Noise should be dampened to such an extent that it no longer interferes with the activity you were set out to do. Just 30 dB(A) is disturbing to sleep. Noise with sound levels of 35 dB(A) or more interferes with the intelligibility of speech in smaller rooms.

Even lower background levels are needed for adequate speech intelligibility for vulnerable groups - such as the hearing impaired, the elderly, children in the process of language and reading development, and individuals who are not familiar with the spoken language.

Rooms with many hard surfaces may result in disturbing ‘echo’ which must be avoided. A reverberation time below 0.6 seconds is desirable, even in a quiet environment.