How To Record Guitar Cabs With One Mic

For the brightest sound, place the mic ‘on axis’ (firing directly at the speaker), and aiming at the centre of the speaker cone.

If you’re new to recording, it often pays to keep things simple, and when it comes to guitar cabs that means learning how to get the best sound with only one microphone.

Professional engineers often choose to put different types of microphone on a guitar cab or combo, sometimes miking two or more of the speakers in a multi‑driver cabinet. But I’d strongly recommend that anyone inexperienced in guitar recording start out by learning to get different sounds using a single mic. It is without a doubt the most straightforward approach, it often gives perfectly good results and knowing how to get the best sound in this way will stand you in good stead when you start experimenting with more sophisticated setups.

Know Your Source

Before considering the type of mic you should use and where to put it, you should know something about the nature of guitar speakers and their cabinets, as well as their relationship to surfaces in the room, since these factors will determine what sound you pick up for different mic positions. A typical guitar combo or speaker cabinet will be fitted with one or more loudspeakers. Typically, these will be 10, 12 or 15 inches in diameter, though some very low‑power combos may even use an eight‑inch speaker.

Most common is the 12‑inch speaker, found singly in small combos, in pairs in larger combos and cabinets, and also in a separate 4x12 cabinet format. Used without tweeters, as is invariably the case in guitar amplifiers, drivers of this size have a fairly limited frequency response; generally, the larger the speaker diameter, the less well it handles high frequencies. Rather than being a problem, this restricted frequency response actually forms a key element of the electric guitar sound, especially for distorted guitar — the low‑pass filtering effect of the speakers smooths away the gritty upper harmonics generated by distortion that would otherwise sound quite unpleasant.

Another important consideration is the way in which larger diameter loudspeakers project sound at different frequencies. The higher the frequency, the narrower the angle over which sound is dispersed. This effect is often referred to as ‘high‑frequency beaming’ and tends to become more pronounced as the driver diameter increases. As the frequency gets lower, the angle of dispersion continues to increase while at very low frequencies bass is radiated almost omnidirectionally.

Low‑frequency projection relies on the speaker being mounted in a cabinet of some kind, which in the case of guitar cabinets might have a partly open back or be fully enclosed, both of which have an influence on the sound. As a rule, the open‑backed cabinet will produce a ‘looser’‑sounding bottom end. The construction of the cabinet also has an effect, as the cabinet walls and baffle will vibrate to some extent; some of this coloration will be audible through the loudspeaker cone. The size and construction also tunes the cabinet, creating resonances, so that some parts of the frequency spectrum are emphasised more than others. Add that to the different characteristics of different models of loudspeaker driver and you can see that there are a lot of variables.

If you place a mic close to the front of a loudspeaker driver what does it actually ‘hear’? When the mic is very close to the speaker grille, the main source of sound will be from the loudspeaker cone itself, but as you move it further away, it will pick up reflections from the floor and walls and, in the case of a cabinet with multiple speakers, it will also pick up some spill from the other speakers. As the other speakers are off to one side of the mic, the spill is likely to be much less trebly than the sound from the speaker being miked and it will arrive at the mic fractionally later. In the case of a 4x12 cabinet, you may find that one of the speakers sounds better than others and it is worth making some test recordings, miking each of them in turn, to find out if you have a preference.

Mic Placement

Because guitar loudspeakers produce very little in the way of very high frequencies, you don’t need a microphone with an extended frequency response to get a good result. Though some studio engineers have favourite ribbon or capacitor microphones for guitar recording, one of the most popular mics for the job is the humble Shure SM57, a unidirectional dynamic microphone that was designed for instrument use. Essentially, this means it doesn’t have so much of a low end roll‑off as a classic stage vocal mic such as the SM58. However, if an SM58 is all you have, you can still get good results from that. Indeed, it is worth trying all the mics you have, even those you’ve already dismissed as sounding cheap and nasty — an amplified electric guitar isn’t a ‘natural’ sound, and sometimes you’ll get a pleasant surprise when miking guitar cabinets.

Using the mic position as a tone control invariably delivers a better result than relying on adding EQ after recording.

Start by aiming a directional mic such as an SM57 directly at the speaker cone (which may or may not be mounted centrally — so do check that if the grille cloth obscures your view of the speaker!), just a centimetre or two from the speaker grille. Then gradually move the mic from the centre of the speaker towards one of the edges. You should hear a significant tonal change as you move the mic: as a rule, miking the centre of the speaker produces the brightest sound, while moving the mic towards the edges tames the highs and adds a little ‘depth’.

Turning a directional mic off axis (angled relative to the speaker) will typically darken the sound, which can often be helpful for electric guitar.

