This paper describes an original method for speech quality evaluation in the presence of different types of background noises for a range of communications (mobile, VoIP, RTC). The model is obtained from subjective experiments described in [1]. These experiments show that background noise can be more or less tolerated by listeners, depending on the sources of noise that can be identified. Using a classification method, the background noises can be classified into four groups. For each one of the four groups, a relation between loudness of the noise and speech quality is proposed.