Insulation

Typically in noise insulation a barrier is placed between the source and receive positions. The barrier may be partial or complete.

Good isolators are generally heavy or rigid. Like absorption, the insulating property of materials is frequency dependent; in general it is harder to attenuate low frequencies.

Good absorbers are generally poor isolators and visa versa

Successive layers of insulation are not directly additive. If a single layer of plasterboard provides 10 dB insulation at 250 Hz then two layers do not provide 20 dB: in fact the result is closer to 12 dB. For two structures to be strictly additive a significant space or space layer is required between them.

The actual insulation provided is often limited by either flanking transmission or leakage. Even small gaps or leakage paths can severely degrade the performance of a partition.

With partial partitions, such as non-continuous barriers, the effects are dominated by the height of the barrier and the distance of the sound source and receive points from the barrier.