Measurement plan

As mentioned earlier, ODEON Acoustics was used to create a model of the sports hall (see Section 5 for more information). This model was used to create the measurement plan. Receiver positions were set out on every meter for three lines. Line L2 is drawn parallel to the wall and formed the 0°-line. The other two lines are created by rotating L2 30° to the left and to right (see Fig. 4.2). The source and receiver positions are placed at a minimum distance of 2 m from the walls. After interpolating the resulting STI-values, it is chosen to set a measurement position for every Just Noticeable Dierence (JND), which for STI is 0.03 [68]. Although it is unlikely that all the recorded BRIRs will be used for the tests, these measurements will produce a wide selection of samples. The measurement grid can be seen in Fig. 4.2.

4.2 Equipment

This section describes the microphone and sound source that was used during the measurements.

HATS

The B&K Head And Torso Simulator (HATS) was used to measure the BRIRs.

HATS is a model of a human head and torso (see gure 1.3). This model has two microphones (left and right) placed at the locations of the ear canals. The ears, head and torso of the model ensure that the recorded sound have a comparable diraction to that caused by an average adult body [6]. The dierence in arrival time between the left and right ear is also taken into account by the placement of the two microphones at both ear canals.

Echo Speech Source

The directional B&K Echo Speech Source Type 4720 (abbreviated as Echo) [69] was used for this study. This source is designed to perform speech intelligibility measure-ments. The speaker is designed to simulate the directivity of a human speaker. It is provided with ve calibrated built-in signals, but also has the option for external in-put signals. A rotation measurement of the source was available. The corresponding directivity plots of the ECHO can be found in Appendix A.

The measuring equipment can be seen in Fig. 4.1 and Table 4.1. The Echo Speech Source can produce a calibrated signal which ,in combination with Dirac Room Acoustics Software [69], makes it able to perform quick STI-measurements. The measurements were performed in an unoccupied and relatively quite room. In this environment, a Exponential Sine-Sweep (E-Sweep) signal has a higher possible signal-to-noise (SNR) ratio than other signals as the as Maximum Length Sequence (MLS) and Inverse Repeated Sequence (IRS). The SNR-ratio is described as "the ratio in decibel between the average power of the signal recorded by the microphone and the average power of the noise and distortions present in the tail of the deconvolved (linear) impulse response [20]". Since the distortions are not present in the tail when using E-Sweep, this signal has a higher SNR-value than MLS or IRS. Another ad-vantage is that, although more time-consuming and computationally demanding, the E-Sweep is also more accurate than MLS [70]. The E-Sweep signal was thus used for the measurements.

Table 4.1: Used measurement equipment Sound Source B&K Echo Speech Source

Receiver B&K Head And Torso Simulator (HATS)

Input/Output USB Audio interface (ICP Trition - Audio Engineering(+10dB)) Signal Exponentially Sine-Sweep (E-Sweep)

Laptop Toshiba Satellite M50D-A-10D Software B&K Dirac Type 7841 v6.0

Figure 4.1: Used measurement equipment: a. B&K Echo Speech Source b. Toshiba measurement laptop c. B&K Head And Torso Simulator.

During the measurements, the gain of the source signal was set at -24 dB in Dirac.

Higher levels would risk damaging the source. An impulse-to-noise (INR)-ratio higher than 37 dB for T20and 47 dB for T30is required to determine these parameters with

a maximum error of 5% (1 JND) [71]. The INR is dened as the dierence between the root mean square (RMS) of the impulse response in dB and the noise level in dB and is an estimator of the decay range of the impulse response [72]. To get these values for all the dierent source positions, a source signal of 95.1 s and a pre-average of 2 was used. The used measurement plan can be seen in Fig. 4.2.

Figure 4.2: Measurement plan in the sports hall

4.3 Results

The INR-values of the measurements for both channels can be seen in Fig. 4.3 and 4.4. As expected, the INR for the lower frequency bands is lower than for the higher bands. When assessing the rotation plot of the Echo Source (see Appendix A), it is clear that the source power is much lower for the lower frequencies. At line 1, a signicant drop of the INR-value for the 1000 Hz, 2000 Hz and 4000 Hz can be seen at the distance of 5.7 m (receiver position 10). The lower frequencies do not seem to have been inuenced. The measured and simulated STI-values for L1 and L2 can be seen in Fig. 4.5 and 4.6. A gap can be seen in the measurement line of Fig. 4.5. Due to an unknown error, the BRIR for the position L1S5 was found to be unusable for analysis. The simulated STI-values for L2 follows the same trend as the measurements. Overall the simulated values are higher than the measured values, both at L1 and L2. The same can be seen when evaluating at the STI-values of L1. The dierence between measured and simulated STI-STI-values is lower at L2. When looking at the average deviation of the simulated STI-values from the

measured values, L1 has an error of 0.069 and L2 0.03. An example of a measured impulse response can be seen in Fig. 4.7.

0 2 4 6 8 10 12 14 16 18 20

Figure 4.3: INR-values for Line 2

0 2 4 6 8 10 12 14 16 18 20

Figure 4.4: INR-values for Line 1

0 2 4 6 8 10 12 14 16 18 20

Figure 4.5: STI-values for Line 1

0 2 4 6 8 10 12 14 16 18 20

Figure 4.6: STI-values for Line 2

0 50 100 150 200 250 300 350 400 450 500

Figure 4.7: Measured BRIR Sports hall, L2S1, left channel

5 | Simulations

As mentioned in Section 2.2, ODEON acoustics was used to create the simulated BRIRs. This section will rst describe the ODEON Model of the sports hall, includ-ing the dimensions and the used material properties. The used ODEON simulation settings will also be discussed. Concluding, the obtained parameters and BRIRs will be analysed and compared to the measurements.