Trying to understand the limitations of Helmholtz resonators in LF absorption

[Delrin]

Here's an old but very informative thread on a successful Helmholtz absorber project that gives lots of build details, great references, and testing results. It meets pretty much all the criteria I listed earlier.

It's worth reading the thread from start to finish if you're interested in Helmholtz absorption.

A few highlights:

• the project uses plywood boxes with lengths of 2" ABS pipe as necks in the resonator
• the only absorption added is speaker fabric (or equivalent) across the mouth of the absorber (no insulation inside the cavity)
• numerous measurements and photos are shown, and the absorbers appear effective at improving the targeted room modes

The poster also found Ingard 1953 to be one of the best references on Helmholtz absorbers.