Crowd noise spectra for the calculation of the speech transmission index for public address systems

Knowledge of interfering noise is necessary for the correct design of a public address system. Noise sound levels can be obtained, for example, from BS 5389-1. It is more difficult to acquire knowledge of the interfering noise spectra, and the spectrum is also important for calculating speech intelligibility. As shown in the paper, for crowd noise, it is possible to determine the spectrum by pairing the level of noise to the speech spectrum for appropriate vocal effort. The error in determining the speech transmission index for public address systems for such selected noise spectra, relative to values for measurement-acquired noise spectra, is acceptable.