Page 15 - Jul2009

importance of identifying the location of a sound at a distance
for the average civilian and a soldier. For a civilian, listening to
sounds at a distance is not a common occurrence in daily life
and the inability to identify the location is considered at most
a nuisance. In the life of a soldier, the failure to identify the
location a sound at a distance can be fatal. Previous work in the
area of auditory localization of distant sounds has shown that
increases in the distance between the listener and the sound
source create uncertainties in the listener’s perception of its
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location. The Distance Hall will enable expansion of this
research under additional conditions.
Listening Laboratory
The Listening Laboratory (Fig. 6) is a multipurpose room measuring 4.6 m wide by 6.4 m long and is 3.5 m high. It is designed for studying speech perception, as well as the effects of room acoustics and sound source configurations on sound perception. Acoustic features and instrumentation of this space were designed to facilitate comparative studies of various sound reproduction systems, comparison of loud- speaker, headphone, and bone conduction sound systems, and the effects of room acoustics, noise level, and reverbera- tion time on speech perception.
The Listening Laboratory is equipped with 14 wideband
Genelec 8030A self-amplified loudspeakers and two sub-
woofers. The loudspeakers can be arranged to represent var-
ious sound reproduction systems (up to 10.2) or to simulate
multiple talkers. The loudspeakers can be raised or lowered
from floor to ceiling height through the use of chains mount-
ed to the ceiling of the room and the use of loudspeaker
stands. Sound absorptive panels cover the wooden walls and
can be removed in any desired combination. Reverberation
times can be changed through the removal of panels to a
maximum of 400-450 msec when the majority of panels are
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removed. This provides the means to study both the global
effects of room reverberation and the effects of discrete sound reflections on auditory perception.
In addition to the loudspeakers, the room contains five headphone stations with two headphone jacks on each for a total capacity of 10 pairs of headphones. Each headphone jack is wired with an independent volume control. The com- bination of the self-powered loudspeakers and headphone boxes can allow for the evaluation of speech recognition through different communication systems in quiet or in noise, with or without various amounts of reverberation in up to 10 listeners at a time. This will save both cost and time in studies examining speech intelligibility, and ensure that environmental variables are the same for all participants.
OpenEAR
OpenEAR is a 4,500 square meter outdoor research facili- ty designed for studies of auditory perception in natural field environments. It consists of an open field between two ware- house buildings. Access to this facility is through two door- ways on the outside wall of the Distance Hall. Use of this area will allow studies of distance perception conducted in a labo- ratory environment to be replicated in a natural field environ- ment. The proximity of OpenEAR to the Distance Hall will allow comparisons to be made in evaluations conducted with the same listeners at almost the same time that will reduce data uncertainty resulting from laboratory and field studies con- ducted at different times and with different listeners.
OpenEAR includes outdoor loudspeakers and micro- phones as well as the cabling and power needed to operate them. The loudspeakers enable generation of sounds at vary- ing loudspeaker-to-listener distances to replicate outdoor environments encountered in military operations. The micro- phones enable a researcher to record sounds in the outdoor environment or to directly route the sounds taken from the outdoors through loudspeakers in the indoor research spaces.
Fig. 6. A soldier listens to speech presented through headphones in the Listening Laboratory. The foam panels within this space can be removed to increase the reverberation time of the space.
The creation of OpenEAR will allow additional research to be con- ducted (in combination with the Distance Hall) in the area of audito- ry distance estimation. Previous studies conducted within ARL have taken place in an open field located approximately 5 km from the ART labs. OpenEAR will provide an out- door research area that will be more accessible by the ART. Previous work by the ART in distance estimation at loudspeaker to listener distances of up to 800 m has demonstrated that individuals grossly underestimate the distance to sound sources and that errors increase non-linearly
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with distance. At distances of less
than 20 m, listeners are fairly accu- rate but estimates drop off at dis- tances as short as 100 m. Further work in this area is needed to evalu- ate the reasons for this and to deter-
14 Acoustics Today, July 2009