A very interesting acoustical phenomenon, which we call sweeping echoes in a two-dimensional (2D) space, is described and investigated. Sweeping echoes in a three-dimensional (3D) space have recently been reported. In this paper, the regularity of reflected sound in a 2D regularly shaped space is first investigated based on number theory. The reflected pulse sound train has almost equal intervals between pulses on the squared-time axis as in a 3D space. This regularity of arrival times of the reflected pulse sounds generates sweeping echoes whose frequency increases linearly with time. Computer simulation of room acoustics shows good agreement with the theoretical results. In a practical situation, sweeping echoes were observed in a long hallway having a square section.
Unidirectionally fiber-reinforced composites for the soundboard of musical instruments were made using glass fiber or carbon fiber and light-weighted hard polyurethane foam. The vibrational properties and frequency response characteristic of the composites were investigated by changing fibers, volume fraction of fibers and fiber distribution, and the results obtained were compared with those of Sitka spruce for soundboard. The composites, which had 5 to 6 volume percent of carbon fiber filaments distributed uniformly, exhibited almost the same acoustic property as Sitka spruce for soundboard. The results indicated that the acoustic characteristic of wood for soundboard in all audible frequency range could be mostly represented using a simple wood model composed of unidirectionally oriented fibers and porous matrix foam.
We conducted human language identification experiments using signals with reduced segmental information with Japanese and bilingual subjects. American English and Japanese excerpts from the OGI Multi-Language Telephone Speech Corpus were processed by spectral-envelope removal (SER), vowel extraction from SER (VES) and temporal-envelope modulation (TEM). The processed excerpts of speech were provided as stimuli for perceptual experiments. We calculated D indices from the subjects’ responses, ranging from -2 to +2 where positive/negative values indicate correct/incorrect responses, respectively. With the SER signal, where the spectral-envelope is eliminated, humans could still identify the languages fairly successfully. The overall D index of Japanese subjects for this signal was +1.17. With the VES signal, which retains only vowel sections of the SER signal, the D index was lower (+0.35). With the TEM signal, composed of white-noise-driven intensity envelopes from several frequency bands, the D index rose from +0.29 to +1.69 corresponding to the increasing number of bands from 1 to 4. Results varied depending on the stimulus language. Japanese and bilingual subjects scored differently from each other. These results indicate that humans can identify languages using signals with drastically reduced segmental information. The results also suggest variation due to the phonetic typologies of languages and subjects’ knowledge.
In this paper, we have proposed contrastively static and dynamic type two practical and methodological approaches in order to overcome the complexity of actual electromagnetic (abbr. EM) and sound environments. One is an extended regression analysis of static type intended for employing a standard Gaussian distribution for evaluating mutual relationships between sound and light leaked from a video display terminal (abbr. VDT) in a room, and the other is an establishment of Kalman’s filtering algorithm of dynamic type with help of an equivalence transformation toward the standard Gaussian distribution for estimating a sound absorption coefficient in a reverberation room. The effectiveness of the proposed methods has been also experimentally confirmed by some applications to an actual stochastic evaluation of room lighting and acoustics.