Studio Sound Treatment

Posted: Mon Sep 30, 2002 12:31 pm

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

Posted: Mon Sep 30, 2002 2:20 pm

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

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! Smile

Posted: Mon Sep 30, 2002 4:42 pm

DH,
Yeah I thought that would make you smile... Very Happy

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

Posted: Tue Oct 01, 2002 4:53 pm

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

Posted: Tue Oct 01, 2002 6:26 pm

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!

Quote:

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!

Posted: Wed Oct 02, 2002 12:51 am

DH and Knightfly,
The reason I specified the foam around the ceiling perimiter is to eliminate the dihiedral and trihedral corners. It helps to put this up before you do the walls as it help the istall look a little cleaner. I don't think it is overkill and it is always where I have started. Plus it looks really cool..... Very Happy

Fats

Posted: Wed Oct 02, 2002 9:40 am

Hey Fats, I agree that's a cool way to go - the only reason I mentioned the minimalist way was that James was starting to sound a little "sticker shocked" until he found the Markertek prices so I was trying to get him as far for as little as possible. I like the idea of "fat foam" at the corners, you would kinda get double duty out of putting it there, as you pointed out.

I think we've just made a "convert" - I can tell James has seen (heard) the light (sound) - it's always amazing when you first hear what you've been missing and realize that not all the acoustics hype is hype... Steve

Posted: Wed Oct 02, 2002 10:19 am

Knightfly,
Just wait until he gets the diffusion and the bass traps finished! The traps I suggested will run about $75 for each corner from Markertek ( Very Happy

CHEEP!

) and they should be effective in the ranges of 50 Hz to 350 Hz.! I was going in the same direction as you as far as trying to minimise the "sticker shock" factor and that's one reason I specified the foam on the ceiling around the parameter of the room. It should help to control upper bass freqs in the room and it may reduce the amount of foam that will be needed to cover the side walls. The side walls should only be treated to the mix position and in many cases it is only necessary to stagger the foam. That is if one wall has foam on it on a given section it is not required to use foam on the opposing section of wall. Especially if you have the luxury of having 15 feet width! IMO it's more important to consider standing wave rather than flutters and early reflections in this situation. I have to stress that diffusion is the element that is going to need to be addressed next. After the treatments are complete, just wait until you hear what a mic sounds like in this room....keep the kleenex handy!.....Fats

Posted: Wed Oct 02, 2002 10:30 am

By the way, the best way to cut foam is with a table saw or an electric carving knife....Fats

Posted: Thu Oct 03, 2002 8:34 am

Never tried it with a table saw, but I absolutely LOVE the electric knife... Steve

Posted: Fri Oct 04, 2002 2:07 pm

OK...I am putting together my shopping list for Markertek for this weekend, and a I have few more questions/comments: (just when I *thought* I understood things!!!)

I did some more measurements of my room, and here is a more accurate picture of what is there:

It is in reality a very long "L" shaped room, with a very small "L" part (I hope that makes sense). When I look at the room blueprint, it shows the dimensions as 30' x 15', but that is not quite true for a couple of reasons. First, there is a staircase at one end that shortens the length dimension from 30' to 27'. Also, only the *wide* part of the "L" is 15', the narrow part (where the mixing desk is) is really only 11' wide (bummer). I also checked the ceiling, and it is 7'7" (in decimal feet that is 7.58').

The "L" part of the room is 4' wide x 10' long, and I am just pretending that it does not exist for purposes of calculations...

So I guess I have the following numbers to plug into RoomTune:

27 x 11 x 7.58

After plugging in these numbers, what does the program tell me? Are all of those red bars the standing waves? Can you help me to interpret the data?

Do I need diffusion on the ceiling as well as the back wall? For the celing, how much foam and how much diffusion? I am still a bit confused here I guess.

Fats: As far as the 4" foam next to the corner bass traps...you add 16" of 4" foam along *both* sides of the traps? And what is the deal with the ceiling wall junction and the 4" foam, I guess I missed that.

Steve: Unfortunately, I do not have the space to put the monitors 3' from the walls...they are about 18" now, and that is pushing it.

For the back wall (behind the monitors), do I need to put foam from floor to ceiling, or just from the top of my desk to the ceiling?

Whew! Almost got it licked! Thanks!!!

Posted: Fri Oct 04, 2002 3:20 pm

DH,
You asked a lot of questions so here goes;
" Are all of those red bars the standing waves?"
I'm guessing that they are the room modes.
"Can you help me to interpret the data?"
Not without seeing it.
"Do I need diffusion on the ceiling as well as the back wall?"
It would help, once again you can never have too much diffusion. Anywhere. I have seen rooms that employ no absorption, only design and diffusion. That's the real hip room set up nowadays.
"For the ceiling, how much foam and how much diffusion? I am still a bit confused here I guess."
Just as with the side walls, you may cover the ceiling with foam to the point where you sit. (your listening position) Typically this is about 1/3rd to 1/2 of the room.
"Fats: As far as the 4" foam next to the corner bass traps...you add 16" of 4" foam along *both* sides of the traps?"
Yes.
"And what is the deal with the ceiling wall junction and the 4" foam, I guess I missed that."
I would use 2" foam on the ceilings and the walls. Save the 4" stuff for the corner bass traps.

