For my measurement and instrumentation class, I decided to research and experiment on the various structural modes and excitation methods of wine glasses. I was inspired by the glass harp instrument, a collection of wine glasses where people rub their fingers around the edge of the glass to produce different tones. This method of excitation is named the stick-slip response, given that the vibration is generated from the finger sticking due to friction, and then slipping when the built up force is too great to continue sticking.
Aside from the stick-slip response, I chose to investigate the impulse and frequency sweep responses. The impulse response was tested by impacting the side of the glass with a rigid object. The frequency sweep was tested by attaching strain gauges to the side of the glass, and then using a speaker system to deliver a frequency swept sine. This experiment unfortunately failed, due to the lack of power from the speaker setup and the lack of resolution on the strain gauges.
You can see the poster I generated from the class above, with a condensed version of the paper’s abstract. The full abstract may be seen below:
Wine glasses have been studied for their acoustic properties due to their relation to bells, their use for creating music by rubbing the rim, and their use in physics demonstrations to show resonance by breaking them with a loudspeaker. However, not much work has been done in characterizing the stick-slip response, comparing it to the impulse response, or comparing different models for calculating frequencies of different modes. To do the above, frequency responses were measured using two types of input: slick-slip friction around the rim of the glass by rubbing a wet finger around it and an impulse from striking the glass with a metal spoon. Results show that both resonate with a fundamental doublet at 359.98±0.42 Hz and that the impulse response shows inharmonic overtones while the stick-slip response shows a harmonic spectrum up to 32±1 harmonics. Using mode names of the bell model, 98.1±1.0% of power lies in hum for stick slip, while 64.5±0.78% lies in hum for impulse with 33.5±0.93% in tierce. French’s theoretical model and a bell model from tabulated tuning ratios were compared. French’s model shows a slope of 0.99±0.14 of measured frequency ratios to the prime frequency vs theoretical ratios, while the bell model shows a slope of 1.0012±0.0016. Both show a one to one correspondence, but French’s model has more uncertainty, implying the bell model is more precise. Finally, to explore the stick-slip mode of vibration, tests were done at different rotational speed around the glass. Tests show that there is a shift in the fundamental resonant frequency of 0.013±0.010 Hz per RPM, and that the beat frequency of the nearly degenerate doublet peaks increases by 0.0661±0.0072 Hz per RPM.