help with control room bass trapping

audio hobbit · Post by **audio hobbit** » Tue Jul 15, 2003 11:19 pm

Hey all, I am working for a studio that i did not spec out and it turns out that I have a huge low end problem.. mixes that leave the CR are massively bass heavy in the 40-60 hz region and they sound fine in the CR.. I am thinking bass trapping, but I am unsure how much.. the room dimentions are ( brace yourself) 19'9" long, 15'5" wide with a 7'6" ceiling for the first 4 feet and then 8'. my console is centered on the 15'5" wall, about 3' from the glass ( there are 2x 6' wide by about 32" tall glass windows into the cutting room) and I am using genelec 1031s on stands. the mixing end of the cr is pretty much covered with auralex 2" wedge foam, and there are several of the auralex "t-fusors" on the back wall, and two auralex bass traps in each back corner. thereis also a fabric couch and love seat along the back wall and the rear of one side wall.. there is also a 2'x4' section of foam directly above my head as i sit at the console that is flanked by a pair of t-fusors.

I am thinking that I neeeed to ditch the diffusiors and install so0m bas trapping n at least the rear wall, but I am really shooting in the dark here...

giles117 · Post by **giles117** » Wed Jul 16, 2003 1:25 am

Ethan Winer sells bass traps your you can DIY them.

Me, personally, I'd consider building a rear wall design consistent with one of Johns designs as seen on the SAE sight.

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

If you look at the absorbers/Low frequencies page you will see a diagram of the rear of the control room. AS your room is 19.75 feet deep, you have some room to play with to build out a bass trap wall.

Bryan Giles

As for the Auralex Bass trapping (Lenrd's), they should go ceiling to floor (4 in each rear corner) and I'd add 2 venus flytraps on that back wall.

audio hobbit · Post by **audio hobbit** » Wed Jul 16, 2003 2:17 am

ok.. looked on the SAE site.. do you all suggest the hangars, or the panels? also do I alternate the directions of the hangars, or all one direction?..

Ethan Winer · Post by **Ethan Winer** » Wed Jul 16, 2003 3:24 am

AH,

> mixes that leave the CR are massively bass heavy in the 40-60 hz region and they sound fine in the CR <

Yes, this is a very common problem.

> I am thinking bass trapping, but I am unsure how much <

The more bass traps you install, the flatter the low end response will be.

> two auralex bass traps in each back corner <

Those are ineffective at the frequencies you mentioned. Even panel traps do little that low unless you make them very large. How did you determine that 40-60 Hz is the main problem range? For most rooms having standard sheetrock walls, the biggest problem is between about 80 and 300 Hz. Frequencies below that tend to go through the walls, and even be partially absorbed by them. Also, the bass instrument "speaking range" is from 80 Hz and up, so that's where low frequency absorption does the most good.

As Bryan said (thanks Bryan!) my company sells bass traps, and they will do a great job for you. You'll need several of them to really flatten a room that large, but our MiniTraps are not expensive at all. Especially compared to what you've already invested in outboard gear.

Have a look at the MiniTraps page on our web site, here:

www.realtraps.com

--Ethan

Post by **John Sayers** » Wed Jul 16, 2003 9:12 am

Hobbit - the low end problem you have is very typical. Firstly, how do regular CDs sound on your genelecs?? is there plenty of low end matching your mixes or do they sound light on the low end compared to yours?

Bryan's suggestion of treating your rear wall with traps could be a good idea but you must get the genelecs setup correctly to start with.

cheers
john

audio hobbit · Post by **audio hobbit** » Thu Jul 17, 2003 10:36 am

John, I ahve the gennies set flat on the bottom with a 2 db rollof on the top. I have set them this way in 99.99% of rooms I have been in for the last 7 years ( sorry, I jsut realized that came off a bit like a prick.. ) When I first came int this room, I was thinking that wow, the 1031's are bottoming out quick, then I realized when I left that the mixes were crazy bottom heavy.. since then i have been doing th eNS10 trick ( read: since I have no idea what the heck is going on down there, I will just mix with no apparent bottom and hope...) and the owners are now willing to put some cash into the situation.

back to your question, My ref cds have less bottom than they should , and doing some very unscientific tests with a tone generator the rooms bass response takes a pretty suden dip between 250 and 160 hz.. and is next to gone at 40 ( the gennies are no powerhouse down there anyhow though) I spoke with Eathan yesterday ( thanks again!) and he was quite helpful.. I am looking at doing some trapping to start, and rearrangin gthe foam that was put up during construction..

I am also ;curious if you all think that I would benefit from changin the room dimentions a bit.. I am not real excited about this option, but I could go a little smaller if it would help.. the dimentions are in my first post.

Post by **John Sayers** » Fri Jul 18, 2003 9:31 am

OK - so the genelecs aren't the problem. I'd get rid of the diffusion behind you to start with. Put it somewhere else. You are going to need traps but NOT behind you - on the side walls or ceiling maybe?? Make the wall behind you as dead as possible.

No chance of turning the room around so you are centred on the short wall with all the room length behind you??

cheers
john

audio hobbit · Post by **audio hobbit** » Fri Jul 18, 2003 11:10 am

Actually I am centerd on the short wall.. sorry for the confusion! I am actually in the process of removing a bunch of the 2" foam that they put up in the beginning.. maybe I can utilize that with some more bradband stuff on the rear wall? I will try and make a drawing....

Post by **John Sayers** » Fri Jul 18, 2003 1:05 pm

maybe I can utilize that with some more bradband stuff on the rear wall?

that's the way to go mate.

cheers
john

audio hobbit · Post by **audio hobbit** » Wed Jul 30, 2003 10:10 am

ok.. I am partway through building the "rear wall" absorber on Johns site ( and trying to re-allocate the money to get 4 of Eathans bass traps, unforseen expenses suck..) is it possible to subtitute regular 3'1.5" "bat" insulation for the rigid fibreglass? how much of it would I need to make up for the lack of 3 inches of 705? I have 2 feet of depth to play with..

knightfly · Post by **knightfly** » Wed Jul 30, 2003 11:07 am

705 has a density of 6 PCF, where fiberglas batts are around 0.2 to 0.3 PCF for the 3" - so even if you could cram 20 of the batts into the front 4" of your trap, it probably wouldn't be as effective.

Bass trapping works when the restrictive material (705, etc) is placed away from the boundary by a quarter wavelength of the frequency to be trapped. This puts the sound VELOCITY at maximum when trying to pass through the absorbent, therefore the most sound is converted to heat.

So, if you stuffed a cabinet full of loose fiberglas, only the part closest to the surface would have much effect on lower frequencies... Steve

audio hobbit · Post by **audio hobbit** » Wed Jul 30, 2003 2:04 pm

so much for the easy way.. guess I am off to order some 705...

My plan was to use a layer of 3&1/2" and a layer of 6/12" and then a 14" airgap to the wall.. but if the density is that far off I cant imagine that it will work..

audio hobbit · Post by **audio hobbit** » Thu Jul 31, 2003 8:31 am

I put the wall in today, almost done, it is essentally a 2 ' airgap with 2 layers of 2" 703 fsk in front of it.. huge diffrence just in casual listening, cant wait to mix in there now...

knightfly · Post by **knightfly** » Thu Jul 31, 2003 2:48 pm

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