"Steve: Unfortunately, I do not have the space to put the monitors 3' from the walls...they are about 18" now, and that is pushing it. For the back wall (behind the monitors), do I need to put foam from floor to ceiling, or just from the top of my desk to the ceiling?"
I'll leave this for Steve, who you addressed it to but if there is no answer or if you would like my slant on it I'll return to answer.

Posted: Sat Oct 05, 2002 1:21 am

James, the red bars are a chart of the frequencies of each axial mode of the room, as entered into the L, W, AND H cells. The left scale is frequency, and the bottom legend notes which mode each bar represents. For example, L5 would be the 5th harmonic of the Length mode, and W3 would be the 3rd harmonic of the Width mode. The ideal, at least for a room with parallel walls, is that no two modes are closer than 5-6 hZ, and that there are no gaps in response greater than 20-25 hZ. The only way to change these figures is to move a wall or raise a ceiling, so if your room is already built then Roomtune can only alert you to the likely frequencies that will cause problems with getting an even response in that room, so that you can plan absorption, bass traps, resonators, etc. accordingly.

I plugged your dimensions in and, while they're not ideal, they don't suck too much. You might have some noticeable peaks at 100 and 150 hZ, but the bass traps and 4" foam should take care of that. I then plugged your room into a more esoteric sheet I found (fortunately) just before I was going to expand on mine, and the modal distribution looks OK in that sheet also. Some low bass problems, but no room smaller than about 4000 Cu.Ft. isn't that way.

On the monitors, you should shoot for 3 feet and take what you get. If they have rear firing ports, the bass boost will be more exagerated. About all you can do if moving away from the wall isn't an option, is use any roll-off switch they might have, or in the absence of that option I would use Fats' technique and apply 4" foam about 2 feet wide across the bottom of the rear wall, across the top of the rear wall, up the corners next to bass traps, so there is 4" foam framing the rear wall about 2' wide as well as vertical 2' wide 4" foam on the two side walls abutting the rear wall. On the rest of the rear wall, 2" or 3" should be enough, since bass buildup is worse at walls/floor/ceiling. You can compensate somewhat for bass levels without resorting to electronic EQ in the monitor path, by mixing at a little lower or higher than the optimum 85 dB - even though that level puts things in a relatively neutral part of the Fletcher-Munson curves, you can lower it to 80 to lessen the perceived bass or raise it to 90 to increase it. I wouldn't recommend raising it though, 85 is about it for OSHA safe levels for 8 hours without hearing protection.

Oh, and don't put your speakers exactly halfway between the floor and the ceiling - dead center between ANY two parallel surfaces is one of the two worst places you can put a mic or speaker or sound source - the other is right against a wall. If you have to raise them to get them away from the half-way height, make sure you set them on a tilt so that they point directly at your ears, not over your head. Nearfields are touchy about keeping the baffle, and therefore the woof and tweet, time-aligned to your ear. Don't set them on their sides either, especially if you have a fairly tight triangle - your head is more likely to move side to side during a mix than up and down, and if the monitors are on their side you will experience HF phasing shifts due to unequal distance from woof and tweet relative to your ear.

Fats, feel free to chime in here, especially if you've experienced otherwise - a large part of my acoustics info is based on about 14 years of part-time study while being able to put very little of it into practice other than sporadically. I hope to drastically change that ratio in the next year or two, but there's a reason why one of my favorite sayings is the one that goes "Life is the shit that happens to you while you're busy making plans..."

James, hope this helped some. IF Fats has opposing ideas based on practical experience, I would go with that. Books help, but nobody ever learned to ride a bike by reading a book... Steve

Posted: Sat Oct 05, 2002 7:35 am

OK...I am crusing on over to Markertek right now, and will be ordering most of the pieces I need (minus the diffusion, obviously). I am going on a trip Mon - Thu, so the stuff will hopefully be here when I get back, and I can start my sawing! I don't have an electric carving knife, so I'll probably take the primitive approach and use my stone axe!!! Smile

Hehe...

Once again, I was down in the studio last night working on a mix until about 1:00 am, and just by adding that 2" foam to the back wall behind the desk (from the desk to the ceiling), it sounds 1000% better, so I am excited by the prospect of how it is going to sound by the end of the week!

You guys have been great (and patient)...thanks! Smile

Posted: Sat Oct 05, 2002 9:04 am

Knightfly,
Wow, I'm impressed! :tu: All that is great info. I agree with everything you brought to the table. I was going to say the same thing about using 4" foam around the parameter of the front wall. Lets all get on the same page here so there isn't any confusion. When I say "front wall " I mean the wall you face while you're at the listening position. I call the wall that is behind you at the listening position the "rear wall". OK that said, it looks like you on the way my friend. Now it's time to get the foam up and then shoot the room with pink noise. Get a RTA plot of it. This will show where you need to do some improvements.......Good Luck, Fats
P.S. don't forget the diffusion

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