Abstract: The influence of low-level noise has not been widely noticed. This
paper discovered that low-level and low frequency noise (Aweighted equivalent
level L_{eq} < 45 dB) causes higher probability of
subjective annoyance. The fuzzy mathematic principle was applied to deal with
the threshold level of subjective annoyance from noise in this study; there is
preferable relationship between the indoor noise and noise annoyance at low
frequency noise level. Study indicated at the same centered noise level, the
change of annoyance probability is mainly caused by the change of the frequency
spectrum characteristic of the indoor noise. Under low noise level environment,
without change of the medium-low frequency noise, the slight increase of
medium-high frequency noise level with the help of noise sheltering effect can
significantly reduce the noise annoyance. This discovery brings a new
resolution on how to improve the environmental quality of working or living
places. A noise control model is given in this study according to the acoustic
analysis.