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Miking Guitar Amps On Stage

Going Electric
By Jon Burton

Electric guitars are one of the cornerstones of modern music, but miking them up can prove tricky. We round up some top tips from professional engineers.

Miking up guitars at live shows can simultaneously be both one of the simplest and most difficult jobs for a sound engineer. It is very much part of our 'bread and butter', as the electric guitar is synonymous with modern music — most engineers I know grew up working with guitar bands. In its simplest form, a guitar‑based show would involve throwing up some mics on the drums, a DI on the bass and a mic on the guitar. However, as shows become more sophisticated and in‑ear monitoring more prevalent, the guitar has come under much greater scrutiny.

Traditionally, guitar (and bass) amplifiers had a single, stand‑alone role: to make the guitar loud. In the early '80s, Mesa Boogie actually introduced a range of amps called the Coliseum, designed for the largest touring acts of the time — the Who, the Rolling Stones and Santana. With this amplifier and its massive 200W output, your guitar could fill a whole large auditorium without help. This was still at the turning point where mixers were really just amplifying the vocals and the drums using a minimum of microphones. These days, even the most modest club has a mixer capable of miking up quite large bands easily, and a microphone on the guitar amp is the norm. This has led to smaller amps being used on stage, for several reasons.

Anyone who has owned a Marshall 4x12 cab will know what a great sound it makes; a full stack, better still. Anyone who has ever had to transport one themselves knows how heavy they are, and how much room they take up in the hallway. In the last 10 years or more there has been a return to smaller, more flexible combos, some of which would not look out of place in your living room. This trend towards using smaller guitar amps has done a lot to reduce the level of the guitar on stage, and improve spill on the vocal mics at the same time. It has also meant that reliance on the engineer to capture the guitar sound has increased. In this article I want to talk about some of the techniques that engineers are using to help capture the electric guitar live.

Taking The Mic

Sticking a dynamic microphone in front of the guitar speaker is still the go‑to technique used by most engineers, and it is also the simplest approach. The choice of a dynamic microphone is easy and practical: dynamics will be able to handle the sound pressure levels of the speaker; they will have the warmth and body needed while not sounding unduly harsh. They are always my first choice. As to the model of microphone, Shure have always had the historical upper hand with their SM57, which remains a very popular choice. Another popular choice at the moment is the Sennheiser E906. This square, side‑address dynamic microphone has its roots in the MD409, which was originally released in the '60s and can be spotted in use as a vocal microphone by such acts as Pink Floyd in the late '60s and early '70s. When Sennheiser released the cheaper, more robust E906 in the '90s, it began to catch on as a guitar mic. All of a sudden you didn't need a mic stand — you could just wrap the cable through the amp handle and dangle the mic in front of the speaker. No more worries that the stand would get knocked out of place, and with a bit of gaffa on the cable it would sit in position all night. This practicality still dictates microphone choice for many engineers, since having a consistent, easy answer to a problem will usually outweigh any other requirements.

The simplest and most common way to mic up a guitar amp is simply to park an SM57 up against it.So does the dynamic mic tick all the boxes? Well, yes and no. For most applications it is a great choice and will remain so. All dynamic microphones have their own characteristics, however, and since the most common use for dynamic microphones is for vocals, most tend to have a presence peak added to help the vocal cut through. The SM57 and E906 both have a slight presence peak, and on guitars this can bring out the 'crunch' nicely. However, in some cases, this may not help, and a flatter‑response mic may be needed. This is where your choice can become more difficult, as neutral‑sounding dynamic microphones tend to be less common. However, with the increased number of microphones available more specialist models are now on offer. Manufacturers are increasingly looking at live concert use, as they have realised what a huge market this is. Not only are there loads of venues out there buying microphones, along with hire companies and bands, but live engineers also regularly break, lose and destroy them, on an almost nightly basis. A studio may keep a microphone in smoke‑free, pristine condition for many years, but the mic box at your average BarFly venue looks like the contents have been used for trench warfare.

Most of the major manufacturers offer instrument mics which have been optimised for use on stage for, among many things, guitar. Ruggedness, ability to stand high sound-pressure levels and with low handling noise are now standard features. You can now find a short‑barrel mic that can easily be placed in front of a speaker and which will put up with even the greatest effects pedal-inspired excesses.

