Land Lord Friendly Superchunks

[Crazy Daylight]

Hey All,

I just moved from Aus to Vancouver and my new room sounds like crap, its small 4.3 x 2.3 x 2.8 Meters and has no windows so its quite boomy, lots of strong modes. I produce EDM so the room will rarely have any live instruments tracked in there so I'm going for a fairly dead sound.

> On a side note, I made a tutorial video about how to make better mixes through knowing your room acoustics if anyone is interested in checking it out here. I'd love to get any extra input in to that knowledge in the video!

So I'm renting this place for a year or two (its a non commercials studio at homes) so I don't want to do any damage to walls by building extensive support for my superchunks so this is the build that I've come up with after checking out some other designs. It would be great if anyone wanted to give me criticism or advice about how this could be better etc:

1. Using roxul AFB with a density of 2.5 pounds per cubic foot because lighter is better for bass absorption.

2. Cutting in to triangles 24"x24"x ~28" and stacking up as high as the roof will allow ~5'

3. Putting giant garbage bags over the traps and wrapping the slack of the bag around itself then bonding the bag with spray on adhesive. This step is to keep the rockwool fibres enclosed and also hold it in place somewhat.
(this is the step I'd most like critique on) I will not be making the bags "airtight" like with a real trap, but air may be slightly restricted. Is that going to cause any issues? I just figure its a cheaper option than buying enough tight weave fabric to enclose all of the absorbers.

4. Then I'll wrap them in the most kitch looking bed sheets I can find from the local thrift store, throw them in the corners and get to making music!

If they seem unstable I might put in a single screw in the and run some string around the top to stop them falling over

Thoughts??

Cheers!

James

[Soundman2020]

Hi James, and welcome to the forum!

its small 4.3 x 2.3 x 2.8 Meters

So the height is 2.8m, and the width is only 2.3 m? That's unusual, but at least you have good height. You should try to make the best use of that in your design.

But yes, that's not a good ratio, and part of the reason why it sounds so bad.

I produce EDM so the room will rarely have any live instruments tracked in there so I'm going for a fairly dead sound.

So if this is the tracking room, where's the control room, and how big is it? Tracking rooms and control rooms need different treatment for their different acoustics. And since you don't track live acoustic instruments, there isn't really too much need for fantastic treatment in there: just enough to make it pleasant to work in. Since there won't be any mics recording in there, there's no need to have world-class acoustics (unless you want to, of course!) So this is just basically for tracking things like keyboards, electronic drums, and DI'd bass and electric guitar?

I made a tutorial video about how to make better mixes through knowing your room acoustics

Whoa! But that video is all about MIXING! From what you said above, it seems your room is a tracking room! Now I'm confused...

So this IS control room? As in a single, combined "all-in-one" room, for both tracking and mixing? If so, that's a very different situation. It will need lots of treatment.

I'd love to get any extra input in to that knowledge in the video!

Well, I'd suggest improving the accent of the instructor first! He sounds like an Aussie, or something.... (Sorry! Couldn't resist that! I'm also an Aussie living abroad, so I know what it's like to get comments on your accent all the time... )

One thing. I did notice from that video is the room sound is pretty bad: It's clear from the sound of your voice (regardless of the accent!) that the room is very reverberant, even in the mid range. So superchunks is not all that you will need.

I'd also suggest that instead of trying to use the DAW to analyze the room, that you show how to use REW to do it. That's what REW is designed for, and it does a fantastic job. In fact, it's the best tool I know of for doing basic acoustic analysis. That will reveal exactly where the issues are with the room. Then you can extrapolate the REW results into the rest of your suggestions. REW is also very accurate, and would help you avoid all the obvious uncertainty that you had in the video in trying to identify frequencies and notes.

I'd also suggest using a more comprehensive room ratio calculator, such as Bob Golds' or Andy Mel's. Those are the best ones I know of. At one point in the video you mention that you aren't sure at what point on the spectrum room modes are close enough together to not be an issue: you suggest 2k, but that's way too high: that's the transition from mids to highs. The answer is more like 200 Hz, the transition from lows to mids. I normally analyze up to 500 Hz, just to be safe, but for most typical home studios, the modal issues are below about 200 Hz. You can clearly see why if you look at Bob Golds' or Andy Mel's calculators, since they both show the modes overlaid on a keyboard, and you can therefore easily see at what point you start having more than one mode per note.

Using roxul AFB with a density of 2.5 pounds per cubic foot

That will work fine.

Cutting in to triangles 24"x24"x ~28" and stacking up as high as the roof will allow ~5'

There's something wrong there! If the sides measure 24" x 24" then the front face will be nearly 34", not 28". 34" superchunks are fine, but 28" is a bit small.

Also, if your ceiling is 2.8m high, then how come you only want to go up to 5' with the superchunks? Why not go all the way? Especially considering that modes terminate in corners, so it is more important to have the trap up in the ceiling-wall-wall tricorner.

Putting giant garbage bags over the traps and wrapping the slack of the bag around itself then bonding the bag with spray on adhesive. This step is to keep the rockwool fibres enclosed and also hold it in place somewhat.

