Treatment for (slightly) odd shaped mix room

[civvie]

Hi all. Great forum, glad I found it!

OK here goes:

I've got a smallish mixing room, it's an odd shape, slightly trapezoid, the front wall is narrower than the back with the sides fanning out. (It wasn't designed as a RFZ or anything, it's just how the room is). I've been mixing in this room for 3 years with some basic treatment, and it sounds OK, but there are issues I now want to sort out.

The Room

177 sq foot. 3 walls are drywall on wood stud and the 4th is cement and brick exterior wall.
The floor is cement with hardwood parquet on top, the ceiling is cement.

Treatment
The treatment I have so far:
Large hanging cloud (Rockwool RW3, two layers total 150mm, not hardbacked)
Two first reflection side panels (single layer 75mm RW3)
Two corner panels (single layer 100mm RW3)
Back wall panel (4 x 75mm RW3)

I'm not sure how to post photos here so please visit this link for photos, sketches and the REW mdat and screenshots: https://drive.google.com/drive/folders/ ... sp=sharing


What I want to achieve

I think my biggest issue is the difference in the construction of my L + R walls. This is throwing the imaging off and I think you can see that in the REW results. I want to try and improve this as well as improve the bass response and definition.
I'd love to get some advice on the amount and method of bass trapping, I've got plenty of space behind my speakers to build some superchunks which is my current plan, but not starting anything until I get more advice. I'm also planning on building new first reflection broadband absorbers and I'd love some advice on the best kind to improve my imaging. And of course, I'm hoping there are many things I can do to improve my room acoustics that I have not thought of, which is why I'm here!

So, what do you all think?

============EDIT=============
Here are the pics:

Current working mess

Dimensions:

Ceiling is 326cms

REW

[SoWhat]

Greetings civvie,

Can you post exact dimensions of your space?

You can drag attachments into your posts.

All the best,

Paul

[SoWhat]

Greetings once again,

I found the dimensions pic. Disregard my previous.

Sorry about that.

All the best,

Paul

[civvie]

Thanks Paul,

I forgot to include the ceiling which is 336cm

So the complete dimensions in cms are:

Front: 216 (drywall)
L side: 594 (drywall)
R side: 597 (cement rendered brick)
Rear: 337 (drywall)
Height: 326 (cement ceiling)

Cheers,
Civvie

[SoWhat]

Greetings Civvie,

I would suggest looking through Jennifer's build (if you haven't done so already). Her room is a little bit bigger than yours, but you'll get the idea.

viewtopic.php?t=8

It is worth reading the entire thing.

All the best,

Paul

[ericwisgikl]

Greetings civvie,

Some things you should do in order to achieve your goals is:

- Improve room symmetry:
Is it possible to angle both front and rear wall? It would give you better imaging. Symmetry is a very important aspect of listening rooms. Something like this:

- Improve speakers layout:
It seems you have your speakers a bit far from the front wall. This is one of the main causes of SBIR (Speaker-Boundary Interference Response). The easiest way to get rid of it is moving them against the front wall. Or better yet, soffit mount them! This last thing is maybe the best you could do for your space, improving image, bass response and getting rid of front wall SBIR.
Here is some more info about monitor placement in order to avoid SBIR.
http://arqen.com/acoustics-101/speaker- ... erference/

These improvements could be your starting point, and then it would be clearer to see which steps are next.

I hope it helps you.

Best regards,

Eric

[civvie]

Paul,

Thanks for the thread link to Jennifers build. The thread is a whopper but seems like a great source of information. I've saved the whole thing as a PDF and I'm going to look over it for the information on treatment (as that is all I'm focusing on right now).

Eric,

Yes symmetry is ideal, I understand your point. Rebuilding the walls is probably a bit beyond the scope of what I can aim for at this stage. It is a rented studio and I don't expect to be here for a long time, but I want to do what I can within a reasonable budget, say £1-2k. I'll be doing the building myself with a friend. I'm wondering if a bigger problem is the fact that the left wall is concrete while the others are drywall. Surely that is throwing off my imaging a lot too, right?

From the back of the speakers to the wall is 64cm. When I first set up in the room I tried them closer in various positions and this is where they sounded best. Also because of the narrowing walls, to have them closer to the wall means having them closer together which in turn means sitting closer to them and the whole thing starts to become unergonomic. I'm actually about to replace the monitors (Dynaudio BM6A's) with Barefoot MM45s, which is what is spurring on this whole acoustic refurb. (if you're going to have great speakers, better have a great room hey?) The MM45's are bigger in size and I really don't think I'll get away with having them closer together than I currently have the Dynaudios. I see sofit mounting is popular here and I appreciate that it is the ideal solution to boundary interference. I'll certainly look into it, I've seen a number of build threads with them and I'm concerned that I don't have the space to play with, also I'm wondering if speakers are easily removed from sofits as I want to be able to easily take my monitors out of the studio when needed (I do location work too).

