Carl,
> Can anyone give a good explanation or point me to some info about "Hemholtz Resonators" ? <
Helmholtz resonators are a type of bass trap. They differ from more modern designs by being tuned to a single problem frequency. They are usually narrowband - they absorb only a small range of frequencies - and that is sometimes useful in some situations. By adding damping it's possible to broaden the range of frequencies a Helmholtz trap absorbs, but they're still inherently narrow band devices.
Current thinking recognizes that peaks and deep nulls occur in all rooms at all low frequencies, not just those related to a room's dimensions. So a better solution is broadband low frequency absorption. Panel traps are a step in that direction, though you still need two or three different trap types to absorb the entire range of low frequencies. Better still are bass traps built using rigid fiberglass or rigid mineral wool. These are not frequency selective and therefore do a more complete job with fewer pieces to install.
--Ethan
