Sound isolation at low frequencies, only an extension of the traditional frequency range?

Abstract

The expression ‘‘low frequencies’’ implies a frequency range where the rooms’ dimensions are comparable with the wavelength of sound in the rooms. In this range (below 150 Hz for normal room sizes) the sound field in the rooms consists of a few modes only, and changing of parameters that are not connected to the partition influences the sound insulation. This is not a problem of a correct measurement procedure. It is far more the description of the sound insulation itself in which problems arise. The measured or calculated sound insulation is only valid for the specific case under consideration. Numerical studies of the sound insulation of a flexible partition (characterized by a limp mass) between two rooms show that the dimensions of the sending and receiving rooms have the most important influence. This has to be taken into account when extending the frequency range in the standards concerning sound insulation which is necessary since neighbors low frequency stereo equipment, as well as the all present traffic noise from outdoors, demands a sufficient sound insulation even below 100 Hz.