Home-made pipe resonators reproduce theoretical resonance frequencies closely

Evidence

An earbud (with the soft tip removed) was fitted snugly into a bottle cap, and the cap was held tightly, allowing the earbud to sit in the tube with an airtight seal (figure 16.2). The tube had an inside diameter of 1.9 cm and length 65.4 cm. Using Signalsuite, a 1-minute-long chirp from 100 to 1500 Hz was played into the earbud. The open end of the tube was held near the laptop microphone, and the recording was frequency analyzed in Amadeus. The earbud has very poor low-frequency output into the rather large tube (it does much better in the ear canal), but peaks were quite noticeable above 700 Hz. As long as the peaks were clearly defined, their Q could be measured as Q = f/Δf. This gave Q ~ 29 for the peaks at 1178 and 1454 Hz (predicted from equation 16.3: 1180 and 1442 Hz for a pipe of length 65.4 cm). — Eric J. Heller, Why You Hear What You Hear- An…, 1447

Categorization

• XREF: Provides a concrete experimental methodology for auditing the prediction equation 16.3 on open pipes