Measurement and prediction of voice support and room gain in school classrooms

Abstract

Objective acoustic parameters have been measured in 30 school classrooms. These parameters include usual descriptors of the acoustic quality from the listeners' standpoint, such as reverberation time, speech transmission index, and background noise level, and two descriptors of the acoustic properties for a speaker: Voice support and room gain. This paper describes the measurement method for these two parameters and presents a prediction model for voice support and room gain derived from the diffuse field theory. The voice support for medium-sized classrooms with volumes between 100 and 250 m(3) and good acoustical quality lies in the range between -14 and -9 dB, whereas the room gain is in the range between 0.2 and 0.5 dB. The prediction model for voice support describes the measurements in the classrooms with a coefficient of determination of 0.84 and a standard deviation of 1.2 dB.

Speaker-Oriented Classroom Acoustics Design Guidelines in the Context of Current Regulations in European Countries

“…Room acoustics parameters relevant for a speaker, their relationship with voice, and their prediction models have been presented separately in previous research [1,13,18].…”

“…The voice support ST V is a measure of the degree of amplication of a room to the voice of a speaker at his own ears [18]. More specically, it is dened as the dierence between the reected sound level (L R ) and the airborne direct sound level (L D ) of the voice of a speaker, as found in an OBRIR.…”

“…The prediction model for the average ST V in a room [18] disregards the importance of the surroundings of the speaker in determining the actual ST V at the speaker position and provides a unique value for a room, averaged across positions, assuming the systematic presence of the direct sound and a oor reection; all other reections are assumed diuse. The model is expressed as…”

“…opposed to the original reference [18], where V is the room volume and T 60 the reverberation time. The motivation to choose Eyring's formula is that it provides more accurate results in highly absorptive environments (ᾱ > 0.3) than the ones obtained with Sabine's formula, which assumes a low mean absorption coecient in the room.…”

“…• Direct sound characterization with the term −K, which represents the dierence between the source sound power level and the SPL at the eardrum, empirically determined from laboratory measurements of these quantities using a head and torso simulator B& K type 4128 [18]. The frequency-dependent values of Q * , ∆L HRTF and K are given in Table 3.…”