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Fig. 3. A participant prepares for an experiment in the Sphere Room. The central location of the listener station and platform allow for the creation of a completely immersive auditory environment.
room to provide background noise when needed. These loudspeakers are each capable of providing background noise up to 110 dBA at the position of the listener. The combina- tion of spherically located loudspeakers and the central posi- tion of the listener can result in a completely immersive audi- tory environment.
Soldiers, more than the average civilian, listen to sounds arriving from all directions; above, below, behind and beside. The ability to place a listener in an environment where sounds can arrive from any angle opens up a wide range of research possibilities. One potential line of research is the evaluation of the effects of different types of headgear on a listener’s ability to identify the location of a sound arriving from any direction. Soldier headgear includes helmets, com- munication systems, hearing protection devices or any com- bination of these. The Sphere Room is intended to examine auditory localization ability in a more global sense than in
12 Acoustics Today, July 2009
the Dome Room, which is intended for more precise evaluation. Prior work at ARL suggests that wearing a helmet decreases your ability to deter- mine the location of a sound, and fur- ther, as helmet coverage of the ear increases localization performance
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Dome Room
The Dome Room (Fig. 4) was named for its dome-like loudspeaker configuration. It measures 6.6 m long by 8.1 m wide and is 4.1 m high. It is designed for research studies investi- gating the human’s ability to localize real or virtual, single or multiple, and stationary or moving sound sources distributed in a hemispherical space. As opposed to the Sphere Room which has widely spaced loudspeakers, the Dome Room is designed for more pre- cise studies in auditory localization. The room contains a horizontal circu- lar array with a diameter of 6 m that can be populated with up to 180 Meyer Sound MM-4XP loudspeakers arranged every 2 degrees of angular separation. All of the loudspeakers are connected via quick-disconnect plugs, allowing for rapid loudspeaker recon- figuration as experimental designs dictate. The dense loudspeaker config- uration within this room allows research studies to be conducted examining precise identification of a sound source location.
The horizontal array is com- prised of 12 removable segments, each corresponding to 30o of arc. The array is supplemented by two vertical
arcs that can be manually moved along two wheeled tracks: one track mounted to the ceiling and the other track attached to the outside of the top of the horizontal array. The two vertical arcs can be populated with 30 loudspeak- ers each in rows of 5 loudspeakers each at -20 to +40o (10o increments) in the vertical plane. The two arcs can be posi- tioned on opposite sides of the horizontal array to form a nearly 180o arc above the listener, side-by-side to form a nearly 40o span in horizontal and vertical space or in any other location for maximum flexibility in loudspeaker placement. Moving sound sources can be simulated by pan- ning sounds across the loudspeaker arrays through soft- ware. As in the Sphere Room, four loudspeakers are located on height-adjustable stands in each of the corners of the room to provide background noise when needed.
The structural components of the horizontal array are offset from the walls so that acoustically reflective panels
deteriorates.