Questions:

With my speakers on stands, would it make sense to completely fill in the gap behind them with absorption? Current space from speakers to wall is 64cms, so say something like a 30cm wall of Rockwool RW3 (wall to wall, floor to ceiling) with a 34cm air gap behind it. Would this help reduce the effect of asymmetry in the front wall and also be a big bass trap?

No one as yet commented on the REW results. I don't know a great deal about interpreting this, how good/bad are they? Where are my biggest issues?

Many thanks everyone!

[ericwisgikl]

Source of the post Rebuilding the walls is probably a bit beyond the scope of what I can aim for at this stage. It is a rented studio and I don't expect to be here for a long time, but I want to do what I can within a reasonable budget, say £1-2k. I'll be doing the building myself with a friend.

I understand perfectly your point.

Source of the post With my speakers on stands, would it make sense to completely fill in the gap behind them with absorption? Current space from speakers to wall is 64cms, so say something like a 30cm wall of Rockwool RW3 (wall to wall, floor to ceiling) with a 34cm air gap behind it. Would this help reduce the effect of asymmetry in the front wall and also be a big bass trap?

It sure will be a nice big bass trap, which will help with some issues you actually have at the low end. I can't tell you exactly how it will behave anyway. What I can say is that it will affect your TR in mid and high frequencies, where it is already a little short.

Also, I don't know how would this help with your stereo image, since the room would still be asymmetric, and, as you pointed out, maybe some of the difference is due to the fact that side walls are made from different materials.

Source of the post No one as yet commented on the REW results. I don't know a great deal about interpreting this, how good/bad are they? Where are my biggest issues?

May you attach the .mdat file? It's easier to analice it directly from REW rather than from pictures. Anyway it seems to be what is expected from a not so treated room, specially in the low end.

[endorka]

Eric's suggestions are really good, but as you say with it being a rented room, perhaps not all of them are practical.

I wonder if there is a way of making at least the front wall symmetrical without incurring too much cost, damage to existing wall, and also without creating a triple leaf effect?

I've not much time to write this at the moment, but something to note though;

From the back of the speakers to the wall is 64cm.

That is a really bad distance as far as front wall SBIR is concerned. Ideally you should be much closer to the wall (say 10cm or even closer - pushes the SBIR up high where it is easier to deal with) or much further away (at least several metres - pushes it below the bottom range of the speakers). In between will give you an SBIR null in the low mids or bass. Your waterfall chart confirms this. You can't get far enough away from the front wall in that room, so your best options are to get closer or build soffits

It may not be possible due to the ergonomics of your situation, but in your shoes I'd do the following;

- There's a lot of surfaces at the front of the room that will be confusing your REW results with reflections. I'd empty out the whole of the front of the room - desk, keyboard, all the stuff. Except the speakers on separate stands. Get the speakers as close to the front wall as you can, with no rockwool at all behind them. Even as close as 1cm. Get your side panels at the first reflection points, then measure with REW again. You might get far cleaner results that will give a better indication of the best way forward.

Cheers,
Jennifer

[civvie]

Thanks for the reply guys. I really appreciate having input from such knowledgable people.

Source of the post It sure will be a nice big bass trap, which will help with some issues you actually have at the low end. I can't tell you exactly how it will behave anyway. What I can say is that it will affect your TR in mid and high frequencies, where it is already a little short.

Also, I don't know how would this help with your stereo image, since the room would still be asymmetric, and, as you pointed out, maybe some of the difference is due to the fact that side walls are made from different materials.

Yes it would be huge alright. Maybe a little overkill... I think I'll stick to superchunks behind the speakers and also put superchunks along the ceiling and side wall corners. I can't put them at the back due to a door in the corner and a high shelf and bookshelf you can see in the picture of the back wall.

What is TR? Is that related the RT60 information? (I don't really know how to interpret REW data yet) I've read that for small rooms 200ms is a good place to aim for, I'm a little under that above 200hz and then things get out of control under 100hz.

Here is the mdat:

Civvie July 21.mdat

(11.07 MiB) Downloaded 1315 times

Civvie July 21.mdat

(11.07 MiB) Downloaded 1315 times

Source of the post That is a really bad distance as far as front wall SBIR is concerned. Ideally you should be much closer to the wall (say 10cm or even closer - pushes the SBIR up high where it is easier to deal with) or much further away (at least several metres - pushes it below the bottom range of the speakers). In between will give you an SBIR null in the low mids or bass. Your waterfall chart confirms this. You can't get far enough away from the front wall in that room, so your best options are to get closer or build soffits

Ah yes, I see. This room is tricky in that regard as if I have the speakers placed against the back wall then they will be exactly in the two corners, and I dare say speakers in corners is not going to be good! I was somewhat aware of the SBIR theory when I first set up the room but the speakers just didn't sound good against the wall and I expect that has a lot to do with the corners. I've been reading a bit of this thread about sofits https://www.digistar.cl/Forum/viewtopic.php?f=14&t=788 and I was surprised to see Stuart talking about how they don't have to be a 'hugely massive, very heavy, very rigid structure" which is the way I always thought they needed to be. So maybe it's not as daunting a task as I'd imagined. I don't know if Barefoot MM45s can be mounted this way, I'll investigate further about this path. I'd also like explore the non-sofit speaker stand route. My stands are very heavy and solid (homemade, two columns full of builders sand ) so that's a good start.

