Analysis and Ranking of the Acoustic Disturbance Potential of ...

Report No. 6945
BBN Systems and Technologies Corporation
Transmission Loss, TL
The reduction in sound level with distance along a given acoustic
path caused by spreading loss and absorption loss components
2. BIOACOUSTIC TERMINOLOGY
Critical Bandwidth
The frequency band of noise surrounding a pure tone that is most
effective in masking the tone. It is approximately equal to antilog,
(critical ratio)/lO but is often broader.
Critical Ratio
The signal-to-noise ratio that is required to detect a sound signal
in the presence of ambient noise. This ratio varies with frequency
and is usually lowest in the frequency range where the hearing
threshold is also lowest.
Hearing Threshold
The intensity of sound that is barely audible in the absence of
ambient noise. The absolute hearing threshold varies with frequency,
and the curve relating the threshold intensity to frequency is called
the audiogram.
3. SPECIAL TERMS USED IN THIS REPORT
Acoustic Interaction
The transmission and reception of sound during a specific source -
species encounter at levels sufficiently loud to be at least 20 dB
above the local ambient noise level in the dominant source bandwidth
or 20 dB above the species hearing threshold in the same frequency
range, whichever is highest.
Avoidance
A form of behavioral response to sound in which a species is observed
to move away from the vicinity of the sound source or change normal
movement patterns so as not to come as close to the source as would
be expected in the absence of the sound.
Dominant Bandwidth
The portion of an acoustic source output spectrum including the 1/3
octave band with the maximum level and bounded by the 1/3 octave
bands with levels within 10 dB of the maximum.