Jukka Keränen, David Oliva Elorza,
Vesa Koskinen, Valtteri Hongisto
Finnish
Institute of Occupational Health, Indoor Environment Laboratory,
Lemminkäisenkatu 14-18 B, 20520 Turku, Finland
jukka.keranen@ttl.fi
Inside Finnish dwellings and schools,
A-weighted noise levels caused by external noise
sources shall be below 35 dB at day time and below 30 dB at night time. In
offices, the Aweighted
daytime level should be below 35 dB in meeting rooms and below 45 dB in
work
rooms. Similar requirements apply in most European countries. In certain
situations,
external noise can contain low frequency noise (LFN) in such a degree that
the risk of
annoyance should be considered separately. In such cases, current knowledge
and
accuracy of engineering is not sufficient. The requirements for LFN levels
are not
harmonized between countries, sound insulation data of facade components is
not
available below 100 Hz, and measurement methods of LFN level inside a room
are
controversial. The aim of this study is to present an engineering model which can
predict
the possible variation of the LFN level inside a room from an external
sound source. The
prediction requires the outdoor noise level in front of the facade, the sound
reduction index
of the facade, and the sound absorption area of the room. The
essential contribution of the
model is that it takes the important uncertainties into account. They
appear in the
measurement of outdoor noise level, sound reduction index and indoor noise
level. The
predicted indoor noise level is presented with variation range and compared
to
requirements for LFN level. The results are easy to inspect and enable objective
risk
assessment for low frequency noise annoyance. The model includes the third
octave
bands from 20 to 5000 Hz. The model is demonstrated by using the emission
of road
traffic noise.