The experiments on intelligibility, listening difficulty and optimum speech level by adjustment method were carried out for the aged under the condition of various noise level and reverberation. The following findings were obtained.
(1) The optimum speech levels for the aged are higher than that for the young, and the difference between them becomes smaller at higher noise level.
(2) The listening difficulty score does not achieve the minimum value at the optimum speech level in noisy conditions.
(3) The performance of intelligibility and listening difficulty shows quite unsatisfactory level at the optimum speech level in reverberant conditions.