That's not the normal reason for wrapping superchunks in plastic! The usual reason is acoustic: it keeps the highs in the room will allowing the bass through. You only really need to be concerned about fibers for the overhead treatment, on the ceiling: Your cloud will certainly need plastic underneath it, to keep those fibers out of your gear and off you! And superchunks need them to prevent them from sucking out too much of the high end. But other wall treatment does not need it. For example, putting plastic on your first reflection point absorbers on the side walls, would not be useful: in fact, it would defeat the entire purpose of those devices!

I will not be making the bags "airtight" like with a real trap,

The don't need to be airtight! Superchunks are not tuned: they are broadband. There is no resonant cavity in there, and no resonant slots, holes or membranes up front, so there is no need to seal them at all. The purpose of the plastic is not to seal them: it is just to keep them from absorbing too much of the high end, and making the room too dead. So all you really need to do, is to cover the front face of your supercunks with plastic: the sides, top and bottom don't need it.

so I'm going for a fairly dead sound

If it really is a control room, then it cannot be either live or dead: it has to be neutral. That's the entire goal and purpose of a control room: to not affect the sound of the speakers at all! Or rather, as little as possible. A control room should not "color" the sound, either on the frequency domain or the time domain (and therefore also the phase domain). It should be neutral, so that ALL you can hear is the clear, unchanged direct sound of the speakers. The room should be "invisible", acoustically. If it is either "live" or "dead", or if it skews the sound in some other way, then it won't be a good control room, and your mixes won't translate very well.

I just figure its a cheaper option than buying enough tight weave fabric to enclose all of the absorbers.

If you do cover them with fabric, then it should not be tight weave! Fabric for acoustic treatment should NOT affect the sound that passes through it. It should be "breathable" and acoustically transparent. It is only there for aesthetic reasons, not acoustic reasons. It "hides the ugly", keeping the actual guts of the acoustic treatment hidden from the room, while still allowing for the full and free passage of sound through it. Some of the best acoustic fabrics are made by Guilford of Maine, so if you do decide to cover yours, take a look at their catalog first. But in reality, and good quality fabric that is breathable will work just fine.

Then I'll wrap them in the most kitch looking bed sheets I can find from the local thrift store,

Provided that the sheets are mostly natural fiber (eg. cotton) and breathable, then that would work fine very likely, but I'm not so sure about the aesthetics! Take a look around some local fabric stores: you can probably find some inexpensive open-wave stuff that looks decent, or at least looks much better than a bed sheet!

If they seem unstable I might put in a single screw in the and run some string around the top to stop them falling over

Many forum members have built superchunks in a simple frame with plastic and fabric stretched across the front. The frame can just be basically a rectangular shape, like a picture frame, with the plastic and fabric. It can be attached to the walls or ceiling unobtrusively with a couple of nails or screws. It will hold your superchunk in place quite well, and also look good. Other members have built "superchunks on wheels", with a complete 3D frame all around, so that they can then just wheel the entire thing out to the moving van when they leave. You might want to consider those options.

Thoughts??

Before you do anything at all to your room, I'd suggest running REW on it, exactly as it is right now: empty and sounding really bad. That will tell you exactly what is wrong with the room, and orient you in how to treat it. Superchunks will certainly be needed, no doubt at all about that, but they will just be the beginning. You will also undoubtedly need the rest of the "standard" treatment that all small rooms needed: that goes without saying, too. And REW will also reveal where to put that treatment, and if you need anything more beyond that. If you then do additional REW tests after you install each device, then you'll be able to see the progress by comparing readings: so you'll see what is working at each stage, and what still needs to be treated. It's the only sensible way of treating a room, when you are just starting out learning acoustics. More experienced folks can pretty much decide what needs to be built and where to put it just by looking at the room and listening to it, but even the experienced guys still use things like REW to test and check along the way.

So those would be my suggestions!


- Stuart -

[Crazy Daylight]

Thanks for being so thorough with your answer Stuart! Its really weird living here, when someone comes up and speaks to me with an Aussie accent now, it takes me by surprise, like... whats wrong with this persons voice?? ohhh they talk like me haha..

So if this is the tracking room, where's the control room, and how big is it?

Might not have been clear here - this is the control room, I wont have a tracking room, because I'll be mostly using VST instruments. So yes, lot of treatment will be needed by the sounds of it!

Before you do anything at all to your room, I'd suggest running REW on it, exactly as it is right now: empty and sounding really bad.

I got excited and built the chunks before I saw this reply, they sound like they have bought the reverb time down a bit, but the modal activity is still quite audible, especialy in the sub range. I'm going to buy an SPL meter and run REW. Should I take the chunks out first? or run it with them in and build on what they are already doing?

I have left about 50 square feet of 4" rockwool left so once I have the data I can make some mid range absorbers with fabric.

Many forum members have built superchunks in a simple frame with plastic and fabric stretched across the front. The frame can just be basically a rectangular shape, like a picture frame, with the plastic and fabric.

