Semester

Spring

Date of Graduation

2008

Document Type

Thesis

Degree Type

MS

College

Statler College of Engineering and Mineral Resources

Department

Industrial and Managements Systems Engineering

Committee Chair

Steven Guffery

Abstract

The US Coast Guard is prototyping a new small boat communication system which consists of the MSA Sordin Supreme Pro headset in combination with a wireless communications system. The MSA Sordin headset receives wireless communications input independently from an amplitude-sensitive sound transmission feature which amplifies ambient noise in certain frequency ranges. The purpose of this study was to determine the extent to which the communication system improves speech intelligibility in noise and to measure the noise reducing capabilities of the headset with the amplification feature activated and with it turned off. Overall noise reduction was calculated based on four different noise spectrums to compare actual noise reduction to the manufacturer advertised Noise Reduction Rating (NRR). Additionally, clamp force was measured to determine its relationship with noise reduction. This study found that the communication system, consisting of wireless communications and the activated headset amplification feature, drastically improved verbal communications when compared to the case of the headset donned but wireless communication disconnected and headset amplification off (88% vs 44% intelligibility score in 90 dBA background noise; 82% vs negligible intelligibility in 100 dBA background noise). The MSA Sordin headset amplification feature had a profound effect on the hearing protector's noise reducing capability. When it was activated, noise reduction was dramatically lower in all frequencies above 315 Hz. This resulted in lower overall noise reduction when this feature was on. Mean overall noise reduction values ranged from 11.2 to 27 dBA with the amplification feature turned off and 6.7 to 0.2 dBA with the amplification feature activated. The difference was least in low frequency dominant noise (11.2 vs 6.7 dBA) and greatest in high frequency dominant noise (27 vs 0.2 dBA). The low frequency dominant spectrum used in this study was recorded onboard an operational USCG 47' Motor Life Boat, the system's intended operating environment. In this intended environment, the calculated overall noise reduction was less than the manufacturer advertised rating of 18 dB (study values; 11.2 dBA without amplification, 6.7 dBA with amplification). A weak positive correlation was found between clamp force and noise reduction but the association was not statistically significant, meaning that clamp force was not the reason for the noise reduction performance of the MSA Sordin headset.

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