Helmholtz and cavity resonances
April 1, 2021: Updated Helmholtz data using a sandbox. Sand better immobilizes the back and sides than Rockwoool does, and we find significantly lower frequencies. We now understand the Helmholtz resonance of our f-hole archtops if each f-hole is modeled as an independent, uncoupled circular aperture!
Helmholtz resonance expectations and results. We can understand the Helmholtz resonance of our f-hole archtops if each f-hole is modeled as an independent, uncoupled ellipse. We can understand the Helmholtz resonance of our archtops with leaf-holes if the 8 individual leaf-shaped apertures are grouped according to proximity, and then modeled as two independent circles.
Cavity mode expectations and results. Cavity modes are the equivalent of room modes: Standing waves set up inside a box. Again we have some understanding of their measured frequencies.
Helmholtz resonance equations to be used in experimental comparisons
Here we look at some of the equations we need to predict the Helmholtz frequency, especially for our multi-apertured "leaf-pattern" guitars. In these we have apertures of different sizes, and need to know the mass of air moving in and out of them. How can we model them? We also look at the expected "quality factor" Q for these resonances (how sharp are they in frequency space?) , and how it might change with frequency.
A part of this is summarizing what Q is, and how to measure it.