Steffen Pedersen

Indoor Measurements of Noise at Low Frequencies - Problems and Solutions

Due to standing waves, the sound pressure level within a room may vary as much as 20–30 dB at low frequencies. Principal properties of low-frequency sound in rooms are illustrated by simulations, and sound pressure distributions as well as the performance of Swedish and Danish measurement methods are studied by measurements in three rooms. For assessment of annoyance, mainly areas of the room with high sound pressure levels are of interest, since persons present in such areas are not helped by the existence of lower levels in other areas. The level that is exceeded in 10% of the room (L10) is proposed as a rational and objective target for a measurement method. The Swedish method showed results close to the target, but, due to a doubtful use of C-weighting in the scanning, it may give results below the target in case of complex sounds. The Danish method was found to have a high risk of giving results substantially below the target, unless complainants can precisely appoint measurement positions, where the sound is loudest/most annoying. An alternative method using measurements in four three-dimensional corners of the room is proposed. This easy and straightforward method seems to give reliable results close to the proposed target.

Comments to the Article “Sound Insulation of Dwellings at Low Frequencies” I

It is well known that, at low frequencies, the sound level normally varies substantially with position within a room. It is thus not straight-forward to measure and characterize indoor sound levels and to describe sound insulation from the outside to the inside of a building. It is therefore with significant interest and motivation that we have read this article. In the work reported, the sound insulation was measured for the same rooms using three different methods to measure the indoor sound level. Unfortunately, the authors forgot to report results from the first method, and even more unfortunately, a critical error was made in the second method. The comparisons between the second and third methods are thus flawed, and the conclusions as well as the main outcome of the work, a set of recommended sound insulation data for the second method, are wrong. To confuse matters further, the authors seem to be unaware that the measurement methods have different objectives and aim at different measures for the indoor sound level. With the present comments, we want to call attention to these detrimental errors, which – if unnoticed – may lead to serious misunderstandings and misuse of the data in the community. We will abstain from discussing in general the quality of the work, its use of statistics, and its presentation.

Measuring low‐frequency noise indoors

At low frequencies, the sound pressure level may vary 20‐30 dB in a room due to standing waves. For assessment of annoyance, mainly areas with the highest occurring levels are relevant, since persons present in such areas are not helped by the existence of lower levels in other areas. The level that is exceeded in 10% of the volume of a room L10 is proposed as a rational and objective target for a measurement method. In Sweden and Denmark rules exist for measuring low‐frequency noise indoors. The performance of these procedures was investigated in three rooms. The results from the Swedish method were close to the L10 target, but, due to a doubtful use of C‐weighting in the scanning, it may give too low results in case of complex sounds. The Danish method was found to have a high risk of giving results substantially below the target, unless complainants can precisely appoint measurement positions, where the sound is loudest/most annoying ‐ which they often cannot. An alternative method using measurements i...