In room acoustics, it is necessary for establishing a method of measuring the acoustical effect of halls and a reasonable method of designing room acoustics to find correspondences between physical and psychological quantifies. This paper deals with the correspondence of the physical quantity of a sound field which we measured in a reverberant room in which reverberation time was varied in four steps from about O. 3sec to 2. Osec to the psychological quantity of two syllable signals which we recorded stereophonically in the same sound field and then reproduced in an anechoic room. It has been found from the result of our experiment that physical and psychological quantities are in linear oorrelation with each other. Among the measured physical quantities, reverberation time and integrated sound pressure value are in good correspondence to psychological scale. The ratio of time-sound pressure and the ratio of space-sound pressure which represent the time and space construction of decaying sound are in correspondence to psychological scale.
Correlation techniques which use M-sequence signal are applied to some acoustic measurements. The band noise modulated (intermitted) by the M-sequence signal is emitted from the speaker. The microphone output after receiving the sound is squared and the cross-correlation of M-sequence signal and the squared signal is computed. Then we may be able to find from the correlation peaks the sound intensity and the acoustical delay time without the influence of external noise. If there are multiple sound paths from speaker to microphone, each sound ray can be measured separately by this method. These are the properties similar to those of the correlation measurement by white noise, but M-sequence method has the following advantages:1) The shape 00 the correlation function with delay time r is triangle, and the amplitude and the delay time of the correlation peak can be detected very easily. 2) The triangular form of the correlation function remains unchanged. if the frequencies of band noise are varied. This is because the shape of the correlation function depends only on the nature of the M-sequence signal, while the amplitude of the correlation peak depends on the properties of noise.
This paper presents the results of the analysis of variations in frequency response and directivity pattern of the 2nd order pressure gradient directional microphone due to combining method of the element Ist order pressure gradient directional microphones. Especially discussed matters are the degradations of the frequency response and of the directivity pattern due to differences in the sensitivities, electrical impedances or directivities of the element microphones. The allowable difference in these values are obtained. The paper also presents characteristics of the 2nd order pressure gradient unidirectional capacitor microphone that have been realized.
This study shows our successful attempt to simulate speech mechanism with the aid of an analog computer, thereby devising a speech synthesizer which can speak continuousty in real time. We began with developing an ultra-high speed analog computer which can operate in the speech frequency band width. This computer was used for making a vocal tract simulator, making it possible to synthesize Japanese vowels of fairly good quality. Next, in synthesizing Japanese consonants, the parameters corresponding to conrigurations were controlled dynamically by the use of a newly developed high speed analog multiplier. As a result, control noises were eliminated and smooth control was ensured, thus making it possible to synthesize all of fifty Japanese alphabets. By the way, in order to get continuously synthesized voices, the hybrid system was employed for control. Our new method has been producing a satisfactory result in synthesizing songs as well as speeches.
In this paper is given theoretical considerations for providing a sound source which is flat in frequency characteritic and can radiate large sound power all over the range of audio frequency. A constant sound pressure source can be obtained by the following method. Many small diaphragms are arrayed in concentric circles on a rigid sphere. Outer diaphragms are caused to vibrate in the same phase in the low frequency range, and the vibration is moved inward with an increase of frequency, while the total volume acceleration is kept constant. It is made possible to obtain a nearly ideal constant sound pressure source by using the active dividing networks which keep the total volume acceleration constant, delay networks connected in cascade, and an equalizing network. Some results of experiments on the sound field characteristics of vibrating diaphragms on a sphere are also shown.
The Bessel type distribution worked out in our previous paper is not a very practical expression as an explicit expression of the conditional probability in the field of random street noises, since it is expressed mathematically in a complicated form. For the purpose of introducing a truly practical expression of the conditional probability density, it is advisable to find an approximate expression in a more simplified form instead of using the above Bessel type distribution. Thus, we can find out that a lognormal probability distribution can be approximately calculated as a universal expression of the conditional probability distribution of random noises. First, a joint moment generating function of noise variables Z_h (h=l, 2) defined by a logarithm of random noise level X_h (db) is given from a general expression of the bivariate joint probability in the form of statistical Laguerre expansion series. Then, the 2-dimensional normal distribution can be approximately derived as an expression of the bivariate joint probability density P(Z_1, Z_2) in the closed form. Accordingly, we can easily obtain an explicit expression of the conditional probability density P(X_1 X_2) given by a lognormal distribution, where information of linear correlation between two random noise levels X_1 and X_2 is reflected in the parameter of the conditional average. If our attention is focussed on the shape of a conditional probability distribution irrespective of the internal structure of the linear correlation effect reflected in parameters, a lognormal probability distribution can be more simply found from another point of view. Finally, detailed experimental considerations of street noises sufficing to corroborate the above theoretical results are given in the following two cases:(i) the conditional probability density function P(X_1 X_2) in the form of a lognormal distribution, (ii) the detection of weak periodical signals buried in random street noises.