Nishimura K., Ina R.

Acoustic phantoms and sound quality of replay sound of stereophonic equipment suffer from effects of vibration on equipments, signal and power transmission cables, a jitter of digital audio system and etc. Then, the high order acoustic and sensational information like as representation of acoustic sources' distribution (e.g. musical instruments) and circumstances of recording scene may deteriorate due to the above distortion factors. That is, the above spatial information is preserved and recorded together with major acoustic signal, but the background noise and harmonic distortion of stereophonic equipment cover its spatial information and make them blurred one. Vibrations occurred in stereophonic equipment seems not a minor cause of above noises especially for harmonic distortion. In this report, we propose a new method on treatment of vibration in stereophonic equipments to suppress higher harmonics of vibration and electric and/or acoustic signals. To evaluate the effect of vibrations, we employed an amplifier composed with vacuum tubes, because of its faithful replaying ability which is convenient to evaluate the effect of vibration on not only speaker system and chassis of amplifier but also plate electrode in vacuum tubes. To suppress vibration of equipments, we employed doubled spike of circular cone made of brass for speakers and chassis and tube radiator made from wire gauze of cupper for vacuum tube of amplifier. The effects of suppressing vibrations were measured as the changes in higher order harmonics of not only vibration on speaker baffle, speaker enclosure, chassis of amplifier and electrode in vacuum tube but also electric signals and radiated sound under sinusoidal input. The correspondence of the above change in higher harmonics to sound quality and summing localization was checked up and compared with the changes in recognition by listening test.