Sonar Headphone Selection for Optimum Performance: An Overview

Abstract

Summary PageThe ProblemTo improve the real-time auditory detection and aural analysis capability of passive broadband sonar systems. The FindingsThe most blatant source of acoustic signal degradation on auditory sonar systems is in the acoustic performance of headsets. Recent detection performance data have shown the need for upgrading sonar headsets to reproduce electrical energy accurately over a wider bandwidth. Headphone measurement data on commercially available headphones have shown that headphones of more appropriate bandwidth and frequency-response accuracy have not been of sealedcircumaural design. Headphones designed to completely seal around the listener's ear exhibit low-finequency variations with placement on the head and with deterioration of ear-cushion as a result of a less than perfect seal. Unfortunately, current noise levels preclude use of the more accurate, less variable, open-air types. Reduction of noise levels in sonar spaces to permit use of better headphone designs is a highly desu^ble solution. Recent developments in active noise canceling headsets show promise as an interim solution. A commercial model having adequately flat frequency response has been found and improved through active equalization. A prototype version of this improved headset has been evaluated. ApplicationAdvanced auditory sonar system design. Aural analysis and tactical sonar headphone requirements.Administrative Information This research was carried out under Naval Medical Research and Development Command Work Unit 65856N-M0100.(X)1-5001. It was approved for publication on 27 Jun 95, and designated as NSMRL Report 1197. u Abstract Real-time auditory detection and aural analysis capability of passive broadband sonar systems needs improvement. A weak link in these systems is the use of communicationsbandwidth low-fidelity headsets. Unfortunately, no procedure for headphone (earphone element inside headshell) frequency response measurement exists in military headset specifications. An accurate technique for headphone calibration was devised which provides the earphone element with an acoustic load similar to the one provided by a human wearer. Using this technique, headphone measurement data on commercially available headphones was collected and compared to the current sonar headsets. The advantages and disadvantages of open and sealed circumaural headsets and recent developments in noise canceling headsets are discussed, along with the possibility of reducing noise levels in sonar spaces to permit use of higher fidelity headphone designs.

Sensor-Operated Headset Selection for Virginia Class Submarine Consoles (3CI)

“…Since the overall level of the sea noise signal in the headset must be kept at a reasonably comfortable and safe level, these constraints result in airborne noise masking the low-frequency component of the target signal to be detected within the sea noise. This explains why previous reports (Russotti, 1993;Benedetto et al, 1995;Russotti, 1995) found improved sonar operator performance with ANC headsets. Should the target of interest have most of its radiated energy in these lower frequencies, the decrement in performance caused by the interference of this low-frequency airborne noise becomes even more detrimental.…”

“…As a consequence, passive noise-occluding headsets, which require a good seal for noise attenuation, are not a desirable design for accurate sound reproduction. Tests of military and commercial headsets have found that noise-occluding headsets are also characteristically band-limited (Russotti, 1995). Such headsets were originally designed for communica-tions and are cost effectively band-limited to the speech range for that application.…”

“…Interactive work between Bose Corporation and NSMRL has produced a modified version of their ANC commercial aviation headset with enhanced frequency response for use in passive sonar. These headsets (Bose Series I commercial aviation headset-[nsmrl prototype]) have been tested at-sea with highly favorable results and commensurate acceptance by the sonar community (Russotti 1993, Russotti 1995, Benedetto, et. al.…”

Noise Reduction Stethoscope for United States Navy Application

“…The earpieces of the Littmann were carefully fitted into the ear canals of a Kemar ® manikin. This device, equipped with Zwislocki ear simulators that model the acoustic impedance of the ear, has been used extensively in our headphone research (25,26). Pliant bags of lead shot placed within the manikin were used to block sound transmission to the calibrated microphone "eardrum" from pathways other than the ear canals.…”

Sonar-Operator Active Noise Reduction Insert-Earphone: Prototype Preliminary Test and Evaluation

“…As a consequence, passive noise-occluding-earphone headsets, which require a good seal to occlude the ear canal for noise attenuation, are not a desirable design for accurate sound reproduction. Tests of military and commercial headsets have found that noiseoccluding earphones are also characteristically band-limited (Russotti, 1995). Such headsets were originally designed for communications and are cost effectively band-limited to the speech range for that application.…”