Directionality and Hearing Aids

Hearing is a miraculous process.

This is how it works: Your ears receive sound. Then, the sound travels down the ear canal through the middle ear and into the cochlea, where tiny hair cells that reside there vibrate to the different frequencies. Those signals are ushered to the brain, which deciphers the incoming messages and makes sense of them. Your brain automatically filters out the background noise and non-important information to allow you to center on speech and other important signals, when you have normal hearing.

Distinguishing speech from noise is a much greater problem for people with hearing loss. Because the small hair cells in the ear are damaged, there’s trouble separating speech from noise. Also, loud noise can create discomfort for those with hearing loss.

Hearing aids with directionality combat the issue of not being able to separate speech from noise. They have two or more microphones separated by a specific distance on a hearing aid. But not all directional systems are the same. For glossary terms and technical specifics, below are some points about directionality and hearing aids.

Glossary terms:

• MEMS microphones - These are microphones produced from silicon crystal to make them resistant to temperature changes and moisture.
• Null - The null is the least sensitive portion of the microphone response or the area that turns toward the sound to make it less noticeable.
• Drift - the drift is when microphone sensitivity isn’t matched. But there are systems available to minimize drift.
• Electret - This type of microphone use is in most hearing aids today. The microphone uses a polyester diaphragm held a few microns away from a metal backplate that holds an electric charge. Sound moves the diaphragm and allows the hearing aid to detect, amplify, and process the sound in an electrical equivalent of the original sound.

Now, here’s an overview of directional systems:

• Fully adaptive directional microphone array - Each hearing aid creates a map of the type and location of sound in the patient’s surrounding environment. Based on the sound information coming in, the hearing aid finds the source of the sound and continuously moves the null (reminder: the least sensitive portion of the microphone response) toward the main noise source, which optimally reduces the noise around the listener. The cool thing is that the null can be virtually anywhere the noise is, not just in specific areas like with the simple directional array.
• Simple adaptive directional array -  Directional microphones switch between fixed points, which can limit the amount of noise suppression if the noise is outside of the null region.

The importance of directionality

Having directional microphones in hearing aids is important because they handle or manage noisy environments well. It’s a solution to better performing hearing aids.  
For a more detailed analysis of directionality and hearing aids, please contact our hearing instrument specialists at Pure Sound Hearing Aids.

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