Satisfactory, difficult and impossible noise levels for telephone use in noisy areas.
Background noise interferes with telephone conversations, and
- conditions are satisfactory at levels less than 65 SIL (dB) (approx. 72 dBA)
- conditions are difficult at levels in the range 65 - 80 SIL (dB) (approx. 72 - 87 dBA)
- conditions are impossible at levels above 80 SIL (dB) (approx. 87 dBA)