Acoustic treatment for small mixing/rehearsal room in Sydney

[gearjunk1e]

My first post…though I’ve been doing a lot of reading!

Here’s my project…
I have a room at the back of my house that I use for both mixing and rehearsing – it was not built for this purpose though and I am hoping some treatment can improve the space acoustically despite its limitations. It’s what you guys would call a small room – 4.1m x 4.6m x 2.2/2.6m.
The internal walls are gyprock fixed to wooden framing which backs onto the external brick wall. There is no insulation in the cavities. The floor is wood floorboards. There are lots of windows which is great for light but probably is not helping acoustics.

I first sensed the room had some acoustic issues when I compared the sound of my guitar amp in this room versus how it sounds on the same settings in well treated studios…my amp sounds much brighter at home – I didn't know whether it was that I was losing some low mids through cancellation and/or getting too much reflection of the high mids and/or something else. Trying to understand that, led me to this forum and a wealth of information about the likely acoustic performance of the room. That led me to REW, an omni mic and Sketchup. Anyway, I’m hoping that in deploying some treatment I can kill two birds with one stone – both improving my mixing/listening environment and the acoustics for the guitar amp.

I have no noise level constraints to be overly concerned about – the issue here is balance. I'll be doing panels DIY.

I have attached:
• some sketchup drawings of the room
• the REW waterfall to ~300hz and
• some pics

In the folder in this link https://drive.google.com/folderview?id= ... =drive_web are
• A REW measurement file - untreated (measured at the listening position about 40% back from the wall - my monitors are Adam A7X's - no sub)
• the Sketchup file itself
(Too big to post)

From reading other posts/replies its clear I’ll need some corner traps and some early reflection absorbers as well as some slight rearrangement of the desk/monitors ie monitors off the desk and onto stands.

My questions are:
1. What do you make of the REW file? – looks broadly similar to others I’ve seen from small rooms...maybe a bit more going on at ~75 and ~150hz than I've seen on some other charts…is there anything different here to think about?
2. Is there any clever way to deal with the problem this room presents for corner trapping – that is that the windows at each end are very close to the corner (0.27m) – thus making it more difficult to put decent size panels in there – at least on the 45 degree angle - without blocking part of the windows. I’d wondered about using the wall/celling corners to mount traps but the weight of opinion seems to be that the best value comes from addressing wall corners first.
3. Is there anything different I should do differently around early reflection absorption panel placement, given the raked celling at each end? Needless to say the windows (on the RHS wall – facing to the desk) and doors/windows at the opposite end complicate early reflection panel placement as well.
4. Does anyone based in Sydney have a line on where I can get some sensibly priced 48kg/m3 (mineral wool) or 32kg/m3 polyester insulation in Sydney for my panels? I’ve listed below what I’ve looked at but it seems hard to drum up much supplier interest in small product orders

Products I’ve been looking at

• Fletcher 50mm 40kg/m3 Glasswool (244251) – John S has recommended this in the past…just trying to locate a supplier in Sydney who’ll do a small quantity
  Higgins pacb32100580 – polyester 32kg/m3 – John also recommended this maker to others – they were helpful when I contacted them but I’d need to get it shipped from QLD which sort of prices it out of the market
  Tontine Acoustisorb 2 - polyester 32kg/m3 – this product seems to polarise opinion - I’m not sure what to make of all of that
  Autex Acoustic blanket AAB35-50 - polyester 32kg/m3 – this looks promising if I could find a retail level supplier for just the panels
  Polymax absorb – polyester 32kg/m3 - this is locally produced but yet to hear back from them on retail supply

….It seems I can get Bradford Soundscreen Rockwool any place and time I want but at 24kg/m3 it doesn’t seem dense enough for the job from what I’ve read so far....Fletcher's Pink SonoBatt's are also relatively easy to find and get closer at 32kg/m3 (glasswool) but still not enough

Hope I've ticked all the boxes for posting - happy to provide any other info...but any advice would be gratefully received!

