Basement tracking room, Reno nv. question about room ratios

[JeromyReno]

im building out a room in my basement for tracking guitars and some drums(a tight dead drum sound for metal, i already have a 800sf drum room). im not as much worried about making noise or bothering my neighbors but i would still like to contain a lot of it. im more just trying to make the room sound at it's best than anything. it is a tiny room and i know im going to need a whole lot of treatment. im going to frame out an inner leaf with walls made of metal studs to decouple all the walls and ceiling, and insulate with roxul safe n sound, and drywall nice and air tight.. i will be limited to about a 6'5" ceiling if i get tricky and run the ceiling rafters between the joists.
getting a ratio to work out well with a 6'5" ceiling doesn't give me many options. the room i'll be building in is 10'11" x 11'11".

if i build the room with a ratio of 1 : 1.5 : 1.6 (77" x 123.2" x 115.5") it looks pretty good on the http://www.bobgolds.com/Mode/RoomModes.htm calculator.

the walls already up in the room are wood 2x4 construction with roxul comfortbat and comfortboard with no drywall facing.

my real question was if the extra space left to be an air gap will be 6.25" on two of the sides. would it be in my best interest to make the room 12" wider and add another 6 inches of treatment on two walls and have a bad ratio or should keep the best ratio i can. i already have enough roxul safe n sound to make 9" deep traps all the way around. i know safe in sound isnt as effective after 8". would a good ratio have an advantage over an extra 12" of treatment.

sorry if this is long winded for a simple queston, just trying to get the most information i can about the project out there.

ill be doing a lot of guitar reamping in it, and drum sampling in it.

i'll get some pictures when i get home.

[BobJ]

if i build the room with a ratio of 1 : 1.5 : 1.6 (77" x 123.2" x 115.5") it looks pretty good on the http://www.bobgolds.com/Mode/RoomModes.htm calculator.

Hi Jeromy, i'm also building a small studio. Interested in the above RoomModes calculator. How does this work? Is it pretty much all good if you get results in green? Sorry, not very clued up on this. Many thanks

[JeromyReno]

if i build the room with a ratio of 1 : 1.5 : 1.6 (77" x 123.2" x 115.5") it looks pretty good on the http://www.bobgolds.com/Mode/RoomModes.htm calculator.

Hi Jeromy, i'm also building a small studio. Interested in the above RoomModes calculator. How does this work? Is it pretty much all good if you get results in green? Sorry, not very clued up on this. Many thanks

Oh hey,

Yeah as far as I know it is used to calculate where modes over lap front to back, side to side, and up and down. I used a ratio that was close based on my roof height cause it was the most confined. I just wiggled around numbers until I got something that would fit inside the foot print of the pre existing room. I will have a ton of base trapping in there witch will probably throw it all off over 250hz but anything I can do to reign in below that will be pretty critical.

On that calculator page there is a picture on the bottom right that shows what's good and bad on the graph and i kinda used that to fine tune it.

I could be 100% wrong though haha, I have read and looked up everything I can find and I'm still laxking knowledge in a lot of these areas.

[Soundman2020]

Hi there Jeromy, and Welcome!

tracking guitars and some drums

Just checking: That's the sole purpose of this room? For tracking guitars and drums? It does not also need to function as a control room?

i will be limited to about a 6'5" ceiling if i get tricky and run the ceiling rafters between the joists.

You should be able to do better than that! What is the height of the bottom edge of the floor joists above you? IN other words, the clear span from your floor surface up to the lowest "thing" above you?

A 6.5" ceiling for tracking drums is going to be pretty bad. You will be getting pretty nasty comb-filtering artifacts in your overheads, due to the very close proximity of the ceiling. If you put the mics down lower to minimize that, you mangle the clean overhead sound and start to get too much focus. And if you move them up high to get a clear general sound, then you get comb filtering! Murpy's law: you can't win no matter what you do, so we need to get the acoustic height of your ceiling as great as possible.

getting a ratio to work out well with a 6'5" ceiling

This is a tracking room, not a control room, so you don't need to be too worried about ratios.

the walls already up in the room are wood 2x4 construction

That's the framing visible on the right in your photo? And that is one of your inner-leaf walls? If so, then why is it touching the joists above it? Also, why is there only a single top plate, and why is there no space to put the inner-leaf ceiling joists on top of the top plate? There's something major wrong here....

