Design and verification of a measurement setup for wireless remote microphone systems (WRMSs)

Figures & data

Figure 1. Measurement setup visualised from two perspectives. P1 indicates the position of the remote microphone, and P2 the position of the user.

Figure 2. Speech (underlined) and noise levels for the measurement without wireless remote microphone system (WRMS) (a) and for the measurement with WRMS (b).

Figure 3. (a) Photograph of realisation of the simplified setup (left) and photograph of the position of the remote microphone (right). (b) Schematic drawing (left) and photograph of the classroom used for the measurements.

Table 1. Five different measurement conditions were considered in each test room (simplified setup/classroom) with and without wireless remote microphones system (WRMS) and with an omnidirectional or directional hearing aid microphone characteristic.

Condition	WRMS	Noise level	Hearing aid mic. char.
C1	Without	60 dB SPL	Omnidirectional
C2	With	60 dB SPL	Omnidirectional
C3	With	65 dB SPL	Omnidirectional
C4	With	70 dB SPL	Omnidirectional
C5	With	70 dB SPL	Directional

Figure 4. Speech intelligibility for all conditions (C1–C5 as listed in Table 1) and for the classroom (CL) and the simplified setup (SS). The conditions with WRMS are indicated with a grey background.

Table 2. Results of the post-hoc pairwise comparison with Bonferroni correction for all conditions (C1–C5) between the classroom (CL) and the simplified setup (SS).

Condition	C1	C2	C3	C4	C5
Setup	CL-SS	CL-SS	CL-SS	CL-SS	CL-SS
$p$	<0.001***	0.20	0.15	0.84	0.61

Table 3. Results of the post-hoc pairwise comparison with Bonferroni correction for both rooms (CL or SS) between all conditions (C1–C5).

	C1	C2	C3	C4	C5
C1		<0.001***	<0.001***	<0.001***	<0.001***
C2	<0.001***		0.056	<0.001***	0.004**
C3	<0.001***	0.17		0.02*	0.19
C4	<0.001***	<0.001***	<0.001***		1
C5	<0.001***	<0.001***	0.02*	1

The p-values for the class room (CL) are listed in the upper right (underlined values) and the p-values of the simplified setup (SS) are listed in the lower left part of the table.

Table 4. Overview about the five different WRMSs tested.

WRMS	Transmission	Remote microphone characteristic	Manufacturer
W1	Digital	Directional	A
W2	Digital	Omnidirectional	B
W3	Analog	Omnidirectional	C
W4	Digital	Omnidirectional	A
W5	Digital	Directional	B

Figure 5. (a) Speech intelligibility for all five WRMSs (W1–W5) and two noise levels. (b) Ratings of speech intelligibility and sound quality for a noise level of 65 dB SPL.

Table 5. Results of the post-hoc pairwise comparison with Bonferroni correction for both noise levels (60 dB or 65 dB SPL) between all conditions WRMSs (W1–W5).

	W1	W2	W3	W4	W5
W1		1	0.18	1	1
W2	0.68		0.08	1	1
W3	0.001**	<0.001***		0.20	0.08
W4	1	1	<0.001***		1
W5	1	1	0.001**	1

The p-values for a noise level of 60 dB SPL are listed in the upper right (underlined values) and the p-values for a noise level of 65 dB SPL are listed in the lower left part of the table.

Table 6. Results of the post-hoc pairwise comparison with Bonferroni correction for all WRMSs (W1–W5) between the situation with a noise level of 60 dB SPL and 65 dB SPL.

WRMS	W1	W2	W3	W4	W5
Noise level (dB SPL)	60–65	60–65	60–65	60–65	60–65
$p$	0.04*	0.04*	<0.001***	0.08	0.02*

Table 7. Result of Friedman’s test performed on the data of the subjective ratings on speech intelligibility (SI) and sound quality (SQ) shown in Figure 5(b).

Source	SS	df	MS	${\chi }^2$	$p$
Rating on SI	46.7	4	11.7	24.3	<0.001***
Error (Rating on SI)	107	76	1.4
Rating on SQ	64.5	4	16	35	<0.001***
Error (Rating on SQ)	83	76	1.1

Table 8. Results of the post-hoc pairwise comparison with Bonferroni correction for the subjective ratings depicted in Figure 5(b).

	W1	W2	W3	W4	W5
W1		1	0.04*	1	1
W2	1		0.001**	1	1
W3	0.001**	<0.001***		<0.001***	0.001**
W4	1	1	<0.001***		1
W5	1	1	<0.001***	1

The p-values for the ratings on speech intelligibility are listed in the upper right (underlined values) and the p-values on sound quality are listed in the lower left part of the table.

Figure 6. Real-ear measurement for all 20 subjects to check acoustic transparency, as defined in the EUHA guidelines using the ISTS at 65 dB SPL. The plots show the level difference between free field and the remote microphone in a test box. As reference the free field is defined so that positive differences indicate a transmission of the WRMS with higher level.

Figure 7. Speech intelligibility with and without WRMS for 20 normal-hearing listeners at noise levels of 60, 65, and 70 dB SPL.

Table 9. Results of the post-hoc pairwise comparison with Bonferroni correction for the results of the speech test depicted in Figure 7.

Noise level	60 dB SPL	65 dB SPL	70dB SPL
with WRMS	yes/no	yes/no	yes/no
$p$	<0.001***	<0.001***	<0.001***

The situation without and with WMRS is compared for all noise levels.

Table 10. Results of the post-hoc pairwise comparison with Bonferroni correction for the results of the speech test depicted in Figure 7.

	60 dB SPL	65 dB SPL	70 dB SPL
60 dB SPL		<0.001***	<0.001***
65 dB SPL	<0.001***		<0.001***
70 dB SPL	<0.001***	<0.001***

The p-values for the results without WMRS are listed in the upper right (underlined) and the p-values with WRMS are listed in the lower left part of the table.