Abstract

The paper deals with a problem of the influence of the number and distribution of loudspeakers in speech reinforcement systems on the quality of publicly addressed voice messages, namely on speech intelligibility in the listening area. Linear superposition of time-shifted broadband waves of a same form and slightly different magnitudes that reach a listener from numerous coherent sources, is accompanied by interference effects leading to a deep modification of the received signal waveform and, consequently, of its frequency spectrum. The mechanism of formation of the acoustic field is described both in the special case of a linear array of sources, which in areas respectively distant from the aperture allows to determine either a regular transfer function in a given direction, or a directional characteristics at a given frequency, and in the general case of randomly distributed radiating elements. The results of simulations and measurements illustrate the impact of the multiplication of sound sources on the parameters of formants important for speech intelligibility. The measurements performed by the authors in auditory rooms, and the analysis of results point to a significant need to adopt standardized measures related to the effect of broadband interference, particularly of its degrading influence on the listeners’ ability to discriminate and recognize speech elements. Such a measures should complete existing standards, being at present related mainly to room reverberation effects.

Authors (3)