I would suggest taking down that framing, and re-building it correctly, as an inside-out wall that is fully decoupled from the rest of the building.

my real question was if the extra space left to be an air gap will be 6.25" on two of the sides. would it be in my best interest to make the room 12" wider and add another 6 inches of treatment on two walls and have a bad ratio or should keep the best ratio i can.

Forget about ratios: This is not a control room, so ratios are but much of an issue. What you need to do is to maximize the air volume inside the room, and get the ceiling as high as possible (the acoustic ceiling, not necessarily the visible ceiling).

So make the room as wide as you can, use inside-out construction all around, and build it as a completely isolated room that does not touch any point of the existing basement structure.

i already have enough roxul safe n sound to make 9" deep traps all the way around.

That would make your room sound very dull, boxy, lifeless. Drums need more life than that (yes, even "dry", dead, metal, drums). You don't want your kick sounding like a wet cardboard box being slapped by a dead fish! Nor do you want your snare to sounding like a trash can lid covered with carpet... You still want the "snap" of the snare, and the "tick" of the beater hitting the kick. Those would be lost if you make your room sound like the interior of a pillow.

i know safe in sound isnt as effective after 8".

Really? Where did you read that? Because wherever you read it is a place you can safely ignore from now on, as they don't know what they are talking about. I often build bass traps that are 24" deep (or even deeper) with that type of insulation, and I can assure you that it works REALLY well, much better than if I just build them 8" deep! Basically, the thicker you make it, the further down the spectrum it will absorb. 8" will absorb flat down to about 120 Hz, but room modes, SBIR, "boom", and other unpleasant things have far longer wavelengths. 24" is flat down to about 39Hz, and there's not much below that, that needs damping.

sorry if this is long winded for a simple queston,

No problem! It's better to explain the question clearly, even if it takes more words.

- Stuart -

[JeromyReno]

Thanks so much for your reply soundman2020,

Yeah the floor joists bottoms are about 6'7" from the floor, I was going to leave a ½" air gap then double up ⅝ drywall on the ceiling, and the thinnest flooring I can find so I'll be down to about 6'5" in the end.

This room will only be for tracking, I am running snake cables threw the walls to another room that will be a mixing room. Also not very big room but over 8' ceilings at least.

That's great news about the roxul, I read on gearslutz that the air flow raiting on the safe n sound wasn't great on things over 8 inches thick but that is awesome if I can just keep stacking up more for even better absorbsion. I have quite literally more bats of safe n sound then I can fit into the room haha.

The wood framing is just to hold the comfortboard 60 and comfortbats that insulate the house, the frame isn't structural or anything it's just what they recommend for insulating basements. I'm going to start framing the inner leaf frame out of metal studs tomorrow. It won't come into contact with anything already in the room. I'm going to leave an air gap between all the walls and ceiling.

Thanks for all the advice, hopefuly I'll have something to show off tomorrow after I get something framed up.

[Soundman2020]

the floor joists bottoms are about 6'7" from the floor,

Wow! That's really low. Not much chance you are going to get good acoustics in there for drums. Any possibility you could dig down, and move the floor lower?

and the thinnest flooring I can find

Question: Do you really NEED flooring? You have a concrete slab, I assume, and that's hard to beat for a good acoustic floor. Unless there's something terrible wrong with it, I'd just use that as your floor, and save the headroom.

I am running snake cables threw the walls to another room that will be a mixing room. Also not very big room but over 8' ceilings at least.

OK; I would seriously consider flipping the two rooms. Use this one as your control room, and the other with much higher ceilings for your drum room.

