confusion over acoustic treatment design

Posted: Thu Jul 24, 2008 1:19 am

Hmm I like this studio construction forum, hopefully someone can answer a few questions I have about my project.

I have a room to be used as a control/mixing setup and I could use some tips on placing absorbers and possibly diffusers. The room is 24' long, 11' wide, 8' high (weird dimensions fo sho). Right now it is a bare concrete floor and 8" double walls with drywall all around. Nothing else is in the room. In one back corner there is a doorway which opens against the backwall, so any backwall treatment has to allow that door to open. In the other back corner it disappears with no wall into the garage and an entryway, so it's like a phantom corner. The monitors will be positioned on the frontwall which has 11' width side to side.

The echo in the room right now is very lively, of course. Here's my questions for trying to treat this as a mixing room:
-How should I treat the backwall?
-How should I treat the frontwall/front sidewall area for an accurate stereo image?
-Should I use basstraps in the forward corners? If so, how many axises?
-Because of the low height of the ceiling, what kind of treatment can I use up there?
-How can I clean up room modes?
-Any other tips on how to make the room sound good in other areas beside the mixing spot, like while sitting on the couch for instance.

Thanks for any info you guys can give!

Posted: Thu Jul 24, 2008 7:00 am

Can you hook up some pics?

Or a floor plan. I can visualise only so much.

Posted: Thu Jul 24, 2008 12:29 pm

Okay here is a pic of the frontwall. Where the boombox sits is the general monitor location except raised to be in middle of floor and ceiling. Don't mind the mess, drywall and windows need to be replaced.

Here is the backwall and the phantom corner.

The right monitor's line of sight.

The left monitors's line of sight.

Where the couch will be placed.

I just had an idea of diffusers on the ceiling, a bit behind the mixing spot. It should even out the echo a bit I think, and spread more sound across the room.

Posted: Thu Jul 24, 2008 1:47 pm

PLEASE follow this link to Rod's READ THIS BEFORE YOU POST... or read it below...

Either way, you will not receive much help without at least some of Rod's minimum required information being a part of your post.

Rod Gervais wrote:

Finally I have to put up one of these.

Before you post please make certain you do the following:

IF YOU FAIL TO DO THIS STEVE AND I WILL NOT RESPOND

Use the search feature to look for threads that may contain the answer to your question. There is a wide variety of projects represented in this forum -- everything from relatively low-budget residential rehearsal rooms to full-scale, professional recording studios. If your searches return too many results, try multiple terms with "Search for all terms" enabled.

If those efforts do not lead you to the answers you need, you are welcome to post your questions on the forum. If you do so:

Edit your profile to include your location. This is very important, because this is a worldwide resource, and as such, material costs and availability vary widely. For example, masonry is cheaper than gypsum in some parts of the globe, whereas it's the exact opposite in other regions. We're not asking for your address or credit card number, just a country will do.

Start your post with an overview of your goals and where you are in the process... Research? Planning? Construction already underway? Finished, and wanna know why it doesn't work?

HOW LOUD are you, and how picky/loud are your neighbors? How close? This is subjective, so you will need to buy something like the Radio Shack Sound Level Meter

Trust me, if you're recording/mixing music you should be using this ALWAYS, so it's not a waste of money. For music at typical mix levels, you want to use "C" weighting, slow. The human ear has no way of "measuring" ABSOLUTE sound levels; it just adapts to what's there, and calls that "normal" - so if you keep raising the volume, pretty soon you're mixing at 110 dB, ruining your hearing and neighbor "atta-boy" points, etc - the SPL meter helps you keep levels constant and safe.

For all other tests, the authorities virtually ALWAYS use A weighting, and (I think) slow response. So for compliance, use "A" weighting measurements.

Include as much detail as possible about the existing construction. Having details about anatomy of your existing floor, walls, and ceiling is critical. In your searches of the forum, you'll likely find examples of the kinds of details that are needed, and you'll see that the quality and timeliness of the advice given are affected by the level of detail provided.

Please don't tell us you want to float your floor if you are building on an upper level - this is almost always impractical, and ALWAYS will require a LOCAL ENGINEER to verify that it will be safe.

Remember that acoustics is THREE DIMENSIONAL, not two - when you give dimensions, we need Length, Width, Height, plus any NON-parallel features of the room.

Include drawings of what you're describing if at all possible. They do not need to be professional or perfectly to scale, but they do need to account for the necessary details. Cropping your drawing will allow you to make the important parts larger and more legible without increasing the overall size. See next...

Please resize as necessary to keep graphics BETWEEN 700 and 750 pixels wide - otherwise it's either too small for details or it forces people to scroll sideways to read every line of text.

If you link to pix OFF this site, please make sure THOSE pix aren't oversized either - it causes the SAME PROBLEM.

_________________
Rod Gervais
Acoustics Moderator Sometimes - late at night..... when the wind whips
through the trees........ and the moon shines bright in my
face......... I think deep thoughts.......... and my head hurts.

Rod Gervais' book "Build it Like the Pro's" is an excellent source of information.

