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Linear-response reflection coefficient of the recorder air-jet amplifier
John C Price1, William A Johnston2, Daniel D McKinnon3
1Department of Physics, 390 UCB, University of Colorado, Boulder, Colorado 80309, USA.
The Journal of the Acoustical Society of America
|December 3, 2015
Summary
This study investigates recorder acoustics by isolating the air-jet amplifier. Researchers measured its reflection coefficient, revealing insights into flute drive models under simplified conditions.
Area of Science:
- Acoustics
- Fluid dynamics
- Musical instrument physics
Background:
- Recorder oscillations depend on blowing pressure and resonator frequency.
- Oscillation amplitude is linked to gain-saturation, complicating independent control.
- Existing flute drive models require validation under controlled conditions.
Purpose of the Study:
- To isolate and analyze the air-jet amplifier's behavior in a recorder.
- To measure the air-jet amplifier's reflection coefficient under linear response conditions.
- To test and refine computational models of flute sound production.
Main Methods:
- Replaced the recorder body with a waveguide reflectometer to open the feedback loop.
- Measured the reflection coefficient of the air-jet amplifier against blowing pressure and acoustic frequency.
- Investigated system stability based on whether the air-jet flow into the transmission line was blocked.
Main Results:
- The air-jet amplifier exhibits instability via edge-tone oscillations when flow is unblocked.
- Blocking the air-jet flow stabilizes the system, enabling linear measurements.
- Reflection coefficient measurements provide a direct test of flute drive models.
Conclusions:
- Opening the feedback loop allows independent control and measurement of the air-jet amplifier.
- The experimental setup simplifies testing of flute drive models with minimal parameters.
- The study highlights the strengths and limitations of current flute drive models.
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