It's interesting that nobody has really mentioned internal with a Beta 91A. Is there a reason for this ?
while I have personally never been a fan of the beta 91 or the beta 91a
The original sm91a is a killer kick mic ! if you have not tried one try it . You owe to yourself and your subs to thoroughly give them a work out . They may be a little hard to find today .But they are well worth the investment and time to find one. I personally find it to be ne of my favorite go to kick mic's along with a re-20 original d12e, m88 , and 380 , beta 52 , and the new mic's from heil are all good ...my 2cents worth .
Since you mentioned the beta91a, Id like to share a little story.
About two years ago I mixed a unkown band on a rig that I was also systeching.
By chance a Heil drumkit was flying around and one of the cable guys brought a brand new beta91a.
So I had the chance to compare the PR48 and the beta.
Man was this PR48 sounding good, deep low end and very nice attack, but I managed to combine both mikes to an even better sound.
What I forgot to tell
Because I didnt trust the patch guys, I had engaged phantom power on both mikes, so after some songs decided to switch phantom power off of the PR48.
What you might guess already, my favorite mike turned out to be the beta91a and not the PR48.
The BE of the next band followed my advice to use the same combination on kick, but the poor guy was not up to my skills
, I always knew Im the Kickdrumizer.........
until the beater head of that kick drum died.
So the kick of the former band came back on stage and down went my "superior skills", because now the sound also came back.
Hope that helps
Uwe ( owns two beta91a )