toddy0191
500+ Head-Fier
You can use the sound generated with this web:
http://www.szynalski.com/tone-generator/
You can play sound below 200 Hz with every channel in order to show whats differences are between each channel.
I did it some time ago with some earbuds that had a similar problem.
One channel sounded different from the other. I played a fixed tone and brought one channel to the microphone of the phone while recording and then the other.
Here you can download the video if you are interested (only for a week):
https://we.tl/Peq4M5KGvu
That's really useful, thanks!