AF’s Weblog

February 11, 2011

Capturing Guitar Amps in the Wild: Multi-Channel Micing for Live Sound

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.

A Vox AC30 with a Shure KSM32

(above) and an Orange 4 x 12

with an Audio- Technica AT4050.

 


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 mic’ing 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 engineer for a quarter century, 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.

Desired Response

Dual Shure SM57s – one for each

speaker cone – on this 65amps

Monterey 2×12 combo.

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’s AT4050 is the largeformat 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.

Now let’s take a closer look at other solutions…

The Direct Route

A Radial JDX DI can capture the

warmthof tube guitar amps while

addingresponse that emulates a

guitar speaker.

In the world of live hard rock or heavy metal, it’s common to find amplifier DIs which take their signal from after the guitar amp and in parallel with a speaker cabinet.  The original is the Hughes & Kettner Redbox, and Radial Engineering makes a modern JDX “amplifier DI” that’s active and employs Class A discrete electronics. These devices capture the warmth of tube guitar amps, while adding response that emulates a guitar speaker.

 

Redbox DIs eliminate inconsistencies from mic selection and placement, accidental misplacement of the mic and speed up changeovers on multi-band concerts by requiring only a re-patch of an XLR – no mic to move.  They employ electronics to emulate the response of a guitar cabinet’s speaker cone, rolling off the highs like a real speaker.  They’re specially equipped to take the higher voltage of a guitar amp’s output, but the big warning is they don’t act as a speaker load and must be used with a cabinet, or the amp will fry them.  When used in combination with a single microphone, the results can provide a wide range of creative options, and their relative distances are only determined by the one mic’s position.

 

This is a personal favorite for in-ear monitor mixes learned from Meredith Brooks, with the DI

The desired mic position can be clearly

marked on the cabinet’s grill using

gaffe tape. (That’s a Royer R-121L

ribbon mic, by the way.)

panned away from the rest of the band and the mic towards the band, but it’s a stereo effect and works best with a stereo IEM mix with both ears in.

The distance from the speaker cabinet is considered important in most studio recording applications, but in live sound, the inverse square law dictates that placing the mic right against the grill cloth reduces bleed from adjacent sound sources.  That said, when guitar amps are placed next to each other, use of gobos can increase their isolation from each other.

 

With modern in-ear monitoring, guitar players no longer need their cabinets on-stage with them, so it’s common for the guitar tech to set them up off stage (hopefully on the opposite side of the stage from the monitor console).  This gives the guitar tech full access to the amps during the show, and keeps them from muddying up the sound in the venue.

Today’s live sound systems provide opportunities to easily make multi-track recordings that allow engineers to compare various approaches to many sound reinforcement applications by swapping different combinations of inputs and auditioning them in the PA, without having to annoy the band to play the song over and over.  It also allows the engineer to demonstrate mic choices to a guitar player while he’s standing at the console and listening instead of playing.  Do this, and it leads to better communication and collaboration, and you may even become friends for life.

To read the full detailed article see:   Capturing Guitar Amps in the Wild

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