I went ahead and made the chunks using garbage bags, mostly because my tools are back in Australia so building a frame isn't achievable right away. I put 5 layers of ABF in each bag, then stacked 3 lots of bags on top of each other to reach 60" height. The structure is stable, but would the fact that its non breathable adversely affect the low end absorption coefficient? The plastic is fairly loose, so air can move inside, but it is still isolated.

if your ceiling is 2.8m high, then how come you only want to go up to 5' with the superchunks? Why not go all the way?

I just remeasured and I made a mistake they are only 1.95 M. The 2.8 was the distance from the rear wall to the closet. So yeh, this room keeps getting worse, haha! Corrected dimensions 4.3x2.3x1.95

There is also a protruding ventilation duct on the roof that hangs down 10 cm on the long wall and 40cm on the short wall, here's a rough plan to give better detail:


Maybe I could put in some corner panels above the chunks?

[Soundman2020]

they sound like they have bought the reverb time down a bit, but the modal activity is still quite audible, especialy in the sub range.

Yup, that's the way it goes in small rooms: the smaller they are, the more bass trapping they need. Yours will need a LOT of bass trapping, since the ceiling is so low. You might even have to do some of the horizontal corners, too, in addition to the vertical ones. You have probably taken care of some of the modes, bringing down their decay time a bit, but obviously not enough yet!

I'm going to buy an SPL meter and run REW. Should I take the chunks out first? or run it with them in and build on what they are already doing?

You'll also need a measurement mic, or a good omni mic that has flat response. Take care to calibrate REW correctly before you test: You need to calibrate your audio interface ("sound card" in REW jargon), and you also need to calibrate REW to reality in terms of SPL levels: If you don't tell REW how loud it really is (as measured with your hand held SPL meter), then REW has no way of knowing, and basically just guesses: it normally guesses way wrong, so make sure you do the calibration for that.

I put 5 layers of ABF in each bag, then stacked 3 lots of bags on top of each other to reach 60" height.

That's about 1.5m, but your ceiling is 1.95, so there's 45cm of empty gap up top with no trapping: That 45cm is the most effective place in the room for bass trapping! The "tri-corners" of a room are where all modes terminate, so they are the best possible place for putting bass traps. You are guaranteed of hitting all the modes at those locations. But since yours are empty, you aren't hitting them...

but would the fact that its non breathable adversely affect the low end absorption coefficient?

No problem at all. That will be fine. Low frequency sound doesn't even "see" the plastic at all, and just goes straight through. High frequency sound does "see" it, and reflects back to the room, which is good!

here's a rough plan to give better detail:

Bingo! There's another issue that needs to be fixed: you have your speakers firing across the room (short axis), but they should be firing down the room (longest axis). There are several reasons for this, but the two big ones are:

1) Your head is located roughly in the geometric center of the room, which is the worst possible location! It is the peak point for all first-order modes, and the null point for all second-order modes. So you have the worst possible combination of modal response at that location.

2) Your head is too close to the rear wall, and you will be hearing reflections, LBIR, comb filtering and other nasty things well within the Hass time. That's bad.

So you need to turn your orientation 90° to face the short wall and have the speakers pointing down the long axis of the room. Set up your desk so that your chair and ears will be about 38% of the distance from front wall to back wall. That's the ideal best starting point. Set up your speakers with the correct geometry too, then do some tests while moving the speakers / listening position by slight increments (a few inches at a time), to find the best possible location. Then treat.

That gets' your head out of the central modal null, and also gets your head far away from the rear wall.

. . and run REW. Should I take the chunks out first? or run it with them in and build on what they are already doing?

If you can take them out easily, then yes, take them out. Run REW, put them back, then run REW again. And run REW every time you change something, such as adding more treatment, or moving things around.

But there's an important issue here: the first time you run REW, you will set up the mic exactly where your head will be while mixing. You then need to measure the exact location of the mic in the room, taking the precise distance to fixed points in the room, so you can always return the mike to the identical location every single time you do a new test. If you don't, then you cannot validly compare subsequent readings to what changed. The mic MUST be in the precise same location, to within a few mm, for all readings.

- Stuart -

[Crazy Daylight]

OK, I've got my graphs plotted, I took the measurements using just one monitor, I assume thats the right way to do it under these circumstances... here is what I ended up with. Pretty massive trough at 130 Hz!

Waterfall


Frequency response



I didn't take the existing chunks out because the desk in the new position is in front of then and it would be too much effort! I'm going to extend the superchunks to the ceiling and put in some first reflection absorption then run another test this week.

[Soundman2020]

OK, I've got my graphs plotted, I took the measurements using just one monitor, I assume thats the right way to do it under these circumstances...

We'll need the actual MDAT file, to do the analysis. Please post it to some sort of file-sharing service, such as DropBox, then post the link here.

Also, it looks like you either did not calibrate REW using a sound level meter, or you ran your tests at a level that is way too low. You need to be averaging around 80 dB for each individual speaker (86 for all speakers at once), and it looks like you are way below that. Did you calibrate?

- Stuart -