It is very important to pre-estimate the sound pressure levels around the roads before the construction. We have derived the formulas to estimate the sound pressure levels on the banks of a depressed road with finite acoustic impedances. The formulas were produced by setting two imaginary boundary surfaces on the break-lines of the depressed road and applying Green's theorem. These formulas are used to estimate the effect of the finite acoustic impedances peculiar to the surfaces of the depressed road. The agreement between the theory and the experiments is excellent.

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This paper discusses various ARMA digital lattice filters. The design procedures of these filters have been proposed as various forms. However, if we notice the orthogonal method based on a linear estimation theory, all design procedures are treated with an understandable coherent form. First, this paper examines the ARMA lattice filter whose section increases either AR order or MA order by one independently. The filter section is regarded as elementary. In order to derive this section, the subspace used in the or-thogonal projection method is carefully processed with the other subspaces. In other words, this paper shows the implicit dependency in each elementary section. In addition, this paper develops the ARMA filter associated with the Mullis-Roberts' algorithm. This algorithm estimates the AR parameters for the ARMA reference model. Thus, it used to have nothing to do with the construction of the lattice filter. However, if an ap-propriate subspace is selected, we can design a Mullis-Roberts' algorithm type ARMA lattice filter. In this paper, all relations in the design procedures become clearto under-stand them easily.

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A new method to evaluate visual/tactual systems for the hearing impaired has been proposed and quality of vowel information to be transmitted has been discussed. In this method with synthetic vowels, three fundamental abilities which indicate categorizing a large number of stimuli, normalizing male/female voice and compensating for coarticu-lation effect are tested and evaluated in comparison with normal auditory abilities. According to the results obtained by applying the testing method to two visual and two tactual systems, both visual systems can present much better vowel information than it by the tactual systems in the sense that a large number of vowels different in the formant frequencies are correctly categorized. Furthermore, the visual system (V-color) only which converts voiced portions of connected speech into color pictures on a TV screen transmits information available in normalizing male and female voice and in compensat-ing for coarticulation effect to be appeared on connected vowels. It is considered that strict evaluations on goodness of information give a guide to the development of new aids.

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This is to propose a simple method of correction for the depolarization in the determina-tion of electromechanical constants of a piezoelectric bar transducer. The sound propaga-tion along a piezoelectric rod is one-dimensionally analyzed on the assumption of sinu-soidal strain distribution within the bar wave approximation. The flux leakage of depo-larizing field is taken into account with the introduction of a degree of depolarization which is related to the appropriate depolarizing factor. The formulation is simple and intuitive. The results agree with those of the previous approximate calculation based on the consideration of space and surface charges distribution.

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