Andrew

Music room OH.jpg

Music room from desk end 2.jpg

Music room 6.jpg

Music room 8.jpg

music room wfall untreted js forum.jpg

From doors to workstation.jpg

Cnr 1.jpg

Cnr 2.jpg

[Soundman2020]

Hi there Andrew, and welcome to the forum!

The internal walls are gyprock fixed to wooden framing which backs onto the external brick wall.

That sounds like what seems to be called "brick veneer" construction in Australia. There shouldn't be too much of a problem with that, except that it doesn't give fantastic isolation unless there's insulation in the cavity and the drywall is thick.

The floor is wood floorboards.

Probably not so good. Any idea what is under that?

Trying to understand that, led me to this forum

Excellent!

I have no noise level constraints to be overly concerned about

I'm not so sure about that: your REW data shows a very high level of ambient noise in the low frequencies, below about 65 Hz, and it gets really loud below about 50 Hz. Is the room near some heavy machinery (generator, pump, etc)? A major road? Waterfall? Railway line? Something else that is causing that low "roar"? Whatever it is, it most likely needs isolating or dealing with in some other way.

From reading other posts/replies its clear I’ll need some corner traps and some early reflection absorbers as well as some slight rearrangement of the desk/monitors ie monitors off the desk and onto stands.

Correct! Definitely get the speakers off the desk and onto massively heavy stands, and definitely get them into better locations / angles.

And one other thing: I would also try rotating the layout 90° right, and also perhaps 90° left. Yes, that would mean firing the speakers along the shorter axis, instead of the longer axis, but it would improve your acoustic symmetry, which I suspect might be an issue. There's no rear wall in your SketchUp model, so it's hard to say what might be going on there, but I suspect that setting up the room facing the window might work. That would allow you to place the thick, deep absorption that you'll need on the new rear wall (where the piano is), and also the absorption that you'll need on the side walls, which would not be easy to do right now due to the windows.

It might not make a huge difference, but it's worth a try. If there's no real difference, then leave it like it is, and treat.

What I would suggest you do with the REW tests is to do independent measurements with just the left speaker, just the right speaker, then both together. That will help reveal issues with symmetry. Do the same set of tests with the room oriented in all three directions, and see which gives you the best symmetry.

1. What do you make of the REW file? – looks broadly similar to others I’ve seen from small rooms...maybe a bit more going on at ~75 and ~150hz than I've seen on some other charts…is there anything different here to think about?

The 74 Hz dip is spot on for your 0,2,0 mode, and the 149 Hz gully is spot on for the 0,4,0 mode, which is the same axial issue, one octave higher. So clearly you need heavy bass trapping to deal with that. There's also the 107 Hz Dip, which doesn't seem to be modal so is probably SBIR.

There's some modal ringing going on too, but nothing too serious. Good bass trapping should take care of that.

I’d wondered about using the wall/celling corners to mount traps but the weight of opinion seems to be that the best value comes from addressing wall corners first.

Acoustically, it doesn't matter too much. Vertical corners are easier to do, from a construction point of view, but any corner is good, provided that you pay attention to the "tri-corners", where you get the most bang for your buck.

3. Is there anything different I should do differently around early reflection absorption panel placement,

If you do end up with the room staying oriented as it is, the I would put some absorption on those angled sections of the ceiling.

REW shows a very strong reflection at about 3.4ms, which implies a distance of 117 cm, so I'd try to find out what that is. I suspect it might be that angled ceiling section. You could use the "string trick" to check.

where I can get some sensibly priced 48kg/m3 (mineral wool) or 32kg/m3 polyester insulation

32 kg/m3 is for fiberglass, not polyester. I'm not aware of any research showing the optimal density for polyester. I'm sure that there must be some data somewhere on that, but I've never really gone looking for it. I would suspect that it would need to be a bit lighter than that, but I may be wrong. If you do find something concrete about that, then please post a link to it here on the forum.

