Jaw Harp: An Acoustic Study Acoustical Physics of Music Spring 2015 Simon Li
Introduction: The jaw harp, or Jew s trump, is one of the earliest non percussion instruments, dating back to 400 BCE in parts of China and SE. Asia. The instrument supposedly traveled throughout Eurasia by the silk road. The first evidence of Jaw harp in Europe dated back to around 1200 CE. Despite the name Jew s trump, only the English term carries a racial term. Other languages does not allude to the religion or race in particular. The origin of the term Jew s harp in the English language is unknown, mostly passed down by folklore. The term in every other country includes mouth or jaw in describing the instrument. Fig. 1) The distribution of jaw harps around the world. Note the evolution of design from east to west. Not enough official history was recorded on the jaw harp in Europe, since it s primarily a folk instrument, passed down by generations. Therefore, in Europe, the jaw harp tradition is in danger of becoming extinct. There are not many manufacturers of this instrument and the
appearance of this instrument is decreasing in folk music. The primary players of the jaw harp lies in Hungary and Austria, attributed to the Bohemian Diaspora. In Asian cultures, particularly Central and South East Asian, the jaw harp, with various percussion instruments, are still the most important shamanic instruments. It is deeply rooted in the classical tradition and folklore in many regions. These examples are especially prevalent in small ethnic groups in Asia as a part of their lifestyle such as matchmaking ceremonies. Archaeological findings of the jaw harp is very hard, since before the 1800s, most of them are made out of wood and therefore have deteriorated. All the history and usage that we have now is from primary documents that references the jaw harp. For the full detailed history of the jaw harp, the book The Jew s Harp: A Comprehensive Anthology is a one of a kind book that discusses the jaw harp with references from official documents. It is on sale on Amazon for only $120. Components and Playing the Jaw Harp: The European jaw harp consists of a metal frame and a tempered steel tongue that is allowed to move and vibrate. The tongue of the instrument lies between the jaws of the frame and it s played by plucking the tongue with your finger (See Fig. 2) Fig. 2) Diagram of a modern jaw harp
The steps to play the jaw harp is as follows: 1. Using one of your hands, carefully grasp the frame of the jaw harp. Make sure not to touch the base or the tongue of the jaw harp. 2. Place the harp against the front teeth, with the trigger pointing out. The teeth must be slightly apart so the tongue could vibrate between the teeth. 3. Orient the jaw harp so when plucked, the tongue won t be chipping your teeth. 4. With your forefinger, pluck the tongue of the jaw harp. The sound that the jaw harp produces could be described as a twang. The quality of the sound could be changed by altering the shape of your mouth opening and moving your tongue. More of these will be discussed in the next part. How the Jaw Harp Produces Sounds Throughout history, the most prevalent theory on how the jaw harp produces its sound involves the vibration of the tongue itself. It was thought that during playing, the tongue, being plucked by the finger, vibrates freely between the parallel arms and through the teeth of the player, whose mouth cavity acts as a resonator. Thus, many people agreed that it was the vibration of the tongue that resonates the mouth cavity, and the instrument is classified as a plucked idiophone (same category as the thumb piano). However, the theory accepted has many holes. The main problem is this: jaw harps, which are made out of various materials all over the world, are found to sound very similar to each other, with minimum differences in timbre. If it was the vibration of the tongue that contributes to the harmonics of the jaw harp, why does a bamboo and a metal jaw harp sound so similar? The theory in which how the jaw harp produces its sound is not put forward until 1972, independently by Ledang and Adkins. Even though the tongue of the jaw harp constitutes a harmonic spectrum, the spectrum is different than the spectrum produced when you alter the mouth cavity. The main idea is that there must be something else contributing to the harmonics of the notes being played. Adkins sound producing mechanism is shown in the figure below.
Fig. 3) Adkins proposed mechanism. The tongue of the jaw harp is represented by the middle rectangle, and the arms are shown by the upper and lower shapes. The proposal is as follows: When the tongue moves through the frame, the airflow around the tongue is relatively free. When it moves parallel to the arms in the middle figure, the airflow becomes interrupted. For a second, the tongue acts like a piston driving forward the air in front of it, and dragging the air behind. This sudden change increases the air pressure in front and decreases the air pressure behind. When the tongue clears the parallel arms, the pressure balances out in front and behind the tongue, causing air to flow backwards. This characteristic period is what s resonating the mouth cavity. Ledang at the same time, arrived at the same conclusion. His experiment was on varying the space between the arms to see if the harp could play. However, what he found was the if the space between the arms were too wide, the sound played would decay much quicker. This finding supports the conclusion Adkins made. The Experiment
Fig. 4) The Alto Harp (G) and the Tenor Harp (F). The length of the arms differ by about 1 centimeter. In my project, I choose to test two types of jaw harps: The tenor and the alto harp. These harps are made out of steel, and follows the normal design. These two harps are featured in figure 4. I had no actual starting goals other than see how the two harps compare. I first recorded one note from each of the harp, with a normal mouth cavity. Professor Errede has kindly provided a MATLAB wave analysis script so we can take a look at the phase and spectrum of the two harps, and various overtones of the harmonics. I recorded 6 different samples from each harp, resulting in 12 total examples. The samples are as listed: 1. Normal Mouth Cavity 2. Breathing Out 3. Increased lung capacity and holding breath 4. Vowel A 5. Vowel O 6. Vowel I In 4 to 6, I did not pronounce the vowels, only change the shape of my mouth to the respective vowels.
