Hearing Instruments

Modern integrated circuits have enabled sophisticated hearing aids to come in a variety of sizes and forms. There are two main form factors in hearing aids. These are:

  •  BTE (behind the ear) These types of aids have the microphone and amplifier behind the ear like the bow of a pair of eyeglasses. The receiver (speaker) can either be contained in this unit, in which case the sound is sent to the ear via a tube; or at the end of a wire, in which case the receiver is place directly in the ear canal.

  •  ITE (in the ear) These types of aids come in a variety of sizes ranging from a very small one located completely in the ear canal, to ones that fill the whole bowl (concha) of the ear.

As a general rule, the larger the hearing aid is, the wider the range of hearing loss it will encompass. In addition, generally, the larger the hearing aid, the more features and controls will be available. For instance, a small completely in the canal hearing aid does not have a volume control. The form factor an individual may obtain is dependent on three personal parameters: Severity of loss, budget, and physiology.  Since the two form factors are interrelated to the three personal parameters, choosing a hearing aid is complex. It is best to seek the guidance of a professional.

Digital hearing aids have multiple features that determine their level of sophistication, and, correspondingly cost.

Compression: This fits the range of the sound in the environment into the residual hearing range of the user. According to the hearing loss of the patient, weak sounds are made audible, medium sounds are made comfortable, and loud sounds are kept below the patients ‘uncomfortable’  level. This is done by varying the amount of amplification given to sound of differing amplitudes.

Directionality: This feature has to do with 'Background Noise'.  Noise coming from behind, or more specifically, not where you are listening.  Hearing instruments with this feature have two horizontally oriented microphones. The processor can detect front sounds from rear sound by the temporal difference between the two microphones, and then reduce the amplification of sounds in the undesired direction. Basic “d-mics” reduce amplification behind the wearer. From there they very in sophistication up to the ability to track speech in a 360 degree plane.

DNR: Digital Noise Reduction. The ability of modern hearing instruments to ‘classify’ sound is an important feature.  The machines can then modify their frequency responce to accommodate the situation.  They are pretty good at recognizing specific environments. The basic categories are : noise,  speech in noise, speech in quiet, and quiet. Basic DNR can identify any steady state noise (hum or buzz) and reduce the amount of amplification where the offending signal resides in the sound spectrum. As the instrument capability increases, the processor can pinpoint ‘noise’ more specifically, and detect and classify more environments, such as music, or automobiles.



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