Sennheiser's side‑address dynamic mics are another popular choice for electric guitar, partly because their design means you can simply dangle them in front of a speaker and eliminate the need for a mic stand.So what are the drawbacks to the dynamic microphone? Well the very rugged nature of the capsule, which is what allows it to withstand high SPLs, also restricts its ability to move quickly, which is reflected in its frequency response. It isn't able to respond as quickly as other types of mic to transients and high frequencies. Most guitar amps have quite a small frequency range, however, relying, as they do, mainly on paper‑cone 12‑inch drivers that are often chosen for their coloured and restricted sound. Why, then, would we need a microphone with a huge range to cover what should be quite a narrow frequency range? Well, despite the speakers in most guitar amps not having the widest range, they are still pushed to those limits. Guitarists will crank the top end and get the most out of their amps. You still need a microphone that can capture as wide a frequency range as possible.

I first remember 'Big Mick' Hughes (Metallica) telling me about using large‑diaphragm condensers on his guitars live about 20 years ago. At the time, most microphones of this type were extremely expensive, but companies like Audio‑Technica were producing comparatively cheap models like the AT4050, which I believe Mick was using. I had the chance to try them some time later and was suitably impressed. All of a sudden the guitar began to sound more full‑range and open. As with all these things, though, there was a rub. The presence peak that was apparent in most of the dynamic microphones was missing. The guitar sound could lack the ability to cut through, and it was difficult at times to add depth or warmth without risking feedback. These mics are also more prone to mechanical noise, so an elastic suspension is usually needed.

When dealing with multiple speakers, make sure the one you put your mic in front of is actually working!Photo: Jaakonam / WikimediaIn recent years, good condensers (either small‑ or large‑diaphragm ones) have become common and are often reasonably priced (sometimes costing not much more than their dynamic counterparts). Another microphone type has also re‑entered the ring after many years: the recent resurgence in ribbon microphones has led them from the studio and on to the stage. Ribbon microphones are great at capturing guitars. They have a very smooth response, but can also be very flattering in a way that other microphone types may not be. The downside with those, though, is that they tend to be fragile. Recently, however, more robust models from companies like Royer have started appearing on stage — and not just on the largest tours. They still need to be treated with respect, but if you are doing a very guitar‑orientated act they can really help.

Meet The Pros

One engineer who has taken to using them live is Marc Carolan, who tours with Muse. "Lately I've favoured ribbon mics, particularly the Royer 122L, as I like the smoothness in the high mid/highs even at high SPLs. This has the added bonus of not fatiguing the audiences' ears.”

Capacitor mics are increasingly being used for live guitars, but their response is very different to that of dynamics, in particular their lack of a mid‑range presence peak.So what do other engineers have to say? I approached a few colleagues for their opinions on miking up and working with guitars. One of my favourite engineers is Ray Furze, whom I first met when he was doing the Pixies at their peak, and who has also worked with such notable acts as James, Chris Rea and the Spice Girls. "It depends so much on the man and the music,” says Furze, "but to generalise, it is well accepted that there are two given truths about guitarists. One, they will be too loud. Two, they will have strong opinions about their sound. To take the latter point first, it is not at all surprising that they are fussy about their sound. It is their day job and they spend hours and hours rehearsing and working on that sound, so give them the respect that deserves, listen and talk about what they are trying to achieve.

"The reason they are often too loud is most likely not to piss off everyone around them, but to use the power for sustain, which can't be achieved at low levels — so find other ways of dealing with this level, such as speaker positioning.”

Marc Carolan adds: "I always start with the source. Knowing what the guitarist is trying to achieve is central in my approach, and this allows me to comment on the source so that we get that right first before thinking about the mic or signal chain. I'll also work closely with the monitor guy and the guitar technician on this. With the Muse guys, they have such a good grasp of their sound I'll generally only get involved if they ask me to, as it always sounds pretty amazing! The same can be said of Robert Smith and Simon Gallup in the Cure. After all, who would know better what the Cure should sound like? I also enjoy working with the Snow Patrol guys; Pablo (bass) is very dialled in and Nathan (lead guitar) is always up for a bit of experimenting.”

To get a more rock‑orientated view I spoke to me colleague Martin 'Arnie' Annables, who bravely mans the faders for Motörhead. He was given strict instructions on day one: "Lemmy only ever wants to see a Shure SM57 on the main stack. I am not to ever use a DI box on the bass either, he's the boss.” Having said that, in an effort to keep the sound as clean as possible, Arnie is not adverse to using a DI on the guitar and using a phase-adjustment unit to align its signal with that of a mic.

