Directional Microphones

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The most common complaint about hearing aids is that they don't perform well in background noise. Now, at the end of the century, hearing aids are providing significant help in noisy places such as restaurants and meetings, and there is promise of even more benefits in the near future.

The digital revolution created major breakthroughs in hearing aid technology, leading to the introduction of digital hearing aids. Newspaper, radio and television news accounts generated tremendous interest in these new hearing aids, which used miniaturized micro-processors to digitize and process incoming acoustic signals.

Another, equally important advance has received less media attention, perhaps because it is not as familiar as the concept of "digital." However, advances in microphone technology, especially when coupled with the capabilities of digital processing, are already providing impressive results for people with hearing loss.

Directional Microphones
Directional microphones have been available for years, but have been improved significantly due to recent advances in technology.

Audiologic research has consistently demonstrated the benefits of directional amplification. In recent years, however, there has been more interest in miniaturization and directional microphones have not been commonly used.

The most challenging listening situations facing people with hearing loss is understanding clearly in noise (e.g. restaurants, parties). In situations where interfering background noise is present, much benefit can be obtained by using directional microphones.

An ordinary (or omni directional) microphone picks up sound from the front, sides and back of the listener equally. A directional microphone focuses on amplifying the sound source directly in front of the listener, while reducing sounds from the side and back. This translates into better understanding of speech in noisy situations.

Laboratory studies have measured improved signal-to-noise ratios in the 4 to 8 dB range, significantly better than the 2 to 4 dB improvement for earlier directional microphones. Clinical measurements have yielded scores for word recognition in noise that are 10 to 20% better than with conventional omni-directional microphones. Not surprisingly, studies have not indicated any multi-microphone advantage in quiet situations.

Multi-microphone technology is already providing important benefits for hearing aid users, but these instruments are not suitable for everyone. In addition to the added expense, many hearing aid users may not want to use a directional switch (although this can be eliminated), or may want the smallest instrument possible. Still, a number of researchers believe this technology holds the greatest promise for improved hearing and that in the near future many people with hearing loss will be able to hear as well in noise as their friends with normal hearing.