A new field measurement method for sound absorbing materials is proposed. The subtractive holographic technique is applied to reject spurious interferences and to extract waves scattered by a sample. The application of holographic techniques for room acoustics promises greatly to observe the effective absorption characteristics of materials.

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This paper summarizes the study of active cancellation of noise due to vibration of a panel at the output terminal of microphone. The vibration of panel, which radiates noise, is picked up by an acceleration pick-up. The noise output of the microphone due to vibration is estimated by computing the convolution between the output of acceleration pick-up and the transfer function from the pick-up to the microphone output. By subtracting the estimated noise output due to vibration, the noise in the microphone output is suppressed, and the necessary acoustic signal is left. The effectiveness and the limit of this method are experimentally shown. And the existence of zero points in the transfer function from the driving point to vibration pick up point due to vibration of panel is pointed out as the reason why the noise can not be completely suppressed when the vibration pick up point is far from the driving point.

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The radiation characteristics at the lips are measured by using plaster replicas maintaining actual lip shapes under several articulatory conditions for vowels. The experimental results are represented in terms of reflection coefficients of volume velocity to facilitate interpretation in physical conditions. It is shown that the measured data are different from theoretical values of a circular piston model both in amplitude and in phase characteristics. We then present a radiation model approximating experimental results under the assumption of plane wave propagation, which is a highly simplified model but has sufficient approximation accuracy. By use of the proposed radiation model, we can determine the equivalent radiating plane, and can consequently remove ambiguity of vocal-tract length due to uncertainty of the radiating region for actual lips.

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Planar ultrasonic transducers using piezoelectric ceramics poled with interdigital electrodes are theoretically analyzed on the basis of a weak-coupling approximation. The piezoelectrically induced stress, the radiation conductance, and the conversion loss for the PbTiO₃ ceramic planar transducers are numerically evaluated. The theoretical results for the frequency characteristics are almost in agreement with the experimental ones and well explain the experimentally observed variation of the minimum-conversion-loss frequency with generator conductance. The dependence of the conversion loss characteristics on the metallization ratio of interdigital electrodes is also examined.

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This paper describes the design of our speech understanding system and reports preliminary experimental results which support an underlying idea. Our speech understanding system is based on the idea that since we can locate some phones very accurately in the incoming speech, an interval bounded by such robust phones should be taken as the unit of matching. This eliminates the problem of ambiguous word boundaries in searching the most likely sentence, as such an interval have little correspondence to word boundaries. We introduced a new processing level called partial lattice hypothesis level to realize the above idea in our hierarchical SUS. The typical word pronunciation and their varieties are precompiled a lattice form, while modifications at word boundaries are performed by applying the phonological rules during the linguistic decoding. In order to observe how the unit of matching affects the search space of a SUS, we carried out a preliminary experiment of spotting two sets of short phonetic strings against a phoneme lattice-a set containing those strings bounded by robust phones, and the other set for the counterpart. The results verified the validity of our idea.

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This report describes a practical probabilistic evaluation method for the stochastic noise reduction effect when a stationary random noise excitation of arbitrary non-Gaussian distribution type is attenuated by inserting a sound absorbing material into a room. The effectiveness of the proposed method has been confirmed by applying it to the actual noise data observed in a reverberation room. The experimental results are in good agreement with the theoretically predicted curves.

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