You need to remember that although there may be some change in the response of the human ear depending upon age and frequency, I'm pretty sure the volume variations caused by the changes in the response/efficiency of the equipment used to produce the audio tone will have a much more marked effect on the levels.
Changes in resonance caused by case volume, positioning, and materials used all add to these effects. I have three sound level meters here that I use from time to time when setting up equipment. I once tested a Datong Morse Tutor at various tone frequencies (the tutor had a balanced armature speaker, not the piezo type sometimes used in the later models), and I found a number of points where the tone coincided with the resonance (or overtones) of the speaker and caused increases of 10-15dB at least at those peaks over the response at other 'dead' frequencies.
Also, when you approached the resonant frequency of the speaker the output level would rise rapidly over a 50Hz or so range.
Ideally you need to use a studio quality amplifier with a flat response from say 20Hz-20KHz, and a studio quality speaker (a studio monitor speaker), also designed to have an extremely flat response, before you really judge the effects of various side tone pitches.
But, even with the above equipment you would only at best be reproducing a standard hearing test! To my mind it makes no odds what the levels are set to, the important things to look out for are:-
1) Is the tone chosen more 'restful' or 'pleasant' to the ears?
2) Does you ability to copy CW improve at the newly chosen pitch and also is it less fatiguing?
At times I drop the pitch of my pocket MFJ tutor down quite low, sometimes only just above 300Hz (the minimum setting for the pitch), for no reason other than it is more restful to listen to for extended periods. I did test to see if my copy speed improved, but it seemed pretty much the same at the time I tried it..
Side tone pitch arguments are like arguments about the best way to hold a key, or the best methods of paddle key operation, and so on. They rage on and on but at the end of the day it's down to what works for YOU. Trial and error shows us that some things may work better than others for us, but obviously not for everyone. Just the same as tastes in music, colour preferences etc.
Sometimes I think that maybe we're all looking for some magic Morse panacea, but with how many hundreds of thousands of op's that have gone before us you would think that one of them would have stumbled across this 'magic' by now.
Just a thought...
:w:
