Tube traps or corner traps in my room?

[jraffertyuswest.net]

The room I am working in is a 9x13 space. It is a free-standing box surrounded by 6 inches of insulation and another room.

 

Should I use Tube Trap types or corner trap/resonator types?

 

I will be making them myself from DIY plans on the net. My dilemma is that

I have heard that corner traps are room specific and need precise calculations in order to work effectively. I have also heard that tube traps placed in the corners can confuse the stereo image.

 

I would prefer to have the corners near the speakers angled off to bounce sound out of that end of the room so that the stereo image is not muffled.

Can I put the tube traps BEHIND a wall if a triangle is open at the top? Or do they need direct contact with the sound wave?

 

Should I just stick them on the wall behind the speakers but in the space that is not occupied by the corners?

 

I am afraid if I stick the tube traps all the way at the other end of the room I will still have some kind of bass problem at the end where the speakers are.

 

Also the room is open to the 6 inch fiberglass space in two places. There is a 3x4 window and a 3x7 doorway opening. (The door which closest is flush with the OUTSIDE room, the inside room has no door)

 

Do these spaces suck up bass? Should I be worried about having one of the speakers near one of these openings as it might cause unsymmetrical sound?

 

Lastly I was planning on putting the speakers on the short wall to immitate layouts of rooms I have seen. But should I put them on the LONG wall instead?

 

Thanks for any help

-Josh.

[Guest]

Hi Josh, you definitely want to put the speakers on the short wall, to leave the bigger part of the room behind you. Also since the length of the room will leave a space of less than 12 feet between you and the back wall, you'll want to put some sort of absorbtion on that wall. You NEED bass traps in the corners. At least in the speaker corners, ultimately in all four. How high is the ceilings? If your room is cubic ( every surface parrallel) you're gonna have standing waves . These frequencies will determine what needs to be absorbed thus defining the size of the traps. For basic improvement the calculation is fairly simple. For more you'll need a lot of money and an acoustician.

 

If you give me more details I can give you my estimation for the basstrap size.

 

Emile

[jraffertyuswest.net]

The ceilings are about eight feet high. The back wall is actually about 4 inches hihger than the front. All the walls and ceilings have a layer of carpet padding and tight knit carpet. (The room was originally intended for soundproofing only)

 

Should I angle the front corners of the room? Should I put tube traps a little further in towards the center on the same wall? (this would put them roughly behing the speakers.

 

The are mackies.

 

Thanks,

-Josh

[Philip OKeefe]

Bass absorption is going to be most effective in the corners of the rooms, not nearer to the center. Bass builds up and radiates from the junctions of two (or three) wall (or ceiling / floor) surfaces, so this is going to be the most effective area for you to place your bass traps.

 

The carpet is a problem. With that much carpet you're going to *really* have a disproportionnate amount of bass and mids in the room. Carpet and pad are really only good at soaking up upper mids and highs. They are invisible (for all intents and purposes) to the lows and low mids. With that much carpet your room is really going to be spectrally unbalanced.

 

Carpet is pretty much useless for soundproofing. What you need for that is mass (weight), and / or trapped airspaces (airtight). If you need more isolation and soundproofing, a layer of Auralex sheetblock between two sheets of drywall is a good place to start.Acoustics First also makes a limp mass vinyl barrier product. Hemosote sandwiched between a sheet of 1/2" drywall and a 5/8" sheet of drywall is pretty good too. Make sure your two structures are mechanically decoupled. It's probably too late, but "floating" your new walls on top of U-Boats (Auralex) or other neoprene is a good idea.

 

A good source for sound absorption is 2" compressed fiberglass board. Don't confuse this with the fluffy yellow or pink stuff. It's much harder and denser. Check with insulation contractors. There's a place in Garden Grove CA called Southwest Insulation that I always get mine from. It's made by several companies (Knaupf, Ownens /Corning, Manville) and is actually better than acoustic foam if you use it right. WAY better than the carpet you're using now. Just make sure you cover it with some sort of semi-open weave cloth so the fibers don't become airborne! you can apply it directly to walls and ceilings with liquid nails (I'd suggest the front of the room, the sides back to just past where your ears are when you sit to mix, the ceiling back about the same distance from the front of the room, and since your room is so small, on the back wall as well).

 

You can angle this stuff across the corners (45 degrees) from floor to ceiling and fill the space behind it with the loose fiberglass stuff for a pretty low tech bass absorber.

 

your frequencies you'll have problems with in this room are based on axial modes, and the math *is* pretty easy. The resonent frequencies for each dimension have to be calculated, and any resulting "matches along two (bad) dimensions or (worse) tree dimensions are the frequencies that will cause your room to "go off like a cannon" whenever sound at those frequencies is present. Formula is 1127/length/2. So, for your 13 foot room dimension, you have 43.34 Hz, 86.68 Hz, 130.02 Hz, etc. For your room width dimension, you'd have 1127 (speed of sound in feet per second) divided by the room dimension (9 feet) = 125.22. Divide 125.22 in half and you get 62.61 Hz. So that dimension is going to be reinforced at 62.61 Hz, 125.22 Hz, 187.83 Hz, etc. Your heght is going to be a bit more of an issue because of the slope, but that's not too tough either. Average the height! 8' at one end and 8' 4" at the other end? Use 8'2" for your calculations. Remember that an inch = .0833 of a foot, so you'll have to convert inches into base ten decimal for the calculations. So 1127 / 8.1666 = 138.01. Divide that by two and you get 69.01 Hz, and the harmonics at 138.02 Hz, 207.03 Hz, etc. It's usual practice to calculate modes up to about 500 Hz. There's also tangental and oblique modes, but they're more difficult to calculate and are not as big an influence on the room as the axial modes, and doing that calculation isn't really needed for the size and type of room you're talking about.

 

Please feel free to double check my math - I did this all in my head, so I make no warranties in terms of accuracy.

 

 

Phil O'Keefe

Sound Sanctuary Recording

Riverside CA

http://members.aol.com/ssanctuary/index.html

email: pokeefe777@msn.com