John Sayers' Recording Studio Design Forum Archive

Hello All,

I am hoping to get some advice on how best to treat my new mix/prod room here in Glasgow. Here are the details:

Goal: to create a mixing/production room.

Dimensions: W 9'6" x H 11'7" x L 15'10"

Construction: room is in a stone tenement building with thick floors, and solid walls - possibly gypsum with plaster. Lower half of walls are wood panelled. floor is cheap wood laminate.

Irregularities: door at side of back wall, Deep window embrasure on centre of front wall with sheet metal radiator beneath window. WIndow is very slightly off centre (2")

Planned furnishings: small mix table and chair in front of speaker position. small low table and couch in centre of room. Soldering work bench in centre of rear wall. Symmetrical freestanding shelves on each side wall. Rug to cover 50% of floor area.

Stage: Planning - the room is empty and ready for analysis.

Listening levels 76 DB SPL C weighted

Monitor system: 2 way stereo on stands w/ single subwoofer (Genelec 8030A, 7050B)

Budget: £4K (ish)

Errata:
I occurs to me that, in addition to overall treatment, I may need to block the window embrasure. I thought perhaps some sort of stackable custom built diffusor blocks to fill in the window well and cover the radiator, making the front wall flush.

In the rear of the room I will have a work surface W120 x D60 cm with shelves above, for doing electronics work. I wondered if I might be able to build a diffusor into the area below the work surface to a depth of perhaps 30cm?

Some visual aids:
Please let me know if any additional information is needed, and I would be most interested to hear any thoughts anyone may have about the best way to proceed with making this room as acoustically neutral as is possible, for the relatively modest budget I have to spend.

I will be doing some acoustic testing/analysis as per the recommendations on this site, over the next several days and will post that data.

Many thanks,

Richard

Hi Richard, and Welcome to the forum!

Dimensions: W 9'6" x H 11'7" x L 15'10"

The relationship between those dimensions is not ideal, but it's not too bad either. It's a little narrow given the length and height.

room is in a stone tenement building with thick floors, ... floor is cheap wood laminate.

So the sub-floor is stone?

room is in a stone tenement building with thick floors, and solid walls - possibly gypsum with plaster. Lower half of walls are wood panelled. floor is cheap wood laminate.

Do you need to use that radiator, or could it be blocked off / removed?

WIndow is very slightly off centre (2")

Not a problem.

Soldering work bench in centre of rear wall.

That might need to move a bit. The rear wall is where your bass trapping and SBIR treatment is most effective.

the room is empty and ready for analysis.

Excellent! Then do the analysis! Download, install, configure, and run REW, and post the MDAT file some place where I can download it. Calibrate and run the tests at 86 dBC with both speakers on (which implies 80 dbC for each individual speaker).

I occurs to me that, in addition to overall treatment, I may need to block the window embrasure. I thought perhaps some sort of stackable custom built diffusor blocks to fill in the window well and cover the radiator, making the front wall flush

It's possible yes. Hence my question about that radiator. But I would not use diffusion on the front wall.

In the rear of the room I will have a work surface W120 x D60 cm with shelves above, for doing electronics work.

As mentioned above, the rear wall is where your deep bass treatment goes, perhaps with diffusion in front of it (although the room is a bit too small for diffusion).

I wondered if I might be able to build a diffusor into the area below the work surface to a depth of perhaps 30cm?

A diffuser BELOW the work surface would not do much. It would have to be higher up, at speaker height, roughly, and extending a good few feet up from there, plus a couple of feet down.

I would be most interested to hear any thoughts anyone may have about the best way to proceed with making this room as acoustically neutral as is possible,

Start with the REW tests to see how the room is behaving at present, an based on that we can help you decide on the best course of action.


- Stuart -

Hi Stuart,

Many thanks for taking the time to reply.

Soundman2020 wrote:So the sub-floor is stone?

No, only the exterior wall is stone. The floor is quite solid - doesn't feel springy at all, like joists, but I don't know its construction.

Soundman2020 wrote:... Do you need to use that radiator, or could it be blocked off / removed?

I can block off the radiator, but not with anything permanent. I thought to build a cover that brings the front of the embrasure flush with the room, but that can be pulled out. I could leave the radiator off and build the cover (as much as possible) with whatever acoustic properties are needed. Continuing on up from the window sill level, I could build a set of stackable trapezoidal blocks to fill up the embrasure, if necessary.

Soundman2020 wrote:... Soldering work bench in centre of rear wall. - That might need to move a bit.

