Hi Pano
I want to say I had mixed feelings about posting about this from the beginning.
I really like the DIY area, that is my background. When I was a teen, a person I met and was mentored by, gradually put me on a different and better set of tracks in life. Some years later when I realized the impact he had, I gave him an invention I had, an acoustic levitator transducer which he then demonstrated to the new group of kids he was mentoring.
I asked what can I do to repay him, he said you will be able to answer questions, to help is what you can do for me. When Robert Oaks Jordan passed away, we lost an unsung audio pioneer but a person who changed many lives. Anyway, that’s why I post on some DIY forums occasionally and when I am working on something new, it is for me, essentially the same feeling I had playing in the sand box. I figure, most of the people who would be interested in this stuff are probably drawn to that feeling too.
I have had some time to think about “what it takes” and actually maybe the real issue is “do you have enough” for what you’re playing. Using the sine at the frequency you chose makes sense too, nothing I am talking about can be seen at the signal level without equipment most don’t have. The last thing I wanted to do was make anyone less likely to do the test or be curious.
In that vein, it has occurred to me there may be another test you could try or add, at least for people with two requirements, one, they have some ability to make an attenuator and that their amplifier is a conventional one where one side of the output is ground. The attenuator is one that lowers the amplifier output voltage down to approximately the same as the input voltage and of an input impedance that will not go up in smoke.
There is a freeware program an acquaintance has written which is for comparing music files for differences.
The idea is that it takes two files, aligns them in time and by inverting one and adding them, it adjusts to a null or residual difference. Thus, if the two signals really are identical, there is nothing left but what comes out is the difference signal. If one uses a sound card, most are identical L to R (except for latency) so this should work fairly well for this.
Audio DiffMaker
http://www.libinst.com/Detecting%20D...8slides%29.pdf
Now loudspeakers have far too many issues to use this with but if one used the input signal and the output voltage (through an appropriate attenuator) as the other, the same null would result, the difference between them you can hear.
While playing music X at level X, one can see if the amplifier residual has spikes or transient like stuff in it which happens when the output doesn’t track the input (including things like distortion). The cool part is you can hear it, the not cool part is there are no measurements, just auralization of it via the output file.
Best,
Tom
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