Intelligibility at High Voice Levels and the Use of a Megaphone Available to Purchase

A small megaphone was tested for use in direct voice communication high levels of vocal output against backgrounds of noise. Intelligibility scores were determined for 12 talkers, speaking with and without the megaphone, over a range of field voice levels of 70 to 100 db SPL (at 1 m). Nearly the entire over‐all acoustical gain produced by the megaphone was realized in improved intelligibility above backgrounds of white noise and low‐frequency noise. The acoustical gain of the megaphone permitted a lower voice level, and, hence, delayed the deterioration in intelligibility associated with distortions due to shouting. Frequency shifts in the voice spectrum were measured, with and without the megaphone, over a range of vocal efforts from conversational to maximum shout. Control tests demonstrated that the voice‐frequency shifts associated with shouting are not the primary factor in the deterioration of intelligibility; the frequency shifts appear to be only symptomatic of serious vocal distortions in shouting.