Bass traps using RWA45 Rockwool

[jrm1]

I've just built a writing room and would like to know if tri traps made of RWA45 Rockwool would do a good job bass trapping in the corners.

Dimensions of the triangular sections = 600mm x 424mm x 424mm. 100mm thickness piled on top of each other up to the ceiling. Enclosed in a basic frame of ply or MDF and the face covered in fabric. Max front to back depth is 300mm, but it's a triangle. Overall volume of 1.9 cubic metres per corner trap.

Dimensions of room are 4.1 x 3.85m x 2.1m with a big rooflight which probably skews any room mode calculations a bit.

Is it best to mix materials densities or is the floppy(ish) RWA45 a good bet for bass absorption?

Should I use some kind of room tuning software to home in on room modes?

[DanDan]

That will work fine. There are nicer materials though. Knauf Ecose Universal Board or Batts doesn't itch or scratch or smell.
Isover High Performance Duct Cladding or equivalent Glass product has better absorption afaik.
DD

[Soundman2020]

Hi there "jrm1", and welcome. Please read the forum rules for posting (click here). You seem to be missing a couple of things!

The type of bass trap you are describing is often referred to as a "suberchunk" trap, dating back to an old thread on the Studiotips website, ir I recall correctly. As Dan said, your plan will work: that's a good way of making superchunks, and there are other materials that could be used instead of mineral wool.

Regarding your room testing and tuning: Yes, it's always a good idea to run tests on your room, starting with an initial "baseline" test with the room empty of everything, except the speakers and a desk to put your DAW on. Here's how to run those tests: How to calibrate and use REW to test and tune your room acoustics

Should I use some kind of room tuning software to home in on room modes?

This might seem to conflict with what I just said, but no, it is NOT a good idea to use room tuning (a.k.a. "room correction") software or hardware to tune your room at this stage. Not even to identify some of the issues. What the manufacturers of those products conveniently neglect to tell you, is that you can only use those products in a TREATED room! You can't use them in an untreated room, because the major problems in such a room are relate to resonance and reflections, and "room correction" hardware or software can do absolutely zero to "correct" such problems in a room. Those are basically just glorified parametric equalizers, and as you probably already know, you can't use equalization to fix resonance, nor can you use it to fix reflections. EQ can only fix frequency related problems, but those are acoustic issues. They are related to the time domain, and the phase domain, not the frequency domain. EQ can only adjust frequencies, not time or phase. Think of it this way: after the sound wave leaves the speaker, it bounces around the room in various ways, interacting with the walls, floor, ceiling, furniture, etc., and carries on doing that for several hundred milliseconds, before it eventually dies away. If you think about it logically, there is NOTHING that an equalizer can do to fix problems that occur AFTER the sound has already left the speaker! It can only fix problems that cause frequency changes up to the point where the sound is leaving the speaker.... And you won't even be able to find out what THOSE problems are (up to the speaker), until you have already treated the room, because the basic room issues are so much larger than they are, and overwhelm them in the acoustic testing: you won't even be able to see what they are until you first treat the room.

Here's an example of a room that was initially designed, properly, then treated properly, then finally tuned digitally in the end. thread about Studio Three Productions' studio

Here's another case that is currently under construction, where the room has NOT yet been tuned, but HAS been treated: thread about Steve's high-end control room in New Orleans We are about to start on the digital tuning in that room in a few days, so check back on that one regularly, to see the results.

So: first, test your room with REW, then treat it as well as you possibly can... and only then, at the end, can you use software and hardware for the final tuning.

Digital tuning is the "icing on the cake", so to speak: you can't ice the cake until you first mix it, and bake it!


- Stuart -

[jrm1]

That will work fine. There are nicer materials though. Knauf Ecose Universal Board or Batts doesn't itch or scratch or smell.
Isover High Performance Duct Cladding or equivalent Glass product has better absorption afaik.
DD

Thanks Dan. Do you know the Knauf product with the best air resistivity figures for bass? For Rockwool I think it might be RWA45 but I'm unfamiliar with Knauf products. If I have to tolerate the scratches I will (I've built 2 sets of walls and ceiling already so a few more pieces of it won'y hurt).

