HOW TO TUNE A CAJON
Before adjusting the sound of your cajon there a couple of important things to consider. Firstly, that not all cajons are built in the same way – some are designed to be deep and resonant with a clear distinction between sharp snares and a tonal bass. Others are built to be dryer, with much livelier snare wires and less separation between the corners and a softer, deader bass sound. It may be difficult or even impossible to create the sound of one cajon with another, so knowing the character of your instrument is crucial to understanding what you can realistically expect from your cajon.
The second important consideration is why you want to adjust the sound of your cajon. Is there an element of the sound that you don't like and wish to get rid of? Is there a particular sound you have in mind that you want to achieve? Are you just curious about what sounds your cajon could potentially produce? Testing the boundaries of what your cajon can do is an exercise which needs to be approached with care. Snare wires can be over-stretched and screw holes can be stripped of their threads if over-tightened. It is also essential that you measure how much you alter anything, keeping a record of how far you turn each screw so that you can always put the cajon back exactly the way it was before. For the screws on the front of the cajon, particularly the ones around the top, a small alteration can make a significant difference, so attention to detail is crucial.
There are three main elements of a cajon's sound which can be adjusted, and adjusting one will usually have an effect on one or both of the others. These elements are pitch; resonance; and snare response.
Pitch refers to what note or tone your cajon produces. This can be measured in terms of high and low. The easiest way of adjusting the pitch is by turning the screws around the top of the cajon. Most cajons leave the workshop with the screws about as tight as they'll want to be, so first try loosening them slightly. About 45° or an eighth of a turn should be enough to make an audible difference, any more than 90° or a quarter of a turn and the screws will be standing proud of the front and getting in the way of your hands while playing. This will also produce a very harsh 'click' or 'slap' sound which you will probably want to avoid. Loosening the top screws slightly will give you a lower pitch and a deeper tone.
It is also possible to very slightly loosen the screws around the sides and bottom of the cajon. This will lower the pitch further, but will have a significant impact on the response of the snares, allowing them to vibrate more freely and potentially create problematic buzzes a rattles. This can be compensated for by adjusting the snares themselves, although over-tightening the wires can stretch them and ultimately lead to similar unwanted harmonic vibration or buzzing. It is far easier and safer to stick to using only the top five screws to change the pitch.
Resonance and pitch are closely related – the resonance being how strongly the pitch features in the overall sound of the cajon. This can be measured in comparison to the other elements of the instrument's sound, so a very resonant cajon could be described as open, ringy or tonal, and the pitch would be a more noticeable feature than the percussive sounds such as the impact of hands on the playing surface (attack), the slap sounds, or the hiss of the snares – basically anything that doesn't have a prominent pitch of it's own. So a cajon with very little resonance could be described as dry, dead, dampened or muted. Adjusting the resonance is tied very closely to adjusting the pitch, and it is almost impossible to alter one without affecting the other. With all the screws around the front on very tight, the cajon will be resonant and produce a clear, quite high pitch. As you begin loosening these screws, the pitch will not only drop in frequency but will also become quieter, shorter and less prominent against the slap of the corners, the dull punch of the bass and the hiss and rattle of the snares. A good tip to slightly reduce overall resonance without affecting the pitch or snare response too drastically is to slightly loosen the screw in the middle of the top line.
Snare response describes how much the snare wires are allowed to vibrate. They are usually adjustable with one or two allen key screws on the underside of the cajon, although a few cajons have these adjustments on the sides or the top. If your cajon does not have adjustable wires, the only way to alter the response of the snares is by adjusting the front. Loosening the front will give the wires more room for manoeuvre and result in a looser sound. A tight front will be pressed more firmly against the snares, restricting their vibration and creating a more controlled or choked snare sound.
Tight snare wires will produce a short and subtle rattle and tend only to be heard in the corners, with the bass tone isolated and unaffected by the snares. Over-tightening snare wires can prevent them from vibrating at all and rendering them obsolete - as if they weren't there - like a Peruvian cajon. Doing this also risks stretching the snares. This can result in individual wires buzzing and producing a sustained pitch or harmonic resonance of their own. This is usually quite annoying and so it's best to avoid completely choking the snares by over-tightening them. Tightening the snare wires more subtly is a good way of achieving greater separation between the corners and the bass, and tends to work well with a slightly more resonant bass tone. If you want a sound with no snare response at all, it is better to get a Peruvian cajon.
Loose snare wires will produce a more prominent hiss which dominates the corner sound and softens the bass tones. This works well with a less resonant sounding cajon and produces a livelier, warmer sound. With the wires responding to both the corners and the bass there is less separation between the two areas, resulting in a more gradual consistency when moving from one spot to the other.
Go easy with all of these adjustments, make sure you do everything evenly and symmetrically and keep testing the sound as you go. Listen carefully, some changes will be subtle and hard to notice at first. Each time you alter anything play the cajon for a while so you really get the feel for it's new sound and then decide if it's better or worse and whether it needs more or less of each adjustment. This way you will not only be able to tune your cajon more accurately, but you will fine tune your ears in the process.
Video explanation by Tom McAllister