I have an 8 channel mixer which sends phantom power to all mic inputs when the phantom is activated. I would like to run a SM81 and a SM58 through this mixer in a live performance situation. My question is, if I enable the phantom power on the mixer for the SM81, will it affect the operation of the SM58?
No. Any dynamic microphone with a low impedance balanced output, like the SM58, is not affected by phantom power.
Phantom Power will not damage a professional dynamic microphone.