Figure 6.

Sensor response for the acoustic sensing yarns where the hardware module was used. Experiments were conducted using the acoustic sensing yarns before (black; ) and after (red and purple; , ) the yarns were inserted within the helmet cover. (a) Sensor response as a function of sound pressure level at a fixed frequency of 1000 Hz. Tests were carried out between 0.1 and 8.1 Pa (73.8–112.1 dB), with the sensor operating correctly at all amplitudes across this range. For the acoustic sensing yarn outside of the cover (black), averaged data using four samples is shown. (b) Sensor response as a function of frequency at a fixed sound pressure level of 0.43 ± 0.02 Pa. For the acoustic sensing yarn outside of the cover (black), averaged data using four samples is shown. An 8000 Hz signal was also tested; the variation in results at this frequency was very high, and it has been negated from the graph for clarity. Variation in the result when the hardware module was used was also seen to be significant at high frequencies (2000 Hz and 4000 Hz). (c) Sensor response for the four acoustic sensing yarns at a fixed input sound of 45.5 ± 3.1 Pa with a 1000 Hz frequency. The sample numbers are consistent with Figure 3.