John Sayers' Recording Studio Design Forum Archive

Hi there,

Thank you so much for all the information provided on this forum !
I am trying my hand at designing a small control room in a spare space of my recording studio and - while basstrapping the corners - I would also appreciate understanding the Heimholz mysteries a bit better.

Downloading the "Corrected Helmholz Spreadsheet" I could see that slats over fiberglass (covered with a cloth) mounted in a frame could serve as a broadband low-mids absorber. What I understand is the Heimholz principle happens in-between the slats, am I correct ?

All the other Heimholz-things I've seen so far are actually resonators and not absorbers (basically, a box with a whole - following specific dimensions).
Regarding the latter, I have a few questions :
- is the material indifferent ? wood, metal, plastic, cardboard etc. would all work ? (I guess not ...)
- is it possible to combine different material ? I am thinking of building wooden boxes with a plastic tube mounted on them, would that work ?
- I guess it's preferable to mount those resonators at the exact peak of the standing waves I'd like to tame, am I right ?

Any help is welcome !

Cheers,

Hi. Please read the forum rules for posting (click here). You seem to be missing a couple of things!

Helholtz resonators are not much use as bass traps: they are tuned to one specific frequency, are hard to tune, and need to be located correctly in the room. For bass trapping at low cost, simple absorption is the best way to go.

What I understand is the Heimholz principle happens in-between the slats, am I correct ?

Yes. Those are slot resonators, where the slot acts as the mouth of a Helmholtz resonator. But slot walls are not appropriate for deep bass trapping, for the same reasons above. The are great for mids, but not to good for lows.

All the other Heimholz-things I've seen so far are actually resonators and not absorbers

Slot walls are not absorbers: they are tuned resonators, just like any other Helmholtz device. Yes, they also absorb at other frequencies, to a certain extent, and they also diffuse, but the primary purpose is to act as tuned resonators. That said, from one point of view all resonant devices are "absorbers", since they do in fact "absorb" the frequencies they are tuned to...

- is the material indifferent ? wood, metal, plastic, cardboard etc. would all work ? (I guess not ...)

As long as it is rigid enough, thick enough, and reasonably massive, it will work.

- is it possible to combine different material ? I am thinking of building wooden boxes with a plastic tube mounted on them, would that work ?

Yes, if you get the dimensions right and follow the above: rigid, thick, massive. All Helmholtz devices must also be sealed in order to work, so the material must be airtight.

- I guess it's preferable to mount those resonators at the exact peak of the standing waves I'd like to tame, am I right ?

Assuming you are trying to use them to treat standing waves, then yes, they do need to be at the pressure peak (not the velocity peak), or close to it. They will have no effect at the pressure null of a standing wave. Of course, if the idea is not to treat standing waves specifically, but rather the sound field in general, then location is not that important.



- Stuart -

Thank you so much, Stuart - this really helps me focusing on the right things.

I've actually read the forum rules (trying to be a well-behaved user ), but I am only getting into SketchUp now...
Anyway, here are some details :
- goal : create an extra pre-production and - acoustics allowing - mixing control room in my music studio. Learn about acoustics both theoretically and practically.
- am I loud ? Sometimes, but the more I mix the less loud I get. I sometimes mix bass-heavy stuff, though. Neighbours : my studio mate's control room - but he's less in the studio than I am. I would like to focus on room tuning and not sound-proofing anyways. Location : 2nd sub-floor (lowest in the building).
- testing equipment : Neutrik measurement microphone, Prism Orpheus interface/mic pre, REW. Speaker : PSI A14-M http://www.psiaudio.com/product/active-monitors/a14-m
- room dimensions (shape is a bit weird - I will soon post a SketchUp) : 489 cm (L) x 305 cm (w) x 309 (h). Concrete ceiling is in reverse U shape (SketchUp ...).
- floor was already installed when I started working on the acoustics (will try to include it in the SketchUp), it's basically 4cm fiberglass on the floor topped by floorboards on wood.
- budget : $500-$1000 // more if result justifies.

SketchUp is ready - I guess I should move this control room project to the "studio construction" section of the forum ?

should move this control room project to the "studio construction" section of the forum ?

Done!

- Stuart -