| 摘要 |
PURPOSE:To determine a sound absorbing characteristic, by forcibly irradiating a surface to be measured with sonic wave beam having strong directionality and analyzing the incident and reflected wave of the sound field formed to said surface. CONSTITUTION:Sonic wave beam using sonic wave parametric effect low in diffusibility is allowed to forcibly irradiate and sound pressure is measured by microphones 1a, 1b and amplified by amplifiers 2a, 2b to form signals Pa(t), Pb(t). These signals are converted to digital signals by an A/D converter part 3 and respective or mutual spectra Gaa(f), Gbb(f), Gba(f) are operated by a spectrum operation part 4. A sound impedance operation part 45 uses three kinds of the spectra G to calculate sound impedance Zn with respect to three kinds of spectra, an incident wave Pi(t) and a reflected wave Pr(t) and a reflection coefficient operation part 6 uses Zn to calculate sound pressure reflection coefficient rp(f) and particle speed reflection coefficient ru(f) and an acoustic absorptivity operation part 7 uses Zn to calculate the acoustic absorptivities alpha0, alpha(psii), alpha of vertical, oblique and random incidences to output the same to an operation result output part 8.
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