavelength;

complex pressure spectrum at the measurement point x;

complex spectrum of particle velocity at the measurement point x;

spectrum of the active part of the intensity at the measurement point x;

spectrum of the reactive part of the intensity at the measurement point x;
P _i (ω) is the complex spectrum of sound pressure of the signal of the i-th receiver;
Ai = (m - 1)! / {(i - 1)! (m - i)!} is the actual coefficient;
ΔP _i (ω) = P _{i + 1} (ω) - P _i (ω);
Z = jkΔx is a complex frequency-dependent coefficient;
k is the wave number;
2Δx is the distance between adjacent group receivers when they are equidistantly located on the same measuring axis;
ρ is the air density;
c is the speed of sound in air;
Re {S _pνn (ω, x)}, I _m {S _pνn (ω, x)} - the real and, accordingly, imaginary parts of the complex mutual pressure spectrum - velocity;
x is the coordinate of the measurement point, it is defined as the half-sum of the distances from the sound source to the first and last receiver.

Images