Filling a closet as a corner bass trap? Advice welcome!

[musicwins]

You will need absorption on the first reflection points nonetheless.
But i'd definitely fill the closet, remember room modes don't just create peaks and longer decay times at specific frequencies and places, but also cancellations (dips), which are also reduced (filled) using absorptive material of appropriate depth (or other methods like pressure absorber etc), which results in more even decay times and frequency response. The more low frequency absorption the better if you can sacrifice the space. Period.
At such a thickness it gets very effective, 650 mm using the lowest gas flow resistivity material you can get (most probably ~ 5 kPa*s/m2 glass wool, else it gets expensive) will give you significant absorption down to 35 Hz.
A layer of 25 mm or so polyester batting (dacron) in front of it to keep fibers in and a breathable fabric on top gives a nice finish.
And don't waste your money on those overpriced ready-made panels / clouds / diffusers etc. Rather diy them, it's plain simple and as efficient if not more than bought ones for a fraction of the price. Plus you can customize them, their size, depth and looks etc, suitable for your specific needs and circumstances.
There are many myths / misinformation / snake oil / ripoffs out there so watch out and in case you need help or information just ask.

Cheers

Right on. Thanks. That's my plan at the moment - fill the closet to the brim, so to speak. I was Modeling out air gap vs. no air gap using acousticmodeling.com. Any disagreement with with their models (See first post). What product would you recommend in the USA?

 

[musicwins]

@Keith_W I attempted the method outlined in the book. I named the files as suggested. However, I don't have 2m of width from my MLP, so I named the files accordingly: https://www.dropbox.com/scl/fo/ro7h...wtEXDBH0?rlkey=5lvcmw888ln1tq5nwhpzd1mhe&dl=0

Also, here are a few screenshots if anyone is following along.

To be clear, when I posted this, I was already planning on treating first reflection points and getting a cloud. The question I was specifically asking that @Truth Ness answered is about the bass trap in the closet. And, if I go that route (which I likely will) I would love more input on the questions I outlined (Thanks Truth Ness for your replies there).

However, I'm interested in getting the data set right from the get go, so I'm happy to to guided accordingly.

 

[Keith_W]

There are more than 20 files in your dropbox. I'm not going to download 20 files and hunt for the relevant ones. Put all the measurements into one MDAT and reupload it please.

 

[musicwins]

The grouped mdat is already in there: https://www.dropbox.com/scl/fi/pvkr...ey=wyflbeex2c4hxc717qc7zwe4k&st=s0hj8wwq&dl=0

 

[Keith_W]

I don't see much in your new set of measurements that changes what I thought from the previous set. Go ahead and get your room treatment, install it, and see what happens. Remember that the effect of these things is profound, especially for a small room. So buy fewer than what you need, you can always buy more later.

 

[Truth Ness]

Right on. Thanks. That's my plan at the moment - fill the closet to the brim, so to speak. I was Modeling out air gap vs. no air gap using acousticmodeling.com. Any disagreement with with their models (See first post). What product would you recommend in the USA?

Since i'm from Germany, i can't exactly recommend a specific product, but there's what they call "pink fluffy". I think its trade name is Owens Corning Pink fiberglass insulation or so. There may be several different types with different densities etc., make sure to check its gas flow resistivity (gfr) number which has to be ~5 kPa*s/m2 or lower (density approx 10-15 kg/m3). Every glass wool / fiberglass insulation with that specifications should work. Look for uncovered one, some have some kind of paper attached which you don't want.
There are products like hemp insulation etc with even lower gfr but they are usually much more expensive.
Rockwool with such gfr usually is much heavier and not as effective (at least for thick bass traps).

Regarding the air gap:
I would just fill it. i tried both. In my case it even reached lower without it (not very significant though), and it was quite an "effort" to even "install" an air gap and prevent the insulation batts from filling it and remain stable (2,6 meter height). I tried cords/strings which was kind of working but it's not worth the hassle.

Regarding the modeling:
You can download an unrestricted 30-day trial of AFMG Soundflow Pro, which is a modeling/simulation tool which has advanced features and takes some other things into account which allows for more "realistic" results in my experience.
Consider that there (and also at acousticmodeling.com) are different "models" to choose from which will give different results, for thick porous traps i'd recommend the "Miki" model. But keep in mind that in general these simulations assume an infinite expansion or a whole wall covered. Else there will always be diffraction and sound bending around at bigger wavelenghts (lower frequencies), which is a complex topic on its own, so results are just an approximation and may differ more or less depending on a specific situation/geometry etc.

Oh almost forgot:
For first reflection point absorbers you'll need another kind of glass wool or foam if they are not deeper than 20cm.
If your ceiling is high enough, cover as much and as thick of it as you can, but at least the first reflection points.

Cheers

 

[Truth Ness]

One more thing:
It's usually best (at least if a room is not very large) to put the monitors / speakers as close to the wall as you can, almost touching. At distances from ~50cm to ~150cm to the front wall there are cancellations in the important bass region, for example 80cm (speaker baffle to wall) results in a null at ca 107 Hz. It is called SBIR and for the wall behind the speaker it happens at 1/4 the wavelenght (343/0,8 = 428, *1/4 =107) The more the distance the lower the null. With enough distance it gets shifted to a low enough frequency to not cause trouble but even 1,5 meter are not really sufficient low (~ 60 Hz).
If you place them directly in front of the wall the null gets shifted high enough into the hundreds, depending on the depth of the speaker, to not impact the bass, is easier to treat if you wish to, and in general is not that severe.
You also get an increase in low frequency gain (for free!) by doing so, so you may need to (or not) use some kind of low shelf filter to counter the elevated low frequency response which ultimately results in less LF distortion which is always good. Your speaker may even have switches or so for this to adjust. Else just use an eq.
And don't listen to those who say it is detrimental to soundstage and whatnot. That comes from people who don't know the physics/acoustics behind it or think they "know" it from hearsay (it's a myth like there are many regarding acoustics, really) or have done it wrong.
It isn't If done right.
Best would be in-wall flush mounting though but that's no easy task and better left for professionals and not worth it or doable in a home studio.