# Moveable Bass Traps (or Broadband Absorbation)???



## brad (Sep 18, 2012)

I have a tricky problem of a room 11'-8" x 11'-11" x 8'-0" high that is packed with equipment (as in Audio Hoarding) also books and cd's on shelves, and I am trying to tame low freq modes (like 70hz). Room is used as control room for mixing. Not much room on the walls (expect up high) I was thinking of building 8" roxsul bass trap panels with floor mounting than can be moved out of the way, say, to open a closet door or something. Would they work? Do people use moveable absorption?


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## bpape (Sep 14, 2006)

That can absolutely work just fine with moveable panels on stands, casters, just legs, etc.

Bryan


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## brad (Sep 18, 2012)

Thanks Bryan,
You are one of the Masters of Audio on this site and I'm thankful for your (and others') help. I have read much on this forum where you and others speak a great deal of broadband low end correction with bass traps and other absorbers. Here are my graphs, which are indicative of the room dims so you can see some trouble modes ([email protected] 70hz, for instance). MY plan is to construct maybe 2 or 3 24" wide freestanding panels. (I could go thicker than 8") 
Will the height make a difference, beyond, say 4'-0" (which is what the Roxsul is sized)? And, should I use some luan substance that is more reflective and vibrates or just fabric like Muslin? I'm not sure if I need them to have a membrane on front or rear or just be insulation wrapped with rigid sides (with holes in the side & top of frames).
What do the graphs say to you ?
Thanks


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## bpape (Sep 14, 2006)

Based on the waterfalls, you already seem to have plenty of higher frequency absorption. I would use some sort of heavier membrane certainly. Size, quantity, and location depend on where the problems are coming from.


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## brad (Sep 18, 2012)

Do you mean a panel front with inside sealed airspace and roxsul inside (not touching the face) type of trap? Maybe using 1/8" or 1/4" masonite faces?


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## bpape (Sep 14, 2006)

No sealed air space. No hard back. Don't want it narrowly tuned. Just put the membrane on the front of the absorbing material before wrapping.

Bryan


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## brad (Sep 18, 2012)

Oh, So by making a true box (like a speaker) one tunes the resonant frequency, but with open back and insulation, it is more broadband? So I can affect that mess down in the 70hz range better, but not soak-up any more mids &highs?


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## bpape (Sep 14, 2006)

As soon as you seal it, it makes the air act like a spring. If you do it without sealing it, it becomes more broadband. 4" with a stiff membrane is pushing but you can probably get 70 Hz.

Bryan


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## brad (Sep 18, 2012)

Great, Thanks for your input! I'll probably try to go for 6-9" thick and see what that does.
I'll post back on how it goes.
Thanks


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## brad (Sep 18, 2012)

The New Year sounds better than last year! 11 traps installed (8 movable) I am amazed at how tight and crisp and clear things sound. The room is more dead, as a control room I would rather have that, though I may add some diffusion... great stereo imagery
(I don't have to say the Pink is before and Green after traps)

Not quite done yet, but way better. My thanks to Bryan, and the others here on on other forums as they speak the holy words.... corners, broadband, density, speaker placement ... etc etc. the only eq used was a 2db roll-off on the main speakers above 2k to prevent me from going deaf. Nearfield mixing at 80-85 db, but it is so easy to pass 100db and not really realize it, as most of the muddy reflections are gone, so I must use caution..
Also thanks for REW outstanding piece of software!


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## bpape (Sep 14, 2006)

Nicely done. Within +/-5 is what you shoot for without EQ . In an almost square room with a lower ceiling, that's really good.

Bryan


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## robbo266317 (Sep 22, 2008)

That really is an impressive result. Well done.


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## Patzig (Oct 10, 2012)

Pretty cool stuff Brad. Could you elaborate on your traps? Material, thickness and locations? Maybe even pictures? My room size is very close to yours, and I'm about to start putting up diy treatments as well.


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## jim1961 (Apr 8, 2011)

brad said:


> The New Year sounds better than last year! 11 traps installed (8 movable) I am amazed at how tight and crisp and clear things sound. The room is more dead, as a control room I would rather have that, though I may add some diffusion... great stereo imagery
> (I don't have to say the Pink is before and Green after traps)
> 
> Not quite done yet, but way better. My thanks to Bryan, and the others here on on other forums as they speak the holy words.... corners, broadband, density, speaker placement ... etc etc. the only eq used was a 2db roll-off on the main speakers above 2k to prevent me from going deaf. Nearfield mixing at 80-85 db, but it is so easy to pass 100db and not really realize it, as most of the muddy reflections are gone, so I must use caution..
> Also thanks for REW outstanding piece of software!


Looks nice. Good job!

Question though. Is it by design that your 10db down after 8500hz ?


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## brad (Sep 18, 2012)

Thanks, a lot of work more to go.
Patzig: here are a couple of photos. I am a cabinet maker and have a shop, so I can rip what I need from a sheet of plywood ($30.00 at Home Creepo) and plywood is light, straight and smooth (cabinet grade) I used Roxsul rock wool all the way, notched into the frame for a flush fit. All is fabric wrapped . 3/4" x 1-1/2" plywood made the frames, exposing as much insulation as possible, 47" tall 15" x 11" deep. all corners rounded with a laminate trimmer and round-over bit and sanded on the wood. 8 panels are moveable and can be arranged at any location needed. Also 1 cloud (not in photo) & corner trap and wall trap behind speakers all Roxsul ranging from 4" to 19" thick. I will eventually either put feet or some frame on the exterior (at least on the bases) to better protect them, but I don't have animals or kids running around to beat them up. Fabric is either Muslin or black speaker cloth (Joanne Fabric coupons up to 50% off- awesome store.) Also an investment in an air-powered stapler (Harbor fright Tools) for $25.00 was a good investment. I also highly reccomend titebond Hi-PUR polyurethene hot glue as it can make fast solid joints that really strong.

I highly recommend checking your graphs with REW but then having REW play sine waves at the problem frequencies (either peaks or nulls) and moving around the room to hear the differences for yourself. Then you can really hear the peaks and nulls, quite amazing.
Reflections off the equipment is also an issue. And I had to cover all musical speaker cabinets with packing blankets and also the cast-iron radiator as they were resonating and not helping. carpet & pad on most of the floor.

Jim1961: actually I was closer to flat, but the I am not used to the flatness. My hearing is so good, I can hear a wristwatch in a quiet room 8 to 10 feet away (not digital of course!) so I rolled back the high end a bit and let the bass bump a bit. I'm sitting 36" from the speakers, so really near-field!! 
I have been reading about control room curves and it seems to be not recommended to be totally flat. I am still getting used to the sound of the room and I will put some high-end back in it but with diffusers so I can get a little more sound around me, otherwise I risk monitoring at levels too loud and I worry about hearing fatigue and loss.

Having the moveable traps lets me set-up to mix or master, then break down when I need to have a real bedroom, plus I can use the traps in other rooms when tracking. They are light and easy to move around.


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