You can also try the search function of the forum for what you are looking for.

Posted: Thu Jul 24, 2008 5:02 pm

Loudness level will be about 100dB SPL max. More likely to be used around 85.

The concrete floor is a part of the room's sound. Plus I prefer it over hardwood or carpet. It gives the echo a large space quality that I think will help mixing audio for a larger environment. The main goal of the treatment is even bass response, accurate stereo image in the sweet spot, and a half second echo. The echo right now lasts about .8 to 1 seconds. Any advice is very appreciated.

Posted: Thu Jul 24, 2008 5:46 pm

The first step (and in my experience the only step that makes a "holy crap" difference) is putting as much bass trapping as you can in as many corners as you have access to. All the other stuff makes a real difference, but nothing measures up to your first bunch of bass traps.

Posted: Thu Jul 24, 2008 6:03 pm

Scale them for: "Please resize as necessary to keep graphics BETWEEN 700 and 750 pixels wide - otherwise it's either too small for details or it forces people to scroll sideways to read every line of text.

If you link to pix OFF this site, please make sure THOSE pix aren't oversized either - it causes the SAME PROBLEM." /Rod

As per http://www.recording.org/ftopict-36851.html

Posted: Thu Jul 24, 2008 6:28 pm

I know scrolling is annoying so I fixed them. I just use the middle scroll button... life's easy!

Posted: Thu Jul 24, 2008 6:36 pm

Doesn't work on Linux Wink

For me anyway, damn gaming mice with specialised drivers.

Seems well planned out. I'm probably out of place in asking, how does the room's concrete floor make it good for mixing for large spaces?
"It gives the echo a large space quality that I think will help mixing audio for a larger environment."
I really don't get that (acoustics isn't my forte) but again, I don't get that.

Posted: Thu Jul 24, 2008 7:10 pm

Codemonkey wrote:

Doesn't work on Linux Wink

For me anyway, damn gaming mice with specialised drivers.

Seems well planned out. I'm probably out of place in asking, how does the room's concrete floor make it good for mixing for large spaces?
"It gives the echo a large space quality that I think will help mixing audio for a larger environment."
I really don't get that (acoustics isn't my forte) but again, I don't get that.

Heh I guess it just doesn't sound like the usual carpet and drapes. How often do you listen to music in a place with a concrete floor? Not the ipod, not the car (unless its really loud), and most usually not the house.

Posted: Thu Jul 24, 2008 8:35 pm

"Nothing else is in the room." /quote

Actually there is a big hole in the room. You might see it as a window. I see it as a hole. Bass traps are good but holes are not good, in respect to how it interacts with your listening pleasure. As for that concrete floor, you'll get a rug, I don't know when and I do not know of what size it will be, but there is an area rug in your future.

Posted: Fri Jul 25, 2008 5:44 am

camsr,

Looks like a 60's-70's style ranch. In the first picture, I can see a tree and what is either another part of the house, or you've got a neighbor that's right next to you.

You've got two big holes, that could actually be 3-4 in the long run.

The worst is the window, then the door(s) then the hallway leading out of the living room.

One thing to remember is that mass is your friend... and you need lots of friends to keep from disturbing your neighbors.

While I know it's popular to jump in and start working and getting the room augmented to become a control room ASAP... DON'T DO IT!

Think about a couple of things and plan this bad boy out a bit more. It will save you a LOT of money, headaches and grief in the long run.

1st... look for a mode calc spreadsheet. Eric Desart's and Bob Golds are both excellent tools. You should find out what nodes you are going to have as known problems. That will give you an idea as to whether you should be getting used to the idea of any kind of specialized trapping or diffusion or not.

Next, your walls don't have enough mass to stop 100db of low frequency energy from leaking out into the street. That's partly why Rod asks about neighbors, etc. If you are right on top of a neighbor, you will likely need a lot more mass. If your nearest neighbor is 10 acres away... it changes the construction issue quite a bit.

Since you don't mention neighbors, I'll assume the pic is of a very close neighbor's home. You'll likely need to beef the walls AND the ceiling up with some added mass... off the top of my head, I'd say at least one more layer of 5/8" fire rated drywall with Green Glue in between the layers. More if you like.

Which brings up the subject of electrical. Adding the gypsum is going to mean moving your electrical boxes out with what are called mud-rings. If you are so inclined, you can easily DIY, but realize, you should be comfortable doing so. Otherwise, get an electrician.

And that gets down to the big nasty... permits and inspections. Anything sub-major like this can possibly go either way as far as needing permits.

I'd suggest making a general inquiry with a coupla of contractors to suss out whether they would need permits to do the work. If they seem at all wishy-washy... call the inspectors and ask them.

If they indicate that you do. GET THE PERMITS AND INSPECTIONS! If you are required to get them and you don't, the problems can be serious. Including the building being condemned, fines and lawsuits from anyone and everyone you can imagine.

One last thing to remember... if air can get in/out of it... so can sound.

