TITLE:
Unidirectional Sound Signage for Speech Frequency Range Using Multiple-Loudspeaker Reproduction System
AUTHORS:
Vecky Canisius Poekoel, Koshiro Hira, Yoshifumi Chisaki, Tsuyoshi Usagawa
KEYWORDS:
Uni-Directional; Reproduction System; Multiple-Loudspeaker System; Adaptive Filter; Propagation; Low Frequency
JOURNAL NAME:
Open Journal of Acoustics,
Vol.3 No.4,
December
24,
2013
ABSTRACT: Human safety is the most important issue in disaster management.
Speech is a sound signal containing information that is easily and quickly
understood by humans. Using speech as sound signage in emergency systems can
effectively increase human safety in low or poor visibility conditions such as in
smoke-filled situations. However, reflections of sound through walls, floor
surfaces, and ceilings will affect clarity of speech. Unfortunately, because of
the characteristics of sound reproduction systems, a single loudspeaker propagates
sound waves omni-directionally at low frequencies. This paper proposes a simple
multiple-loudspeaker system for reproducing sound with uni-directional
characteristics. The proposed system consists mainly of a primary loudspeaker
for introducing sound in the desired beam, a secondary loudspeaker for reducing
gain in the undesired direction, and digital filters. An adaptive finite-impulse-response
(FIR) filter is used to produce the controlling sound by implementing a
filtered-x least-mean-square algorithm, and a delay filter for adjusting the
time alignment of sound propagation between primary and secondary sources at
the control point. Several operational conditions for illustrating real
situations and reflections were considered in an anechoic chamber. Experimental
results show the directivity patterns of the proposed multiple-loudspeaker
system for the required conditions. In a low frequency range, the system is
able to control unidirectional propagation; there is a sound beam in the
desired direction and, conversely, reduction of gain in the undesired direction
around the control point.