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. Author manuscript; available in PMC: 2013 Jul 29.
Published in final edited form as: Comp Med. 2005 Feb;55(1):12–23.

Figure 1.

Figure 1

Sample acoustic spectrum recorded from a representative animal housing unit in the Division of Laboratory Animal Medicine at Southern Illinois University School of Medicine. This recording was collected under normal quiet conditions with a Bruel and Kjaer Pulse System using a ½″ free-field microphone (Bruel and Kjaer model 4191-A). The microphone was attached to a model rat at head level in the middle of a plastic shoebox cage with a wire-top lid (A). Measures were also taken with a small particle filter attached to the top of the cage (B). The filter had no noticeable affect on the measurement. Approximately 30 other individually caged rats were present in the 2.5 × 2.5-m room. Baseline levels of noise across the spectrum appear to be around 42 dB SPL. Note the high level of low-frequency noise (≤ 1 kHz) and the harmonics of a 7-kHz signal (i.e., 7, 14, and 21 kHz). These peaks are presumably the result of inherent ventilation and building noise. Particularly interesting is the ultrasonic content ≥ 38 kHz, some of which might be due to rat vocalizations or other unidentified sources.