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Using multiple amp mics isn’t hard, but there are a few things you need to think about before the red light goes on. First, decide on the kind of mic that will work with its partner. For simplicity’s sake, we’ll assume the first mic is a dynamic cardioid like the above mentioned SM57, simply because this type of mic is so common and you can always rely on it to deliver the goods.
That said, the strength of a 57 lies in capturing punchy midrange frequencies, so you might think about putting a second mic with different sonic characteristics on the cabinet. A perennial champ in that department is the Sennheiser 421, which paired with the 57, provides a nice bottom end and a smooth top.
Or you could turn to a ribbon mic. Ribbon mics are known for their smooth, natural sound, and they can easily handle the low end of a speaker cab. Some great ribbons for recording guitar are the Royer 121 or 122, Beyerdynamic M160 or M88, AEA R84, and even the $100 MXL 990. Most modern ribbons can easily handle the high sound pressure levels that can come from a loud cabinet, so don’t worry about turning up.
As nice as ribbons are, you don’t have to break the bank just to pick up a second mic—just about anything will work as long as it has a different character than the first mic. Also, make sure to record each mic on its own audio channel, which is usually not a problem with the high track counts of today’s DAWs (Digital Audio Workstations).
When placing mics next to each other, try to make sure the sound from the speaker hits each mic’s diaphragm at the same time. This helps avoid any phase-cancelling issues. Also, if your mic preamps have phase switches, be sure to confirm that the two mics both have the same phase settings. More than once I’ve heard an unusual sound when recording an amp and realized the phase switch was reversed on one of the preamps. That’s not to say you shouldn’t try using an out-of-phase mic, but to begin with, I’ve always found it a good practice to first record with everything in phase. Once you know how that sounds, you can start experimenting.
A little side story on phase: A good friend of mine, engineer John Holbrook, told me a story of the first time he recorded Brian Setzer. John said he couldn’t figure out what was going on with the guitar sound after he set up the mics, but didn’t have time to analyze the problem before Brian wanted to roll. Only after the session did he realize, thanks to Brian’s tech, that one speaker in the cabinet was wired out of phase. John said it’s actually a very cool sound.
With the two-mic technique, you should also try placing one mic on axis and one off axis. Off axis simply means you’re changing the angle of the microphone in relation to the speaker. Instead of pointing the mic straight at the speaker (on axis), turn it slightly to the side (off axis). This angled position alters the tonality. The only way to understand what it sounds like is to try it. If you’re working alone, record a minute or so of various axis setups and compare the results.
If you’re using two mics, consider mic’ing the back of an amp. Open-backed cabinets offer some nice tones when you mic them from behind. But be sure to flip the phase on one of the mic preamps, because the speaker will be pushing and pulling, and you want the mics to correctly capture that dual movement. That said, perhaps having the mics out of phase will create exactly the sound you’re after.
If you have extra mics and the urge to explore sonic options, try placing a third mic a few feet in front of the amp. This can impart a nice sense of space to the recording. It’s common to use a large diaphragm mic in this situation, as they tend to capture a good balance of lows, mids, and highs. But again, any decent mic will get the job done.
Once you’ve got all the mics from your guitar part recorded, it’s time to mix. This is where the effort you’ve invested in a multi-mic setup will pay off. With one mic, you can reach for the EQ if the sound lacks something frequency-wise. But with multiple mics, you’ve got many more options. By panning the different mic tracks to the same basic position and raising and lowering each relative to the others, you’ll hear a range of different and unique frequency blends. Obviously, the song will dictate what’s needed, but you may now have everything you need in front of you— meaning, you can possibly skip that EQ.
To create some extra space, try panning that third room mic to the opposite side of the main mics. This will open up the guitar sound and provide extra depth. Room mics don’t always work though, as they sometimes can “cloud” the upfront sound of the guitar in a mix. Do a quick pan and trust your ears to tell you what’s working and what’s not.
So, if you haven’t explored this technique, think about recording with two or more mics in your next session. Just take the time to set it up correctly, check your phase, and make sure you’re not overloading the signal to “tape.” This is certainly one of those cases where more is truly more.
Rich Tozzoli is a Grammy-nominated engineer and mixer who has worked with artists ranging from Al DiMeola to David Bowie. A life-long guitarist, he’s also the author of Pro Tools Surround Sound Mixing and composes for the likes of Fox NFL, Discovery Channel, Nickelodeon and HBO.