If you have a lot of power in your voice this is common problem.
I would suggest just holding the mic farther away if you are having trouble
adjusting the volume. No offense to redhead, but when people hold the mic upright I lose more control of the vocals -most mics are unidirectional which means they pick up the meat of the sound from the center of the mic. I suppose it depends on what kind of equipment you or they have. But really it is what works for you. You might take the opurtunity also to practice getting more control of your vocals. I know this is a huge challenge for me personally especially in the higher range. If I know I'm going to get really loud trying to push into that higher range I just back away from the mic. Some singers will scream when they go higher range and don't back away - this is a nightmare for me to adjust the equipment too.
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