So after all this time, my acoustic treatment is doing ALMOST NOTHING??!

[Jens Eklund]

Originally Posted by DanDan

In any case they are all just predictions. Predictions which omit some very significant factors.

e.g.
Angle of incidence is limited to just one.

Room modes (usually what your after in terms of treatment in the lower region) are not random incidence. Quite the opposite; very specific angle of incidence depending on what kind of mode (Axial, Tangential or Oblique).



EDIT: Brain shortage ...

[amishsixstringe]

Yes, 0 degrees is worst case. At 45 degrees, the absorber appears to be thicker than at 0 degrees (90*) Grazing is not a concern when considering modal ringing to the best of my knowledge.

Neil

[DanDan]

L and W modes hit vertical SuperChunks and Corner Straddlers at 45 degrees.
Tangential and Oblique modes hit Side and Ceiling traps at similar inbetweenie angles.
In this (very) real world case, 0 or 90 degrees and Random are all about equally irrelevant.

OP could you post or send me the original REW .mdat?
That ALMOST NOTHING may have been in reality a little something nice.

Frequency Response graphs can be very disappointing, not showing time based improvements.
I am glad you moved to Waterfall later, and I will bet you are enjoying the room more than before treatment.


DD

[Mister Fox]

Originally Posted by DanDan

Mister Fox, I reckon you are overthinking this big time.

Well, it's never bad to overthink things too much. This way you are save of wasting time while building and then realising "crap man, this didn't work and I wasted like... 5 days on this - now I have to do it all over".

Originally Posted by DanDan

We have seen Owens Corning state GFR of 703 as 16000.
Nasa consider it to be 27000.

I went by my manufacturer ROCKWOOL (Sonorock to be precise), since we don't have OWENS CORNING and I still prefer rockwool over fibreglass anyday. The official pages state that the GFR (or flow resistance) of r >= 6 kPa * s/m2. So in short, 6000 Pa. That's 1/3rd of your stated number for 703, and Sonorock is semi-rigid (not rigid). Does that mean it's inferior?

The OP even used non-rigid material.

Originally Posted by DanDan

So do we trust any GFR numbers?

If we need to go my calculators and the liking, yes we do have to trust these numbers.

Originally Posted by DanDan

And what algos are those calculators using?
The online one does give a choice.

What does it help if a non-acoustician or normal DIY builders don't know which algo to go for, or what settings? I can steal myself through it since I know some of the basics and digged through GS. But others might have problems.

Originally Posted by DanDan

In any case they are all just predictions. Predictions which omit some very significant factors.

e.g.
Angle of incidence is limited to just one. The normal incidence typically used gives a Worst Case Scenario for LF.
A corner placement radically enhances LF behaviour due to the 1/4 space.
On top of this semi rigid panels behave differently across a corner or blocking a tunnel.
There is a diaphragm or drum head thing going on.
Such panels, in corners or otherwise are often enhanced using FRK or other membrane bonded on.
None of this is in the calculation algos.

Personally I also wish to add/remove the capability to have membranes or MDF panels as "final walls" or "no walls" at all to see what's going on. I even activated the "random incidence" mode (webpage calc) to see how the absorbers react since sonic waves definitely don't hit at one angle alone (expansion is omnidirectional to a certain extend, then there are reflections of the walls, etc). Suddenly the graphs look better on the long run and I got some inspirations for minor enhanced designs.

Originally Posted by DanDan

Plse note that 1/4 wavelength fibre absorbs incoming sound 100%.
We can work with less than that perfection.

Many including Cox, suggest guides like 1/10 wavelength for small rooms, or even 1/20 for Rev control in large performance spaces.

See, this is a bit "too technical" for some to understand. I for example have a hard time following once in a while since english is not my native language and I don't know all technical terms and abbreviations.



The thing is, and to get back to the OP's post, we've seen a small room with 1,5" thick (around 3,8cm) fibreglass material to absorb reflections and room nodes. Turns out that the initial placement of both speakers and desk weren't optimal and a replacement added to reduced reflection times.


So what does that tell us?

I'd say "one calculation (math) alone doesn't help", and to my opinion (not experience, I've yet to build DIY absorber myself) thin material absorbs just as good (if dense enough) - and may it only be for early reflections.

And I think this is what it's all about: reducing early reflections and then(!) taming nodes and standing waves. And here I can (hopefully) say, that 2" panels on the wall and ceiling work just as good, and 4-6" panels in the corner (or where the node hits) work as expected.

Again... I don't think that we want to soundproof a room, we just want to tune it to our liking. And here I don't get why we constantly have to fill our room with 4" and 6" panels if maybe 2" work just as good at the reflection points. Granted, better "bass" control, but is it really needed?

[DanDan]

Granted, better "bass" control, but is it really needed?

Of course it is, and much much more than that. We sit in the middle of the W and often the H dimensions. As such we are at a very busy spot for nulls and peaks. Guaranteed. We definitely need all the bass control we can get.
100mm plus 100mm airgap is the minimum many of us recommend. To be frank I believe this centre null spot is strangely ignored. We should really treat the sides and ceiling just as well as the front and back walls.
DD

[Mister Fox]

I can agree on the treatment at the reflection points and the listening position (if your ceiling is able to hold it, or if you have a "floating" floor), but the main Q in this thread is still:

Are 1,5" - 2" sheets suitable for reflection points/ceiling and 4" for bass trapping? Everything else could be created with custom designed GOBO's behind/around the listening position and/or the recording environment. At least at small/budget/home/living room studios.

I mean... if you add spacers behind the 2" sheets, you get a more effective absobtion. If the bass traps are put in an angle (45 degree on floor/in corners), you have at least a 350mm airpocket at the center of the 4" absorber.

It's all about proper placement to tame the peaks and nulls, no? And looking at the waterfall diagram, it worked.

[JulianFernandez]

Originally Posted by JulianFernandez

I did without that much luck... I was able to find some info on this Isover rigid panels (50kg/m3 and >50 kPa.s/m2). What´s the best use for that kind of wool? Thanks again!

What do you think, Jens? Guys?

[Jens Eklund]

Porous Absorber Calculator V1.58