Measuring Air Flow in Various
Mouthpieces of a Bb Clarinet
Mike Cannistraro
Chip Jones
Chris Rogers, PhD.
Abstract
Three different clarinet mouthpieces (Selmer, Ebolin, and Selmer Paris) were analyzed by measuring the air velocity vibrations on the centerline inside the clarinet from the reed to beyond the sounding tone hole and by taking acoustic measurements outside the clarinet. Velocity measurements were taken using a hotwire probe inside the clarinet, and acoustic measurements were taken using a microphone outside the clarinet. The waveforms and normalized power spectra were analyzed, and three findings were made. It was found that the Selmer mouthpiece has stronger high harmonics than the Paris or Ebolin. It was also found that the waveform changes as you move downstream, away from the reed, on the centerline for each mouthpiece. The waveform is chaotic close to the read, becomes more coherent from peak to peak, then becomes chaotic again near the tone hole, and appears to settle again. The data show that the acoustic power spectra and hotwire power spectra from inside the clarinet between the tone hole and the bell showed dominant odd harmonics. This is consistent with what we would expect to see from a clarinet; however, the power spectra from the hotwire between the reed and the tone hole appeared to contradict theory and showed dominant even harmonics for the first 6 harmonics. Most notably, the 2nd harmonic overpowered the the first harmonic by about 15 dB.
Introduction
The clarinet is a single-reed woodwind instrument. A reed is attached to the mouthpiece and sound is generated when the player puts the tip of the reed and mouthpiece in his or her mouth and blows while also applying pressure to the reed with the bottom lip. The reed vibrates which then causes a column of air to vibrate down the the length of the clarinet to the first few open tone holes (notes only sound from these holes.) If all holes are closed then the clarinet only sounds from the bell. There exist hundreds of types of clarinet mouthpieces differing in shape and material. Each mouthpiece sounding different from one another. Players have their mouthpieces that they prefer and usually players can not agree. There is some consistency in opinions that sound quality goes down as ease of play goes up.
Each note played on a musical instrument contains many frequencies. The lowest frequency defines the pitch of the note and is called the fundamental. The higher frequencies, known as overtones, follow what is called the harmonic series where the first harmonic is the fundamental, the second harmonic is twice the frequency of the fundamental, the third harmonic is three times the frequency of the fundamental, etc. The differing power of each of the overtones is what gives an instrument its individual character or timbre. This is why a C4 on a piano sounds different than the same note played on a guitar or a trumpet. A clarinet has a very characteristic harmonic structure where the odd harmonics, the fundamental, 3rd, 5th, etc., are more powerful than the even harmonics, the 2nd, 4th, 6th, etc. (in most instruments, the harmonics just decrease in power as the frequency increases.) Theory actually determines this; the nature of a clarinet being a closed-open pipe forces the odd harmonics. Our acoustic data and our hotwire data taken beyond the tone hole agree with that theory; however, between the reed and the tone hole, we found that it is actually the even harmonics that are more dominant. This is interesting because it appears to contradict theory.
To take data, a mechanical player Junior was employed. It would be nearly impossible to completely duplicate a human player because there are too many variables, there is no feedback (junior can not not adjust itself while playing), and two humans do not even sound alike. The mechanical player we started with needed to be altered to sound more like a human. Over the course of the semester, we improved Junior to sound more more like a human both qualitatively and quantitatively.
Abstract and Introduction