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Compact Speaker Array for Clinical Testing of Ear-level Devices



OBJECTIVE: Develop and demonstrate a speaker array system with a minimal profile that can easily be installed and used to obtain consistent sound field performance measurements of hearing devices in multiple clinical environments for the purposes of determining the functional effects of hearing devices on Warfighter spatial hearing ability and situational awareness. 

DESCRIPTION: Clinical audiometry is most often conducted over headphones, which provides very consistent results across a wide variety of clinical environments as long as the background noise levels do not exceed the Maximum Permissible Ambient Noise Levels outlined in ANSI S3.1. However, there are certain cases where regulations require the functional performance of hearing impaired listeners to be evaluated while they are wearing hearing devices, such as hearing aids. For example, AR190-56 specifies the use of a sound field hearing in noise test for the evaluation of candidates for civilian security guard positions in the Army who wish to have their hearing tested with amplification. There are many practical cases where it may be desirable to measure the hearing performance of listeners wearing hearing aids, hearing protection devices, or implantable hearing prosthetics, both for evaluating fitness for duty and for evaluating outcome measures of clinical interventions. Traditional sound-field audiometry is generally limited to two speakers attached to an audiometer, with very little standardization in terms of where those speakers are placed. Consequently, there is no reason to believe that functional hearing measures conducted with these sound field speakers will be consistent across different audiological test booths, even within the same clinic. Conversely, large speaker-arrays, which can easily evaluate the hearing performance of Warfighters with hearing devices, are currently reserved for research facilities and cannot easily be deployed into clinical settings; as such, the development of standardized tests using larger systems is impractical. As the DOD Hearing Center of Excellence builds its DOD-wide hearing registry, it will become increasingly important to have a standardized method for conducting audiological sound-field testing that is compact and affordable enough to be deployed in a large number of DOD Clinics and will produce results that are consistent and reliable enough to allow direct comparisons of data across multiple facilities. A survey of commercially available systems has revealed that no systems currently exist that are compact enough to be permanently installed in a clinical sound booth (without severely limiting the usability of the booth) and flexible enough to allow independent control of the individual sound channels (commercial 5.1 and 7.1 sound bars incorporate multichannel processing that does not allow the channels to be controlled independently). Also, no current systems have been validated to allow comparable spatial hearing performance in multiple sound booths: they typically require the collection of normative data that is specific to each individual sound booth. The ideal system would: 1) Be compact enough to be retrofitted in most clinical sound booths with minimal interference with current clinical operations. 2) Take advantage of commercial multichannel formats like HDMI or ADAT to provide a multichannel sound field solution (5-8 channels) that can be controlled from a single wire from a PC sound card or Android Tablet. 3) Be capable of simulating both discrete, spatially separated sound sources and simulated room reverberation. 4) Be completely self-contained in terms of amplification and decoding 5) Provide a method for controlling/maintaining the location of the subject’s head in the center of the array 6) Provide a method for reliably calibrating the system 7) Develop some novel methodologies for improving the robustness and consistency of auditory testing across multiple rooms with different acoustic environments. 

PHASE I: Phase I should identify a feasible technological approach for the speaker array system that addresses all of the major requirements for consistent clinical testing across a wide range of test environments, demonstrate a bench-level prototype that meets these requirements and all applicable ANSI standards, and develop a plan for implementing a compact version of the prototype suitable for integration into clinical sound booths at a minimal cost. The system should be able to connect to various tablets and PCs sound cards which are equipped with tests that evaluate speech perception in noise and localization. The system should have the ability to accommodate single and multisource sound localization including front-back confusions, separation and perception of multi-talker speech, and spatial hearing from masking for speech perception in noise. A feasibility study should be completed using the Knowles Electronics Mannequin for Acoustical Research (KEMAR). 

PHASE II: By the end of Phase II, the contractor should deliver at least 10 viable prototypes for pilot testing in DOD Audiology Clinics. The products should have demonstrated success in a small sample of human subjects demonstrating repeatable spatial hearing and speech perception performance across a variety of typical sound booth acoustic environments for: 1) normal hearing listeners with and without hearing protection devices and 2) hearing impaired listeners with and without hearing protection devices and with hearing rehabilitative devices (i.e., hearing aids and auditory implantable devices). Tests should include tasks of spatial hearing (i.e., localization and speech perception in noise). Other deliverables include technical reports document the appropriate performance measurements for the device, specifications with diagrams on setup of the equipment, and proposed roadmap addressing additional research activities, cost, and time required to make the technology commercially available. 

PHASE III: Phase III the contractor should develop a plan for medium-rate production of the systems for integration into clinical audiological booths both within the US Government (DoD and VA) and in the commercial sector. Customers would include hearing conservation and clinical audiology settings in the DOD for use in auditory fitness for duty evaluations for hearing impaired Warfighters with hearing rehabilitative devices. It is likely that the HCE would support deployment of the system at major MTFs where audiological implants and cochlear implants in order to increase the accuracy. In clinical audiology settings in the VA and DOD, the units could be used for evaluation of outcomes with auditory rehabilitative devices. Commercially, the department of labor estimates that there were 13,000 audiologists in the US in 2014, suggesting a potential market size of at least several thousand units if an affordable and reliable solution could be developed. 


1: American National Standards Institute. (1991). American national standard maximum permissible ambient noise levels for audiometric test rooms. Standards Secretariat, Acoustical Society of America.

2:  Army Regulation 190-56. (Effective: 15 March 2013). Military Police: The Army Civilian Police and Security Guard Program. Headquarters: Department of the Army

3:  Appendix C:8(30-31).

KEYWORDS: Audiological Testing; Sound-field Testing; Spatial Audiometry; Auditory Fitness-for-duty Testing; Speaker Array; Hearing Loss 


Dr. Douglas Brungart 

(202) 294-8747 

Dr. Amy Boudin 

(210) 215-9200 

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