If the sound is still too bright, you can exploit the polar pattern of the microphone, by angling it so that it isn’t pointing directly at the loudspeaker. The further you move it off‑axis in this way, the more high end you’ll lose. So already, by placing the mic between the centre and edges of the speaker, and angling it between the on‑ and off‑axis positions, you have a lot of control over the sound. You can also move the mic further back from the speaker grille, of course, and this brings other actors into play. Notably, if using a directional mic, this should lessen the proximity effect, in which case you may perceive a drop in bass energy — the drop might or might not be helpful to you, but the point is that knowing this happens gives you more control over the sound when placing your mic.

Other Factors

I know that a lot of engineers like to get a mic in close, but I often prefer to place the mic around 20cm from the cabinet. I find that this allows the sounds from various parts of the speaker cone to integrate, and it also allows some of the cabinet resonance, room ambience and some floor reflections to subtly influence the sound, and I think this often produces a more ‘organic’ result. There isn’t a right and wrong here, though: so much depends on your idea of the perfect guitar sound, as well as the characteristics of the loudspeaker cabinet, mic and room acoustics. As a rule, the greater the mic distance from the speaker, the greater influence these factors will have on the sound. So while a flattering room can really enhance a guitar sound, if you have a boxy‑sounding room, you might not want to move the mic too far from the speaker.

Here the mic is on axis again, but it’s now pointing at the edge of the speaker, where it will pick up less of the high frequencies, because large drivers tend to ‘beam’ them from the centre. At the edge of the speaker, turning a directional mic off axis will darken/soften the tone even more.

There are other considerations to keep in mind relating to spill in multi‑driver cabinets and to floor reflections which may influence the best place to put both your mic and your speaker. Obviously, the path length for sound bouncing off the floor and reaching the microphone will vary depending on how high the speaker is from the ground, so the result will be slightly different depending on whether the speaker is sitting on the floor or on a stand. When this reflection is combined with the direct sound from the speaker cone, a degree of shallow comb‑filtering will occur: the path length affects both level and time delay of the reflected sound, and thus has some influence on the overall tonality of the sound at the mic. If the cabinet is open‑backed, the sound coming from the rear of the cabinet will reflect from the wall behind the cabinet, in which case the distance from the wall deserves similar consideration.

You don’t have to place the mic close to the grille. Here, the mic is about 15cm back, and ‘firing’ at the top edge of the cabinet: the floor reflections and room more generally will make a greater contribution to the sound.

If you’re miking a 4x12 cabinet, the influence of floor reflections will naturally be different depending on whether you mic one of the upper speakers or one of the lower ones. Another variable when miking off‑axis in a multi‑speaker cabinet is the direction you move the mic off axis. If you move it towards the edge of the cabinet, the spill from the adjacent speaker will be reduced slightly, whereas if you move the mic towards the centre of the cabinet, the amount of spill from other speakers will be increased.

When miking a cab or combo with a grille cloth you can’t easily see through, do make sure that you know where the speakers are positioned in the cabinet! For example, it’s only with bright light shining on this Fender Blues Deville that you can see where When it comes to the low‑frequency performance of your speaker, the position within the room comes into play. Room modes will cause cancellation of some frequencies and reinforcement of others, and as you move around the room these frequencies will change. This is why engineers often try to locate the best place in a room for kick drum — to obtain the most punchy sound — and the same applies when miking guitar speakers. So if, as many do, you normally keep your combo amp up against a wall to free up space, it’s well worth moving it around the room when you want to record it, to see where it sounds best.

Get It Down

Having thrown all these variables at you, where do you start? The first thing is to get the amplifier’s controls adjusted so that you hear the sound you want to record — don’t rely on fixing that ‘in the mix’. Then start with the mic two or three cms from the speaker grille and make test recordings with the mic at the centre of the speaker, at the edge and at one or two in‑between points. If the sound you are hearing is too bright, rotate the mic to around 45 degrees off‑axis and try again — using the mic position as a tone control in this way invariably delivers a better result than relying on adding EQ after recording.

For a less claustrophobic tone, move the mic a little further from the grille and make some more test recordings. But in all cases you have to remember that (unless you are adding spring reverb at the amp) what the mic captures is still going to sound very dry, so you may find you need to add some room ambience using a reverb plug‑in before you can evaluate it properly.

Because electric guitar sound is such a personal thing, there’s no such thing as the definitive way to record it and the old adage ‘if it sounds good, it is good’, certainly applies. But it’s nice to be able to know how to get it sounding good every time! By following the guidelines in the previous paragraph, you should be able to get to a point where the sound you record is close to the sound you hear in the room, as long as you accept that the recording will include very little of the room ambience.

The tried‑and‑tested guidelines explained here will get you started — but if you get a better sound hanging the mic over the top of your combo or by picking up sound reflecting from a nearby wall, then by all means give it a try. The key is being prepared to experiment and to make a note of what works and what doesn’t.