The three different kinds of otoacoustic emissions (OAE) measured in the human closed ear canal and their characteristics are described. Spontaneous OAE are picked up by sensitive microphones as very faint tonal components at about 70% of normal ears. Simultaneous evoked OAE are measured as rippled frequency response at low levels which disappears at higher levels. Delayed evoked OAE can be observed at about 97% of normal subjects as a delayed response to short sound bursts, but at low levels only. The correlation between these different emissions as well as their relation to the fine structure of threshold in quiet are discussed. A model simulating the nonlinear cochlear processes with active feedback describes these effects as well as many characteristical dependences like tuning curves, delay times, spectral compositions, suppression-period patterns or (2ƒ₁-ƒ₂)-difference tones in good agreement with human data. This way, otoacoustic emissions are used as an effective tool in research of the hearing system's peripheral processing.

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The dependence of perceived loudness on frequency, duration and bandwidth of sounds is briefly reviewed. The implementation of these dependencies in sound level meters and loudness meters is discussed. The main features of a loudness meter in accordance with ISO 532 B are illustrated. In particular, the simulation of the duration-dependent decay of psychoacoustic excitation is addressed. Finally, the subjective evaluation of the loudness of different types of printers is compared to their objective rating according to A-weighted sound power and loudness measured with a loudness meter.

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This paper describes a new method for automatic detection of slight flaws on the outer race of a ball bearing using two vibration pick-ups. On production lines of mass-produced precision ball bearings, the detection and classification of flaws on the balls and races have been carried out by aural monitoring of vibration signals of the outer ring. Some useful automatic methods based on the analysis of the periodicity of vibration pulses excited by the flaws have been developed as alternatives to aural inspection. However, slight flaws on the outer race are not always detected by those methods because the vibration pick-up is almost completely insensitive to the vibration due to a flaw in a direction perpendicular to the pick-up point. Therefore, we have developed a new method to detect slight flaws on the outer race, regardless of the position of flaws. With this method, slight flaws are detected from the cross spectrum between the squared envelope signals of the vibration signals detected by two vibration pick-ups.

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Parabolic approximation is effectively used to analyze the nonlinear acoustic field generated by a directive sound source in layered media. Quasi-linear approach and linear boundary condition are applied to obtain the fundamental and second harmonic waves transmitting through a plane interface that separates two media. The interface is placed in nearfield for the harmonic. The spectral contents of sound pressure are measured and compared with the theoretical prediction. Both the results are in good agreement for propagation curves and beam patterns. Transmission loss by insertion of a thick layer across an acoustic beam is also investigated. It is shown that unlike the fundamental wave loss the harmonic loss varies with source-layer distance. All experiments are conducted in water, methanol and castor oil.

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The signals maximizing the wide-band ambiguity function, in which the effects of both phase-fluctuation and Doppler shift are taken into account, are derived by using techniques of variational calculus. These signals are found to be very similar to some of the waveforms used by dolphins and bats for echolocation. It is indicated that these signals can be also produced by changing only the coefficients of the derived differential equation. Their vocal tract shapes are estimated from these theoretical signals by applying linear prediction techniques and found to resemble the configuration of human whistling.

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