If you keep both mics equidistant from the speaker cone, phase cancellation is unlikely to be problematic.
Many classic electric guitar sounds have been captured using just one microphone. So when and why might you use more?
My article in SOS July 2021 (www.soundonsound.com/techniques/how-record-guitar-cabs-one-mic) focused on the basics of recording electric guitars using a single mic. In many cases that can deliver perfectly decent results, and I’d always recommend that inexperienced recordists start there. But it’s long been common in professional circles to blend more than one signal when tracking electric guitar. There are various established multi‑mic techniques to try yourself and probably plenty more awaiting discovery, so in this article, I’ll explain when and why two mics might be better than one.
Take Two
The most obvious reason to use two microphones is when, despite having tried all the mics at your disposal, you can’t quite get the sound you want using only one. Perhaps the best mic choice and position deliver the tonal ‘bite’ you’re looking for, but lack a little punch in the low end. When you add a second mic, the relative position of the two mics can make a big difference to the sound, but it’s best to start by choosing mics for their tonal characteristics and placing them right next to each other. That said, if you have the time to experiment, it’s worth trying all of your mics in different pairings, as it’s not always immediately obvious why two mics happen to work well when combined.
A popular, well‑established tactic is to pair a moving‑coil dynamic mic, such as the ubiquitous Shure SM57, with a ribbon mic. The Royer R121 is a popular choice in the latter role but they all have broadly the right characteristics: typically, the full bottom end and smooth, rolled‑off high frequencies of a ribbon mic combine very well with the more mid‑ and presence‑focused SM57, without either needing much EQ. You can balance the two to taste and either record that blend to a single track, or capture them separately on two tracks. The latter approach can leave you with greater tonal control when mixing, without needing EQ — though I’m of the opinion that having lots of options when mixing isn’t always a good thing!
A classic combination is to pair a ribbon mic with an SM57: the frequency responses of the two seem to combine particularly well.
Combining a dynamic mic with a capacitor model is also common practice. The Neumann U87 and various AKG C414s, usually in cardioid mode, seem particularly popular but, while the results seem to vary more from one capacitor mic to another than with ribbons, you can try any of them — that’s how I came to know that one of my personal favourites in this role is the Audio‑Technica AT4050. Don’t worry too much about whether the moving‑coil or capacitor mics you try have a cardioid or hypercardioid polar pattern, as it’s the subjective end result that counts. But you should be aware, when it comes to spill from unwanted sources, that hypercardioid mics are more sensitive at the rear than cardioids.
Pairing a capacitor mic with a moving‑coil dynamic is also common. Here, you can see a Neumann U67 and SM57 combined by engineer Vance Powell on a Fender Princeton amp.
Close Mics & Phase
When two close mics are placed on the same source, their phase relationship is naturally a consideration. However, because the electric guitar is inherently an ‘unnatural’ sound, the comb‑filtering effect you hear when moving one mic a little further from the speaker isn’t necessarily problematic. In fact, it can be a useful means of fine‑tuning the overall tonality without resorting to EQ.
If you treat the two‑mic blend as a single signal (ie. pan the two mics identically, maintain the same blend of their signals throughout the song, and apply any processing on a group bus) then phase cancellation needn’t really be a concern. But if the mics aren’t in phase and you choose to pan them to create a sense of width, the tonality will sound different for mono playback than for stereo — it might or might not be a problem, but you should definitely consider the impact on the mix balance. Also, if you change the balance between the two mics during a song, the nature of that tonal change can be less predictable if the two aren’t broadly in phase.
A coincident array, which places the two mic capsules as close as possible, ensures that you avoid phase problems, but a simple rule of thumb is that if you make sure that both mics are the same distance from the speaker cone, phase cancellation is unlikely to be a significant problem. For more precise alignment, you can position one mic, then flip the polarity of the other and move it around while feeding a noise source through the amp. Cancellation between the two mic signals will be greatest in the most phase‑coherent positions, and once you’ve found one, filpping the polarity back to its original setting should give you a satisfyingly full sound. With the amp in a live room, you’ll need to listen on headphones for the cancellation, but if your amp is near your DAW you can feed both signals to the same level meter and watch for the lowest reading as you move the second mic.
