Dynamic properties of the artificially blown bassoon have been studied by simultaneous observations of the reed vibration and the sound pressure variation at the bocal entrance, the former being measured by an optical method and the latter by a probe microphone. It has been found that (a) the waveform of the reed vibration is almost the same as that of pressure variation and the phase of both vibrations coincide well with each other ; (b) the waveform of the reed vibration is peculiar to the bassoon especially in lower tones, i. e. , the reed closes completely for a short time once in a cycle and opens during the rest of the cycle to its full extent, with small vibrations being superposed ; (c) features of waveforms of the above-mentioned small vibration depends on the tone blown but not on the individuality of the reed ; (d) spectra of the reed vibration are not of the form of sinc function in spite of the sharp pulses repeated in the reed vibration ; (e) the first formant is obtained at about 200 Hz for the sound pressure at the bocal entrance, but that of the radiated sound pressure is found at about 500 Hz. Reed vibrations in the played bassoon observed in the player's mouth by an another optical method are also described.
Three series of psycho-acoustical experiments are performed to investigate how to evaluate the noisiness of randomly fluctuating sound. In these experiments, two hundreds and sixteen fluctuating pink noises, which have the same level pattern as various kinds of actual sounds or the artificially generated patterns, are used as stimuli and six to twenty four subjects judge the perceived noisiness by means of the magnitude estimation or the rating scale method or the constant method. The experimental results show that the noisiness of most fluctuating sounds is increased more than that of steady sound with the same acoustic energy by the level fluctuation, so the relation between PSE of the stimuli and some noise indices is investigated. The results of regression analysis show that L_<eq>, L^^^-+σ, L_<10>, ESL have a comparative good agreement with PSE and the model accounting for the level-fluctuating width or the level-fluctuating speed can predict the noisiness more accurately.
There are some studies on measurement of ultrasonic attenuation constant of human tissues using RF waveforms of echo signals obtained by medical ultrasonic equipment. It seems to be more useful to measure the attenuation using video signal of conventional medical ultrasonic B-mode image. However, there are some difficulties to measure the attenuation in vivo, because of the effects of sensitivity time control (STC) and ultrasonic beam pattern. We devised a technique for evaluating the attenuation constant in ultrasonic scattering medium form its echo signal level compared with that from the reference phantom with attenuation constant measured beforehand, without above mentioned effects. In this paper, the principle of this technique is described, and it is also shown that the technique is successful for attenuation constant measurement through the experiments carried out by using the samples made of fine glass balls dispersed in agar as tissue phantom. Application of this technique to in vivo measurement of human tissue would give valuable information to clinical examination.
An experimental investigation is presented for acoustic oscillation sustained by axi-symmetric jet impinging a straight pipe. The experiment has been carried out in axi-symmetric air jet facilities with nozzle diameter d=28 mm. Data presented for this nozzle are for U_0 ≈ 10 m/s corresponding to the jet Reynolds number Re(=U_0d/υ) of 1. 7*10^4. The pipe of finite length is positioned in line with the axis of a jet. As impinging length l is increased from zero, an acoustic tone abruptly appears and dominant frequency of the tone decreases with increasing l. With further increase in l, at a certain length a frequency jump to a higher frequency occurs, making the beginning of a new stage. The average frequency remains the same at successive stage and is the instability frequency of the shear layer stabilized by feed back from the impinging edge. Flow visualization shows that the vertex shedding from the nozzle appear to be locked in this frequency. Acoustic tone corresponding to resonant modes of the pipe are produced when the condition are such as to ensure close coincidence between the instability frequency of the shear layer and a natural frequency of the pipe. These pure tone, however, are not stimulated when a screen mesh is introduced in between the nozzle and the pipe, since the discrete vortex shedding is a almost completely damped out.
The signal compression method is used to measure the acoustic particle velocity by a constant temperature hot wire anemometer. The signal compression method, which was proposed by one of the authors, was proved useful to improve S/N ratio in measuring the impulse response and the frequency response of any linear system. It is necessary to add bias flow about 1-2 m/s to measure the particle velocity by a hot wire. Four methods were tried, using (1) natural air convection by the hot wire, (2) steady flow in a pipe, (3) vibration of the hot wire, and (4) air suction by a pipe. Methods (2) and (4) were successful to measure the particle velocity with sufficient accuracy. From measured waveforms of particle velocity and acoustic pressure, acoustic intensity acoustic impedance and reflection coefficient were calculated and showed good agreement with theoretical values. Methods (1) and (3) were not so good because sufficient bias flow could not be generated. Nevertheless apparent particle velocity pulse signal could be detected by virtue of the signal compression method.
An acoustic directional coupler is a device which separates out the incident and the reflected waves in a waveguide. A slot-coupled type consists of two adjacent waveguides coupled with a slot-window between them. By tapering the coupling distribution of the slot-window smoothly to zero at each end, the directivity is improved at the insignificant expense of a wider main lobe. As a new attempt, commonly used windows for FIR digital filters are utilized as coupling functions for the slot-coupled type. Under the assumption of the loose-coupling, the directivity characteristics of various slot-windows such as rectangular, Bartlett, Hamming, Hanning, Blackman and Kaiser are presented. It is also clarified both theoretically and experimentally that the frequency band width of the slot-coupled type is much broader than that of the two-hole, the binomial array and the Tchebycheff array types. Therefore, the slot-coupled acoustic directional coupler is potentially useful for a swept-frequency reflectometer.
A signal processor for the signal compression method was developed. It uses 16 bits microprocessor 68000 as the CPU. It is very powerful for the signal compression processing. It was applied for the measurement of the impulse response and the reverberation response of acoustic systems. In this paper, responses of guitar strings for acoustic excitation are explained. Reverberation responses were calculated from impulse responses by the Schroeder's method and the FFT method, which was proposed by one of the authors before. Reverberation responses for very narrow band input signals could be obtained by FFT method. Discussions are made about the reverberation curves which do not monotonically decrease, and about effects of truncation error n computation of reverberation curves.