Studio Sound Treatment

[Doublehelix]

I have read several articles about treating the studio for proper acoustics, and it confuses the hell out of me. Just when I think I have a plan, I read another article that turns my brain to mush.

This pertains mostly to monitoring and mixing as opposed to tracking...

My home studio is in my basement, and so far, I have no "wall treatments" other than felt pennets that my kids have hung up! I am not even really sure where to begin...bass traps? Acoustic tile behind my monitors (which are fairly close to the wall)...how do I decide? The room is approx. 15 ft. x 35 ft., with the monitors pointing toward the 15 ft. direction.

I have heard that at the absolute minimum I should get a couple of bass traps, a couple of tiles behind the monitors, and one or two above my head (on the ceiling) in my normal listening position. I have my monitors (Event 20/20 bas) on nice monitor stands, pointed at an equilateral triangle with my hear, etc...no subwoofer.

Do I need to get software, enter my room dimensions to find the standing waves, etc...??? I am pretty lost here! Any help would be appreciated.

 

[Sound Waves Rec.]

There is a formula that is available on-line to enter your room dimensions to calculate standing waves.

The only place where I know this is, is homerecording.com. I am a member there and asked about this not too long ago.

Look in the "Studio Building and Display" forum.

Sounds like you have the basics down. You may want to see what the formula says for different monitor placement options for your room size.

I can just picture in my head what would be going on if you placed them the long way. You really will need to get something on those walls for absorbers. The bass traps are a good start for the low end.

 

[knightfly]

DH, here's a link to the Excel spreadsheet I wrote about 12 years ago - it's one of the two mentioned at homerecording.com - go to this page, download roomtune from the "other application" section.

http://www.prorec.com/prorec/downloads.nsf/category

There are some basic directions included in the self-extracting file, if you need more I can help.

With no more than 15' front-to-back, you'll need some diffusion on the rear wall or you'll have smearing from too-early returns off the rear wall. Ideally you want at least 20 milliseconds between the direct sound and any reflections, which translates to about 19 feet round trip from your head to the rear wall and back. You might want to consider rotating the mix desk so that you face the long way in the room if possible. Symmetry around the mix position is also important. Any place you can put a mirror and see either speaker from the mix position, should have absorption such as Auralex or homemade fiberglass absorbers to control early reflections. Parallel walls should be treated with absorption/diffusion panels to eliminate flutter echoes. You can tell if this is REALLY bad by standing at the mix position and sharply clapping your hands. If you hear a boing, like you are in a rain barrel, you need a LOT of help. Even if you don't hear anything, if the walls are parallel it is there. In a small room flutter echo can easily be masked by happening too soon after the hand clap to be differentiated by your ears.

I know what you mean about the confusion factor, I've been studying this stuff for about 14 years off and on, ever since I built a room thinking I knew what I was doing - I still don't know, but I know more of what I don't know so I guess that's a step in the right direction.

John Sayer, who hangs out at homerecording.com, has a lot of really useful info on this subject - here is a link to a basic bedroom redo -

http://www.locall.aunz.com/~johnsay/HR/index1.htm

and here is a link to his SAE site, where I've learned a lot

http://www.saecollege.de/reference_material/index.html

click on everything there, plan to spend several hours. John has DONE it, while my info is about 90% study.

When you're even more confused, post back and I'll try to help sort it out for you... Steve

 

[Doublehelix]

Thanks Steve...I downloaded your file, and will check out the links!

 

[Kurt Foster]

Calculating the standing wave is great if your going to build a room from scratch but your dealing with a pre exsisting space. I don't think it will be of much help. It never hurts to know where you stand but what you want is to make your space useable. You didn't mention how high the ceiling was but if it's less than 9' (very typical in a basement) your going to have trouble with bass modes. Assuming the ceiling is of appropriate height , the safest way to approach this is to do a LEDE (live end, dead end) set up. Start with absorption on the front wall.
1. Run a 2 foot wide line of 2" foam along the ceiling where it meets all the walls.
2. Completly cover the front wall with foam at least 2" thick (except where your mounting the bass traps in step 3, ). Also the side walls and cieling up to where you sit at the listening position. You may leave the bottom 2 or 3 feet of the wall untreated. (This is the dead end)
The goal here is to insure that all you are hearing at the listening position is direct sound from your monitors.
3. Get some bass traps for the front and rear of the room. You need both the corner types like Auralex Lenrds and also something like the Auralex Venus Bass traps. These work on different frequencies and you will need both, especally in a low cieling room. You may also consider something like the ASC tube traps. (If you have the funds ASC will do a computer plot of the room and provide you with all the correct treatments.)
4. Diffuse the rear wall. This is most important. Do not try to substitute absorption in this area. It will absorb to much sound, forcing you to run your monitor system too loud, screwing up your bass and treble reference. It will also deaden the room too much and cause you use more reverb / ambiance than necessary. You may also want to add some diffusion on the side walls in the back half of the room (past where you installed the foam) and on the cieling above / behind the listening position. Diffusion is good but expensive. Use as much as you can. It is almost impossible to diffuse a room too much.
5. Symmetry in the set up is critical except on the side walls. You should try to have absorption and diffusion / reflective and dead surfaces opposing each other on this portion of the room.
6. After you do all this fire up some test tones and read the room with a spl meter and see what you've got. Pay particular attention to the frequencies below 300 HZ. That's where your going to get your bass modes. These will show up as spikes and nulls in the response, reinforcing and canceling out making it impossible to tell what is going on with the low end. If the response is too uneven you will need to add more bass trapping until you achive a reasonable room response. That should at least get you started. If you need any more help you can send me a private message and I will try to assist you any way I can. Fats
--------------------------------------------
"Everyone thinks they're Stevie Wonder"

