John Sayers' Recording Studio Design Forum Archive

Hello all!
I have been lurking here for a number of months while designing and building my electronic music mixing/mastering room.
I have attempted to treat the room with a broadband approach because of my lack of knowledge and the size of the space. I created a decoupled room inside of my garage that (first reflective surface) is H: 8'-7 1/8" W: 11'-2 1/8" L: 16'-4" (Louden #2 ). The ceiling is entirely absorbed (2" rockboard 60). The floor is reflective. And all of the walls are absorbed with a combination of 2" rockboard 80 and 3" safe n sound. The back of the room is layered; 2" rockboard 80, 2" rockboard 60, and then 3" safe n sound. The side wall treatments are angled at 6 degrees, from flush to the wall of the room, to 1'-10 3/4" air gap at the front of room. Bass Traps are filled with Comfortbatt r15.

Now I am preparing to install slats over the front end of my room. My sidewalls are not truly sealed and so will not act as resonators. Too much potential for error for me to want to go that route; I would rather a more broadband approach.
I intend to use REW as I go as well as my own ear to taste for liveness. But I need a starting target for what percentage of absorption makes sense. I have read a lot of people suggest something on the order of 25% absorption. I've read also that less than 10% is resonator territory whereas above 20% is slat absorption territory. But when I look at the actual designs they are building, I get something much closer to 15%.
After some research, my own design came out to about 13% which seems like very little.
To be honest, this topic is obviously much deeper than I am prepared to deal with in a very tangible manor. However seems as though I should be able to approach it practically given the information I do have and the intended use. I just need some clarification on what the differences are between these ranges for slat absorber percentages also considering the small size of my room.



*Side note I am SUPER grateful to the contributors of this forum for all the information I have taken from here. I fully intend to provide a complete slideshow/plans for the studio I have built when it is finished as most of what I have done, I have taken from this forum.

Welcome to the forum!

Why didn't you post your design before you built it? The reason I say this is because your design looks very odd and appears to be a three leaf construction! I also do not see any HVAC in your design.

I created a decoupled room inside of my garage that (first reflective surface) is H: 8'-7 1/8" W: 11'-2 1/8" L: 16'-4" (Louden #2 ).

I'm not sure where you got your calculations, but your dimensions fail the 1.1w / h < l / h < ((4.5w / h) - 4) test.

Your ratio is closest to Louden's, but it isn't Louden's ratio.

Your room is only 192 sq ft. The minimum recommended room size for a critical listening room is 215 sq ft. That doesn't mean your room can't sound good. But it may not live up to "world class mastering suite" standards. What this means is that you need to be VERY careful with your room treatment. So I'm glad you're here reaching out.

The ceiling is entirely absorbed (2" rockboard 60).

Why didn't you use Rockboard 40 instead? It has way better low end performance? Also, why didn't you completely fill (or at least 4+ inches) your inside out ceiling modules? 2" is fine for treating the higher end of your spectrum but the ceiling can greatly improve the bottom end if you use appropriate insulation and have it deep enough!

The floor is reflective.

And all of the walls are absorbed with a combination of 2" rockboard 80 and 3" safe n sound.

Any reason you chose that insulation combination?

The back of the room is layered; 2" rockboard 80, 2" rockboard 60, and then 3" safe n sound.

7" of insulation on the back wall. That's decent. If you want a mastering room, you are going to need 24+" thick back there though. Same question as above, why did you use that combination of insulation?

The side wall treatments are angled at 6 degrees, from flush to the wall of the room, to 1'-10 3/4" air gap at the front of room.

Looking at your diagram and the fact that you want a mastering room, I assume you soffit mounted your speakers? 6 degrees or 16 degrees doesn't matter though. What matters is that you did ray tracing in SketchUp and you made sure that you designed your wall angles such that you have at least a 2ft diameter sphere of RFZ around your head.

Bass Traps are filled with Comfortbatt r15.

After some research, my own design came out to about 13% which seems like very little.

What you just described to me is that every single surface of yours has absorption except your floor. How does that only work out to 13% of your room?

I intend to use REW as I go as well as my own ear to taste for liveness.

It is VERY important to use REW with an empty room to measure what we call our "baseline". If you look at some of the control room treatment threads on the forum you'll see why. There's no way you'll be able to tell how many milliseconds your decay time is at each frequency. REW is a wonderful tool we must use if we want an accurate listening room.

But I need a starting target for what percentage of absorption makes sense. I have read a lot of people suggest something on the order of 25% absorption. I've read also that less than 10% is resonator territory whereas above 20% is slat absorption territory. But when I look at the actual designs they are building, I get something much closer to 15%.

