Entering into the anechoic chamber is like entering a foam womb. Designed to measure sound at 125 Hz and above, foam wedges line the floor, ceiling and walls.

The primary goal of the research and development program is to improve the performance of hearing aids and enable a hearing-impaired person to function better in a hearing world. This goal is accomplished by measuring the physical properties of the speech signal and relating those measurements to auditory speech perception by hearing-impaired individuals.

Traditional audiology concepts suggest that the fitting of a hearing aid should provide amplification in the frequency regions where there is a hearing loss. The most common type of hearing impairment in adults is a form of high frequency sensorineural hearing loss, which is characterized by a mild hearing loss in the low frequencies and a moderate to severe hearing loss in the high frequencies. Using the traditional concepts of hearing aid fitting, the low frequencies are attenuated and the high frequencies are amplified. Many people with high frequency sensorineural hearing loss, however, continue to recognize unaided, conversational speech, which indicates a person can perceive whole speech signals with only a limited amount of information from that speech signal in the low frequencies.

Researchers with The Hearing and Speech Foundation’s (HSF) Hearing and Speech Research Laboratory believe that energy in the lower frequencies is important to the perception of a high-frequency speech signal. When fitting hearing aids, HSF researchers believe, it is important to match frequencies in a speech signal with the residual hearing of the hearing loss in order to structure the perception of speech. Researchers hypothesize there is significant acoustic information in lower frequencies [defined as below 750 hertz (Hz)], or the information from the transition of the fundamental frequency in the first formant, in a speech signal for the brain to process, perceive, and structure the speech signal.

Researchers have developed a state-of-the-art measurement system in order to measure the acoustic properties of speech at the ear drum. Traditionally, the measurement system is a “real-ear” measurement system, but because HSF researchers have crossed disciplines from strict audiology into sound production, researchers have renamed the measurement to more accurately describe its functionality: Free-field, Multi-channel In-ear Controlled-stimulus (MIC) Analysis System. By measuring acoustic properties of speech at the ear drum, researchers expect to determine the acoustic energy in a speech signal needed to perceive speech; measure what effects hearing aids have on the frequency response of the speech signal; measure the effect ear molds have on the frequency response of the speech signal; and compare speech acoustic information to pure-tone thresholds and sweep frequency information.