[jrm1]

Hi there "jrm1", and welcome. Please read the forum rules for posting (click here). You seem to be missing a couple of things!
Apologies, I've added location and occupation.

The type of bass trap you are describing is often referred to as a "suberchunk" trap, dating back to an old thread on the Studiotips website, ir I recall correctly. As Dan said, your plan will work: that's a good way of making superchunks, and there are other materials that could be used instead of mineral wool.
I was thinking of stretching thin fabric (similar to speaker covers) over the face. Good idea, or should I think about some slotted screen of ply, or a thicker more higher frequency sound-reflecting
material?

Regarding your room testing and tuning: Yes, it's always a good idea to run tests on your room, starting with an initial "baseline" test with the room empty of everything, except the speakers and a desk to put your DAW on. Here's how to run those tests: How to calibrate and use REW to test and tune your room acoustics
Thanks for this too!

Should I use some kind of room tuning software to home in on room modes?

This might seem to conflict with what I just said, but no, it is NOT a good idea to use room tuning (a.k.a. "room correction") software or hardware to tune your room at this stage. Not even to identify some of the issues. What the manufacturers of those products conveniently neglect to tell you, is that you can only use those products in a TREATED room! You can't use them in an untreated room, because the major problems in such a room are relate to resonance and reflections, and "room correction" hardware or software can do absolutely zero to "correct" such problems in a room. Those are basically just glorified parametric equalizers, and as you probably already know, you can't use equalization to fix resonance, nor can you use it to fix reflections. EQ can only fix frequency related problems, but those are acoustic issues. They are related to the time domain, and the phase domain, not the frequency domain. EQ can only adjust frequencies, not time or phase. Think of it this way: after the sound wave leaves the speaker, it bounces around the room in various ways, interacting with the walls, floor, ceiling, furniture, etc., and carries on doing that for several hundred milliseconds, before it eventually dies away. If you think about it logically, there is NOTHING that an equalizer can do to fix problems that occur AFTER the sound has already left the speaker! It can only fix problems that cause frequency changes up to the point where the sound is leaving the speaker.... And you won't even be able to find out what THOSE problems are (up to the speaker), until you have already treated the room, because the basic room issues are so much larger than they are, and overwhelm them in the acoustic testing: you won't even be able to see what they are until you first treat the room.

Here's an example of a room that was initially designed, properly, then treated properly, then finally tuned digitally in the end. thread about Studio Three Productions' studio

Here's another case that is currently under construction, where the room has NOT yet been tuned, but HAS been treated: thread about Steve's high-end control room in New Orleans We are about to start on the digital tuning in that room in a few days, so check back on that one regularly, to see the results.

So: first, test your room with REW, then treat it as well as you possibly can... and only then, at the end, can you use software and hardware for the final tuning.

Digital tuning is the "icing on the cake", so to speak: you can't ice the cake until you first mix it, and bake it!


- Stuart -

That all makes sense. I'll take it in.
I know my room won't be anywhere near perfect and it will be a compromise in terms of air volume and dimensions, but I had constraints. This will be a lovely writing room with space for a couple of other musicians for basic recording. I'd like it to have some life and not be too dead. Bass trapping was going to be my main priority in terms of acoustic control, then absorption higher up the bands only where I need it, perhaps with the option to take down and rehang as and when the situation called for it.
Thanks again for all the advice here and elsewhere on the forum!

[Soundman2020]

I know my room won't be anywhere near perfect and it will be a compromise in terms of air volume and dimensions, but I had constraints.

Don't feel alone! The majority of home studios are like that: Constraints and limitations all around. That's what the forum is all about: helping folks like you to do the best possible within those constraints.

Bass trapping was going to be my main priority in terms of acoustic control, then absorption higher up the bands only where I need it, perhaps with the option to take down and rehang as and when the situation called for it.

Bass trapping will also take out a lot of the high end, but you likely will need something additional especially on the ceiling, to control things like flutter echo and overall decay times. It seems like the priority for your room will be listening, not so much recording or mixing, so the room doesn't need to precision acoustic treatment. You'll probably be fine with general treatment.

- Stuart -

[jrm1]

Stuart, is it possible to confine bass trapping to the bass regions? I need to be able to record and mix as well as write in this space and don’t want to deaden the sound too much.