When you say 'a bit', do you mean a few feet off centre, or onto another wall? I have planned to leave room in the corners for bass trapping, although for the corner by the door, that trapping will have to be movable, to allow the door to open. Are you saying I may need to keep the entire back wall free for treatment? If I moved the soldering station to another wall, would this cause issues of asymmetry?

I will indeed do the tests and post a link for download. Would you have any thoughts about improvements for speaker placement for the testing? Also. I have a subwoofer. Should this be disconnected for the testing?

I am in the process of RTFM for REW, so if this is covered by that, then no need to respond.


Many thanks,
- Richard

Link to REW .mdat file:

https://www.dropbox.com/sh/o9oahysmjkxm ... eJaAa?dl=0

rjuly wrote:Link to REW .mdat file:

Excellent!

I downloaded that and looked at it, but it seems that you did not calibrate REW correctly. I did say "Calibrate and run the tests at 86 dBC with both speakers on (which implies 80 dbC for each individual speaker)." but your test was done at about 60 dBC. I'll PM you some instructions on how to calibrate REW and run the tests correctly.

That said, the room is basically an echo chamber right now! Decay time is around 1400 ms ... It is going to need a lot of treatment....

- Stuart -

Stuart,

Many thanks for your advice and information. I have uploaded an updated set of files to the link I posted above.

Regards,
Richard

Many thanks for your advice and information.

I have uploaded an updated set of files to the link I posted above.

Much better! Now you are triggering all the modes, and it's looking REALLY ugly, the way it is supposed to be! RT-60 is nearly two seconds But that's to be expected in that room, empty.

By the way, you can do all three measurements on ine single MDAT file: each time you hit the "Measure" button, it creates a new measurement and stacks it in the column on the left hand side of the window, and you can click in the tab just above it to name it, as well as putting comments in the "notes" area, below. You can get up to 30 measurements in one single MDAT file.

Anyway, your modal response is crystal clear: Here's a list of the first few modes, first as predicted, then as measured:

35.7 hz (1,0,0 Axial) 35.5
48.8 hz (0,0,1 Axial) 49.7
60.0 hz (0,1,0 Axial) 62.3
71.4 hz (2,0,0 Axial) 68.7
77.3 hz (0,1,1 Tan.) 77.3
85.2 hz (1,1,1 Obli.) 85.2
86.5 hz (2,0,1 Tan.) -
93.2 hz (2,1,0 Tan.) 93.6
97.6 hz (0,0,2 Axial) 99.6
103.9 hz (1,0,2 Tan.) -
105.2 hz (2,1,1 Obli.) 105.3
107.1 hz (3,0,0 Axial) -
114.5 hz (0,1,2 Tan.) -
117.7 hz (3,0,1 Tan.) -
120.0 hz (0,2,0 Axia) 120.6

The ones that didn't show up in the measurements are probably still there, just not triggered, masked by anther issue, or not measurable at the location where the mic was.

Here's the actual graphs o predicted modal response, and measured modal response:

PREDICTED:

MEASURED:
As you can see: a very close match.

So that's the good news! Your room behavior matches the predicted behavior very closely.

Now for the bad news: It's not a pretty picture! That room is going to need some serious treatment. As you can clearly see, the biggest issue by far is the 1.0.0 axial mode, at around 36 Hz. Major big-time bad boy. That's what I suspected, and is the reason why I suggested that your back wall is going to need a ton of treatment. You can set up your soldering bench in front of that, but you are going to need so serious heavy-duty bass trapping on the entire back wall...

Are you saying I may need to keep the entire back wall free for treatment?

Yep! The first axial mode is always that hardest to deal with, and in a long thin room like that, it's even harder.

I would suggest doing acoustic hangers across the entire rear wall, deeper in the corners, less deep in the middle. But the door is a problem! Alternatively, very deep superchunks in the vertical rear corners as well as the ceiling-wall corner, with the rest of the wall covered at least 6" (15cm) in something like OC-703, including the face of the door (as much as possible). That would not be as good as the hangers, but it is an option.

although for the corner by the door, that trapping will have to be movable, to allow the door to open.

Any chance you can move that door? It would be better if it were centered on the rear wall, and not so wide, allowing more space in the corners.

Another option: Build another wall across the back of the room, three feet in, and make that your "soldering closet". If your room ends up being about 12' 10" long (instead of nearly 16), that improves the room ration considerably (it puts it within spitting distance of Sepmeyer's first ratio, generally considered to be the best there is), and gives you the option of having a smaller door, centered in the back wall, with large superchunks on each side and above it, plus it gives you a small extra room, which could be your soldering station, or a vocal booth, or an isolation booth, or storage....