A further degree of tonal flexibility is available by moving the second mic relative to the axis of the speaker: the tone can change quite noticeably as you move the mic from aiming at the centre of the speaker to aiming at its edge. As I explained in the previous article, one of my favourite mic positions is around 30cm from the cabinet, aiming at the cabinet’s top edge, and it’s well worth trying this alongside your favourite close mic sound.
The Fredman technique employs two Shure SM57s, with capsules adjacent but at different angles relative to the speaker, giving you a lot of tonal control simply by varying the balance of the two mics.
Another versatile option, the Fredman technique, which has become popular in metal production, combines on‑ and off‑axis placement. You put one SM57 close up, on‑axis, aiming at the middle of the speaker, and place another right next to it, the same distance from the speaker but angled inwards, about 55 degrees off‑axis. The on‑axis mic delivers a very bright sound, while the off‑axis one is dominated by mids and lows, so you can adjust the balance of these mics’ signals to control the tone. The result tends to sound richer and thicker than a single SM57, retaining some of the highs while also smoothing them somewhat. Again, it’s a good technique if you have a tendency to procrastinate: if you record the mics to separate tracks, you can put off deciding on the final tonal balance until the mix.
Although the trouser‑flapping low end you experience when standing close to a big amp can seem impressive, don’t obsess too much about it when recording.
Rearing Up
The most obvious options involve two mics in front of the speaker, but the cabinet resonance picked up by a mic at the rear of an open‑backed cabinet can often help beef up a top‑heavy front‑miked guitar sound. As with miking the front of the amp, you can try different distances and positions relative to the axis of the speaker, and it’s worth experimenting with both the cab and mic position, as factors such as the distance from a wall or from the floor will also affect the sound.
There’s no right or wrong — just go for what sounds right for the track — but it’s worth a few notes of caution. First, as when using top and bottom mics on a snare drum, you’ll usually want to flip the polarity of the rear mic; it’s pointing in the opposite direction from the front one, so if you forget to do that the combined result will sound thin, weedy and phasey. Second, although the trouser‑flapping low end you experience when standing close to a big amp can seem impressive, don’t obsess too much about it when recording, as very little of it ends up on most records. If you do capture lots of low end, you’ll often find yourself filtering it out when mixing to avoid clashes with the bass guitar and kick drum, and more so when the guitar is one of many instruments in an arrangement.
Room For Improvement
A different reason to add a second mic is to capture room ambience. Typically, you’ll use one or maybe two close mics for your basic guitar tone, as above, and then position another much further from the speaker, usually a couple of metres or more, to capture more in the way of reflections. It’s only really worth attempting this in a room that has a desirable ambience; if you’re working in a bedroom, the result will usually end up sounding dull and boxy, and you’ll almost certainly find that faking it with a reverb processor delivers better results. But don’t write off a room straight away, as you can work to make an unflattering space sound better. For example, try improvising screens behind and to the sides of the more distant mic to dry up the room’s natural ambience; rugs or duvets draped over chairs work well. Also, applying artificial reverb to a room mic can sound very different from adding it to a close mic.
In the right space, using a room mic (shown left) can give the sound an added dimension.Photo: Fantasy Studios
The final sound will be the result of a number of complex interactions between the close and ambient mics, as well as between the direct sounds and the floor/wall reflections. You can experiment with the polar pattern of the room mic and, assuming it’s a directional one, with where you aim it. For instance, you’ll often get different results from pointing a cardioid mic at the amp, past the amp, and directly at the wall to capture first reflections, and aiming a figure‑8 mic’s side null at the amp, so it captures reflections to front and rear, but no direct sound from the amp.
The comb‑filtering effect when using one close and one distant mic might be stronger than with two close mics, and this depends on various factors, including the floor material and how far the guitar cab and mics are from the floor. The higher the amp from the ground, the greater the path length of the first floor reflection and thus the greater the time difference between the direct and reflected sounds reaching the room mic. Again, any comb‑filtering could be seen either as a problem or as a variable for adjusting the timbre. For instance, hard floors produce the strongest reflections, so they’ll emphasise any comb-filtering — but they will also make the timbre of the reflected sound reasonably bright, which could be useful. In short, experimentation with the mic choice, and the speaker and mic placement/orientation is important if you’re to get the best sound.
Nice Spread
Another reason for using two mics is where a single mic produces a perfectly good sound but you want to create a sense of stereo spread beyond simply adding stereo ambience. One way to do this is to mic one speaker in two different ways, then pan the contribution of one mic left and the other right. This could be achieved using two mics, two different mic positions, or both.