Source of the post There's a lot of surfaces at the front of the room that will be confusing your REW results with reflections. I'd empty out the whole of the front of the room - desk, keyboard, all the stuff. Except the speakers on separate stands. Get the speakers as close to the front wall as you can, with no rockwool at all behind them. Even as close as 1cm. Get your side panels at the first reflection points, then measure with REW again. You might get far cleaner results that will give a better indication of the best way forward.

This is great advice, I'll do a bit more testing and report back. My Barefoots turned up today so I'm keen to reshoot the room with them. On that topic, if anyone hasn't heard Barefoot MM45's, I recommend you do when you get a chance. Amazing detail and mid-range clarity and they go down quite low in the bass too. Here's a pic of them in situ.

[Starlight]

Looking at that last photo, the one with the Barefeet, it looks to me that they might be sitting too low. The audio axis, which will be at the centre height of the tweeters and woofers, should be at ear level. Maybe they are, it just doesn't look like it to me.

Symmetry from the listening position forward is especially important so you have two challenges - matching the mass of the side walls and doing something like Eric suggests in his drawing in reply no. 6. The rear wall's lack of symmetry is less of an issue and so mass shouldn't need to be added there, so long as you have a good rear wall bass trap, which is a separate challenge with the door in the corne, albeit solved by traps on wheels or castors.

[civvie]

Source of the post Looking at that last photo, the one with the Barefeet, it looks to me that they might be sitting too low. The audio axis, which will be at the centre height of the tweeters and woofers, should be at ear level. Maybe they are, it just doesn't look like it to me

I know why it looks like that, it's because my desk is too high! The monitor in the picture is also much higher than it would be when I'm mixing (it's on an adjustable arm). Part of this studio refurb is to build a new desk that is lower and adjustable in height. The speakers are actually perfect ear height at comfortable sitting level.

Source of the post you have two challenges - matching the mass of the side walls and doing something like Eric suggests in his drawing in reply no. 6

I've been thinking about this issue and I have an idea that I'm going to run by you all soon, I just need to do some sketches to illustrate first.

[ericwisgikl]

Source of the post What is TR?

Sorry about that. I meant RT, in regard to reverberation time. But, as my native language is Spanish, here we say 'tiempo de reverberación' (TR), so I messed it up.

Cheers,

Eric

[civvie]

OK here is a sketch of an idea I had that could potentially address both the asymmetry and the different building materials of the right side wall.

Studio 1.jpg (39.45 KiB) Viewed 38432 times

Studio 1.jpg (39.45 KiB) Viewed 38432 times

The idea is to build out a frame with wood studs, fill with insulation (or maybe just within the stud frame like with a normal wall? That is how my left side wall is built) and cover with two layers of drywall.

The speaker placements in the sketch are in the same position from the front wall as they currently are. I've added in where the superchunks and first reflection side panels would go.

The issue I can already see with this design is that is will force my speakers closer together, and also closer to the side walls.
A bit closer together might not be bad but it will need testing and I'm concerned that I won't know how detrimental this would be until the 'correction' wall is built and I test it. I'm worried it is just constricting an already small area and that will do more harm than good.

A second option is to correct the angle of the front wall and either just leave the right side wall as is, or board over it with drywall to give it similar acoustic properties to the left wall? I would imagine that the solidity of the cement and brick wall is more the issue, pushing bass energy back into the room rather than passing through like it would a stud wall. So covering it with drywall may have little effect.

What are your thoughts on all of this?

[endorka]

Intuitively your second option seems better as it means the front and side walls can be made symmetrical. With the extra plasterboard leaf at the front wall there's a danger of the triple leaf effect reducing the sound isolation properties of the front wall though, so you may have to pay attention to that.

With a room of these dimensions there will be compromises, and it's really about finding a setup that reduces these to a manageable extent. I'd imagine the difference in response within the room from the brick and plasterboard side walls is the least of your worries. Not a direct comparison, but my main room has a stud built plasterboard wall on the left, then the stairwell. The right is an external wall - plasterboard on the house structure (wood) then block then roughcast. By my reckoning the difference between them is less than other things in the room.

You are still going to to get the front wall SBIR with the speakers in that position. You mention the speakers sounded bad when in the corners; was that established by ear or by acoustic measure? Certainly there will be a bass boost with them in the corner, but most speakers have the ability to roll it off. I'm persisting with this line of enquiry merely because I helped a friend setup a room of similar shape and dimensions, and we got the best set of compromises by having the speakers in the corners!

Cheers,
Jennifer