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Acoustic impedance of orifices with grazing flow

“…Signals from microphones were then subjected to spectral analysis as they passed through the signal amplifier. Then the received spectra were processed in the computer by the method of transfer functions [23,24] to obtain sound pressure characteristics directly at the partition with an orifice. Simultaneously with acoustic measurements and processing, the Pitot tube [25] measures the vibrational velocity in the septal opening and its surroundings along the longitudinal axis of symmetry.…”

“…A lot of work is devoted to modeling the acoustic impedance of orifices with grazing airflow [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25]. It should be noted that in this case, strict mathematical modeling of the mechanisms that determine acoustic impedance is significantly more complicated.…”

Investigating Acoustic Characteristics of Sound-Absorbing Materials by the Three-Microphone Method

“…The first group includes the acoustic characteristics of a material sample that has a certain size. The acoustic characteristics of the sample include: the reflection coefficient R, determined by the ratio of the amplitudes of the sound waves reflected from the sample and incident on it; absorption coefficient α = 1 -|R| 2 , as well as dimensionless acoustic impedance Z s = (1 + R)/(1 -R). The second group of characteristics includes the characteristics of the SAM itself.…”

“…As a rule, the measurements of the acoustic characteristics of the SAM samples are carried out in an interferometer. An overview of methods for measuring such characteristics is given in [2]. Previously, the main method of this kind of measurements was the standing wave method.…”

“…Three-microphone measurement scheme.Sound pressure in impedance tube: B are amplitudes of forward and backward waves.The amplitudes of sound pressure in the impedance tube at measurement points 1 and 2 with coordinates x 1 = −L 1 and x 2 = −L 2 : solution to system(2) gives the following expressions for the amplitudes:; s = L 1 −L 2 .This allows to obtain expressions for the reflection coefficient at the front wall of the sample:…”