There are almost as many ways to capture guitar amplifier sound with a microphone as there are for a piano.
And as with piano (and kick and snare drum, for that matter) single-mic approaches can’t always provide the best solution for guitar amps—we must also explore multiple-mic approaches.
About four decades ago, at the “dawn” of modern live sound reinforcement, there was the Shure SM58 for vocals and the SM57 for instruments. This eventually included miking guitar amps, because as the PA got bigger than the backline, there was a danger that the guitars wouldn’t be heard over the vocals (causing the sound guy’s credibility to be doubted by the guitar player’s girlfriend behind his back).
In the golden days of rock, tuning the PA consisted of saying “check, one-two” into an SM58 and manipulating the faders on a Klark Teknik DN30 graphic EQ until the voice sounded as natural as possible. Because the SM57 and SM58 have nearly identical response, this led to natural sounding instruments as well.
Over the years, sound systems have become increasingly full-range and high-fidelity, with modern systems exhibiting smoother, more even response. At the same time, today’s large-diaphragm condensers have become more rugged and sturdy than their tube-based ancestors, and have made their way out of the studio and onto the stage.
“Big Mick” Hughes, Metallica’s front of house engineer, is credited with putting Audio-Technica AT4050 studio condensers on stage and introducing their use in stereo pairs on guitar rigs. One popular approach is to deploy a pair of matched studio-quality large diaphragm condensers, each on a separate cabinet of a stereo guitar rig, that also act as a pair of stereo “ears” for in-ear monitors (IEM). They also provide redundancy to the PA, and can be panned or doubled as needed.
Most guitar amps don’t achieve their proper “sound” until the onset of clipping, producing that warm, yummy crunch, but yielding high-decibel sound pressure.
Strategies include using a “power soak” to draw some of the power off, going with lower-powered guitar amps, or remotely locating the amp or just its cabinet and isolating it from the performance stage. Dynamic mics produce a contoured response, with warmth in the lows due to proximity effect, and often, a highmid presence.
Besides the Shure SM57, perennial dynamic mic choices for guitar cabinets include the Electro-Voice RE20, Sennheiser MD421 and MD409 (replaced by the 421 II and e609), AKG D 112, joined by a relatively new contender, the Audix i5.
Condenser mics offer extended highs and lows while providing a flatter frequency response. The Neumann U87 is the gold standard for large diaphragm condenser mics, rarely seen outside of studios. It’s heritage also includes the TL103.
The AKG C 414, in all its variations, has been crossing over to the stage for many years, popular in particular for drum overhead and grand pianos. Audio-Technica AT4050 is the large-format condenser that first broke into live sound specifically for guitar cabinets, followed closely by the Shure KSM32.
Ribbon mics, with a bi-directional figure-of-eight pattern, have a transparent sound that allows the amplifier’s character to be clearly heard with a natural roll-off in the highs. They re-entered recording studios several years ago when manufacturers began making them more rugged to withstand normal handling.
The Royer R-121 was the first modern ribbon to find widespread acceptance, and two years ago the company released a ruggedized “live” version with a thicker ribbon. Recently, the new Shure KSM313 ribbon has earned its place on national tours, as has the new A-T AT4081 ribbon mic.
Different mic pairings provide a contrast in the sound, useful when the mics are panned in a stereo mix to create dimension and width.
They’re also used individually to emphasize different aspects of an instrument, but when combined, can equal more than the sum of the parts. The original studio pairing is to combine a condenser and a dynamic mic.
The old studio trick of taping together an SM57 and a pencil condenser, like an AKG C 451, dates back to the 1980s. By picking up the same sound in nearly the same spot, out of phase cancellations at even the highest frequencies can be eliminated. The contrast can provide plenty of control over the texture of the sound without resorting to processing or EQ.
The Audio-Technica AE2500, a unique dual-element mic called the originally introduced for kick drum, has also proven useful for guitar miking. It combines a dynamic and condenser element into the same mic, providing phase-coherent summation of both elements when mixed together.
In contrast, another method is to simply take a single mic and double-patch it to the console, treating it’s EQ differently in each channel and even introducing micro-delay to offset one from the other and intentionally introduce VHF comb-filtering.
Whether introduced by mic’ing distance or by processing in a digital console, the effect of a fraction of a millisecond delay for two signals of similar level is narrow cancellations at regular intervals.