Prepare To DI

The DI box has undergone a renaissance on live guitars. Active boxes that can be put between the amplifier and the speaker have been around for a long time, but tended to suffered from feeling flat. The more recent DIs from companies such as Palmer and Radial are proving increasingly popular, however. By emulating the sound of the speaker as well as capturing much of the sound of the guitar/pedals/amplifier chain, they are great for providing a spill‑free and very controllable sound.

Arnie explains his use of DIs: "My Motörhead guitar rig has two Radial JDX boxes; one 'clean' (ha ha), with no effects, and one with effects. There's also a Shure Beta 56 on a cabinet behind the main stacks for backup.”

Ray Furze has engineered for such diverse acts as the Pixies, Chris Rea and the Spice Girls.I use a Radial DI on the Prodigy for much the same reason: with a very loud stage I can use the DI signal for the body of the sound, and blend in the mic on the cabinet to further capture the tone. This is not without its problems, however, as Marc Carolan explains: "These days, in the live domain I tend to prefer a single‑mic approach, for a couple of reasons. It allows me to get the same position/response more accurately day to day. It also removes the invariable phase problems you get from multiple‑mic approaches, no matter how accurate your mic placement.”

Just A Phase

Overcoming the phase problems caused by multiple mics and/or DI boxes on the same signal is difficult. When similar signals (such as from two microphones) are added together, there will inevitably be some phase issues. This will result in comb filtering, where the slight time differences between them will cause cancellation, or addition, at different frequencies — which gives the combined waveform a 'comb' like appearance when viewed on an analyser (hence the name). In the worst case, these two signals will be 180 degrees out of phase. This can usually be corrected with the polarity switch on the desk. However, in most cases the phase difference will be less, and this will not help to correct it. Some engineers now use phase‑alignment tools like the Little Labs IBP or Radial Phazer. These allow you to adjust the phase of one signal and tune it until the combined signals sound better. It is rare to be able to get the two signals perfectly in phase, but this level of correction helps to bring out the best of the combination of signals. My technique for this is to try and get the combined signals to sound as bad as possible, and then invert one channel, hopefully bringing them into alignment. It is usually easy to hear when it sounds worse than marginally better!

Muse engineer Marc Carolan and his favoured Royer R122 ribbon mics.As an engineer, when you are presented with multiple sources it raises a whole new selection of problems. "You always know where you are when your guitarist uses one rig/combo,” says Furze, "but when they use two, which is often the case, you have to be very clear as to how he/she is trying to use them. First, ask why they are using this particular setup. Is it two completely different setups that will be used individually for different sounds, or will they be used together to create a merged sound? Or is it to hear their stereo effects? This last reason should start alarm bells ringing. At FOH a lot of engineers faced with endless stereo keys and tracks would want to place the guitar in a solid position in the mix, and to do this the temptation is to narrow the pan on the 'stereo' guitar — but beware. Stereo guitar effects can do shocking things to the phasing between the left and right channels, and as you 'mono up' this can lead to unwanted cancellations and comb‑filtering artifacts, and even significant drops in level. The only way to truly fix this problem is to work through every effect and combination the guitarist will use and work out what problems might occur.”

Listen & Learn

What guitarists hear is not always the same as what the microphone hears, and it is very important to listen to the guitar amp from the guitarist's perspective. Most guitarists have their amp just off the ground, either on beer crates or a flight‑case lid. Very rarely do they listen to the amp at head height. The result of this is that the speaker tends to be brighter than the sound the guitarist is listening to. With 2x12 combos and 4x12 cabinets, this is complicated by the fact that you are listening to more than one speaker. These multiple speakers combine, and it is this blend that makes the sound. The difference between the single speaker and the combined sound can vary enormously. It is also worth checking that the microphone is placed in front of a fully working speaker! Several times I have managed to mic up the only blown speaker in a 4x12 cabinet, and on my current tour we miked up what we thought was a speaker only to find that it was in fact the wooden baffle board, as the cabinet had an unusual offset speaker design.

It is also very common, as Ray mentioned, that guitarists using stereo or dual-mono setups will sometimes be unaware of any problems with their various pedals. It is essential when working with a guitarist that you run through the various sounds that they use. I always ask to hear what they consider the loudest and quietest sounds, to give me an idea of the range of levels I can expect. I will then just listen to as many different sounds as they have at their feet, and I will check the phase and levels. A common problem I often come across is that the guitarist's 'loud' solo sound, although more distorted than their regular sound, can actually be slightly quieter. Often you will have to help the guitarist to rationalise the comparative levels between sounds. The same can be said of tone. A bright guitar can at the flick of a footswitch be transformed into an ear‑piercing instrument of torture. Better to discover these things in a soundcheck than at full volume in front of a live audience!

