[thedoc (OP)]

Eion MacDonald asked the Naked Scientists:
   
Thank you for interviews on hearing aids and tinnitus.

I recently got a hearing aid and your site answered many questions I asked in hospital but were not answered. Specifically about battery size limiting the frequency range sampled.

Thank you for this.

Perhaps hospitals should refer folk to your site for understanding.

Eion MacDonald

What do you think?

[evan_au]

Modern hearing aids are marvelously complex devices* - but they consume far more power than the human cochlea, and so power consumption is a major constraint.

There is little difficulty in getting modern electronics to sample sounds with CD quality, recording sounds up to 20kHz with 16 bit resolution. Every smartphone has this capability, but they do require recharging regularly!

However, not much useful information is conveyed at frequencies above 10kHz, and many adults cannot hear frequencies above 10kHz. Most of the energy of human speech is below 3kHz, with some useful sounds extending up to around 6kHz (eg to help distinguish "s" from "f").

If someone has degraded hearing above 2kHz, and almost no response at 5kHz...

• There is great benefit in boosting the sounds between 2 kHz and 4kHz to make human speech much more understandable. This has a big impact on quality of life, as humans have a bias towards communication.
  
• However, there is no benefit in boosting the frequencies between 6 and 10kHz because there is little speech information in this part of the spectrum, and this individual will hear nothing in this frequency range anyway. You are wasting battery power on something that will bring no benefit, and possibly subjecting the surviving sensing cells in the ear to excessive excitation, leading to further hearing loss over time.
  
• What you do between 4 and 6kHz probably depends on how important speech vs music is to you...

This does remind us that modern workplace safety rules prevent us exposing people to continuous loud sounds, as they destroy the sound-sensing cells in your ears. But many people intentionally subject themselves to the same damaging sound levels through their smart devices, which is likely to lead to later hearing problems - not so smart?

*Modern hearing aids can be reprogrammed through a computer as your hearing changes, and the two hearing aids talk to each other "behind your back" using wireless to help localise the source of significant sounds.

[RD]

All other factors being equal, then the only parameter the size of the battery determines is how frequently you'll have to replace it. Very loud hearing aids will require more frequent battery replacement, or a bigger battery, because they use more power.

If your hearing range isn't what it was when using a hearing aid with a fresh battery,
then your hearing may have deteriorated since you first started using those aids :
if so adjusted/replacement hearing aids may be necessary.