John Sayers' Recording Studio Design Forum Archive

What I mean by False Slat:

Looks like a slat resonator. Differences being it is unsealed, completely filled with fiber glass, and has slats with greater spacing (2 to 4cm) for more broadband absorption. The slats providing the function of reflecting highs and upper mids.

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After reviewing my plans for a small tracking room that included slat resonators, I was wondering... what would be the benefit of a slat resonator over the equivalent box unsealed, stuffed completely with fiber glass, and covered with slats? All else being equal such as placement location.

Let's say you designed the slat resonator for 200 Hz... Would that slat resonator be a better absorber at 200Hz than the false slat equivalent modified with large gaps between slats? The false slat being something that looks like a slat resonator, being unsealed, stuffed completely with fiber glass, and faced with slats with 2 to 4 cm spacing.

Has anybody had the opportunity to build both and see which one is more effective?

I've been asking myself that same question. The slotted absorbers are mostly to tune such a device. Having them spaced further appart (as you stated: 1 or 2 inches) will change resonance frq. You might build a super-chunk instead (meaning no slats at all). The slats, however, will indeed do some reflection on mids/highs. But they still resonate, so it's still functioning as a tuned absorber somehow.

But what it REALLY does, I couldn't really tell. I'd suggest getting that resonator calculator (XL sheet) and see what it does!

.....and it looks good
(and keeps your device steady/in place...)

Hmm. Good question. This is a guess, but here goes....

My suspicion is that the total sound absorption will be roughly the same between the 2 different types, given the same amount of absorptive material. What will likely happen (again, I'm guessing) is that a slat resonator will give you more absorption in a narrower bandwidth, and less absorption outside that bandwidth. The "faux slat" will give you a more equal absorption across the spectrum, depending on how many "slats" there are to reflect high frequencies.

Any of our resident experts want to tell me if I'm guessing correctly?

If you're building constant-depth absorbers so the formula actually (sort of) works, then the main advantage of a slat absorber (or perforated, for that matter) is its narrow band performance. A helmholtz will typically have a "Q" of between 1 and 5, 1-2 being most common - at resonance, absorption will be nearly 1.0 but unlike a broadband absorber, this will fall off to about half that within 1-2 octaves either side of resonance.

"Q" is the measure of the steepness of the resonance curve - the higher the Q, the narrower the absorption peak.

Unless you've measured room reverb (RT-60) you won't know what you need - the object here is to get an EVEN reverb time through the audio spectrum, with maybe just a bit longer time at the low end (but not much) - for help with this, find the reverb calculator on the SAE site, or better yet the updated one John posted at the top of THIS forum.

If you haven't already done so, you should buy either the print or the "E" version of Everest's Master Handbook of Acoustics - it's basic, but still explains a lot of what we regularly answer here, including several formulas and drawings, etc... Steve

For PC, a free and helpful tool is Room EQ Wizard - a google should turn it up, its author is quite knowledgeable on the subject.

Great answers, thanks.

So then the conclusion is they are best used to even out reverb times, make reverb times even throughout the frequency range, when broadband has already been applied in corners, ceilings, etc?

Yup; also, in a drum room tuning a couple to around 300 hZ will help pull out some of the kick drum peak... Steve