 

[Doublehelix]

Whoa CF Fats...great message...thanks! One thing that was not clear was the basss traps...how can I use the LENRD and the Venus traps at the same time? One above the other? I think they are standard at 2 foot lengths. Do I go for the middle of the corner, or floor to ceiling with the bass traps?

Also, that is a ton of covering for the back wall and the side walls. Remember that my room is approx 35 feet wide!

If this is the *ideal* situation, what is the absolute *minimum* that I could get by with?

The other option might be to move the setup to the short wall, but that is a bit impractical at the moment the way things are set up. It would screw up the rest of the room design, I have a great space at one end that is used as a vocal booth (not fully enclosed, so it is not *really* a complete booth), and then there is a "sound proofed" closet for guitar amps. (The room is not an exact rectangle.

It is difficult to explain, and this forum is not the place to get into too many details, but just curious if there is a way to get some help with minimum coverage...the entire back wall and sides is just a huge, huge area, and would cost me an absolute fortune.

 

[Kurt Foster]

Doublehelix,
Absolute minimums:
1. 2' x 4' foam on the ceiling where the wall meets the ceiling, the whole room. Mount the foam so you have a 2' wide strip on the ceiling. When treating rooms with foam products, you should always do at least this.
2. Place 2 Lenrd style bass traps in each corner of the room. 2 to 4 Venus style Bass traps on the wall behind each of your main speakers.
3. Diffuse the rear wall behind the listening position.
4. 2 Venus bass traps on rear wall at each corner next to corner/ lenrds.
5. Hang some type of soft absorbtive matierial on the side walls to the point that you sit to listen / work. Area rugs , drapes, moving blankets, anything like that.
That's still a lot of treatments but it is what is needed. If this isn't enough to get a good result start adding stuff from the first list I gave you until you reach somthing that works.

Lenrds are a foam corner bass trap designed to fit in the corner of a room and venus bass traps are square / rectangular thick pieces of foam designed to mount on flat surfaces. Each type of trap works on different frequencies and it is important to use both types to achive desired results. You can go to auralex.com to check out these products. Auralex makes a great product but other companies manufacture these type of products as well and I am in no way specifiying or recomending these products. You can do a search on the web for acoustical sound treatments and perhaps find a less expensive source. I would still recomend the first list of things I gave you but this may be a way to at least get started with treating your room. You never said how high the ceiling is but if it's less than 9' DON'T cheap out.
Let me know how it turns out. Fats

 

[Doublehelix]

Hey Fats...I really appreciate the time you have taken, I will get to work, and will let you know how things go...You posts have really helped, I was getting so frustrated reading all these really confusing articles...I have ended up doing *nothing*! Now at least I have a plan. Thanks again! I should have this done within a couple of weeks.

First off, sorry I was confused on the bass traps, I thought they were *both* corner treatments (Venus and LENRD).

Secondly, the ceiling is at 8 feet...so yes, it is less than 9 feet, and will require the extra work.

I do have an Auralex catalog (and obviously their web address), but have also seen other ads in magazines, and will certainly search online. Even with the minimum treatments you suggest, it will not be cheap.

 

[Kurt Foster]

DH,
From what I can figure it's about 2 to 3 grand to do a full blown LEDE set up in your room. I'm glad to hear that you cieling is at least 8 feet. I saw a basment studio the other day that had a 6'2'' cieling! I couldn't believe it! You can check Marker Tech, they have foam and products that are less expensive than the other we were disscussing. Look around, you may find someone local that can give you a deal. This is a lot of dough and don't forget that this foam doesn't last forever. In time it will degrade and crumble / rot. BUt if you want to make your studio accurate this is what is needed. Good luck and please keep me posted....Fats

 

[Eric Best]

Hey DH, there are other options than giving all of your money to Auralex (and others). A lot of your problem can be addressed with sound absorbers of your own building. Most of the frequencies above 125hz can be absorbed by 4" of Ownens-Corning 703 rigid fiberglass in wood frames covered in burlap. You can use the same materials to make bass traps.