Fig. 5a) Tenor Harp Frequency vs. Amplitude Fig. 5b) Alto Harp Frequency vs. Amplitude
Figure 5c) The plot of the first few harmonics of the tenor on the left, and alto on the right. A comparison between the normal alto and tenor harp vibrating freely is that the difference between the fundamental and the harmonics differ by 200 Hz in the tenor, and 100 Hz in the alto. Figure 5a) and 5b) shows also that the odd harmonics dominate the spectrum, with another peak around 3000 Hz. Fig. 6a) Freq vs. Amplitude Tenor Harp Breathing Out
Fig. 6b) Freq vs. Amplitude Alto Harp Breathing Out Comparing the breathing out graphs with the normal graphs, it seems the general spectrum has not changed, and this was expected. Breathing in and out acts like a driven force, enhancing the force of the airflow. It should not change the general spectrum except for the amplitude of some harmonics.
Fig. 7a). Freq. vs Amplitude of tenor harp, holding breath Fig. 7b) Freq. vs Amplitude of alto harp, holding breath
Compared to the original graphs, the spectrum of figure 7 has changed. We no longer see a resonant peak around 3000 Hz. This is because by opening up the mouth cavity and connect it to the lung cavity, we have somehow changed the frequency at which the airflow resonates at. Professor Errede suggested for the last three data points to compare the resonances made with the airflow and the natural resonance of the mouth. To measure the true resonance of the mouth, we insert a source of white noise and a microphone into my mouth. Professor Errede then helped me take the data using the spectral analyzer. The following are the last three results comparing the true resonance of the mouth and the Freq. vs Amplitude graphs of the tenor and alto harps. Fig. 8a) Freq. vs Sp^2 of the vowel A. The resonance occurs at 1000 Hz, 3000 Hz and past 4000 Hz.
Fig 8b) Freq. vs Amplitude A tenor harp. Resonance around 1000, 3200, and 4200 Hz. Fig. 8c) Freq. vs Amplitude A alto harp. Resonance around 1000, 3000, 3600 Hz.
Fig. 9a) Freq. vs Sp^2 of vowel O. The resonance occurs at 1800 Hz, 3600 Hz and 6000 Hz. Fig. 9b) Freq. vs Amplitude O tenor harp. Resonance around 3300, 4200 Hz.
Fig. 9c) Freq. vs Amplitude O alto harp. Resonance around 3000, 3600, 5000 Hz. Fig. 10a) Freq. vs Sp^2 of the vowel I. The resonance occurs at 800, 3000, and 4100 Hz
Fig. 10b) Freq. vs Amplitude I tenor harp. Resonance around 3300, 4200 Hz. Fig. 10c) Freq. vs Amplitude I alto harp. Resonance around 3000, 3600 Hz.
Although most of the natural resonances did not match up with the jaw harp resonances, I suspect there were a lot of errors while measuring my natural mouth resonance. To prevent my saliva from infecting the microphone, I had to open my mouth as wide as possible while maintaining the mouth shape. This could have introduced the discrepancy between the two types graphs. Nevertheless, one could infer on the importance on the shape of the mouth just by comparing the graphs of the tenor and the alto harp. We could see a general trend in the spectrum between the two, following the same pattern of harmonics, only differing by a shift in frequencies. Conclusion and Further Work From the last three measurements, the work done by Ledang and Adkins were verified. The categorization of the jaw harp is much more complex than previously thought. Although it is proven that the airflow produced by tongue causes the resonance within the mouth cavity, there are still debate whether the arm and the frame contributes to the harmonics produced. It is a known fact that the jaw harp cannot produce a sound (even in a cavity) unless the frame is touching a solid object (like your teeth). Some experts believe that there is a coupling effect between the jaw harp and the body it touches, producing a more direct air flow, but further study on this effect is needed. A lot more comparisons could be made, such as metal vs bamboo, different people playing the harp, etc. I would like to thank Steve Errede and Matt Ziemann for helping me to learn the wave analysis software, and for helping me measuring my mouth cavity by sticking a microphone into my mouth.