Methods of Data Collection
To get data we use a long tube fitted with a hot-wire anemometer inside of the clarinet, attached to a carpenters rule to slide it through the bore easily and to exact measurements. The hot-wire gives accurate readings of velocity, which we use to find the frequencies and the amplitudes of the harmonics of the current note. It works just like a microphone would pick up the different pressure fluctuations, but instead uses periodic velocity differences. We take readings every quarter inch to map the amplitudes of the internal harmonics from the mouthpiece past the first open tone hole. This spacing and measuring area, we feel, will give a good resolution that can accurately represent the inner workings of a clarinet.
Hot-wire anemometers are microscopic wires strung between two prongs, which are connected to a voltage source. The voltage source sends a voltage across the wires, which raises its temperature. After the voltage runs through a wire, the voltage is measured. In a thin wire the temperature it operates at determines its resistance. When an air-flow hits the heated wire, its temperature will drop, which will in turn change its resistance and affect the voltage coming out of it. Since a faster flow will cool the wire more, the change in measured voltage can be used to determine the velocity of the flow. The anemometer is very thin, so it doesn't disrupt the airflow in the clarinet. It is attached to a long, slender pole so that it can reach all the way up the bore.
The complete rig used in this experiment includes a carpenter’s rule, a clarinet, a stand with clamps, and a pressurized box. The stand and clamps were specially designed to hold the clarinet without covering any tone holes and to avoid adding or taking away vibrations. The stand is then attached to the base of the carpenter’s rule, while the slide’s sliding measuring arm is attached to the anemometer. The pressurized box is then placed around the mouthpiece. In the pressurized box there is an artificial "lip" that applies pressure to the reed. The other end of the box is attached to an air pump with a regulator that allows us to keep a constant tone. The entire setup was designed to accurately recreate human playing, while eliminating human inconstancies.
