Creare is actively developing technologies to improve the hearing protection available to military personnel and to enable hearing evaluation in noisy environments (such as for astronauts on the International Space Station). Some of these technologies are likely to have future application in industrial and commercial settings.

Protection from Extreme Noise

Navy flight deck and Air Force line crews work in a very challenging noise environment. Sound levels, which approach 150 dB for high-performance jet aircraft like the new Joint Strike Fighter (JSF), can cause hearing damage and impair communications. Hearing damage is now a common problem among today’s aircraft maintenance crews, which affects job performance and is the most costly Department of Defense disability (greater than $400 million per year in direct payments alone). Improved hearing protection is required to enable flight deck and line crews to work safely at optimum performance levels.

In addition to noise protection, crew headgear must address a variety of other requirements. Equipment and aircraft pose risks of cranial injuries from bumps or falls. Night operations require the use of night vision goggle (NVG) systems, which must remain fixed relative to the head to be effective. The threat of chemical, biological, or radioactive attacks mandates rapid donning of protective gear, including masks and hoods. Operational environments include tropical, desert and polar conditions. Uncomfortable helmets lead personnel to attempt modifications, which further reduces the helmet’s effectiveness. Heat buildup and excessive noise result in distraction and fatigue.

Creare has designed a helmet-integrated hearing protection system that is based on the knowledge gained from a test program using innovative evaluation techniques to understand how to best protect the head from extreme noise levels, and in particular, how to attenuate the transmission of bone-conducted sound. In that test program, we relied on rapid prototyping techniques to develop helmet shells with good sound attenuation characteristics and tested various combinations of commercial-off-the-shelf hearing protection components. A result of that test program is that our solution is layered and modular for the most comfortable and user-friendly design allowing for the addition of optional features or future capabilities as required. For the design noise levels, we have developed a baseline design helmet/headset system that combines modified commercial components using the existing technological base coupled with expendable deep insert earplugs (although our design can also use custom-molded earplugs if desired) to achieve the highest air- and bone-conducted noise reduction levels. As earplug use and fit are difficult to monitor and enforce, our helmet/headset system will provide the maximum noise attenuation possible using purely passive methods to reduce the need for bulky and costly electronics and electro-acoustic components that would introduce the potential for unacceptable failures during use in the harsh field environment.

Hearing Evaluation Technology

Current audiological screening systems require noise-controlled facilities which limit their use in important applications, such as on the International Space Station and Space Shuttle; screening newborns and infants in the clinic; or patients of any age in other locations without access to sound-treated rooms. To overcome the limitations of current devices, we are developing acoustic signal processing algorithms, acoustic hardware, electronic hardware, and software to implement real-time, adaptive noise cancellation in conjunction with standard hearing evaluation tests. Our innovative hearing evaluation system combines a unique feedforward, adaptive, noise-cancellation algorithm with customized Distortion Product Otoacoustic Emissions (DPOAE) test protocols to reduce the background noise in the frequency ranges specific to the tests. By reducing the background noise levels around the test frequencies and customizing the testing protocols, our system enables higher signal-to-noise ratio (SNR) DPOAE measurement. The increased SNR will result in the ability to obtain DPOAE measurements for hearing evaluation and screening in relatively high noise environments such as on the Space Station and Shuttle, in newborn intensive care facilities, offices of pediatricians, schools without special audiology facilities, field hospitals, and remote or mobile clinics.

DPOAE hearing assessment consists of placing two speakers and a microphone in an earplug, using the speakers to excite the mechanical response of the eardrum, and using the microphone to sense the response of the ear to the sound stimulus. This response signal provides an indication of the health of the auditory system. This method of hearing assessment is supra-threshold; it allows the test to be performed quickly, by relatively unskilled personnel; and since the procedure does not rely on the test subject to consciously respond, it takes the uncertainty of the human response out of hearing assessment. This hearing assessment method is particularly useful for hearing screening in infants, but is also routinely used in adult hearing conservation programs. Current DPAOE screening is best performed in carefully controlled, acoustically shielded environments which are not typically found in newborn nurseries or intensive care units; in pediatricians’ offices; in other clinical settings; or on the Space Station and Space Shuttle.

Creare’s feedforward, adaptive, active noise reduction system for DPOAE measurements combines innovative acoustic signal processing, active noise-control algorithms, and special-purpose hardware and software for data collection. The system consists of the following components:

• Ear probe. The ear probe consists of two speakers and one microphone, which are sealed in the ear canal with a rubber tip. An external microphone is also mounted on the back end of the probe facing the external environment.
• Amplifier, filter, interface and data conversion unit. A custom-made interface unit includes a low-noise amplifier/filter for microphone signal conditioning, interfaces to the probes, and a calibration microphone interface. The filtered and amplified signals are converted to digital format using analog-to-digital (A/D) converters.
• Computer system. All data handling and the user interface resides on a standard tablet computer. The data collection software calculates the power spectral density (PSD) of the recorded signal, the distortion product, and the noise floor.

Creare is currently developing a clinical prototype of the system which will be used in human subject tests on Earth and on the Space Station to show improved SNR of DPOAE measurements in both low and high noise background environments.