Some Measurements of the Effect of Geometric Scale on Structural Impedance and Radiated Sound

Abstract

Two wooden structures resembling flower boxes and geometrically scaled in the ratio of four to one were driven in air and water with sinusoidal and random excitation, and transfer impedance and radiated sound measurements were made. It was found that (1) the resonant frequencies of the lower modes were in the ratio of one to four within a few percent, and the frequencies at which the impedance is a maximum and the resonant frequencies at the higher modes do not scale in any obvious pattern; (2) impedance measurements at symmetrical points of the same structure are identical only at the lower frequencies; (3) reciprocal transfer impedance measurements are identical at all frequencies; (4) the impedance magnitude scaled in the ratio of 16 to one only at low frequencies, but the impedance averaged over small frequency ranges and the impedance using random excitation in 13-oct bands scaled at all frequencies.