If I moved the soldering station to another wall, would this cause issues of asymmetry?

As long as it is behind the mix position, then you should be OK: Symmetry is critical for the front part of the room, but not so important for the rear. As long as there are no large reflective surfaces on the soldering station, that could work.

Would you have any thoughts about improvements for speaker placement for the testing?

Sure! Ideal for that room would be to have the speakers 47.2" above the floor, 29.5" from the side walls (implying that they will be 55" apart), tight up against the front wall (rear corner of speaker almost touching the wall). All of those refer to the acoustic axis of the speaker, not the top, bottom or sides of the cabinet. Then place your chair such that your ears will be 72" from the front wall. Set up a vertical pole (eg: mic stand) 12" behind where your ears will be, and carefully rotate each speaker on its stand so the are both aiming at the pole (not at your head!).

In other words, like this:
That's the theoretical best setup, or rather as close as I can get to it reasonably in that room. You didn't give the dimensions for the bay window, so I made a few educated guesses about that. If you give me those then I can refine it more, but it won't change by more than a fraction, I reckon.

Also. I have a subwoofer. Should this be disconnected for the testing?

No. It is part of the testing, since it is part of the "things that make a noise" in your room. First, you need to get the sub off the center line of the room! Bad place to be. Center it exactly between the two mains initially, such that it is perfectly aligned with them (acoustic axes in the same plane), then move it about 16" to the left or right (whichever you prefer) and about 5" closer to the front wall. If it won't fit like that (probably not), then rotate it 90° left or right and push it as far into the wall-floor corner as you can, the maneuver it so the acoustic center is as close to the above position as you can get it (16" offset from the room center line).

Now you need to re-calibrate your setup with REW, such that each of the three speakers by itself is putting out 77 dBC, such that the total level with all three will automatically by 86 dB (a little more, actually: about 86.5, to be precise, but that's fine)

Then you need to add four more tests to your set of measurements: --S, L-S, R-S, and LRS (where "S" refers to the sub. That's in addition to the set of three that you already did (L--, -R-, and LR-).

If you want, re-arrange things the way I outlined above, re-calibrate, and do the full set of seven tests in one single MDAT file.

OK, back to treatment:

You will also need superchunks in the front vertical corners, floor to ceiling, and as wide as you can make them.

Next will be 4" thick panels of OC-703 on your first reflection points on the side walls (use the mirror-trick to find those points). For your room, I would do a full 4' x 8' panel on each side of the room, starting about 22" above the floor and about 24" from the front wall (right where the superchunk ends).

Next, a pair of 2" OC-703 panels on the side walls (one each side) towards the rear of the room, starting about 30" from the rear wall, at the same height as the other panels.

Next, you will need a ceiling cloud, and I would suggest making it hard-backed and angled fairly steeply, maybe 10° to 15° or so. Use 4" of OC-703 on top, and another 4" underneath. Hang it at least a foot below the ceiling.

Finally, I would also add another panel of 4" OC-703 on the ceiling towards the back of the room. That could go flat on the ceiling (no angle needed), maybe with a couple of inches separation above it.

That should get you started on the first round of treatment, and should go a long way to getting the room under control. Do a REW test after you install each treatment device, so you can see how things are changing, what is working, what isn't, and what still needs to be done. You will probably need more treatment than that, but its a good start.

- Stuart -

@Stuart,

First of all, let me say "thank you" for taking the time to write out such a detailed analysis. It a lot to absorb . Since I travel a great deal for extended periods, it will take me some time to work my way through the various steps.

Since there are a number of furniture items that will definitely be part of the room, is it ok to undertake further sonics testing with those in situ (these being audio prod desk, low table and couch/sofa)? I have relocated the soldering station to another room.

Given the law of "pick any two of three" (time, quality, expense); I will be going for quality and time, since my budget is limited. I am prepared to go through an extended step-wise process, making changes one at a time, and fabricating all my soundproofing myself. I recognize that I am labouring under some physics constraints, and will be looking to go as far along the spectrum as is reasonable for the resources I have, especially as this is recreational.

An addition 'challenge' is that my building is 'A' listed, so I am severely hampered when it comes to making physical alterations to the fabric of the room. While I can attach panels etc, to the walls and ceiling, I won't be able to interfere substantially with the wood panelling (except to attach panels to it in the least destructive way possible). I believe this means that as much as I can, I will need to use freestanding bass traps and diffusers, possible attaching them to the wall with a layer of padding between...

