The latest changes in hearing aid microphone technology have revolutionized controlling background noise and improving patient satisfaction. The top manufacturers of hearing aids have spared no expense developing some of the most sophisticated systems ever made in wearable hearing devices. The directional microphone technology spatially reduces the area of sound that they will allow into the hearing aid. The most technologically advanced systems have the hearing aids talking to each other to coordinate the near and far sounds to squelch unwanted noise. This is known as Spatial and Digital Noise Filtering. All hearing aids, except for the smaller in-the-canal hearing aids have this technology.
The pick-up area is usually in front of the listener and adjustable to various patterns to reduce noise. Sound from behind is typically being filtered out the most. There are microphones that pick up only one pattern area and others that are dynamic and change with the environment to selectively reduce noise. Once sound is filtered by the microphones and transformed into a digital signal special comfort programs inside the hearing aid do the rest. However, the prospective hearing aid user should not expect the noise reduction to always perform in every venue as environmental acoustics and ear and auditory processing issues may cloud the results, although sound comfort can be achieved. Furthermore, too much automation for some patients can actually remove wanted sound if not fitted properly or the prescription is poor.
Directional microphones are available in all sizes of hearing aids except the smallest Completely-in-the-Canal devices. Microphone noise reduction is rated based on something called a directivity index or DI. Good DI’s start at 5 dB or more and are available in most hearing aids. Some companies make microphone systems that are very powerful and in some cases, with the help of digital noise reduction, can actually eliminate some noises all together. The amount of noise reduction can be adjusted by the Audiologist to accommodate a variety of hearing losses. The results are less noise, greater comfort, and better understanding for most patients. However, hearing aids should be fitted to maximize auditory processing and learning of natural sound, so too much use of noise reduction when it is not needed can hamper sound training and a more normalized perception. In high degrees of background noise most hearing aids can reduce the noise in half.
If you have a hearing loss and your Audiologist measured your speech discrimination score at 80% or greater, you have a good chance of receiving significant benefit from directional microphones. Below 80%, the use of directional microphones are still indicated for all patients, as they will greatly diminish noise and improve comfort, but understanding is a good example of how damage to the ear results in less understanding of speech regardless of the hearing aid technology or marketing claims.
The best way to measure the benefits of microphone technology is to have an aided “hearing in noise test” performed by your Audiologist. Two such tests are the HINT developed by the House Ear Institute and the Quick SIN developed by Emoytic Research. These tests quickly determine the amount of improvement under the directional microphone setting. Digital directional hearing aids have the ability to reduce noise perception up to 50%, eliminate some soft noises altogether, and enhance speech understanding. Most patients who use directional microphones report 20 to 30% improvement in speech understanding and are considerably more comfortable when listening in noise. The benefits of directional microphones remain consistent across most patients and age groups and should be considered in any hearing aid fitting.