Abstract
The resonance effect in the audible frequency range in small talks studios often results in one of the worst faults known as "coloration". In many cases, this is due to the excitation of the axial mode of vibration with small damping coefficient which exists independently of neighbouring modes. To determine the value of the wall absorption coefficient of small talks studios in order that the coloration of audible low frequency is not perceived, hearing tests were conducted for the just perceptible limit of coloration in terms of Q-values of the relating axial mode and the ratio (D) of the excited level of the mode to that of a mode in the medium or high frequency range. For the tests, four listeners were subjected to speech signals with various degrees of coloration reproduced through a selective amplifier as simulator of transmission characteristics of small talks studios. From the Q-value and the ratio (D) obtained for the just perceptible limit of coloration at 70c/s, 90c/s and 130c/s, it is shown that the absorption coefficient of the wall relating to the axial mode for imperceptible coloration should be larger than 0. 33 for a studio of 6m^3 in volume, and that the absorption coefficient is decreased as the volume is reduced. These values are in good agreement with those hitherto observed in several existing small talks studios of NHK.
