TY - JOUR
T1 - Measurement with verification of stationary signals and noise in extremely quiet environments
T2 - Measuring below the noise floor
AU - Ellingson, Roger M.
AU - Gallun, Frederick J.
AU - Bock, Guillaume
N1 - Publisher Copyright:
© 2015 Author(s).
PY - 2015/3/1
Y1 - 2015/3/1
N2 - It can be problematic to measure stationary acoustic sound pressure level in any environment when the target level approaches or lies below the minimum measureable sound pressure level of the measurement system itself. This minimum measureable level, referred to as the inherent measurement system noise floor, is generally established by noise emission characteristics of measurement system components such as microphones, preamplifiers, and other system circuitry. In this paper, methods are presented and shown accurate measuring stationary levels within 20 dB above and below this system noise floor. Methodology includes (1) measuring inherent measurement system noise, (2) subtractive energy based, inherent noise adjustment of levels affected by system noise floor, and (3) verifying accuracy of inherent noise adjustment technique. While generalizable to other purposes, the techniques presented here were specifically developed to quantify ambient noise levels in very quiet rooms used to evaluate free-field human hearing thresholds. Results obtained applying the methods to objectively measure and verify the ambient noise level in an extremely quiet room, using various measurement system noise floors and analysis bandwidths, are presented and discussed. The verified results demonstrate the adjustment method can accurately extend measurement range to 20 dB below the measurement system noise floor, and how measurement system frequency bandwidth can affect accuracy of reported noise levels.
AB - It can be problematic to measure stationary acoustic sound pressure level in any environment when the target level approaches or lies below the minimum measureable sound pressure level of the measurement system itself. This minimum measureable level, referred to as the inherent measurement system noise floor, is generally established by noise emission characteristics of measurement system components such as microphones, preamplifiers, and other system circuitry. In this paper, methods are presented and shown accurate measuring stationary levels within 20 dB above and below this system noise floor. Methodology includes (1) measuring inherent measurement system noise, (2) subtractive energy based, inherent noise adjustment of levels affected by system noise floor, and (3) verifying accuracy of inherent noise adjustment technique. While generalizable to other purposes, the techniques presented here were specifically developed to quantify ambient noise levels in very quiet rooms used to evaluate free-field human hearing thresholds. Results obtained applying the methods to objectively measure and verify the ambient noise level in an extremely quiet room, using various measurement system noise floors and analysis bandwidths, are presented and discussed. The verified results demonstrate the adjustment method can accurately extend measurement range to 20 dB below the measurement system noise floor, and how measurement system frequency bandwidth can affect accuracy of reported noise levels.
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U2 - 10.1121/1.4908566
DO - 10.1121/1.4908566
M3 - Article
C2 - 25786932
AN - SCOPUS:84925232738
SN - 0001-4966
VL - 137
SP - 1164
EP - 1179
JO - Journal of the Acoustical Society of America
JF - Journal of the Acoustical Society of America
IS - 3
ER -