DIY bass traps vs commercial ones

[Tupisac]

Let's take this panel for comparison: https://www.gikacoustics.net/en-gb/products/flexrange-bass-trap-panel?variant=47341750911204

Producer claims it will absorb down to 50 Hz with only 22 cm thickness.

Now, what to expect from DIY panel, assuming thickness of 30 cm instead of 22, filled with Rockwool? I've played with the porous absorber calculator and it doesn't look that far away but I might be missing something.

 

[anotherhobby]

With basic absorbers like that, absorbed frequencies are a mostly function of absorber depth as well as the material inside. The depth, from the face of the absorber to the wall behind it drives the frequency range. So a 2" panel standing 2" in front of the wall can absorb the same frequency range as a 4" absorber that's flush to the wall, just not as well since the material (quality and amount) inside drives the effectiveness as it converts the sound to heat. Generically speaking, you should be able to achieve similar results using similar fill material, depth, and size.

I have over 30 GIK panels, and they are well made and do the job. I've made my own absorbers as well — while it saves money, it's also messy, takes a lot of space and time, involves working with unhealthy materials, and doesn't save as much money as you think it might.

 

[Tupisac]

The thing is that my room doesn't have much free space left. Most of the bass traps will have to be custom sized.
I also don't intend to build them myself. I've seen local ads for custom built ones for 1/3rd of the GIK's price.

Is denser Rockwool better? The offers of filling in ads I've seen range from 50 kg/m3 to 90 kg/m3.

 

[anotherhobby]

Effectiveness of different DIY filling materials: https://www.bobgolds.com/AbsorptionCoefficients.htm

 

[kemmler3D]

In general a panel of that thickness won't do much to 50hz. However, I think they combine the straight absorptive material with membranes, binary diffusers, or both, which can absorb more low frequency energy than a simple chunk of foam or rockwool. Since the graph shows a pretty narrow peak at the advertised frequency my guess is they put a tuned membrane of some kind in there. If someone wants to look up their patents we can probably figure it out rather than guess.

 

[anotherhobby]

Yeah, it's hard to meaningfully impact frequency response that low in domestic settings with reasonable panels. I put 25 total panels in my theater. The front was was covered in their 7.3" monster traps. The rest of the room was all 6" deep Alpha panels, with total coverage of 25% of ALL wall and ceiling surfaces. That's $5k worth of GIK panels in a 12x14 room. There is a link to the build thread in my signature. Below was the native frequency response with all the panels installed (sorry, I do not have a before). If I dropped $5k on panels hoping to smooth out the bass, this would have been an incredible disappointment. 35db swings in the bass.

So what did I get for my $5k? Well, RT60 is nice and smooth, and decay looks pretty good too for such an ugly native in room response:

The room sits on concrete with 2 concrete foundation walls and double drywall and a 3" door. While soundproofing lowers your noise floor, it harms sound quality by leaving more of that bass energy bouncing around the room, as opposed to some flimsy 1/2 drywall where the bass blows right thru and is gone. This was the RT60 when the room was 100% empty:

So, the panels made a massive improvement overall in the room, but it was not much in the frequency response when it comes to stuff under about 200 Hz. I'm sharing all of this just to provide at least one tangible example of what you might expect with room treatment. People are always looking to try and fix that bass with panels, but it's just not happening. After room correction, this was the final in room response. Flat to 10Hz and compression tests showed no compression until over 110 dB, so not bad:

 

[Bjorn]

A lot of aborption data of commercial acoustic products are incorrect at the lowest frequencies due to the measuring method.

 

[Tupisac]

Well, my hopes are to recover anything from 30-40 Hz region.

Here is my sub FR:

According to specs it goes down to 26 Hz (-6 dB) but in my room at listening position it just plummets at 40.

There is also a huge peak at 50 Hz which got drowned somehow.

 

[R4pture]

The thing is that my room doesn't have much free space left. Most of the bass traps will have to be custom sized.
I also don't intend to build them myself. I've seen local ads for custom built ones for 1/3rd of the GIK's price.

Is denser Rockwool better? The offers of filling in ads I've seen range from 50 kg/m3 to 90 kg/m3.

Not sure if I can help.

I have DIY-Rockwool absorbers in all four corners almost covering the entire corner from top to bottom (two stacked 30x35x100cm absorbers):

They work great until 80 Hz. Everything below is still catastrophic. For simplicity I only focus on raw frequency response:

It is an old measurement, plenty of things I have done since then, but I think it shows how complex it is to absorb low frequencies with broadband absorbers.

Covering the backwall with 60 cm thick Rockwool does make a massive difference:

But space constraints is a concern. It is almost always impractical to implement thick enough broadband absorbers. Other absorber types I find too complex to implement correctly.

I also have 16 GIK-Panels, but they are useless below 100 Hz (12 cm thickness is not nearly enough).

 

[kemmler3D]

If you are willing to DIY something for the 50hz and under range, look into VPR traps. It's a type of pressure/ membrane trap that uses thin sheets of metal damped with foam. Needs to be large but not thick.

 

[R4pture]

Well, my hopes are to recover anything from 30-40 Hz region.

Here is my sub FR:

View attachment 546946

According to specs it goes down to 26 Hz (-6 dB) but in my room at listening position it just plummets at 40.

There is also a huge peak at 50 Hz which got drowned somehow.

I guess there is no way to reposition the subwoofer and/or the listening position?

 

[Tupisac]

I guess there is no way to reposition the subwoofer and/or the listening position?

Unfortunately not without complete room overhaul. It all fits like puzzles now:

I can only switch sub position between corner and a middle of a front wall. Currently sitting at a corner.

BTW, Neumanns are for illustrative purposes. I own a set of JBLs 305 and 310S. I've been thinking about an upgrade for a long time but decided to try acoustic treatment first.

 

[Tupisac]

A lot of aborption data of commercial acoustic products are incorrect at the lowest frequencies due to the measuring method.

How incorrect? Do you mean bullshit?

 

[Bjorn]

How incorrect? Do you mean bullshit?

Unless the measuring rooms is large enough for the frequencies, it can't be trusted. And which seems to be the norm. RPG has a big room and can therefore achieve accurate measurements quite low.

Surface area covered also needs to be large enough for the frequencies, something seldom mentioned by sellers.