I first use simulations (Basta!, WinISd,...) to determine the diameter
and for that diameter to have have an idea about the port length.
Then cut out the hole and do near field measurements and impedance sweeps with different port lengths (1cm steps).
and for that diameter to have have an idea about the port length.
Then cut out the hole and do near field measurements and impedance sweeps with different port lengths (1cm steps).
For what it's worth, I constructed a Helmholtz resonator for a different purpose a couple of weeks ago and its frequency was off by +3.2 %.
The resonator consists of two PVC pipes, a thick and a thin one, and two wooden discs. The end correction for the thin pipe was 73.2 % of its diameter. It could be that I miscalculated the end correction, as both ends of the thin pipe stick out. One side ends somewhere halfway the thick pipe and the other side sticks out in the air.
The resonator consists of two PVC pipes, a thick and a thin one, and two wooden discs. The end correction for the thin pipe was 73.2 % of its diameter. It could be that I miscalculated the end correction, as both ends of the thin pipe stick out. One side ends somewhere halfway the thick pipe and the other side sticks out in the air.