I have this way of thinking about two different kinds of guitar feedback:
-Gain based feedback -Volume based feedback
Gain based feedback can happen at any volume, and requires distortion, adds sustain to notes/harmonics, etc.
Volume based feedback happens at high volumes, doesn't require distortion and is much more sensitive to physical motion (motion of the instrument changes the pitch of the feedback very easily). There is a greater variety of the actual tones that feed back, more tones than the guitar itself can make via notes and harmonics. Microphones feedback in this way.
I'm hoping to have my guitarist use a very low-gain / clear distortion, but I still want lots of feedback. Are there any tips for getting more of this "volume based feedback" that I'm describing, besides the obvious "use more cabinets and turn up louder"?
Here's some examples that feature this sort of harsh feedback I'm trying to achieve: