Not really entirely on topic, but here's a few tips with Drums and polarity and phase that I've learned.
You need to check every single mic of your drumkit for proper phase, and the easiest way to start doing this is flipping the polarity. Look 9/10 half the mics are supposed to have an opposing polarity then what they do. Also, it's not usually so cut and dry as snare bottom always being flipped. In fact I find the opposite is usually true. Some studios have cables wired in reverse, or the output card on a channel strip in their console is in reverse or a number of other things. Blindly assuming the bottom mic is out of phase is a bad idea. It ALWAYS will to be the opposite polarity of the snare top, but maybe it's the snare top that's out of phase with the overheads. Or maybe it's already in phase cause the snare bottom mic cable is reversed. Just check every mic.
With regards to the earlier mention of room mics/ not being able to hear a difference that much, here's a few tips.
1- If you can't hear a difference, then it's likely your mics are in what I call the "grey middle ground". They don't really have a great phase relationship, but they aren't exactly terrible either. My suggestion would be to move some mics closer or further apart (usually with overheads and the snare it's as simple as narrowing or widening the overheads, or sometimes turning the mics in or out more towards the edges/center of the cymbals).
2- Room mics are tough, because of the distance usually involved, the low frequencies are so different that it's hard to just the phase. Low end makes judging phase really easy, so if you have access to EQ, sometimes temporarily adding extra bottom to your rooms can actually make judging the overall relationship a bit better. Again though, sometimes they are in the dreaded middle ground and just need to be moved closer or further away.
The final thing I'm going to share is a trick I learned from an engineer years ago about checking phase on drums, especially in a room you don't trust/has bad low end reproduction.
Step 1. Have the drummer record a buzz roll, preferably as cleanly and as long as he can.
Step 2. Loop the cleanest longest section of said buzz roll you can. Usually a solid 5 second or 10 second loop is perfect.
Step 3. Mute all mics but the snare bottom and one overhead mic. Mono your speakers, or better yet, pan all your drums to one speaker. Balance the 2 mics so that the snare bottom sounds like it's part of the overhead sound...not overbearing or on top. Now flip the phase on the overhead mic. The change should be insanely drastic. All of a sudden you'll have tons of extra weight and low end, or it'll go super thin. Which ever way sounds best, don't touch the overhead mic phase button again. Mute snare bottom.
Step 4. Now bring in the other overhead. Flip the new overhead channel. Compare, and decide which is best. Mute the newer overhead.
Step 5. Now go through each mic individually and compare them to the original overhead track. Again making sure that they are blended pretty well with the overhead. Each and every track should be a clear thick or thin change. If you run into a mic that isn't a clear change, look at the steps above to see if the mics are misplaced.
Step 6. After you've gone through all the mics, open up all the channels at once and just double check what you did. I do this by flipping all the kicks, then all the snares, and just making sure it gets worse if I flip them.
At this point your kit should sound a shitload better then it did.
I used to do something similar but with single shots while looking at the meters to make sure there was a loss in the signal. I tried it with the buzz roll earlier today and it's faster and more obvious.
