Measurement of low-frequency noise in rooms

Measurement of low-frequency noise in rooms is problematic due to standing wave patterns. The spatial variation in the sound pressure level can typically be as much as 20-30 dB. For assessment of annoyance from low-frequency noise in dwellings, it is important to measure a level close to the highest level present in a room, rather than a room average level. In order to ensure representative noise measurements, different positions were investigated based on theoretical considerations and observations from numerical room simulations. In addition measurements were performed in three different rooms. The sound pressure level was measured 1) in three-dimensional corners and 2) according to current Swedish and Danish measurement methods. Furthermore, the entire sound pressure distributions were measured by scanning. The Swedish and Danish measurement methods include a corner measurement position to ensure representative high levels. However, this position has some distance to the walls, and may still be subject to modal influence. It was confirmed by the measurements that the positions from especially the Danish measurement method may not effectively serve their purpose. It is suggested that four three-dimensional corners are used for indoor measurement of low-frequency noise.