Alternatively, you could mic up two different speakers. If working with two speakers in the same cab, note that the direction in which you move the mic when working off‑axis will also affect the composite sound. Moving the mic further away from the nearest adjacent speaker will reduce the amount of spill from that speaker; moving it towards another speaker will increase it. Again, there’s no inherent right or wrong: make the effort to listen for the differences and make a decision. Of course, there’s nothing to say you can’t pan a close mic one way and a distant mic the other, and in a nice room you could also use a stereo pair for the room, for some natural stereo spread.
Whichever option you choose, check the result in mono just to ensure there are no serious compatibility issues, since when you listen in stereo while panning sounds hard left and right, phase problems will tend to be hidden. As when using two mics for tonal reasons, if you keep the close‑mic distances similar you’ll avoid most of the phase issues that produce unwanted tonal changes.
If you’re lucky enough to have two amps, and a big enough space in which to record them, you can split the guitar signal to feed both amps and mic each amp’s speaker using any of the techniques I’ve discussed...
If you’re lucky enough to have two amps, and a big enough space in which to record them, you can split the guitar signal to feed both amps and mic each amp’s speaker using any of the techniques I’ve discussed above. By setting up the amps to produce different sounds, you can fashion hybrid tonalities and convincing stereo sounds without resorting to plug‑in trickery. You can also create a usefully subtle stereo effect by using a chorus pedal or rotary speaker effect on only one of the amps — this can work particularly well on clean guitar sounds. Note that you might need to use a commercial splitter or a DI box with a Thru connection to avoid ground‑loop hum when feeding two amps in this way and, for the same reason, should plug both amps into the same power outlet.
Still More Options?
You can experiment with using even more mics, of course, and you might find some useful results that way. For example, a three‑mic setup known as the ‘phase EQ’ technique can provide you with oodles of tonal control at mixdown. But generally I prefer to keep things uncomplicated, since using multiple mics can easily introduce phase variations that weaken your sound rather than make it stronger. Which options work for you will depend on the tools and spaces you have at your disposal, but I urge you to try any mic and/or DI arrangement you can dream up, just to see what happens. If putting your amp in the bathroom and aiming one of the mics down the toilet gives you the result you’re after, then why not? The only real rule is that it should sound good in the context of the track — curiosity costs nothing but time and the rewards can be very worthwhile.
A Sound To DI For?
Capturing a DI along with a miked amp sound opens up more options, not least ‘faking’ a second amp and recording chain using modelling hardware or software, for the sort of stereo setup I describe towards the end of the main article. You might think that if a modelled tone is good enough to form part of your sound, it would be good enough full stop. Sometimes it is, but in my experience, I play better when I can hear the sound coming from my amp, and there’s something about the more nuanced aspects of the sound that seem to come across better than when relying entirely on modelling. Nevertheless, mixing real and modelled amps can add an extra dimension to your sound.
You can take your DI feed from a conventional DI box placed before the amp or, if it has one, a line output on the amp itself. A major advantage of splitting the guitar’s output is that you can choose a completely different second amp type from the one you’re miking. Using different amps will give a more dramatic stereo spread but also opens up opportunities for combining cleaner and dirtier sounds, to give a sense of power and sustain without losing clarity.
Should you choose to work from your amp’s line output, you’ll have only the cabinet and mic/room modelling to explore, but a good speaker‑emulation plug‑in might still give you enough tonal variety to create a worthwhile stereo image. Note that some amps have only a ‘speaker emulated’ output built‑in, and while these rarely give you the same tonal options as dedicated hardware or plug‑ins it’s still worth feeding that signal through a better speaker emulation, just to see if it sounds good in combination with your miked amp. Often it does.
Most good modelling software also allows room ambience to be introduced, and this can be used to simulate a room mic for your close‑miked amp. Even where it doesn’t, though, you can run the DI signal through your modelling software followed by an ambience patch in a separate reverb plug‑in, to emulate a good room mic.
One important thing to check, whenever working with both a mic and a DI, is that the polarity of the DI’d signal matches that of the mic. Your mono button should tell you that fairly swiftly, but so too will inspecting the waveform in your DAW, or polarity‑inverting the DI track. Hardware processors will add a small amount of delay, so if you record their output on a separate track you can also adjust the negative track delay parameter to ensure that the waveforms from the mic and processor line up correctly.