Natl. Industrial Res. Inst. of Nagoya, 1-1 Hirate-cho, Kita-ku, Nagoya 462, Japan
Source sound pressure has been evaluated without disturbing the sound field using an optical method of schlieren visualization. The intensity of schlieren light is described as a function of the Raman--Nath parameter (nu) and increases monotonously up to (nu)=2.405. Experimental results showed that the light intensity on the sound beam axis changed with the applied voltage to the transducer in a similar manner to the above function. Then (nu) can be obtained numerically by substituting normalized experimental intensity for the function. Because the light passes through inhomogeneous sound field radiated from finite aperture, (nu) is affected by an integral optical effect. If the measuring position is fixed, this effect can be calculated theoretically in relation to the parameter just in front of the sound source defined as (nu)[inf 0]. Hence the source sound pressure P[inf 0] is estimated from (nu)[inf 0] using transducer size, wavelength of the light, and the refractive index of medium. The upper limit for P[inf 0] of this method is 1x10[sup 5] Pa in the present experiment.