After all these risks, why use more than one microphone on an electric guitar amp? Easy. It's the same reason you use multiple mics on acoustic guitars or even drums. You are not getting exactly what you want out of one microphone. On an acoustic guitar, it's quite common to put one mic closer to the soundhole to catch the “boom” and another mic closer to the acoustic guitar nut to capture the “sparkle” or high end.

Multiple Microphones On One Speaker

Some guys like to use multiple microphones on one speaker. Why? Because different parts of the speaker sound differently. It's possible to give yourself more options in mixing and / or come out with a better tone if you can blend the best parts of each speaker. Essentially, the closer you get to the center of the guitar speaker, the brighter / thinner / fizzier it will sound. The farther you move away from the center, the darker / duller / thicker the tone will get. There are numerous variations of this trick. I went through a period where I used to SM 57s exactly one inch apart facing the same way. One 57 went dead on the center of the speaker and obviously, one was 1” from the center of the speaker.

I've heard of some guys using X / Y micing? using a 57 and a 421. The 57 is used to get the fizz and the 421 is used to get the beef. I could never really get this one to work for me, but I've bought and loved records that used this trick.

Different Microphone For Each Guitar Speaker

On an electric guitar cabinet with multiple speakers, you can go ahead and count on the fact that each speaker will sound quite a bit differently. I've heard drastically different tones come out of the same models of speakers at the same time. Some engineers want to blend the tones of the various speakers to create something bigger. Personally, I find this EXTREMELY difficult to get right without the old comb filtering problem showing up again.

Different Mic For Each Amp

A trick that is very popular these days is to use multiple amps all at once. Every amplifier has a different tone and character. By blending too different characters, it's possible that you will end up with something better than the sum of the individual tones. Some guys will record 10 amps at the same time. Obviously, this requires the type of facility that allows for this sort of thing. Most bedrooms would simply explode with that amount of sound pressure level.

This trick is not quite as tough to get right as the “Different Microphone For Each Speaker” trick, but it still takes quite a bit of time to get all those microphones aligned with one another. I find the advantages of using multiple amplifiers to be better