Auditcry response for the unsteady sound has been mainly discussed by means of "masking". In this paper, the effects of leading tone (interference tone) on frequency discrimination of a brief tonal signal were investigated and the auditory response in the transient state was discussed. Changes in frequency discrimination were measured as a function of the signal duration, the frequency separation between the interference tone and signals, temporal delay between the two and the intensity of tonal signal. The results obtained as folllws:1)Frequency discrimination deteriorates as the test tone decreases to the level lower than 20 dBSL, provided that the frequency of leading tone is same as one of the test tones (see Fig. 2). This phenomenon can be interpreted as a rise of minimum audible level of test tone due to forward masking. 2) Frequency discrimination of test tone with the leading tone whose frequency is the same as the test tone is almost same as in the case without the leading tone (see Fig. 4). Frequency discrimination, however, becomes, worse in the presence of leading tone with slightly different frequency from the test tone, and when the frequency of the test tone is 1000Hz, the interference effect of the leading tone is maximum for the frequence difference of 50. Hz. But frequency discrimination is little affected by leading tone when the difference of frequency from test tone becomes over 100Hz. 3) When the frequency of leading tone is 950 Hz, frequency discrimination does not become better, even though the time interval between the leading tone and the test tone is increased (see Fig. 5). Furthermore, the forward masking experiments were performed under the same condition as in the previous experiments to explore the relation between the temporal masking and the frequency discrimination and mechanisms of interference.
The method of obtaining the reverberant sound absorption coefficient α_<rev> of a plane absorber of porous material for any mounting or suspending conditions without measurement of it in the reverberation room is verified experimentally. The energy fraction reflected r_m and the energy fraction absorbed λ_d by the material for random incidence were determined by the experimental data of the energy fraction r_<mΘ> reflected by the material and the energy fraction τ_Θ transmitted through it for oblique incidence (Eqs. (1), (2), Fig. 2). The values of r_<mΘ> and τ_Θ were measured by the cancellation method using a pulsed tone (Fig. 1 (a), (b)). The values of the effective energy fractions r_<meI> and λ_<deI> for a layer-built absorber composed of two different porous materials were measured and compared with the predicted values. Both of the measured and the predicted values were in good agreement (Eqs. (3), (4), Fig. 3). The reverberant sound absorption coefficient of a space absorber, i. e. , the absorbing structure with open back space, was measured under various suspending conditions. Firstly, the values of α_<rev> as a function of the distance h from the ceiling to the absorber were measured. And these values were compared with the theoretical values corrected by the wave theory and the edge-effect. Correction for the edge-effect is referred to Eq. (6) and a constant β in Eq. (6) is assumed to be independent on the distance h. The theoretical values follow the measured values rather good except for a slight shift as a whole (Eqs. (5), (6), Fig. 4). Secondly, the values of α_<rev> as a function of the frequency were measured and also compared with the theoretical values. The theoretical values agree with the measured values except for the disagreement below 250 Hz caused by the undiffusibility of the field (Fig. 5). As a thirdcase, the values α_<rev> as a function of the turning angle θ were measured. The theoretical values follow the measured values very well (Eqs. (7), (8), Fig. 6, 7). The values of α_<rev> of an absorbing structure with closed back space as a function of the distance h were measured for center frequency of 500 Hz. The measured values agreed with the theoretical values for small h, but for large h the measured values took intermediate values between the theoretical values with correction by the wave theory and the edge-effect in which β is independent on the distance h and the theoretical values without correction by the edge-effect (Fig . 8). The results obtained are as follows: (1) The method demonstrated in this study is very useful for obtaining the reverberant sound absorption coefficient of a plane absorber of porous material for any mounting conditions without measurement of it in the reverberation room. (2) The theoretical value of α_<rev> of the absorber with closed back space did not follow the measured values because the method of correction for th edge-effect has not been studied. (3) The energy fractions r_m and λ_d of the material of the absorber can be measured, and these values are very useful for the prediction of the reverberant sound absorption coefficient of the absorber of porous material. (4) The effective energy fractions r_<meI> and λ_<deI> of a layer-built absorber can be determined by the individual acoustic properties of the constituent material.
It is well known that in piezoelectric vibrators higher modes can be excited and that these higher modes act as unwanted spurious responses for those vibrators utilizing only the first mode. In most piezoelectric vibrators, the suppression of unwanted spurious responses is of paramount importance. The author has previously reported on the suppression of spurious responses for a piezoelectric bimorph vibrator, it seems, however, that as to a flexural piezoelectric vibrator, the suppression method of its spurious responses over a wide frequency range has not been found except for the suppression methods of partial spurious modes. This paper deals with the suppression method of unwanted spurious responses for a flexural piezoelectric vibrator with a split-electrode and the experimental results. The method for suppressing the spurious response is essentially the same as that described in a previous paper. In the first place, a method is described to suppress the spurious modes of two piezoelectric vibrators with electrodes of different shapes. The split-electrode of a vibrator is formed functionally for the vibrator to vibrate only in the first mode (Fig. 1 (a), (b)). Secondly, the equivalent circuit constants and the capacitance ratios of piezoelectric vibrators of two kinds (Type A, Type B) are shown. The equivalent circuit constants can be adjusted by changing electrode width, but the effect of spurious mode suppression is kept constant. The equivalent capacitances of type A and type B vibrators becomes equal when electrode width ratio t_1/t_2≒0. 707 for both vibrators and when t_1/t_2=0 for type A and t_1/t_2=1. 0 for type B; the same can be said for the equivalent inductances of two vibrators (Fig. 3). The capacitance ratio is minimal when t_1/t_2≒0. 173 for type A and t_1/t_2=1. 0 for type B. The capacitance ratios are compared with those of vibrators with a non-function-shaped electrode (Fig. 5, Fig. 6). Finally, the frequency responses of rectangular flexural piezoelectric vibrators with electrodes of different shapes are shown (Fig. 8, Fig. 9). These results show that a function-shaped electrode is useful for the suppression of unwanted spurious responses when the width-to-length ratio of a vibrator is small.