Phoenix Hearing Instruments specialises in the supply and design of Assistive Listening Devices (ALDs) and technology to assist people with hearing or voice impairment.
Because assistive technology is not often offered, or even discussed during a hearing assessment, these few pages will give you a brief introduction to the reasons why ALDs may better serve your needs; or actually be the preferred choice!
“What is an Assistive Listening Device?" An ALD is generally any device that is designed to provide some form of enhanced sensory notification of events which may not be detectable by a person with a sensory impairment.
An ALD may be used alone, or in conjunction with hearing aids or Cochlear implants.
It may be an acoustic solution to amplify sounds, a system to transmit sound from a distance, or a transformation of one form of notification into another e.g. sound into light or vibration.
For hearing impairment, a common solution is to use hearing aids, however, a standard hearing aid will not perform well when the user is in background noise or if there is a distance of more than 1.2 metres to the sound source of interest.
It may not be the best solution...
An ALD would be a device (or sometimes devices) that is/are designed to perform in diverse listening environments by minimising the many effects of sound degradation and significantly improving comprehension.
The ALD may provide non-specific acoustic assistance or may be designed for a particular need or situation.
Background noise: While many hearing aids combat background noise by selectively filtering out what the aid ‘perceives’ as noise, this is a subtractive approach. Technically, subtracting the noise components will improve the Signal to Noise Ratio (SNR), but there is also a significant loss of speech sounds that are essential for comprehension.
In this instance it may be more correct to state: "What is left of the signal'' to Noise Ratio.
By positioning the ALD microphone closer to the sound source, the pick up of background noise remains the same, but the sound of interest is increased.
Connecting the ALD directly to the sound source eliminates the background noise completely. This is a positive approach to increasing the SNR and nothing is lost.
Distance: The microphone in an ear level hearing aid or implant is quite small. The diaphragm of these microphones cannot properly react to softer sounds or even louder sounds from a distance. As sound is propagated outwards from the source, it follows a derivative of the Inverse Square Law - the Inverse Distance Law.
The sound pressure is inversely proportional to the distance of the point of measurement from the source, so that if you double the distance you halve the sound pressure. Conversely, if you halve the distance, you double the sound pressure.
The intelligence in speech (mostly consonant sounds) is contained in the higher frequencies where the normal ear is more sensitive (~2.7KHz), but they are produced with far less energy than the lower frequency vowel sounds.
Using a hearing aid, the more energetic vowel sounds will still be heard from a distance, but the softer consonants will be lost and this means lack of comprehension.