Intelligibility of aircraft loudspeakers

Abstract

Commercial aircraft audio systems provide audible messages including greetings, details of the flight, comments on entertainment, and important safety information. Hence, the speech intelligibility of aircraft audio systems is of great importance. Distributed-mode loudspeakers (DMLs) are known to have wider sound dispersion, especially at higher frequencies, than conventional cone loudspeakers. As aircraft loudspeakers are located relatively close to the passengers, the narrower dispersion and beaming of the high frequencies from conventional cone loudspeakers can cause loss of intelligibility for passengers not on the axis of the loudspeaker and produce uneven sound distribution within the cabin. DMLs have demonstrated intelligibility superior to conventional loudspeakers in other applications such as public address systems. DMLs have other advantages in aircraft installations. They are very lightweight and can even be built into the internal trim, resulting in a nearly zero-weight loudspeaker. Their essentially flat configuration also requires less volume. This paper presents a comparative evaluation of the speech intelligibility of current aircraft loudspeakers and DMLs as determined by the STI (Speech Transmission Index) using the RASTI (Rapid Speech Transmission Index) method in accordance with RTCA document DO-214. Tests were performed under representative conditions and for different seating arrangements.