The chances for a phase problem are far greater on the drum kit than in almost any other band-level situation because it usually has more mics on it than any other instrument. That said, there is a simple technique for checking for a problem as outlined in this excerpt from the 4th edition of my Recording Engineer’s Handbook.
Understand that you will never have all microphones completely in phase, but some problems will be diminished by reversing the polarity on some of the channels. The only way to determine this is through experimentation and listening.
For this check, we’ll use the phase switch on the console, mic preamp, or DAW. Flipping the phase switch may cause the problem frequencies to come closer in phase, or it may put them farther away, or it may have no effect at all.
1. Record a sample of the drummer playing, then listen to the overheads panned in stereo, then listen to them in mono by panning them both to the center. Flip the phase switch on only one of the overheads. If the low frequencies seem to drop out, flip the phase switch back to the original position. If it sounds like there’s more low end, leave it in this position. After you’ve found the correct setting, pan the channels back into stereo and go on to the next step.
2. If the overheads still sound thin or swishy and you know that their polarity is correct (they’re pushing and pulling at the same time), then place them in a different position, perhaps using them as a stereo pair or placed farther apart.
3. Once you’re pleased with the overheads, add the kick drum. Switch the polarity on the kick and stay with the position that has the fullest sound.
4. Bring up the snare mic. Press the phase button on the console or preamp. Does it sound better inverted or not? Now place the entire mix in mono (if possible) and see whether it still sounds better.
5. Keep following this procedure for each microphone. On each one, listen to how the mic sits in the mix, then listen to it with the phase inverted, and then do the same thing in mono. In each case, use the phase switch position that gives you the fullest sound with the most low end.
If you have two kick mics, check the phase of the inside kick mic against the overheads and then the outside kick against the inside. Sometimes you might need to move the outside mic to find a more phase-compatible position.
Ultimately, you cannot avoid phase cancellation, you can only make sure it sounds as good as possible.
TIP: Remember that one position of the phase switch will always sounds fuller than the other, and that’s the one to choose. If neither position seems to make a difference, choose the position you started with.