An electric circuit model which explains the mechanism of production of the summating potential is presented. The model is based on assumptions of functional differences between inner and outer hair cells and gives an explicit expression of the summating potential as a function of sound-pressure level(SPL), frequency, and recording position. The expression agrees qualitatively with observations on the summating potential.
We have pointed out the feasibility of the finite element technique on electro-acoustic system analysis, and demonstrated the application to piezoelectric transducer problems. The present work is concerned with another coupled elastic structure-acoustic medium system, that is, a direct-radiator speaker model in which a vibrating shell backed by a closed cavity is to radiate sound into semi-infinite acoustic space. The model is two-dimensional or axisymmetric, and its shape and acoustic cavity profile could be arbitrary. The computer simulation program is developed based on finite element approach and some calculations of the driving-point impedance of the shell under various acoustic loading conditions and far-field sound pressure characteristics are demonstrated. The effects of the coupling to the cavity and the case of a so-called vented enclosure are also discussed. Comparison with a real system and verification of the approach are not given, which would be reported in due course.
In the acoustical engineering such as sonar technique, it is often necessary to remove periodic waves from reflecting signals. The moving target indicator reported here can remove periodic waves with simple circuits. This indicator has two delay lines in its circuit. The input signals are stored repeatedly on these two delay lines in a specified ratios in a pile, respectively. The amplitude of the output signals from the delay lines are processed successively with a specified calculation in order to take out the signals of moving targets. The signal from moving targets can be taken out from reflecting signals and especially would not disappear for a certain time after the stop of the movements of the targets. Some experiments were performed so as to verify the validity of above theories. In these experiments, the results qualitatively agree with the theory. From the results of these experiments, it is found that the moving target indicator designed in this paper is useful in the acoustical engineering and etc.
A method of prediction of the output probability distribution of noise level or L_α is studied in the case when the random sound pressure wave with non-Gaussian distribution type having the linear and non-linear correlation among many sampled time points is passed especially through the N-fold walls of the linear sound insulation systems. The impulse response in a time domain is derived for the N-fold walls from their transfer function in a frequency domain, and the input and output relation is described with this impulse response. The probability density function of transmitted energy through the N-fold walls is discussed by using this input and output relation. The validity of the theoretical results, is verified by the experiment where an aluminium triple walls is set between two reverberation rooms and the sound pressure wave recorded in the actual traffic noise is used as a sound source.
When examining materials by using sound waves, it is common practice to utilize sound waves of narrow beam in order to obtain higher resolution. In this research, a study was made on the acoustic receiver outputs for the reflected waves in the direction of the sound source when sound waves narrow in the beam width compared with the dimension of the cylinder were projected against a cylinder from an acoustic transmitter/receiver traveling along the axis of the cylinder. Two approximate calculations were worked out. The first one was a simple approximation of geometrical optics in which the strength of the reflected wave was assumed to be dependent upon the effective area on the cylinder surface where differences in the pathes of the sound waves were within λ/(12) (λ:wave length). Theoretical values by this method and actual values were in close agreement with each other only when the cylinder was located in parallel with the scanning surface. Then a fairly strict approximate calculation was performed in which cylindrical scatter was integrated to obtain the sound pressure in the direction of the sound source. This method yielded theoretical values which agreed well with the actual values even when the cylinder was inclined, thus being considered applicable to general cases. Through this research, general properties were obtained on the narrow beam sound waves reflected from a cylinder.
In outdoor propagation of sound, the ground surface and other obstacles such as buildings have complex scattering characteristics to the incident wave especially in high frequency region. As an ideal limit of this complex scattering, the obstacle is supposed to absorb a part of incident sound energy and reflect the remaining part of energy equally in all probable directions. The scattered field of sound intensity around the obstacle is shown to be the same as those fields associated with black body radiation of heat and diffuse reflection of light at the surface of the obstacle. As an application of this theory, it is carried out to investigate the scattered sound fields above the plane boundary which diffusely reflects the incident waves. The simple closed forms of the scattered fields are derived for the incident plane, spherical and cylindrical waves. The results are compared with those relevant to the specular (regular) reflection of the incident sound at the boundary. For the diffuse reflection an equivalent image source is introduced which is similar to the one for the specular reflection. The directivity pattern of the image source for the diffuse reflection, however, is not omnidirectional and is proportional to directional cosine of the azimuthal angle.