Amplication and Sound Volume

[shaunnutley]

If someone has a hearing threshold of 40dB and an amplifier amplifies a sound of 20db by another 20dB to make it 40dB will the person be able to hear the sound without increasing the sound volume to 40dB? I'm trying to work out if amplification makes a difference to deaf people as with hearing aids unless they match or surpass their hearing threshold with the sound volume? I understand that hearing aids can make people hear quieter sounds than their threshold, but surely it is the sound volume that does this and not the amplification. If a deaf person walked into a factory with lot's or large, full sounds then these would still have to be above their hearing threshold. Surely such sounds are more than a match for any sounds a hearing aid amplifier can produce.

[WaldoMcFroog]

Your question doesn't seem to make much sense, I'm afraid.

If I understand your question correctly, you are effectively asking how a person who unaided is unable to hear sounds below 40 dB uses a hearing aid to amplify the volume of a 20 dB sound source by 20 dB (i.e. to 40 dB) can hear the sound without increasing the volume to 40 dB... Er... well, amplifing *is* increasing the volume; it's at 40 dB!

Amplification of sound is simply the process of artifically making a sound louder.

Hearing aids are a bit more sophisticated than just an amplifier though - they filter freqencies to suit the environment and the user's particular hearing profile too, ensuring the best possible sound for a given condition.

[tubeway]

It is even more complicated than that - while a conductive loss needs pure gain (amplification). Many sensori-neural losses mean a shortening of the dynamic range and so involve compression to keep hearing comfortable. This is very often not a straightforward subject (believe me - it is my job), but basically a hearing aid will make quiet sounds that are just audible, loud enough to be heard. Mid range sound such as speech should fall into the patients most comfotable levels, and loud sound should not exceed the patients ULLs (Uncomfortable Loudness Levels).
Depending on their type - hearing aids can produce very loud outputs - and aid for somebody with a severe to profound loss can produce sound levels in excess of 140dB and provide gain (amplification) of more than 85dB.