The first question I ask myself when it comes to recommending a hearing aid is "will this hearing aid allow me to meet your hearing loss prescription?". Only then can you start to look for other features and styles of hearing aids.
A Hearing Loss Prescription is a lot like an eyeglass prescription. Different types of vision loss require different prescriptions. You can't just take one prescriptions and fit them to everyone with hearing loss. This is the same when it comes to hearing loss. Different configurations and severity of hearing loss require different amounts of amplification.To explain a Hearing Loss Prescription on a basic level, it is a calculation of the ideal amount of amplification required at each frequency to restore audibility to certain sounds. For example, if you have more hearing loss in the higher frequencies, you would require more amplification to restore sounds you are missing in these ranges, compared to other frequencies that you have less of a hearing loss in.
The amount of amplification required in these ranges depends on a variety of factors, not just the level of loss alone. This is one of the reasons why wearing a pre-programmed hearing aid does not provide the maximum amount of benefit, because individual variations including hearing loss levels are not taken into account.
There are several different prescriptive methods used to determine your prescription for hearing aid amplification requirements.
1. NAL-R - This was developed by the National Acoustics Laboratory in Australia. It is intended for use with Linear hearing aids that apply the same amount of amplification to all inputs (soft, average, loud sounds). Not many people wear Linear hearing aids anymore, but if you do, the NAL-R is the prescription for you.
2. NAL-NL2 - This was also developed by the National Acoustics Laboratory. It is the updated version of the NAL-NL1 which is intended for Non-Linear hearing aids. These devices prescribe different amounts of amplification for Soft, Average, and Loud sounds. This is the most commonly verified hearing loss prescription today.
3. DSL-5 - This stands for Desired Sensation Level Version
5. This was developed based on the need for verifiable prescription for children.
However, adults can also use this prescription. Children often require more amplification than adults and ensures that they have access to sound critical for speech development. This formula results in different frequency response curves, insertion gain, and compression parameters than the NAL formulas.
4. Proprietary Manufacturers Prescriptive Methods - All hearing aid manufacturers have their own Hearing Loss Prescriptions. Phonak has its Adaptive Phonak Digital, Signia has NxFit, ReSound has Audiogram+, and Oticon has VAC+.
However, the biggest problem with these prescriptions is that they cannot be verified like the 3 previous prescriptive methods.
Remember, just because a hearing aid sounds good, doesn't mean the hearing aid is programmed correctly. Not using Real Ear Measurement results in an unverified prescription that won't let you hear your best. The calculation of a Hearing Loss Prescription is more complex than just adding volume to make things more audible.
Fortunately, there are organizations like the National Acoustics Laboratory, and individual researchers who have done extensive research to develop Hearing Loss Prescriptions that will help you hear your best.
So the next time you get a set of hearing aids programmed, be sure to ask your hearing care provider which prescriptive method they are using and why. Oh and don't forget to make sure they verify your hearing loss prescription with Real Ear Measurement.