SU1613874A1 - Method of measuring characteristics of sound-absorbing structures - Google Patents

Abstract

The invention relates to a measurement technique and can be used in determining the characteristics of sound-absorbing structures in an acoustic interferometer according to measured sound pressure levels. The aim of the invention is to improve the measurement accuracy by eliminating frequency errors. In the end surface of the acoustic interferometer install a sample of the material under study. Excitation in the acoustic interferometer at a given frequency of the sound field. The sound pressure on the axis of the acoustic interferometer is measured at two arbitrarily chosen points. The excitation frequency is changed to a predetermined range, for example, 1 Hz. The pressures at the same two points are measured again. The rate of pressure measurement at two points in frequency is determined. Taking into account the measured pressures and the calculated rates of change of pressure, the sound absorption coefficient and the impedance of the structure are determined using the formulas given in the text of the description of the invention. 1 il.

Description

The invention relates to a measurement technique and can be used to determine the characteristics of sound-absorbing structures in an acoustic interferometer from measured sound pressure levels.

The purpose of the invention is to improve the measurement accuracy by eliminating frequency errors.

The drawing shows schematically a device for implementing the proposed method for measuring the characteristics of sound-absorbing structures.

The device is an acoustic interferometer 1, on one side of which sample 2 of the tested structure is located and attached to a rigid piston 3. Using probes 4, the pressure inside the acoustic interferometer 1 is measured. On the other side of the acoustic interferometer 1, a conical horn 5 with sound-absorbing material 6 is installed that fits tightly with the electrodynamic 7,

The method of measuring the characteristics of sound-absorbing structures is as follows.

In the acoustic interferometer 1 using electrodynamics 7 through the horn 5 with sound-absorbing material 6 excite the sound wave of a given frequency f. This sound wave is reflected from sample 2 of the test structure, which is fixed at a certain position with Qs

OJ 00

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With the power of a rigid piston 3. As a result, the incident and reflected meters are installed in the acoustic interfero-superposition, in the interferometer of the sound waves in the acoustic interferometer 1 the ground field at a given frequency f, the sound field is measured. At two arbitrarily sound pressures at the points, the selected points Xi and X2 are located using probes on the interferometer axis, and taking into account 4 the sound pressure Pi and P2 are measured at measured pressures, the axes of the acoustic interferometer 1. Then the sound absorption coefficient a (f ) and an impede in the acoustic interferometer, the excitation z (f) of the structure, which differs in the sound wave at a different frequency G, whereas, in order to improve the accuracy by measuring, the frequency change is chosen equal to 10 rd, the sound pressure measurement Pi and 1 Hz, new part This in selected P2 is conducted at two points Xi and Xg. The points are then measured for pressure P l and P2. In each of the interferometers, a sound is measured at the measurement point, the change in the lef at another frequency f is calculated, the sound measured pressure from the frequency is measured (Pi and P2 pro- cesses at the same points, and gossatural pressures at points Xi and X2). 15 impedance ras- „i | D D is read by the formulas:

P (X,) (X.). A (.), /, 7., „.

where K, k -wave numbers at T and 1 .I R (f) + H Y (fJ

The measured pressures and calculated-2o 7ff1 R (fl + JY (f) values determine the characteristics

ki sound-absorbing structures in the form2

sound absorption coefficient a (f) and im-R (f) + tg).

pedans Z (f) constructions as follows

formulas; 25

"(O-GT-T -CTTTT-Y (f) ()

R (f) + (f), PC -th 2

(T) + j (t), where R (f), Y (f) is active and reactive KOMPO2 impedance factors,

YP) (1 + tg t /) 2). P (density and speed of sound in ascending spirit;

. Btg2 KXi-Atg2KX2.

1p2 0.5arct I. p - I Y (tj () 35 A

-gr -272 / -shift phases;

P th Vi + tg t 2

where R (f), Y (f) is active and reactive com-d 2 P (KiXi) P (X i).

impedance terminals. Xi P (Ki X2) p 1 (X2)

pjC - density and speed of sound in

 YY., Btg2KXi-Atg2KX2. Si are numerical coefficients;

- 0,5arctg ILO

air; - R c ° s 2KH i

. BT2 KXi-Atg2KX2, cos2KX2

, 5arctgi - d in- 1--

- phase shift;, Р (Xi) - - f-derivative davI / IX

A X2P (KiXi) P4.Xi). g COS2KX145, Xi; XiP (KiX2) P4X2)

-number coefficients ;. p, p

, 5arch 0.5ln + (-1) 4X2) - is the derivative of pressure in

- amplitude of sound pressure; cn Ha;

cos2 (kx2) (KXi): K, k - wave numbers with f and f;

 №-1Vi 0,5arch 0,) + (2-1) °

- numerical coefficient; - sound pressure amplitude;

N PizPl.-pressure drop., Cos 2 () -№cos 2KX 1-f 2

l1 - l 2OO g fg -j

Claims (1)

The invention is a numerical coefficient; A way to measure the characteristics of sound. R, co-absorbing structures, I conclude-n y. y, This is due to the pressure derivative structure under study.