The room mode calculator that knighfly sent you to can tell you where you will have mode problems. You can make absorbers that will specifically target the frequencies, in addition to the normal bass trapping that you would use for a room.

The best purchase I ever made was a book called Master Handbook of Acoustics
http://www.amazon.com/dp/0071841040/?tag=r06fa-20

It details a lot of these things. It shows how all of these devices are built, so you don't need to purchase them.

Another link that knightfly already gave you is the one to John Sayer's site. He has absorber construction details too.

Eric

 

[Kurt Foster]

DH,
Eric is correct in what he says about ridged fiberglass although it can be difficult to find in the retail market. The only thing about building traps and absorbers is you need to be sure the calculations and sizes are correct so you get your target frequencies. The foam products however are a kind of sledgehammer or one size fits all solution. Pick the approach that best suits you and go for it! Fats

 

[knightfly]

DH, I just ran your dimensions in my sheet and another more involved one from Studiotips.com, and you will most likely have some really low bass modes, around 20-25 hZ. You also have coincident modes at 113, 133, 188, 201,235,240,283 and 304. these freq's would be more accentuated in that room, so would be good places to tune any DIY absorbers you made.

With that many coincident modal frequencies, Auralex or other foam could get quite expensive since lower freqs require thicker (4" or more) foam for any appreciable absorption.

Fats is right about the difficulty of finding rigid fiberglas such as Owens Corning 703 - Here is a link to one of the threads at one of the sites I use, follow the thread out and there's a few suggestions for sources.

http://groups.yahoo.com/group/acoustics/message/5474

Here's a couple more links, may help or confuse, probably some of each, but if you read it all I guarantee you'll know how much more you DON'T know, at least it sure works that way for me...

saecollege.de/reference_material/index.html"

saecollege.de/reference_material/index.html

moultonlabs.com/slides/smallrooms/index.htm

locall.aunz.com/~johnsay/HR/index1.htm

studiotips.com/


I really think rotating your mix setup 90 degrees and keeping it near one end, if that's possible, would help rear diffusion needs. that would give you more delay between direct and rear reflections and should cut down on the need for as much diffusion. Also, a cheap alternative for the diffusion you DO need could be a couple of large book cases (with books) at the rear of the room, arranged symmetrically either side of the median plane (a plane equidistant between the left/right speakers, passing thru your head when at the mix position) You'll understand my comments here when you price commercial diffusors such as AbFusors, QRD's, etc - Talk about getting paid for your ideas... Also, read carefully anything you find on "Poly's" they could help your room quite a bit. Happy reading, hope your eyes are good and your chair is comfy... Steve

 

[Doublehelix]

Here's a quick update...

1) I have rearranged the room so that I am facing the "short" end of the room (which has caused other problems, but we won't go there...). This change makes it easier to cover the back, since it is *much* smaller!

2) So far, I have covered the back wall behind the desk and monitors, and have LENRD traps in the corners...

Wow!!! What a difference!!! The sound just seems to jump out at me now! I never really thought the room was *that* bad, but now I am convinced that there were definite problems!!!

Thanks to all for your help...I have a few more pieces to add until complete, but I am making *huge* progress!!!

 

[Kurt Foster]

DH,
I found another source for acoustic foam, Markertek.com .....Check them out, they have everything! Cables, foam, mics, cases,everything..I calculated the cost to do my room the way I suggested you do yours,... $500!
At that price maybe you can flip the room around the other way again (that's the way I would set it up). Use the 4" blade tiles as bass traps. These are the same exact thing as the Venus Bass traps only they are cut into 16"x16" tiles. Markertek also has the corner bass traps at $20 each. Once again you will need both types of traps to cover the area between 20 Hz to 300 Hz. Finish off the wall behind the speakers and the ceilings with the 3" foam. It comes in 54"x54" sheets so this will aid in an easier set up. You will still need to get your diffusion products from Auralex but at least you can save a bundel on the foam.....Sorry I didn't get this resource to you sooner.............. Fats

 

[Doublehelix]

Yo Fats...Thanks for the link, I will check them out. I have already been there looking at cable and connectors. I will check out their acoustic foam.

The foam that I have already put up is 2", *not* 3", so I am not sure if I will have to replace what I have (I sure as hell hope not), add more 2" to keep it consistant, or switch mid-stream to 3"?

Thanks!

