The mechanical resonance of a tone-arm system, arising in a frequency range between 5Hz and 10Hz, causes deterioration of sound quality. The peak level of the reasonance reachs to 10dB. The tone-arm, furnished with velocity sensors and linear motors, is developed in order to damp the resonance. Perpendicular and horizontal movement of the tone-arm is detected independently by corresponding velocity sensors. Detected signals of each sensor are amplified and fed back to each linear motor. Motion of the tone-arm is controled by these linear motors. As the result, the sound quality is improved greatly because the peak level of the resonance is suppressed by negative feedback (velocity feedback) gain. Moving speed of the tone-arm is controled to be uniform and stable. The transfer function of the tone-arm motion and its equivalent circuits. The damping factor ζ , which is related to equivalent viscosity resistance, and the corner angular frequency ω_0, on first order lead elements involved in the equation, are calculated with an aid of the negative feedback gain R_2/R_1. If R_2/R_1 increases, gain level rises at very low frequencies bacause ω_0 moves to high frequencies. In this system, the best sound quality is obtained when R_2/R_1=100〜400. Peak level of the resonance and f^`_0(ω^`_0/2π) are 6. 5〜2dB and 1. 08〜4. 32Hz respectively, for this case.
This paper describes the possibility of spherical lenses with two concentric layers having constant refractive indices smaller than 2. The phase distribution in the reference plane which is taken in front of the lens is calculated as functions of the refractive index and radius. The lens parameters for the two-layer lenses are obtained under the condition that this phase distribution in the reference plane is uniform and the lenses of two types are obtained. The validity of this method is proved by the calculation and the measurement of the pressure gain. The lens used for the measurement consists of mixture of RTV silicon rubber and zinc powder. Although the pressure gain of these lenses undergose a small change as the k_0 a varies, the average pressure gains are comparable to the level of Luneburg lens.
As is well-known, in the usual case of evaluating a random noise or vibration, it is very important to study a statistical characteristics (like the lower order statistical moment (e. g. , mean and variance) and/or the probability distribution form) of peak values from various viewpoints of a psychological effect to people and a control of environmental noise and vibration. Furthermore, it is well aware that the probability distribution of the peak value shows the Rayleigh distribution for a special case with random noise (or vibration) process of the Gaussian type. The actual noise or vibration process, however, dose not always show the typical Gaussian type distribution. In the present paper, from practical viewpoint based on the use of Powell's idea, the probability distribution expression for the peak value is derived in the generalized expansion form of distribution applicable to non-Gaussian stochastic process too. Of course, as a special case when the random noise or vibration process is the Gaussian type, the above theory includes the well-known Rayleigh distribution. Next, the validity of the theory is confirmed both by means of digital simulation and by application to experimentally observed actual road traffic noise. It is a noteworthy fact that the present theory seems te be able to give some kind of theoretical basis to the simplified empirical relationship between L_10 and the expectation of peak values.