In this section the measurements regarding room acoustic parameters will be explained. Room acoustic parameters obtained for the LSBU acoustic chambers were not used for further analysis between room parameters and the singer’s data as these rooms do not resemble a real practice room environment, but the room data was measured in order to show the acoustic properties of these chambers as extreme environments to demonstrate the data collection methodology for the Field stage. The parameters obtained via room acoustic measurements undertaken at the Royal Academy of Music practice rooms were further analysed in order to find out the correlation between the room acoustic parameters and the singers' parameters.
3.6.1.
Room Acoustic Measurements
Room acoustic measurements of the LSBU chambers and the RAM practice rooms were undertaken using the exponential swept sine (e-sweep) technique, see section 3.1.2, and see Figure 3.
Figure 3 WINM LS measure ment
Measurements were undertaken when the rooms when unoccupied at two source (S1, S2) and four receiver (R1, R2, R3, R4) points in all three chambers; YG, DR and T rooms and at two source and three receiver positions in LG room as the room was not big enough for another receiver position. The minimum source-receiver distance was kept at 1.5 m whilst the minimum distance from room surfaces was kept at a minimum of 0.5 m distance according to ISO 140-4:1998 since the room sizes of practice rooms were small, see Table 2 in Section 3.2.2. The receiver height was kept at 1.5 m. Data measured at each source- receiver combination were then averaged for each space. The source-receiver points and the distance from walls can be seen for each chamber and practice room in Appendix D.
3.6.2.
Measured and Calculated Room Parameters
In this section, room parameters used in the research will be presented together with their calculation and measurement methods.
3.6.2.1.
T30, EDT, C80, G Parameters
Reverberation Time (T30), Early Decay Time (EDT), and Clarity (C80) parameters were measured via WINMLS method for each octave-band from 63 Hz to 4 kHz. Since the practice rooms were very small, instead of measuring Strength (G) parameter, G was calculated for each octave-band frequency by using Equation 9 below according to Sabine’s diffuse field theory where V is the volume of the room (m3), T30 is the measured
reverberation time (sec), and G is the calculated strength parameter (dB).
G = 10log
10(
T30V
)+ 45dB
28 Room absorptions of each practice room were also calculated for each octave band from the measured T30 values for each octave band using Sabine’s formula given in Equation 4.
3.6.2.2.
Calculations of combined octave-band frequencies
For the frequency-based analysis, which will be explained in Section 3.8, in order to establish whether the average values of octave-band frequencies of the mentioned room parameters might have more correlation with the singer’s data than the octave-band frequencies alone, the octave band frequency results of each room parameter were averaged to create octave-band frequency combinations, see table 4. Combinations calculated for analysis are shown in by hatched areas for example: T30 (125Hz-1kHz) means the average of
measured T30 at 125Hz, 250Hz, 500Hz and 1kHz. The combinations were only calculated for the RAM practice rooms as the correlation analysis between room data and singer’s data were only undertaken for the practice rooms. In further chapters, the calculated and measured parameters will be named together with their relevant octave-band and combined frequencies such as T30 (4 kHz); G (125Hz-1 kHz); EDT (125Hz-1 kHz). (Note that, for combinations of
500Hz - 1 kHz and 2 kHz and of 63 Hz, 125 Hz and 250 Hz, instead of defining the frequency range, “mid” and “low” definitions were used as these definitions match with that taken in various standards.)
Table 4 Octave Band frequencies and Octave-band frequency combinations
used for further frequency-based analysis, hatched areas show the averaged
octave band frequencies for each octave band combination.
Octave-band frequency combinations
N=9
Octave Band frequency N=7
63Hz 125Hz 250Hz 500Hz 1kHz 2 kHz 4 kHz 125-250Hz 250-500 Hz 500Hz-1k 1k-2k Mid Low 125-500 Hz 250Hz-1k 125Hz-1k
3.6.2.3.
Background Noise Levels (L
Aeq)
Background noise levels were only measured for practice rooms at RAM since there wasn’t any significant background noise under laboratory conditions. A NOR140 sound level meter was fixed at a 1.5 m height in each room, LAeq,10minwas measured for each practice
room when the rooms were unoccupied and the building was not in use. But after spending a month in the Royal Academy premises during the trial measurements, these levels were found out to be lower than the real practicing environment, as these levels were measured during the late evening when the adjacent practice rooms were unoccupied. Since the aim was to measure the background noise levels at the time when the singer’s voice dosimetry measurements were collected, pragmatic 2-minute representative background noise measurements were done immediately after the data collection of each subject when the
room under measurement was unoccupied but adjacent practice rooms were in use. Therefore as a result, these 2-minute background noise measurements were deemed more representative and used for the analysis.
In order to find the representative noise levels during the time of singers’ measurements, the 2-minute background noise levels (LAeq,2min ) collected after each singer (N=55) in each practice room were logarithmically averaged for each room, see Equation 10. These representative background noise levels, L1 to LN, were used for the correlation analysis between the measured background noise level and the singer’s perception of the noise levels in the practice rooms.
Laverage = 10log [(10L1/10 + 10L2/10 + 10L3/10 +… + 10LN/10) x 1/N]
Equation 10[35]
3.6.2.4.
Noise Rating (NR) Curves
This is a methodology that is used to rate noise in a room by comparing the noise spectrum with noise rating curves on a graph with an aim to make sure that the noise from outside does not have an effect on the activity inside the room. [35] Calculation of NR Curves are
given in Annex B of BS8233: 1999, “Sound insulation and noise reduction for buildings – Code of practice”. The methodology defined in BS8233:1999 is used throughout the thesis in order to find out noise rating curves of the RAM practice rooms, using logarithmically averaged octave band values of N=55 representative background noise levels for each room.
3.6.2.5.
Room Dimensions
Sizes of each room were measured including room length, width, and height; then the area and volume of each room were calculated from these parameters. Since the rooms had complex geometries, equivalent rectangular dimensions are provided.