 

[Kurt Foster]

DH,
Your going to need the 4" foam in the corners next to the corner traps for additional trapping in the extreme low end. In my room I will be using, in each corner of the room, 2 corner traps and 6-16"x16"x4" thick tiles (3 on each side) to comprise a whole bass trap. These traps should be pretty effective in all but the worst situations. You can use the 2" foam for the ceiling and the walls. Just peel it off the walls carefuly and reuse it. If you do this your going to get as much additional improvement in the low end as you already have in the mids. Then when you add the diffusion to the back wall and the ceiling the whole thing will gel and your going to wonder how you ever got along without it........now, what about the tee vee room?........Fats

 

[Doublehelix]

OK Fats, I get it now, it makes perfect sense!

I checked out Markertek for the acoustic foam, and you are right...it is much less expensive than the Auralex stuff. Now I am sure that the Auralex products are great, but for a home basement, the less expensive product is going to be such a *huge* improvement over having nothing. So far, I have bought some 2 x 4 foot auralex foam tiles (I am so glad I bought the charcoal gray ones, since that is the only color that Markertek sells for the corner bass traps!). These were US$20 each. Markerteck is selling 16" X 16" tiles for US$3.99 each for the 2" ones and US$5.99 for the 4" ones...less than half the cost of the Aurlex tiles. Those big 54" ones look different than the smaller tiles. They look more like the "egg carten" design with foam rather than the blades. Do you think it will effect the sound to have 2 diff types? Heck, for the price of one of those 54" sheets, I would only get one 24" x 48" sheet from Auralex. The Markertek corner bass traps are US$20 each...I have no idea how much the Auralex traps are, but I am sure that they are much cheaper from Markertek. I did not see any diffusion pieces, just as you mentioned, so it does indeed look like Auralex for those...

Thanks for the heads up there Fats...you are going to be saving me some serious cash!

 

[Kurt Foster]

DH,
Yeah I thought that would make you smile... You can use both the egg carton and the blade styles, It has more to do with the deph of the foam as to what pattern is cut into it. For the deep 4" foam the blade cuts are better.........Fats

 

[knightfly]

DH, a good general rule for foam placement is this: Any surface, whether floor, ceiling, or walls, that you can place a mirror on and see either of your speakers from the mix position, should have absorption. Generally, this means foam on ceiling halfway between speakers and your head, foam on side walls (mirror trick) and absorption (foam) behind the speakers on the wall. Diffusion on the wall behind you can be anything from polycylindrical absorbers to QRD's to bookshelves, etc - the farther away the better.

Speakers should be at least 3 feet from any wall if they're not soffited, or bass will be exagerated. If nearfields are above ear height, point them down to aim at the ears. Some people tilt the console forward, so its surface reflections miss your ears and go for the back wall. By the time those reflections get diffused and back who cares? The main thing you need for best imaging is for no sound to reach your ears within at least 10-12 milliseconds, preferably 20 milliseconds, after the direct sound reaches your ears. This can be figured by rounding off - 1 foot = 1 millisecond isn't exact, but close enough to get there. Using that figure, 10 feet to the rear wall from your ears = 20 milliseconds before reflections return (both ways = 20 feet)

The more walls meet at a junction, the more bass build-up, so that's why corners are best for bass traps. What you're trying to do is convert (by friction) the bass freq's to heat so you can't hear them anymore. In actuality, air VELOCITY at a boundary (wall) is ZERO, since it can't go any further - this is why products such as 703, when used for bass traps, need to be thick and spaced out from the wall, AND hermetically sealed except for the path THROUGH the absorbent. If you have no velocity, you have no friction, and convert no bass to heat. Not good. Using this stuff in corners as a triangular trap, spreads out the freq response (different depth of the trap caused by the triangle shape) which, unless you're tuning for a specific frequency, is usually better. Fats' comment about foam around the ceiling perimeter would give a degree of bass trapping, more if thicker foam, as well as general absorption for the room. I would do this AFTER the mirror trick and AFTER listening to reverb time - you're trying to save money, and you could conceivably shorten the RT60 of the room TOO much if you do the perimeter thing first.

Odds are, the main reason you like your sound so much better with the length-wise setup is that the rear reflections are coming back so much later that they don't smear the stereo image by phasing/comb filtering, until your brain no longer cares. (20 milliseconds or more)

Sounds like you got it on the run James, good luck... Steve

 

[Doublehelix]

The advice I have gotten in this thread has been fantastic, and I really appreciate...Seriously! Steve...Fats...Eric...Senheiser...Guys, you have really helped a lot. I have been so frustrated by this topic for well over a year now, and everything I have heard and read just makes it that much more confusing...until this thread!

Sounds like you got it on the run James, good luck...

Yep Steve, I really think I do!!! Just by a bit of rearranging and hanging up US$100 of foam (so far, got guite a bit more to go...), my room sounds soooo much better! It is one of those things that I didn't realize sounded *that* crappy until I started fixing it!

I should get most of it done within the next week, and I'll post my results!!!

Cheers!