# Technical question about hearing level measurement and audiogram

Hi
This is more of a technical question than a discussion about hearing aids and I’m not sure if this is the right forum for it, but here goes anyway
I see that in an audiogram the measurement is plotted in terms of dB HL. I thought this was same as the dB for sound intensity level, but it seems it is completely different, and I cannot find any study material that explains it properly
Can anyone provide me links to some material with intuitive explanations about dBSPL, dBHL and audiogram?
Thank you very much

SPL I believe means sound pressure level, my MPO (maximin power output) is set to 140db SPL. Not sure about the other tho

I’ll see if I can find you a decent link, but to be brief: the dB HL scale used on the typical audiogram is a weighted scale which uses “average normal hearing threshold” at each frequency as the zero point. It adjusts for the fact that the normal human auditory system is more sensitive in certain frequency ranges than others when using the scale based on physical sound pressure (our total frequency range is about 20-20,000 Hz in the normal ear, but we are far more sensitive in the approx. 1000-4000 Hz range). If the dB SPL scale were used on the audiogram , the region considered normal sensitivity would be curved as opposed to the “corrected” flat region we see on the common audiogram. A problem is that all hearing aid measurements are made on the dB SPL scale, so there is always conversion taking place back and forth using the diagnostic testing (dB HL) and hearing aid measurements (dB SPL). I for one am in favor of changing the audiogram to the dB SPL scale to get rid of the conversions, but traditions die hard.

It should also be noted that the decibel itself is not a physical measurement, but describes the ratio of the exponential relationship between a physical measurement and a reference point. Hope this helps and doesn’t confuse more

Thank you very much
This one is quite simple and to the point
I would appreciate some other material as well for further study

dB definition: http://en.wikipedia.org/wiki/Decibel

dB (weighting): http://en.wikipedia.org/wiki/A-weighting