The terms intelligibility, clarity and intelligibility belong to the characteristic values of room acoustics and sound reinforcement. The mentioned parameters depend on the arrangement of the loudspeakers and the position of the listener.
As far as clarity is concerned, it is given as a clarity measure, which stands for speech intelligibility at a given listener position. The clarity measure is determined via an acoustic room impulse and depends on the room response.
The clarity measure is a criterion for halls and auditoriums in which lectures are held. It is determined from the ratio of the reflections of the direct sound within the first 50 ms to the total reflections. For this reason, the characteristic value is also referred to as C50. In contrast, the characteristic value C80 stands for the clarity measure. The clarity measure is given in decibels( dB). If the reflections within the first 50 ms are as large as the remaining reflections, the clarity measure is 0 dB. Good speech intelligibility lies between -3 dB and +2 dB.