Part 3: Mic Placement Options

Mic Placement
Mic placement is an art, and many of its practitioners are reticent to share their closely guarded trade secrets. No mic placement scheme is absolute, but there are some tried and true methods that make good starting points. Still, getting the final sound to work often requires careful adjustment -- and always requires careful listening. The ideal position of the mics can depend on the amp, the guitar, the volume, the room, and of course the way the guitar part's role fits the track.

Miked from the Front
Figure 2 shows an SM57 pointed at a very rare '60s Gibson recording amp. I aimed the microphone exactly at the center of the speaker driver inside the amp. (For those who don't know this amp, this amp’s speaker is not mounted in the exact center of the cabinet. For the sake of this example, though, we’re positioning the mic as if the speaker sits dead center --Ed.) You can shine a flashlight through the grille cloth to help you find the speaker.

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Fig. 2: Straight-on Miking

The position pictured produces the most high frequencies. Moving the mic closer increases level and low frequencies (remember proximity effect?) and reduces the cabinet's contribution to the overall sound. There is a whole group of guitarists and engineers who claim that there's nothing worth recording from the exact center of a speaker. While this may be true of some speakers, you should test this position and judge for yourself.

If you want fewer highs and more warmth, move the mic sideways, parallel to the floor, toward the outside of the speaker. You should move in one-inch increments with someone you trust listening in the control room. With a mic inches from the speaker cone, small increments make a big difference.

Fig. 3 shows an SM57 at a slight angle on a Fender brown-face Deluxe. Usually, this position offers ample highs and more tonality than the straight-on position. Try it from both sides of the speaker, and from the top or bottom. If the mic ends up on the floor pointed at the speaker, and sounds good, nail it down! The floor can trap bass frequencies and enhance tone, especially if it is wooden and built on a raised foundation.

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Fig. 3: Angled Miking

If the floor seems to "close down” the sound, try tilting the amp back. Fenders have chrome legs on the sides of the cabinets for that purpose, and VOX amplifiers, like the AC30 and Super Beatle models, came with tilting carriage stands that completely isolated the amplifier from the floor. If possible, I like to set the amp on a folding chair in the studio.

Figure 4 shows an MD421U on a vintage Fender Tweed Deluxe. I've tilted the amp back so that the bottom of the cabinet couples less with the floor. All of these amps are open-backed; walls (or open spaces) directly behind them greatly affect bass response.

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Fig. 4: Tilted-back Miking

Front and Back
Figure 5 shows an open-backed amp (the Matchless DC30) with an SM57 on the rear and a KSM44 on the front. This setup produces a very unusual tone. You can mix the two mics for a mono track, or route them to separate left and right tracks in your mix. Try moving the mics very close to the speakers and processing the rear mic through a very short delay of less than 3ms. You may also want to flip the phase of one of the mics to test which position sounds best.

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Fig. 5: Front and Back Miking

Multiple Miking
More complex multiple miking techniques can yield great results, but demand even greater care. Multiple miking is a good way find out which speaker sounds the best in a 4x10 cab, and also offers the option of recording each speaker to its own track. Be careful with phase, as some speaker manufacturers deliberately wire multi-speaker cabinets in and out of phase. Some engineers will use a condenser on one speaker and a dynamic or ribbon on another. I like to find the best speaker and use two mics on the same speaker. Even then, I sometimes hear a little "phasiness" between the microphones. A very popular setup is an SM57 up close with a U-87 or the tube U-67 for a cabinet mic four or five feet away.

In the Middle
In Figure 6, I used a Royer R-121 equidistant between a ’60s 4x10 Marshall straight cabinet and a reissue 4x10 slant cabinet, both driven by a single amplifier. This setup won't work unless one of the cabinet's speaker cables is wired out of phase or unless the cabinets are wired out of phase with one another. With both speaker cabinets pushing and pulling together -- and the warm sound of the ribbon in the middle -- you won't find a fatter tone, especially for clean sounds.

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Fig. 6: In-the-middle Miking

Part 4: A Scientific Approach / Other Methods

Scientific Starting Point
Figure 7 shows a scientific approach to mic placement on a Beatles AC30 VOX amp. The tech in the picture is using test instruments rather than his ears to find the "sweet spot." Sound waves coming out of a guitar amp emanate in all directions, setting up patterns much like a stone produces when thrown into a very still pond. Like in the water, sound waves interact, producing multiple reflections and standing waves where sonic energy coalesces. The idea is to place the mic where sound waves add together.

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Fig. 7: Scientific Approach

To find this position, you must measure the output level of a microphone while you move it around in front of the amp. First, set up for a guitar overdub with your microphone and fix the headphones so the musician can hear himself. Next, unplug all headphones and send a steady 700Hz oscillator tone into the guitar amp's input jack. Place a large VU meter so that you can see it from wherever the guitar speaker cabinet or combo amp is located. (If you can't get a sight line to the VU, plug a volt meter into the cue system and read the level there). Set the meter to read mid-scale with the cue system level control. And wear ear protectors! Let's make this science project as painless as possible.

Move the microphone around in front of the amp. In doing this, you'll find many peaks and dips in level. I try to stand behind the speaker so that my body doesn't affect this measurement process. Obviously, the level goes up as the mic gets closer to the speaker, but if you keep a fixed distance and then move the mic left, right, up or down, you'll find a peak level. This is where you should set the mic. Make sure you like the sound you get using the scientific starting point -- you may hate it!

Other Methods
These are some other ways to accomplish the task of recording guitar amps. Whether used alone or in combination with the aforementioned, all require much more experimentation and studio time.

Room Mics
When placed in a great sounding space, room mics are an easy way to dress up a boring guitar sound. And there's a lot of room (pardon the pun) to experiment. Try different distances and heights, microphone types, EQ, compression and delay. I sometimes tape pressure zone microphones to the control room glass, or leave the studio doors open or put a mic down a hallway. If you have an elevator shaft or stairwell handy, try putting the amp at the bottom and a mic at the top.

Recording The Electric Acoustically
Figure 8 shows a Sennheiser e865 handheld condenser miking the "holy grail" of electric guitars: the 1959 Les Paul Sunburst. Obviously, you will have to put the amp in another room for this to work. But I have recorded amps and mics on separate tracks and it makes a very unique combo. Great for arpeggios!

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Fig. 8: Recording the Electric Acoustically

But wait...there's more
The microphone is a great tool for recording guitars, but it's not the only one available. We'll dig deeper into direct recording – recording the guitar without microphones -- in an upcoming piece.

Images courtesy of the Oliver Leiber Collection.

Barry Rudolph is an L.A.-based recording engineer. Visit his Web site at www.barryrudolph.com. ©copyright 2000 by Barry Rudolph