Instrumenting the Instrument

Making music is not just a matter of interpretation and technique, the instrument itself makes a difference. This is especially true of piobaireachd where harmonics and mutual resonances between chanter and drones are so important. The highland bagpipe is famously cantankerous, sensitive to moisture and temperature. An instrument may by sounding sweet one day and refusing to cooperate the next. A musician will often know that they have to play for a certain period of time for their bagpipe to settle. This knowledge quickly devolves into voodoo when trying to predict what is necessary to do in order that it will be in tip top shape, say, as quickly as possible 45 minutes from now after a 10 minute break and taking it into a different room where it is three degrees warmer.
Humidity and temperature graph

Attempts to do anything substantially better than using rules of thumb and wisdom of unknown origin are often met with the objection that, “there are too many variables to possibly understand or predict what’s going to happen”. Perhaps it is so. But let us start by measuring what we can conveniently measure.

The plot at right shows a test session playing in relatively controlled conditions, indoors on a pipe with cane reeds and a synthetic zippered bag. It shows about five minutes of rest, where the humidity sits at about 20%, a half hour of mostly continuous playing, and fifteen minutes of airing out, with the bag open. The humidity stabilises (saturates) after about 20 minutes of playing. Perhaps not coincidentally it is at this time that the sound stabilises as well, with the reeds no longer sharpening, and producing a solid, consistent sound.

The pipe uses a moisture control system that had its desiccant beads replaced with a simple data logger, shown below, that measures the humidity and temperature of the air on its way out of the pipe. A simple bottle trap with absorbent material was used.

DHT11 data logger
DHT11 in pipe bag

The data logger is based on a an Arduino Nano clone and a DHT11 sensor. This is not an especially good sensor, in particular an improved version of the data logger that can also measure pressure is in the works when parts arrive. But it was what we had spare around the Edinburgh Hacklab, and as we can see above, is already enough to get some idea of the relationship between the moisture levels inside the bag and “settling” of the instrument.

The software that it runs is free, albeit very quickly and roughly put together. It records 30 second average measurements for up to about three hours and stores them on its internal flash storage. They can then be read out by a computer over USB. Another improvement might be low-energy bluetooth transmission for to see the measurements in real time on a smart telephone or tablet computer.


2 thoughts on “Instrumenting the Instrument

  1. At last I have succeeded in logging in here and can comment on things! Interesting read, and has caused me to wonder whether the bagpipe is the most temperamental of all instruments!!! But when one considers the human voice perhaps this is comparable. Re piobaireachd playing and a recent recording I was making, and the variables dependent on temperature of room, length of recording session and changes in instrument and player over time, it seemed hard to guarantee that conditions at the outset could be replicated throughout, so that one would end in the place one started. And where more than one player and instrument is involved, multiply the variables many times over! A wonder piobaireachd players manage at all, all things considered.

  2. I had posted this elsewhere, but I think it is probably more pertinent to this discussion, than the original location.
    At the beginning of a playing session, the pipe bag is completely deflated (or at least as much so as any reasonable man might determine. The bag is then blown up, which would generally consist of supplying moist breath at nearly 95% relative humidity and nearly 98.5 degrees Fahrenheit to a pressure of around 20-30 inches/water. For this discussion, let’s assume that the room or outdoor temperature is, say, 70 degrees F, or 21 degrees C. The exterior temperature is not as important as the stability, as we shall see.
    As the bagpipe is initially inflated, some moisture content from the exhaled air immediately will condense as the moist breath comes into contact with the cooler surfaces of the bag. This will deposit moisture on the surfaces of the bag, the moisture control system if any, and the interior of the air pathways out of the bag ( the interior of the drones, the chanter, the reeds and so on.) Some of the air supplied will simply pass through the instrument unaffected by the temperatures in the bag or the bagpipe parts. This is because not all the air contacts the bagpipe parts to lose energy. The transmission of energy for air in contact with the parts is an order of magnitude greater than that of the air exposed by radiative coupling, merely passing through. Even the air in contact with the bag is not particularly efficient at heating the parts. This just means that the time for the bagpipe to come to a steady temperature state where heating of the bag because of the warm moist air ceases to occur and stabilizes, This is a fairly long time 20 minutes or so. The bagpipe components we care about, chanter reeds and drone reeds probably stabilize a little earier, as they are more directly in contact with the passing warm moist air.
    Concurrent with the lowering of the temperature of the air by energy transfer to the parts of the pipe that are at room temperature, these same parts warm up. Some are not very massy, and heat fairly quickly (like the bag), some are more massy (like the stocks and the drone bores). Assuming a playing time sufficient to warm the mass of the drones stocks and the chanter, at some point most of the process of condensation will reduce in magnitude and reach a steady state. There will be a reduced amount of condensation occurring due to warming, but the condensation will continue to occur as energy flows from the warmer parts of the pipe out to the room.
    One would think that air movement would remove some moisture as the bagpipe reaches some equilibrium temperature but this is insignificant as the pipe would continue to lose energy to the environment. Thus air entering the pipe is always at, say, 95% relative Humidity at 98 degrees F and the bagpipe is almost always a bit colder than that due to energy losses to the environment. On the other hand, as the bagpipe and the entering breath get closer to a matching temperature, the amount of condensation decreases. The process is additive, but occurs faster at the beginning of a session than after the bagpipe is warmed up.
    The major source of moisture into the bag is going to be aerosolized spit. Some authors use the term, an aerosolized mild enzymatic solution. The amount varies by individual and some other factors, but this is why we say we have dry blowers and wet blowers. Its not relative humidity, it’s the amount of fluid expelled down the blowpipe. The condition of the piper, the time between playing and a meal are examples of the variabiles. Nevertheless, an amount of this visible moisture is suspended in the incoming air that will be supplied to the bag.
    The tube trap for example uses two methods of action where incoming air swirls down the moisture trap, and suspended material adheres to the sides, thrown there by momentum (the air makes a corner, and the spit travels more straightly, contacts a wall and sticks there. Also for this type of moisture control, there is some condensation as the tube acquires heat from the breath and therefore condensation occurs. A further example, -the Trap-Dri simply adds more swirl to the airway encouraging spit to stick to the walls of the tube.
    Other systems tend to pass the incoming breath over an absorptive bed which removes moisture until the filter material is saturated. Then these systems pass air with no reduction of moisture, except for where aerosolized spit is cast onto the surfaces. As such they probably continue to collect a fair amount acting as does the tube trap above.
    There could be those who argue that the elevated pressures within the bagpipe have some effect on the production of condensate, either for or against, but as the bagpipe is all at the same pressure within the bag (up to the reeds, where pressure begins to drop), I don’t see how a significant change in the conclusions above could occur. The exception is immediately past the drone reeds where pressure approaches ambient.
    So, we can see that the conditions inside the bag generally cannot change due to the relative humidity where the pipe is played. We can see that the bagpipe comes to a humidity and temperature controlled by the incoming breath and the rate of heat loss to the exterior along with a contribution of how long it takes the player to bring the bagpipe to a steady state temperature, especially those more massy pieces. The reeds change due to temperature and their actions related to moisture content. Thus the chanter reed (most commonly Arundo Donax reed cane) is a limiting factor as it’s playing characteristics change to a large degree with variations in moisture content.
    Where this takes us, I’m not sure. Its clear to me, that getting the pipe warm (generally warmer than the end playing environment) before playing will pay off in reduced moisture accumulation. Just how to do that remains a mystery. A bag cover certainly helps.

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