Posted: Fri Jul 25, 2008 9:07 am

MadMax wrote:

You've got two big holes, that could actually be 3-4 in the long run.

The worst is the window, then the door(s) then the hallway leading out of the living room.

The window is being replaced with a double-pane and new framing. Any suggestions for that? Also the window stretches into the front-sidewall first reflection area quite a bit, so I was thinking of a kind of "wallblock" that I could put up and take out of the windowsill. It would be of the size to extend that sidewall to the same length before the other walls hole, the door. I can get a new door so I will consider a heavy one. As for the rear side door, it is less of an issue with the neighbors. The house you see in the window is the only neighbor that might complain. The phantom corner just runs into the house and won't be a problem.

As for any wall construction, that might be out of the question. This should be easy to deconstruct to the original room. Serious wall construction changes are out of my time and skill budget anyway.

Posted: Sat Jul 26, 2008 5:07 am

camsr wrote:

As for any wall construction, that might be out of the question. This should be easy to deconstruct to the original room. Serious wall construction changes are out of my time and skill budget anyway.

**** DANGER **** WARNING ****

When someone all of a sudden says time is more important than the quality of the room, that speaks volumes.

You cannot defy physics. It takes mass and an airtight seal to reduce sound energy from moving from one space to another. ESPECIALLY low frequencies. If you had just said you have a tight budget, that would be one thing, but when you put time above a budget... that indicates that you really don't yet understand what it takes to build a good room.

There are less expensive ways... but they aren't cheap ways to build out a room. Yours is quickly sounding like another case of "there's gotta be a cheap way to sound like a recording studio... let's just throw some foam on the walls and call it done".

If that's the case, then just knock together a coupla' frames, stuff em' with mineral wool and make yourself some hanging bass traps on the reflection points. Get 8 bales of mineral wool, leave em in the plastic and stack two in each corner. Don't bother with OC703, because the difference it makes, you'll not be able to justify the cost difference. Then, line the room with cheap foam, so it's totally dead and devoid of any accuracy.

Viola!

Instant recording studio in a weekend for $500.

Look, cam, you don't have to do a full on build... but you gotta do more than just slap some stuff on the walls. If you're really serious about the craft of recording and you really want to be able to have a decent environment to mix in... you are gonna need to spend some time running the numbers and trying to determine things like what and where the main nodes are... establish a budget to deal with your problem frequencies... then execute that budget... test your room and then treat the room for accuracy.

You've potentially got the start of a decent small room.

It's up to you whether you're gonna do it right the first time, or if you're gonna cheap out and regret not doing it right and end up spending a LOT more money in the long run... and will probably only have a marginal room. At which point, it would have been smarter to spend your money at a real studio.

Adding a layer of gypsum and extending your electrical with mudrings is about the cheapest thing you can do. Using Green Glue is the most expensive part... but it's like adding two more layers of gypsum... so it's a wise decision as far as economics go, IMHO. And, if need be, the room is only 1.25" smaller (5/8" each wall) when you sell or vacate the property.

Clean the concrete floor, acid stain and seal it. Then take some acoustic tile and put it on the ceiling. That will get you a hard floor/soft ceiling environment that should make getting the accuracy of your room in a much more attainable state.

Again, in the end, you've invested in the property and it can become a selling point in that the room would make a dandy home theater or ultra quiet livingroom.

If you want a removable plug for the window, it's gonna have to be in several pieces. Either that or it's gonna take 3 men and a small boy to heft it in and out of place. It needs to be an air tight seal, and have at least as much mass as the wall it's going into.

No, I'm not Rod, Eric, Andre or even Ethan, as far as my being a structural engineer or acoustician. However, I can tell you with a good deal of certainty that this plan of a quick and dirty control room that sounds good just doesn't make sense. There are some shortcuts to making a decent mix room, but none of them start with skimping on the addition of mass to your walls and ceiling unless you have good room ratios and existing high mass walls.

Posted: Sat Jul 26, 2008 5:45 am

MadMax wrote:

.....If that's the case, then just knock together a coupla' frames, stuff em' with mineral wool and make yourself some hanging bass traps on the reflection points. Get 8 bales of mineral wool, leave em in the plastic and stack two in each corner. Don't bother with OC703, because the difference it makes, you'll not be able to justify the cost difference. Then, line the room with cheap foam, so it's totally dead and devoid of any accuracy.....

I think Max is being only somewhat sarcastic here. Other than lining the room with cheap foam, this a pretty good recipe for making a huge improvement in the acoustic quality of the room. (Of course, it does nothing for isolation.) It is only a little less than what I did to my room. After reading Rod's book I decided that if I was going to do it "right" it would have to be in a better space than what I had in my house. So I decided to go with some simple room treatments and I've learned to live with the inadequacies (e.g., I don't record during prime lawn mowing time). The room looks good and is an acoustically pleasant place to play and record music. Didn't take a lot of work or cost a huge amount of money. To me the big danger is getting into the grey area where you do a lot more work and spend a lot more money and only make a small improvement over the quick and dirty approach without really doing it right.

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