I read on gearslutz that the air flow raiting on the safe n sound wasn't great on things over 8 inches thick but that is awesome

The parameter that matters is gas flow resistivity, and it is measured in the strange units of MKS Rayls per meter. It's actually a measure of acoustic impedance. The way you measure it goes like this: If you create an air pressure difference across a sample of the material, of arbitrary thickness, such that the air pressure is higher on one side and lower on the other side, then air will flow through the material. The ratio of how much air flow you get (measured in meters per second) for a certain pressure difference (measured in newtons per square meter, or Pascals) is the gas flow resistance (not resistivity) for that specific sample. So 1 rayl = 1 pascal-second per meter, or 1 newton second per m2. If you divide that number by the thickness of the sample that you tested, then you get the gas flow resistivity in units of rayls per meter (pascal seconds per m2, or newton seconds per m3), which is independent of the thickness, and is a characteristic of the material itself. Now you can figure out what the gas flow resistance would be for a piece of the same material, of any other thickness. Sometimes people get confused by these two terms, because they sound almost the same, but resistivity is not resistance. If you know the resistivity, then you can calculate the resistance of the piece you have in your hand, and yes, obviously, a thicker piece will have higher gas flow resistance than a thinner piece, but they will both have the same gas flow resistivity.

Safe-n-sound has a Gas Flow Resistivity of around 10,000 rayls per meter.

So is there a difference beyond 8" thickness? Does it make sense for me to use 24" thickness, instead of just 8"? You be the judge:

Here's the predicted coefficient of absorption for 8" thickness of safe-n-sound against the wall, vs 24" of safe-n-sound against the wall:

safe-n-sound--diference-8inch-vs-24inch--absoprtion-coefficient.jpg

As you can see, above 100 Hz there's no difference, but below 100Hz there's a significant difference, and the lower you go, the better it gets. So for bass traps, yes, there's an interesting difference.

But when you look at the difference in the actual impedance, things get more interesting!

safe-n-sound--diference-8inch-vs-24inch--impedance.jpg

Yup, I'd call that a rather useful, and rather significant difference: So the person who said that there's no need to use more than 8" of safe-n-sound for bass traps is not correct.

I have quite literally more bats of safe n sound then I can fit into the room haha.

Then you have almost enough!

Seriously, I'd use some of that to make "superchunk" style bass traps in the corners of your room.

The wood framing is just to hold the comfortboard 60 and comfortbats that insulate the house, the frame isn't structural or anything it's just what they recommend for insulating basements. I'm going to start framing the inner leaf frame out of metal studs tomorrow.

So in theory you could gain back those extra inches, if you could use another method to hold up the insulation.... such as an inside-out wall, for example... If you build an inside-out wall that ends up in the same position as that framing, then it would keep the insulation in place, and you'd have a larger room...

- Stuart -

[JeromyReno]

Soundman2020 you make a great point about the flooring. I can probably just clean it up, and paint it or acid etch and seal it.

That picture was kind of deceiving cause I didn't have the comfort bat installed yet cause I was still waiting for it to arrive. It is kind of it an inside out wall like you where saying. It has 1" hard board then 24inch studs to hold the r15 in place between them.

I used to use the room next to this one to track drums before and mic placement for over heads was a nightmare for sure. That room is embarrassingly covered in foam and diffusers, everything just sounded confusing haha, that was over ten years ago before I had any understanding of sound pressure in rooms or absorption.

I was thinking of killing the room and adding diffusion to try and bring it back in a measured and controlled way. I could do 1 or 2 walls 21"~24" deep with roxul then add diffusion with angled slats and and try to dial it in with a reference mic.

I would swap the rooms but the other room that will be a control room has the only bathroom and closet in the house connected to it and it's only a 475sf house that's over a hundred years old.

[JeromyReno]

I didn't get half as far as I planned this weekend, but I cut down anything that didn't need to be in the room to get every extra inch I could, caulked in any air passages with elastomer, sealed and blocked off all the old vent holes and pulled out the old ducts, I filled all the walls with insulation and the ceiling with safe n sound, ran flexible conduit from room to room and ran the snake cables threw the walls, I used flexible mc but I plan on wrapping it with a mastic tape to make it air tight. .

I got a question though. My floor joists above are built out of 2x6, I'm going to use steel struts between them to hold up the ceiling, so I'm not sure how I should go about insulating it, should I leave a lot of air, do double roxul with an air gap between them, or stuff as much roxul in there is I can(maximum mass) without it touching the inner leaf (kinda what I was leaning towards cause I don't know any better.

All n all not a bad weekend worth. I am filming it in time lapse and even doing little videos of how and why I'm doing some of it so other people can get ideas or just see how easy it is and not to be scared to try stuff them self

I'll try to figure out how to post the time lapse photos here