Here is a good starting point:

RT60 (ITU/EBU Control Room Recommended): 190 ms
- ±50ms from 200Hz to 4kHz = 140 to 240ms
- <+300ms at 63hz = 490ms
- 200<RT60<400ms
Absorbtion to achieve ITU RT60: 402 sabins
Volume: 1568 ft^3
Surface Area Total: 836 ft^2
Surface Area Floor: 182 ft^2
Surface Area Ceiling+Floor: 364 ft^2
Surface Area Front Wall: 96 ft^2
Surface Area Front and Rear Wall: 192 ft^2
Surface Area Left Wall: 140 ft^2
Surface Area Left and Right Wall: 280 ft^2
Surface Area 4 Walls: 472 ft^2
Surface Area 4 Walls + floor: 654 ft^2
(sabins - front wall - carpet) / Left+Right+Rear wall: 32 %
(sabins - front wall) / Left+Right+Rear wall: 81 %

The thing is, none of these numbers take your listening position into account. These numbers are a general way of achieving the correct RT60 target. Having a baseline REW mdat file and goals (clearly described in documents such as ITU-R BS.1116-3 or the EBU Tech 3276), each new piece of treatment installed has a purpose. I hate to say it, but if I were you, I would rip out all of the insulation and take a baseline measurement and start from there.

I just need some clarification on what the differences are between these ranges for slat absorber percentages also considering the small size of my room.

Again, read some of the control room treatment threads:

Here is a great one: http://www.johnlsayers.com/phpBB2/viewt ... =2&t=21368

This shows you the proper procedure for treating your room. If you're in over your head, I'd recommend reaching out to John Sayers and see if he's willing to take on your room treatment. If he can't do it, he can recommend someone else.

*Side note I am SUPER grateful to the contributors of this forum for all the information I have taken from here. I fully intend to provide a complete slideshow/plans for the studio I have built when it is finished as most of what I have done, I have taken from this forum.

I'm glad you're here (whatever your name is --> please tell us). I just wish you would have posted earlier so that we could have walked through your design entirely before you started building it. Having said that, let's start RIGHT NOW with you posting a bunch of pictures of your plans and build so far so we all know what was done. If anyone is going to help, they need to know every detail of the room so far.

Greg

My name is Justin (24 yo)

Sorry I am not sure how to properly format the quotations here but I will respond in order to your queries:

I SHOULD have posted my design before I started building that is for sure. I did not because I did not know enough to validate such a post when I began. The context for this build should probably be mentioned as well because it's fair to say I have rushed things a bit. I was sort of forced into building this room as an alternative to where I have been working because I had new neighbors move next to me and start causing me trouble legally. Without getting into the weeds about how that all went (because it is insane), suffice it to say I was working entirely within the law however the new neighbors have a family member in the local PD and this caused me a great deal of trouble and put all of my music work on hold. It became either spend money on a lawyer or a new studio as I saw things. Meanwhile I was spending money to keep going back to court about this situation regardless and so as a result I got tossed into the fire a bit needing to learn about studio design and build a workable thing in as short a time as possible. I rushed things a bit. To be completely honest, this project came not only out of necessity, but with monetary constraints as well because I am a starving (not actually obviously) artist and did not intend to undertake this project this quickly; without savings and a loooong plan to do so.

The HVAC has baffle boxes with 3 fins in each on the output and input. Soft duct. Driven by a an overrated fan which is completely inaudible while running. The heating and cooling is being done with a minisplit system, slightly overrated for the room again. The evaporator unit is to be installed over the door next to the supply duct (I know I know over the door but best place for it and it's more than enough to not matter). In my sketchup the room vents are at the opposite corners of the room from reality but the placement is the same. Originally I was gonna place the evap unit on the opposite wall.

For the dimensions of my room, I may be slightly off with what I listed here I shall check again but I was confined to the ceiling height and width and so best I was able to get was 1 : 1.3 : 1.9 H:W:L for the Louden #2. If not mistaken my room is 8'-7 1/8", 11'-2 1/8", 16' - 4".

I had a hard time locating any rockboard at all even at a premium for shipping and was not able to get access to rockboard 40 whatsoever. I was lucky to be able to get 60 tbh.
I am not entirely sure I know what you mean by "inside out" ceiling modules but I should mention that on top of that, is 16" of cellulose. As well as my walls are all pressure packed 3 psi, 9" thick.
..
The reason I chose that insulation combination is because it was recommended to me by fellow producers who have done a similar thing and seemed the most widely agreed on combo on the forums I read. I had understood that was the proper density for the thickness I am able to have.
Regarding the back wall... it is 7.5 inches of rockboard and sns with about 1'-10 5/8" bass trap in front of that (measured at the corner). The major constraint here being the door, and trying to maintain a workable space in the room.

I am soffit mounting my speakers in the 30 degree traps ideally but I need to make a speaker upgrade before I will take that step. However I have built with that in mind.
According to pure theory I should have the RFZ zone that you mentioned.

