As part of an ongoing action research study, we have appraised our traditional techniques for the teaching of speech and computational hearing and found them to be inadequate in some respects. In particular, they offer little opportunity for students to experiment interactively with concepts in these fields. As a result, students cannot reflect upon their own experiences nor learn from them. In this paper, we discuss a more interactive approach based on software applications which allow the student to explore the parameter space of the phenomena under discussion. Several examples (chosen from a range of more than twenty MATLAB applications) which illustrate the philosophical and pedagogical elements of this ongoing project are discussed.

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The upper thresholds of burst duration that produced continuous apparent motion were measured when stimuli were successively presented using three loudspeakers arranged in the horizontal plane. Stimuli tested were broadband noises with amplitude modulation, tones and bandpass noises. The upper threshold depended on stimulus and tended to be longer than that of 72 ms for an unmodulated broadband noise. For amplitude-modulated broadband noises, there was an increase in the upper threshold from 72 to 290 ms as the modulation index increased from 0.0 to 1.0. However, the upper threshold decreased from 360 to 135 ms with an increase in modulation frequency from 4 to 64 Hz. For tones, the upper threshold displayed a concave function of frequency with a minimum of 71 ms at a frequency of 3 kHz. For bandpass noises, the upper threshold fell from 347 to 101 ms as the bandwidth broadened from 1/12 to 3.0 octaves. These results are discussed in connection with perception for amplitude modulation and mechanisms to detect motion.

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This paper presents a design method of a radiation plate with high load resistance for load testing of the torsional transducers. The calculation method for the torsional load impedance of the radiation plate seen from the transducer is proposed considering the flexural vibration mode excited in the radiation plate. The theoretical study using this calculation method indicates that the use of the “stripe” flexural vibration mode has advantage over the use of the “lattice” mode in controlling and obtaining a high load resistance. Furthermore, by using a combination of changing the node number of the stripe vibration mode and changing the thickness of the radiation plate, the design of the wide radiation plate which achieves a high load resistance without changing the resonant frequency is attempted. In an experimental study, the measured torsional load resistance of the prototype radiation plate agrees with the calculated one, and the torsional load resistance of 4.7 Nms was achieved with a 223 mm × 50 mm radiation plate where the fifth stripe flexural vibration mode was excited. Load testing of the torsional transducer with the high torsional load was effectively conducted using the radiation plate designed by the proposed method.

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The tapping sound of wood, which included sitka spruce and maple used for musical instruments, and isotropic materials was analyzed into power spectra every one milliseconds and their transient characteristics were investigated. The variations of 1/3-octave band power spectra with time were visualized in three dimensions. The rise time T_r and the decrement rate were investigated at each 1/3-octave band. The T_r decreased rapidly with increasing frequencies up to the first mode resonance regardless of the materials, and then the variation of T_r depended on the materials. The former depended only on frequency and the latter on flexural resonance intensity. Sitka spruce used for soundboards showed the high level up to the middle frequency range and then, decreased considerably the level by increasing considerably the internal friction and showed the fastest rising characteristic in the high frequency range. This characteristic in the high frequency range was attributed to the shear effect in which sitka spruce was the greatest.

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A measurement method of structural intensity was proposed by developing the signal processing in near-field acoustical holography (NAH) in our previous paper [Jpn. J. Appl. Phys., 35, 3167-3174 (1996)]. The present paper extends that method to the structural intensity measurement in cylindrical geometry. Two samples used in the experiment are SUS304 cylindrical shells. One of them has a rib and the other has no rib. The experimental data are obtained and reconstructed over the frequency range between about 300 and about 3, 000 Hz. The data at 488 Hz and 1, 877 Hz are selected for specific and detailed investigation of structural intensity distribution, where 488 Hz lies in a pass band and 1, 877 Hz in a stop band of the ribbed shell. According to the discussion of experimental results, it may be understood that the attached rib acts as a “light beam” at a pass-band frequency 488 Hz and a part of the intensity flow is reflected at and the rest is transmitted through the rib. However, the rib almost completely reflects the intensity flow by acting as a “heavy beam” when the driving frequency is a stop-band frequency 1, 877 Hz. The overall modecell structure is thus largely influenced by the action of a rib except for locally induced vortexlike structure. Also, the calculation of the power injected to the shell successfully leads to the identification and localization of the vibration source

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