Fletcher's Pink SonoBatt's are also relatively easy to find and get closer at 32kg/m3 (glasswool) but still not enough

What do you mean "not enough"? That they don't have enough in stock for your project?

It's a reasonably sized room, and the REW data isn't too bad overall. I reckon that with good geometry and good treatment, it should work out well.


- Stuart -

[gearjunk1e]

Hi Stuart

Thanks for the prompt reply and detailed answers/questions...I really appreciate your time and the effort you put in and am starting to get just how interesting this field of study/application is!

I will do some further REW measurements as you suggest including the different orientation of the room to see what happens and also the "string test" to identify the offending surface - I do have one further question at this stage which I have included at the base of this thread.

Some answers to your questions.....

The floor is wood floorboards.
Probably not so good. Any idea what is under that?

Classic old Sydney house foundations....the floorboards sit on wooden joists, they sit on wooden bearers and they in turn onto brick piers that sit on concrete footings...its a long way to concrete! It would be about 0.7m from the under side of the floorboards to the ground level.

I have no noise level constraints to be overly concerned about
I'm not so sure about that: your REW data shows a very high level of ambient noise in the low frequencies, below about 65 Hz, and it gets really loud below about 50 Hz. Is the room near some heavy machinery (generator, pump, etc)? A major road? Waterfall? Railway line? Something else that is causing that low "roar"? Whatever it is, it most likely needs isolating or dealing with in some other way.

Sorry - I should have been clearer here - I was referring to dB issues re neighbours etc...in relation to the low ambient noise we are ~300m from the rail line and have a rail tunnel deep below us in the bedrock. Its possible that we had a train running through while I measured - when I do some more measurements we'll see what transpires.

where I can get some sensibly priced 48kg/m3 (mineral wool) or 32kg/m3 polyester insulation
32 kg/m3 is for fiberglass, not polyester. I'm not aware of any research showing the optimal density for polyester. I'm sure that there must be some data somewhere on that, but I've never really gone looking for it. I would suspect that it would need to be a bit lighter than that, but I may be wrong. If you do find something concrete about that, then please post a link to it here on the forum.

Fletcher's Pink SonoBatt's are also relatively easy to find and get closer at 32kg/m3 (glasswool) but still not enough
What do you mean "not enough"? That they don't have enough in stock for your project?

I've realised that I've totally confused myself on insulation

I subsequently found another post where you explained this in some depth. While that was in the context of wall insulation, if I understand it correctly I should be looking for 32 kg/m3 fibreglass and 48kg/m3 mineral wool for my treatment panels.... though it does sound like I could get away with slightly lower density for the bass trapping.

In relation to my comment about the Fletchers Pink SonoBatts and "enough", I could have worded that section way better...I think it would be clearer if I said "they are glasswool and rated at 32 kg/m3 and that I didn't think that this would not be dense enough for early reflection absorbers".

On polyester, the only thing I've found was a thread on Gearslutz that got some comparative data on gas resistivity on Fletchers (glasswool) vs Tontine Acoustisorb (polyester) vs Bradford (glasswool) and then moved into some comparisons with Polymax (polyester). You may have seen this already but here it is anyway. https://www.gearslutz.com/board/studio- ... l-use.html

My one follow up question at this point is that having read your detailed post on insulation, it does seem that the Fletchers Pink SonoBatts (glasswool 32 kg/m3) might just fall into the acceptable range for bass trapping or is this pushing it too far...what do you think? (I'd still have to find another higher density product for the early reflection panels of course)

Thanks
Andrew

[Samjose25]

Nice room for your instruments. I have mine in our garage it's good for acoustic rehearsal.

[Soundman2020]

Classic old Sydney house foundations....the floorboards sit on wooden joists, they sit on wooden bearers and they in turn onto brick piers that sit on concrete footings...its a long way to concrete! It would be about 0.7m from the under side of the floorboards to the ground level.

