Student Research

The Effect of A Helmholtz Resonator’s Neck Geometry

On The Aero-Acoustic Excitation of Resonance


Asami Nishikawa

Faculty Mentor(s): William V. Slaton


The aero-acoustic excitation of a Helmholtz resonator with different neck geometries has been examined with an improved measurement technique. A Helmholtz resonator consists of a volume connected to a duct and has a well defined resonance frequency which depends on the length of the duct, the volume of the resonator and the cross sectional area of the duct. In the system used during this experiment, two Helmholtz resonators have been positioned at opposite sides of a junction in a wind tunnel. The air speed in the wind tunnel can be varied over the range 0 to 28 m/s. The air flowing over the junction openings to the Helmholtz resonators can excite the acoustic resonance of the system. This is similar to blowing over an empty bottle’s opening and creating a tone. The excitation of the resonators as a function of flow speed in the wind tunnel has been recorded.  The effect of the resonator’s geometry has been seen in the measured acoustic amplitude and frequency in the resonator and will be presented.

Behavior of a Helmholtz Resonator Driven at High Amplitudes


Dustin Morris

Faculty Mentor(s): William V. Slaton


The acoustic behavior of a Helmholtz resonator was studied when driven by a compressed air source. The resonator consists of a 55 gallon drum with 4” diameter necks of different lengths. Compressed air from a 0-15psi regulator is introduced into the resonator using an electronic valve controlled by a signal generator. A pressure sensor was used to study the acoustic behavior of the resonator as it was driven over the resonance frequency with the compressed air source. By closely examining the resonant peaks, the quality factor of the system could be determined for different drive pressures. The measured resonance frequencies are compared to two theoretical models. The resonator’s quality factor (energy stored in resonance/energy lost per cycle ) is shown to decrease with drive amplitude indicating increased losses with higher amplitude.