What I meant about the 13% is that based off the research I did, the design that I thought to use for my slats, worked out to 13% absorption which, if I'm not mistaken is also about what John's 2-3-4 pattern listed here works out to provided you had equal amounts of 1/2, 3/8, and 1/4 spacings. And that is not considering the ceiling or floor since I imagined that those cancelled out in terms of reflection/absorption surface.

I will take some measurements as soon as possible (perhaps today if I can get the mic from a friend) but I don't really know how to properly translate that info to my slats specifically. I am not super confident about tuning specific Q with what I have done so far.
This information that you have provided however looks like the solution and so I will have a good sit down with this and the baseline measurements when I have them so as to glue the pieces together in my feeble brain.

I guess it's also true that I am a bit embarrassed about the monetary constraints here (which I have already exceeded) and I have gotten quite far on a project that is probably a "best I can do" with what I have rather than a truly proper build as I wish I could bring to this forum to discuss. Similar mentality that lead me this far before posting.
That said, my goal is not entirely perfection here. Already this is many magnitudes of order upgrade from what I have had. But I am a bit ashamed I did not ask for more direction early on. I took a lot of advice from fellow engineers that have done similar projects and it's fair to say they have nice studios but not as nice as what you folks do here.

I took mostly video of my build so far but I have some photos of the actual treatment and interior of the hard room as well as a complete sketchup of the build:

I totally understand and respect your situation.

It's impossible for you to get a baseline now with all of your insulation cut perfectly and covered in fabric. So I guess the thing to do from here is take measurements following this procedure:

http://www.johnlsayers.com/phpBB2/viewt ... =3&t=21122

From there we will see how it currently sits!

How is your isolation now with your police officer neighbor listening intently? Are you satisfied with your build other than how it sounds acoustically now?

I am soffit mounting my speakers in the 30 degree traps ideally but I need to make a speaker upgrade before I will take that step. However I have built with that in mind.
According to pure theory I should have the RFZ zone that you mentioned.

Unless I missed something in your pictures or SketchUp, you have pure absorption everywhere. Your soffits are not soffits. They are insulation holding frames. That is all. When you get your new speakers, you will have to tear down the front half of your room and rebuild it properly using very heavy framing and very very hard, thick, rigid sheathing to direct the sound towards your rear wall.

Your room looks cool so far anyway! Now let's try to make it sound cool.

Greg

It was impossible to get a proper baseline due to lack of backordered door and lack of time which combined to "need to move forward cannot wait". By the time the door came, a lot of the treatment was already in the room. But I got a couple reference mic's from my friend yesterday. I noticed the article mentioned specifically NOT Behringer ECM8000 (which is one of the two my friend lent me lol). He also lent me the one that is part of the Arc system. My acoustician friend said he would rather trust the third party mic but that the trouble with the Behringer is that it's not linear, however that it comes with a calibration file individual to the mic that compensates for that. I suppose I can just use both and see what the consensus is.
I do have an Extech meter (became necessary with the neighbor thing to prove my sound levels).

My intention is to today, take a measurement and begin adding slats starting from the back of the side walls and the front wall. Avoiding the FRP's. Measure, add slats, measure add slats, etc.

Isolation is definitely enough. And I am otherwise quite pleased with the build.

You didn't miss anything in my current build except perhaps the amount of room I have to work with at that end of the room. I have about a 2' soffit as it is behind the drywall that will allow me to create a proper soffit in the future should I desire. However I would very much like to have a pair of Barefoot MM-27's and so I may just wind up not soffit mounting at all.

the trouble with the Behringer is that it's not linear,

That's one of the issues, yes, but there are others. Basically: quality. There are many reports of grounding issues with the ECM8000, so that it picks up mains hum very loudly. I can attest to this first hand, sine I was one of the "lucky" ones who ended up with a mic just like that. But it seems to be a common problem with these mics. One day I might try to open it up and see if I can fix it, but I'm not hopeful.

however that it comes with a calibration file individual to the mic that compensates for that.

It does not come like that out of the box (but it should). You have to jump through hoops to get your calibration file, or take it to a third-party calibration company and get it calibrated properly.

I do have an Extech meter (became necessary with the neighbor thing to prove my sound levels).

My intention is to today, take a measurement and begin adding slats starting from the back of the side walls and the front wall. Avoiding the FRP's. Measure, add slats, measure add slats, etc.

What will you be looking for with that? Are you planning to tune the slats, as Helmholtz resonators, or leave the un-tuned as purely reflective / partially diffusive devices? In any event, as Greg mentioned, your room is going to be very dead right now, and will likely need a lot more than just slats to get it usable. What is your target decay time?

I'm looming forward to seeing your data from your first test.


- Stuart -