Helmholtz Resonator in Laboratory Experiments

The acoustic resonance in four glass Helmholtz resonators with diameters of 70, 52, 40, and 32 mm was detected in the frequency range of 360 to 1700 Hz using the simple experimental setup presented in this paper. The measured amplitudes of acoustic pressure required correction since the sound pressure amplitude of the loudspeaker used was not constant over the whole frequency range. The plots of the corrected acoustic pressure amplitude against frequency (resonance curves) showed expected amplitude enhancement (resonance) around the declared resonance frequencies of the resonators used. Fitting the theoretical dependence for the displacement amplitude of forced oscillations as a function of frequency to the plots of the corrected acoustic pressure amplitude against frequency provided the values of natural frequencies and damping constants of the resonators. The presented setup can be included in laboratory experiments or in a modified version as a demonstration experiment in physics lectures for undergraduate students.