Like I suspected: not so good! I suppose there's no chance you could take all that out, and get your room down to concrete? That would probably be a lot of work....

.

in relation to the low ambient noise we are ~300m from the rail line and have a rail tunnel deep below us in the bedrock.

Now THAT'S a problem!

if I understand it correctly I should be looking for 32 kg/m3 fibreglass and 48kg/m3 mineral wool for my treatment panels.... though it does sound like I could get away with slightly lower density for the bass trapping.

Right!

it does seem that the Fletchers Pink SonoBatts (glasswool 32 kg/m3) might just fall into the acceptable range for bass trapping or is this pushing it too far...what do you think?

That should be fine. Just make it a bit thicker than you would have for the other stuff, if you can.


- Stuart -

[gearjunk1e]

Stuart

Thanks

Re the floor being wood...yep I'm stuck with it... the floor and the window/door set-up in this room are not ideal

On that low frequency ambient noise...I've run further tests since and now suspect that my problem in the initial measurement was one of 1. the low hum of the ceiling fan 2. a washing machine or drier in the adjoining room (double brick wall between) being on or 3. my son mowing the front lawn at the time. I can't see the same issues appearing on subsequent files...but maybe I'm not looking in the right place. I did do another measurement pre treatment when none of the other things were happening and have included those in the linked file.

As for room set-up I've done a bit of work since the initial post
1. used the string test and found that part of that early reflection you'd identified at 3.4ms was coming from my 2nd screen - the new set-up has both screens back against the wall and mostly out of the line of fire..
2. got the monitors off the desk - built some speaker stands using pine and PVC pipe and filled the pipe with building rubble; the difference in terms of L/R separation is dramatic. I pinched the design from http://emotivalounge.proboards.com/thre ... ker-stands with a few mods
3. put in some 32" superchunks in on the vertical corners where I could fit them given the position of windows/door using Bradford's Soundscreen (24kg/m3 - they claim 10,500-13,600 rayls/m)

The changes so far seem to have tightened things up - certainly I can hear the difference both from my monitors and the bottom end of my guitar amp is now getting to my ears! ...and the waterfall and spectrogram seem to show signs of improvement

You had suggested I look at changing the room orientation and set up facing the windows to try and help with symmetry...unfortunately the other wall that was not in my sketchup file is mostly french doors and another window so I'd still have windows on my right and wall on my left if I went that way so I've stayed as I am running longways

I've attached a link to the REW files generated post the setup changes and superchunks...this time I did L, R and "both" and have also included some "both", L and R pre treatment measurements without that low freq ambient noise https://drive.google.com/file/d/0BzqNSs ... sp=sharing - file is "gearjunk1e pre and post treatment"

My questions are:

A. the wood floor...what does it mean for me acoustically?

B. your thoughts on my new REW file...?? My observations are
1. I still have some strongish early reflections in the 3.27-3.92ms range - from the string test that is consistent with reflections off the sloped ceiling
2. My L and R monitor waterfalls are quite different in terms of the SPL and waterfall graphs post superchunks

C. My next stage treatment plan - I'm thinking stage 2 of my treatment plan looks like;
a. Some corner traps above my superchunks - while the area covered is smallish, my measurements suggest a lot of lower frequency energy in the top tri corners and when I temporarily placed the larger of these panels into the corner diagonally across from my LH monitor it flattened a lot of the lower frequency response of the LH monitor measurement that still existed in the REW file post stage 1 treatment
b. A couple of clouds on the sloped ceiling over the desk primarily to address the reflections but also to add to the bass trapping
c. Some panels on the wall behind the monitors/screens

Music room treatment plan.jpg

Music room treatment 2.jpg

Basically - its the stuff in yellow in the sketchup images
Does this prioritisation and approach make sense?

I'd appreciate any further thoughts on my comments and questions

Andrew

[ajoyna1]

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