Family doctor

What is hearing loss?

Hearing loss becomes increasingly common as we age. It is estimated that about 20 percent of the population has a significant hearing impairment, and that it will take about seven years for many of them to do something about it.

At the hearing test the person's degree of hearing impairment is identified as well as the shape of the loss, such as whether the low tones, mid tones or high tones are affected, and whether the person has a conductive or sensorineural loss.

The audiologist will provide a report detailing the degree of impairment (mild, moderate, severe or profound), and whether there are features that require a referral to an ENT specialist. The impact of the impairment on the occupation or social life of the patient will also be briefly detailed and whether hearing aids are recommended.

What types of hearing aids are available?

The purpose of a hearing aid is to amplify sounds in a way that will enable a hearing impaired person to utilise his or her hearing in an effective manner.

Today there is a wide range of hearing aids available to achieve this goal, from small hidden aids which sit deep in the ear canal and to ones that fit snuggly behind the ear and send sound to the ear via a tube and ear mould. Equally there is a wide range of technologies to try to achieve the needs and expectations of the individual.

A hearing aid consists of a microphone that turns the sound into an electrical impulse, an amplifier that increases the amplitude of the signal, a battery that supplies the power, and a receiver or loud speaker that turns the electrical signal back into sound.

It is the size of these four components that has dictated the size of the hearing aid. With the arrival of the silicon chip and the decrease in battery diameter to only 6-7 mm, the miniaturisation of highly sophisticated and adjustable "computers" for the ear is a reality.

Linear or conventional hearing aids

Linear or conventional hearing aids are however still the aid of choice for many people. They amplify sound according to the shape of the loss but also amplify soft, moderate and loud sound by the same degree. In general they are a cheaper option, ranging in price from $1600 - $2400 a pair.

Programmable or hi-technology hearing aids

Hi-technology hearing aids can be analogue or digital. They are programmed via a computer or digital source which gives access to a wider range of parameters and with much more precision of adjustment.

Analogue hearing aids may be single band which means that the hearing aid processes the audio signal through a single circuit path whose processing characteristics affect certain aspects of, or the entire frequency response. They may be multi-band, having two or more circuit pathways which allows for adjustments to be made separately for each frequency band.

Hearing aids may be described as automatic, not requiring a volume wheel as the aid adjusts itself according to the intensity and frequency response of the input sound.

The hearing aid may have multi-programmes that are accessed by a remote control or push button on the hearing aid. The different programmes are variations on the basic one and allow the user to enhance speech in background noise or to hear music better.

Switchable microphones are a further feature that allows the user flexibility in receiving an enhanced signal from in front or to receive sound from all round. This "zoom" function has been shown to be very beneficial at enhancing speech in noise when facing the speaker.

Hi-technology analogue aids cost between $2,200 - $6,000 a pair, depending on their complexity.

Digital hearing aids

In a digital aid the sound is converted to an electrical current by the microphone (an analogue procedure). An analogue/digital converter then turns the electrical signal into a series of binary numbers in the form of positive or negative electrical voltage. The central processing unit of the hearing aid is a computer. It is instructed by the programming computer to manipulate the data in some predetermined manner to achieve the desired result for the patient.

The computed digital output is converted back to analogue electrical impulses by a digital analogue converter which in turn is converted by the receiver back to sound.

Digital hearing aids routinely have three or more bands. They may have multi-programmes and switchable microphones. They have sophisticated feedback management strategies because digital aids have a much broader frequency response than analogue aids.

They have speech-enhancement strategies involving multimillions of calculations per second using temporal as well as frequency cues. There tends to be less circuit noise because of fewer moving parts. However, a good analogue hearing aid may still be the aid of choice at the present time.

Digital hearing aids cost between $4,800 - $7,000 a pair.

The future

Digital hearing aids open the way to better solutions for speech enhancement in noise. They allow for better systems for control of feedback.

They also allow for upgrades of the existing hearing aid when new software programmes are developed. They have fewer moving parts, which means less likelihood of damage by moisture or wax.

The myth of large cumbersome boxes that are noisy and do little, is still the perception of many people. However, the reality is now quite different. People are recommended to seek advice from a member of the New Zealand Audiological Society on what type of hearing aid may be suitable for their needs.