[DanDan]

Obviously I concur that hardware treatment of the physicality of a space is the most robust.
However to fully do this requires taking up to 60% of it.
So the vast majority of treatment is woefully inadequate.
Research has shown that the unfortunately named DRC is at it's most effective in the least treated rooms.
In a perfectly treated room, speakers tweaked at the, ahem DSP, Crossovers and Amps, there is no need for it at all.

Well implemented DRC does address the Impulse Response of the Speaker/Room Chain.
For the lowest mode, typically 30-40Hz, typically hardly addressed at all by hardware treatment, DRC is a god send. The level reduction helps with the boom back at the couch, AND the mid room null. The actual Decay Slope is also altered beneficially by the Eq. As I understand it the EQ/Speaker have their own IR's which resonantly piggy back on the room. Actively shortening the mode.
http://www.acousticfrontiers.com/201163 ... odes-html/

I have seen Dirac Research using multiple sound sources, 14 afaik, to entirely flatten LF response in an untreated room. The IR was similarly improved. This, Bag End, PSI, are an additional tools for us. I welcome all of those that are genuinely helpful.

DD

[Soundman2020]

Stuart, is it possible to confine bass trapping to the bass regions? I need to be able to record and mix as well as write in this space and don’t want to deaden the sound too much.

Yes it is possible. It can be done in fairly "slim" devices too. There are several approaches here, such as rigid panel traps, limp membrane traps, perforated panel absorbers, and "slot walls". The only drawback is that they are all tuned devices, and tuning them correctly isn't so easy. Each device also needs to be correctly placed in the room, at the point where the problem itself actually occurs. For example, there's no point in placing a tuned device in the middle of the back wall that is designed to treat a modal issue in the vertical plane, or something on the side wall that is supposed to deal with SBUR caused by the ceiling. So it's more complicated to treat with tuned devices, but it can be done.

Another option is to place some type of reflective surface over the front of your pure absorption bass trapping. The reflective surface would be selected to reflect back certain parts of the spectrum in the high end, as needed by the room. There's basically two ways of doing that: 1) Use thin "foils" such as plastic sheeting over the bass trapping, in which case the thickness and type of foil has an effect on the frequency range that will be reflected back to the room or allowed to pass through to be absorbed, and the amount of area that is covered controls the amount of reflection. 2) Use thin wood / metal / plastic / etc. strips, or "slats" across the front of the bass trapping, where the dimensions of the slats (width of the "planks") can be adjusted to control the frequency range of the reflections, and the coverage area controls the total amount of reflection. The latter can look similar to a slot wall, but is not the same at all. A slot wall is a tuned resonant device, where the resonance is the mechanism responsible for the absorption, but the "slats on the bass trap" have no resonant cavity behind, so they are not tuned in that way. In fact, if you design carefully, it is possible to have a slot wall on the side of the room and slats over the bass trapping that blend into each other, and look pretty much identical... but do very different things. The secrete is in the "guts" of the device...

So yes, it can be done. There are many approaches to treating and tuning a room.


- Stuart -

[jrm1]

Can I achieve great results without using the room EQ wizard? I've gone way over budget with construction costs and am finding it hard to justify to myself £150 on either a USB mic or dB meter.
Could I build my bass traps out of Knauf RS45 earthwool floor to ceiling in each corner and see what improvements come from them and add absorption panels from GIK for example?

Or is that like shooting in the dark?

The absorption coefficient data from Kanauf are attached. Do the numbers look good?

Thanks for all your advice.

Screen Shot 2019-07-15 at 09.44.03.png

[Gregwor]

Can I achieve great results without using the room EQ wizard? I've gone way over budget with construction costs and am finding it hard to justify to myself £150 on either a USB mic or dB meter.

A great mix can be achieved in any room. The more transparent your room sounds, the quicker you can get amazing mixes. Having said that, it's your room and you are the only person that can decide how far you want to dive into getting an amazing sounding room. REW is amazing and really helps you determine where you can improve your room though.

Could I build my bass traps out of Knauf RS45 earthwool floor to ceiling in each corner and see what improvements come from them and add absorption panels from GIK for example?

That stuff looks alright.

Greg