Another common problem is that, with the advent of digital pedals, it is now possible to have a selection of combined sounds in one patch. These inevitably seem to include reverb. Reverb is a very valuable effect, but its impact is often lost if used on every setting. This is made worse by the fact that, quite often, the guitar is being played in an already reverberant room: the pedal reverb combined with the room sound can often reduce the guitar sound to a blurred mess. Backing off the reverb on the amp can help to restore the guitar sound and give it a better sense of place.

Sound On Stage

With the increased use of in‑ear monitoring, stage levels have got increasingly quieter. In‑ear monitoring also requires the musician to rely a lot more on the sound that the microphone produces than just the sound from the amplifier. It also means that the guitar amplifier doesn't necessarily need to be on stage behind the guitarist anymore. I have seen an increasing number of shows where the amplifiers are placed off stage, or facing away from the vocal microphones. This really helps clean up the overall stage sound as there is a lot less spill, especially if you have lots of vocalists. The extreme of this is the use of isolation cabinets. These are boxes, usually flightcases, designed to house a speaker cabinet and a microphone. They are foam lined, and the microphone picks up the sound of the internal speaker, with little leakage either from the speaker or from the rest of the stage to the microphone. They are also very handy in the home studio as you can crank up the level without disturbing the neighbours! There are several on the market, but they are also easy to make yourself and you can find instructions online.

Live engineer Martin 'Arnie' Annables, who bravely mans the faders for Motörhead.Isolating guitar cabinets can be as simple as hiding the cab behind a stage curtain or at the side of the stage. On my last tour, Richie Sambuca, the guitar tech, became quite adept at finding sites for the six guitar combos used, from behind the backdrop to under the stage. Just having the guitar cab pointing off stage or even across the stage can help.

Model Behaviour

The last category of guitar amp you may encounter are the various 'amp free' options that are around. These started a long time ago, with the Tom Schultz Rockman. This was a box, a bit smaller than a paperback book, with an input jack, a couple of headphone jacks and an output. It was designed so you could play your guitar with the supplied headphones, and it became very popular as it had built-in effects, echo and chorus, as well as several switchable 'amp' settings. You could strap it to your belt and pretend to be in a late '70s rock band (Boston). However the in‑built sounds were actually really good and the Rockman sound began to appear on more and more albums, and then on stage. The guitarist could just turn up and DI this little box. More units of a similar type followed, with Nomad's Axxeman and the Tech21 SansAmp being notable examples, and these days there are a plethora of devices that can transform your sound into a whole arsenal of simulated amp styles and speaker configurations. Most need some way of interconnecting with the mixing desk, and the best way is through a DI box (most should be fine with either a passive or active one), though many can be plugged in directly via an XLR mic cable. The secret with all these boxes is to try and stop them from sounding too sterile. Too often they can be slightly fizzy and not sit well in the mix. I will quite often try and use a compressor with some character, preferably a valve, inserted on the channel, not to greatly compress, just to take a bit of digital edge off. Most of these units offer stereo and I would heed Ray's earlier advice on this!

All the amp-free options do have the advantage of no stage spill. You can turn the guitar way down, or even off! With in‑ear monitors you don't need to have loud amps on stage, and you can get a great clean sound for everybody — however this approach does mean that the musicians become even more reliant on the engineer to be able to hear themselves. It is the way some tours are going, however, and with software programmes such as Native Instruments' Guitar Rig, even laptops are beginning to appear on stage — and not just for guitar sounds, but for running the backing tracks, keyboards and the whole backline! The virtual Marshall stack is here, but is it really rock? As for what to do if the guitar is too loud, well, that is a whole article in itself...  

Bass & Treble

On my current tour, guitarist Jamie McCall (Bombay Bicycle Club) is using two amplifiers: a Vox AC30 and a vintage Ampeg Reverberocket. His reasoning is that the Ampeg has a great top‑end sparkle but no low end, while the Vox has a great weight to it but on its own it can be dull. Combining them, he gets a more rounded sound, certainly on stage. For me, I am careful to use similar‑sounding mics that have the same response, and pretty much treat the amps as bass and treble amps, balancing the level between the two to get the sound I am after, and to match what he hears on stage.

Published September 2014