The quality of speech in

The quality of speech in the examined rooms was evaluated by four acoustic indicators: T, L, C50 and STI. In practice, field measurements for the reverberation time (TM) and L at the octave band centre frequencies were carried out according to ISO 3382-2 (I. S. I. 3382-2, 2008) and ISO 1996-2 (1996-2, International Standard ISO, 2007), Figure 6. The measurement tools were Brüel&Kjear instruments, including, but not limited to, a sound analyser (type 2260), an Omni sound source (type 4296) and a power amplifier to drive the sound source. The height of the microphone during the measurements was kept at 1.20m to simulate the height of a seated student׳s ears. A total of 24 reverberation times at a source height of 1.5m were recorded in unoccupied rooms utilizing alternating source and receiver locations. The measurements of L were carried out during class time, where all adjacent spaces were occupied with normal activities. Three discrete measurement positions were recorded in each room to cover the significant variation in noise emission. Since the windows are designed to open for ventilation, the measurements of L were performed with windows open. In addition, lighting and electrical fans were operating normally. During the measurements, the relative humidity and air temperature were monitored and recorded using a thermo-hygrometer device. To estimate the effect of occupation and to calculate both C50 and STI, CATT room acoustic software version 8.0b was used. The trpv1 antagonist coefficients of the various surfaces used in the CATT calculations are shown in Table 4. The properties and location of the sound source, as well as the numbers and locations of the receivers, were simulated based on those used in real measurements. The different setups, calculation conditions and scattering coefficients used in the simulation are listed in Tables 5 and 6. The results of the field measurements were used to validate the CATT model outputs. Figure 7 compares the unoccupied reverberation time obtained using CATT models (TUcatt) and that obtained from field measurements (TM). It can be seen that the difference between the TUcatt and TM curves is less than 10%, which is the assumed error due to differences in daily circumstances (Bradley, 2002). After validation, the rooms, in simulation, were considered to be occupied. The absorption coefficients (α) for the model boundaries were kept constant with respect to the unoccupied case, except for the audience (students), for which coefficients were taken according to Kuttruff (Kuttruff, 2009); see Table 4. The block representing the students was given the absorption coefficients of people sitting on wooden chairs. For comparison, optimal reverberation times (Topt) for both auditoria at 500Hz and above were calculated according to the formula (2005a, , 2005b; William and Joseph, 1999):where V is the room volume in m3. The optimal reverberation time at frequency bands less than 500Hz (ToptOBCF) was calculated by applying the formula (Elkhateeb, 2005a):where n is a ratio that can be calculated from (Elkhateeb, 2005a):where F is the centre frequency of the band. The logarithmic average of the background noise levels (Lave) for the measured L was calculated from (South, 2004):where x is the number of measurements. The results of the simulation were compared to the optimal values, whereas Lave was compared to the ANSI maximum acceptable level of noise (NC-35) for educational spaces (Standard, ANSI/ASA S12.60–2010/Part1American National, 2010). Based on the results, the acoustic defects were specified. Accordingly, proposals to enhance and improve the acoustic quality of the two rooms were suggested. The effects of these proposals were explored using CATT software.
Description of the acoustic performance in the examined rooms
Proposals for improvement
Conclusions Based on an architectural survey, most surfaces in both rooms are reflective, which can cause an excessive reverberant sound. Shape analysis of the two rooms showed that there are many shadow zones that cover more than 20% of the audience area as a result of the ceiling shape. These shadows, in addition to the uneven distribution of the early and late reflections, divide the audience area in both rooms into medium and hard acoustic zones. The results show that TOcatt highly exceeds Topt at all frequencies; for example, TOcatt at 1 and 2kHz is higher than Topt by more than a factor of 2 in room C and 1.5 in room RAZ. It is obvious that energy flow are highly reverberant rooms, and room C is the worst because VP in room C is larger by 21%, although the capacity of room C is smaller than that of room RAZ by 40%. Furthermore, the measured spectra of Lave (Nc-55) in the two rooms are higher than the maximum acceptable noise level (Nc-35) by approximately 20dB in the mid and high frequency ranges. This defect is mainly due to the intrusion of outdoor noise through the permanently open windows. Thus, good sound insulation for these windows is vital for any acoustic enhancement. In this case, natural ventilation in both rooms should be accordingly switched to a mechanical ventilation system. As a result of the excessive reverberation and the high noise levels in both rooms, the values of STI and C50 are dramatically low, excluding the receivers close to the sound source. In conclusion, the two rooms suffer from low speech intelligibility.