Variations in humidity are always a problem for the bodhran player. Especially in countries where the climate varies seasonally from being very dry to very humid. Bodhran skins tend to be quite responsive to the level of humidity in the air - becoming tight in dry conditions, and loose in damp conditions. High humidity can leave a skin damp and loose, sounding like a wet paper bag. Alternatively, very dry weather can leave the drum sounding high and tinny, like hitting a kitchen pot or a high tom-tom. Some bodhrans are so sensitive that even a rainy day can render them temporarily unplayable.
How a bodhran responds to changes in humidity is dependent on two factors; the idiosyncrasies of the skin and the conditions of humidity under which the skin was mounted on the drum. Some skins are simply more sensitive to humidity changes than others, however the tone of the bodhran will usually be best when played in an environment where the relative humidity (RH) is close to that under which the skin was mounted and 'tuned' by the maker.
In recent decades, some bodhran makers have added mechanisms which allow the player to mechanically adjust the tension of the skin. Bodhrans of this type are generally called 'tuneable bodhrans'. Some tuneable bodhrans employ a movable inner ring, which can be pressed against or drawn away from the skin, thereby changing the tension and pitch of the drum. In this way the player will always have control over the tone of the bodhran, regardless of the weather.
Many bodhrans, indeed the majority, are of the non-tuneable variety. The methods for bodhran construction outlined in this paper produce 'non-tuneable' bodhrans. Despite this label, there are certain measures that one can take to tune a 'non-tuneable' bodhran.
If the tone of a bodhran is too low or if the skin is too slack, several things can be done. The simplest and most immediate remedy is to use one's free hand to apply pressure to the inside of the skin while playing. If your bodhran has a cross-beam, merely place your hand inside the drum between the cross-beam and skin, with the palm resting against the inside of the skin. Use the heel of the palm to press against the skin, pushing with the back of the hand against the cross beam for leverage. By maintaining a constant pressure, one can raise the pitch of the bodhran to the desired level.
A second method involves the use of heat. Hold the bodhran for a short while near a low source of heat such as a lamp, hair-dryer, radiator, stove, or hearth. As the skin warms up it will at first loosen and drop in pitch. Take the bodhran away from the heat source and as it cools it should tighten up and its pitch should rise markedly. Be careful to monitor the tightness of the skin by tapping it. Don't let it get too tight. The effect of this should last from several minutes to several hours.
A more long term solution involves the use of cardboard 'shims'. These can be placed inside the bodhran, between the top of the rim and the skin, thereby increasing the tension of the skin. Long, thin, curved strips of corrugated cardboard work well. Add as many as you need in order to remove any slack in the skin. However, you must be careful to remove the shims when conditions become dryer (i.e. with the onset of winter). If the strips are jammed in too tightly to remove, then place the bodhran in a steamy bathroom (you could let a hot shower run for a few minutes). The steamy conditions should make the skin slacken enough that the shims can be removed. (See diagram 10 - Tuning up a bodhran).
Lastly, Dubbin applied to the inside of a bodhran skin is said to make it less susceptible to humidity changes. Dubbin should not be applied to both surfaces of the skin, or the skin will become completely watertight and will no longer absorb water in case you want to tune it down (see below). Dubbin is available in shoe stores and ski supply shops.
It is a little more difficult to permanently tune down a taut drum than to tune up a slack one. Saturating a tight skin with oils or moisturizer will loosen the skin and decrease the tone by a few notes. The effect of this may last from a few days to a few months.
Many players wet their bodhran skins down with water (or sometimes beer!) before they play. This serves to immediately and drastically reduce the pitch of the drum. Depending on how much water is applied, you can tune the bodhran down to its lowest playable note. However, this drop is less controllable and less gradual than that obtained by oiling. Furthermore, the deepening of the tone is often short lived, as the skin dries out quickly. During long sessions of playing, water may have to be applied several times. It has been suggested to me by a parchment/vellum maker that repeatedly saturating the skin with water might be harmful in the long-run. The sudden wetting and drying causes the skin to rapidly expand and shrink. It is possible that each time a wet skin dries, it shrinks a little more than the last time. Over the long run, this might cause the skin to tear away from the tacks holding it on. Therefore, if you choose to apply water to your bodhran skin, avoid soaking the skin or pouring large amounts in the drum. Instead, dampen the skin with a wet cloth, or a small amount of water rubbed in with the palm of the hand.
While beer works in the same manner as water to temporarily lower the pitch of a bodhran, the alcohol content can cause the oils in the skin to dry out sooner than they normally would. As well, alcohol may have a degenerative effect on the fibres of the skin.