Again, many thanks, and I will do my best to repay your efforts by taking your advice.

Regards,
Richard

Since there are a number of furniture items that will definitely be part of the room, is it ok to undertake further sonics testing with those in situ (these being audio prod desk, low table and couch/sofa)?

That's fine. The desk should be as small as possible.

I am prepared to go through an extended step-wise process, making changes one at a time, and fabricating all my soundproofing myself.

Smart move!

I recognize that I am labouring under some physics constraints, and will be looking to go as far along the spectrum as is reasonable for the resources I have, especially as this is recreational.

Take a look at the ITU document BS.1116-2. That lays out he final goal. It defines what the acoustics should be for a critical listening room. You might not be able to actually hit all of those, but that's what you are aiming for.

I believe this means that as much as I can, I will need to use freestanding bass traps and diffusers

It's a limitation, yes, but not huge. You can work around that, to a large extent. The biggest issue is treating the ceiling...

- Stuart -

Soundman2020 wrote:
You will also need superchunks in the front vertical corners, floor to ceiling, and as wide as you can make them.

- Of what material would the superchunks be made? The same as the other panels, or a less dense material?
- As the superchunk is a relatively broad frequency device, and corner real estate is so precious in terms of low frequency absorption, would it make sense to have some sort of tuned device(or two), such as a limp mass absorber, targeted to the largest nodal spike(or two largest) , perhaps at the base (or base and top)of the superchunk column?
- Would it be good to have a superchunk along the front wall-ceiling boundary as well?

-- Richard

- Of what material would the superchunks be made? The same as the other panels, or a less dense material?

Ideal wuold be Owens Corning OC-703, if you can get it. If not, then any semi-rigid fiberglass batt of around 30 kg/m3, aprox. Cut it into large triangles (very large!) and stack them floor to ceiling in the corners, then cover the front with thin plastic, add a nice frame with breathable fabric of your choice stretched across it, and that's it!

- As the superchunk is a relatively broad frequency device,

Actually, it is a deep bass trap. The plastic prevents it from sucking out too much of the highs. You can tune that to a certain extent by selecting the right thickness of plastic. Thin plastic only reflects back the very top end, thick plastic can reflect back way down into the low mid range. You can even fine-tune further, by cutting holes or strips out of the plastic in strategic places.

would it make sense to have some sort of tuned device(or two), such as a limp mass absorber, targeted to the largest nodal spike(or two largest)

That would hit one specific frequency, whereas you need to hit half a dozen, or more. It's also not as easy as you think to tune such a device: The text books make it sound like a piece of cake, with crisp exact equations and wonderful numbers and graphs... but reality isn't so simple. In addition, to fully deal with a very low frequency mode (such as 1,0,0), you need a rather large device that is very deep, and also has a lot of volume and surface area, in order to be effective. And considering that membrane traps work by resonating themselves at the tuned frequency, and the resonant membrane has mass, they can actually add to the problem by continuing to resonate after the mode already died away.... causing that frequency to "ring" even longer than it would have. Even a well damped membrane trap can still ring for a couple of extra cycles... which, at 30 Hz, adds up to quite a few ms... On the other hand, plain old porous absorption does not ring, does not need tuning, hits all frequencies at once, and is cheap and easy to build.

- Would it be good to have a superchunk along the front wall-ceiling boundary as well?

Definitely! Small rooms need lots of bass trapping. Put in as much as you can.

- Stuart -

Soundman2020 wrote:

I would suggest doing acoustic hangers across the entire rear wall, deeper in the corners, less deep in the middle. But the door is a problem! Alternatively, very deep superchunks in the vertical rear corners as well as the ceiling-wall corner, with the rest of the wall covered at least 6" (15cm) in something like OC-703, including the face of the door (as much as possible). That would not be as good as the hangers, but it is an option.

Yes, the door is a problem. Unfortunately, I can't build a wall due to regulation. Would it be better to ?:

- Place hangars across the entire wall, floor to ceiling, with the area of the door covered ceiling to top of doorway, and with OC-703 covering the door to 6".
or
- Place hangars across the whole back wall of the same height (ceiling to top of doorway), and the another method of treatment for the rest of the back wall.

Also, should there be super chunks along the rear ceiling/wall boundary. For that matter, should I have them on all ceiling/wall boundaries? I am assuming superchunks in the rear wall corners.

- Richard