Helmholtz Resonator?
How big should a Helmholtz resonator be, and how does it have to be tuned?
For the effectiveness ...
… of a Helmholtz resonator, size and correct tuning are significant. A resonator should ideally have a volume between 300 and 500 liters so that room modes are effectively dampened. By setting up more of them the effect will be improved. To determine the "problem frequency" with the level peaks in the bass range, a frequency plot (SPL measurement) should be carried out with suitable measurement software or by an acoustician.