#1647782 - 04/19/04 04:18 PM
Bass traps with Rockwool RW4 (in UK)
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holygrounder
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Registered: 04/19/04
Posts: 4
Loc: UK
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Hi Ethan / forum, (I'm a new member),
I found your site very thought provoking and helpful. I'm in the UK, and finding rigid fibreglass is hard. I do have some 50mm slabs of Rockwool - RW4. It's not rigid, but nor is it fluffy like roof insulation - you can stand on it and it depesses very little, but you can tear it apart easily. It cuts very easily with a bread knife.
I've measured my room and I have a large low peak, followed by a fairly wide cut from there over the mid bass range. Above that it's reasonably flat. The peaks are : 40 to 100 centred sharply on 56 (15dB); dip from 100 to 250 centred sharply at 140 at (5dB); gentle peak from 250 to 800 centred on 500 (4dB); dip from 2K to 3k centred on 2.5k (6dB); peak from 3.6k to 6.3k centred on 5.5k (4 dB)
I am considering making two ceiling mounted traps - in the corners above the JBL 4431 speakers. I have bought some 11mm ply for the front panels. I'm planning to make a deep box (say 7" sides of spruce), 26 inches x 24 inches, screwed to the back wall and ceiling. All joints screwed and glued, plus caulked.
From "front to back" I plan:
ply panel : 11mm
airspace : 1 inch
very thin white polythene - (used as waste bin liners) - to keep rockwool in place
2 x 50mm Rockwool slab, total 150mm (6")
(back panel? I have some 1/2" mdf or would chipboard 15mm do?)
Am I OK with this? I could make the box 8" deep, and / or I could make each trap 4' x 2' so they would span the whole area between the speakers.
Shame you're in the USA, Ethan, - otherwise I'd consider buying your traps!
Regards,
Mike.
_________________________
from Mike Levon :::::::::::::::::::::::::::::::::::::::::::::::::: HOLYGROUND RECORDS http://www.holyground.co.uk England's first independent label 1970's Bill Nelson ELECTROTYPE ::::::::::::::::::::::::::::::::::::::::::::::::::
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#1647783 - 04/19/04 04:31 PM
Re: Bass traps with Rockwool RW4 (in UK)
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Ethan Winer
MP Hall of Fame Member
Registered: 06/12/00
Posts: 5405
Loc: New Milford, CT, USA
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Hi Mike,
> I've measured my room <
Just curious, but how did you do that? What analyzer or software did you use?
> I am considering making two ceiling mounted traps <
You'll need a lot more than that to make a meaningful improvement! If you look at my plans article you'll see it recommends basically going around the entire room. At the minimum you should have one of each trap type - high-bass and low-bass - in each regular corner, and then also line the rear wall.
> ply panel : 11mm
> airspace : 1 inch
I'm not fluid with metric, but if those dimensions are close to what my plans call for you'll be fine.
> (back panel? I have some 1/2" mdf or would chipboard 15mm do?) <
When I've made back panels they were heavy MDF and also had crossbars screwed and glued every two feet. This type of trap is meant to go on a wall. You can make a back, but it must be very rigid.
> I could make the box 8" deep <
No, make them the same depth as shown in my article.
--Ethan
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#1647784 - 04/19/04 07:36 PM
Re: Bass traps with Rockwool RW4 (in UK)
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holygrounder
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Registered: 04/19/04
Posts: 4
Loc: UK
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QUOTE Originally posted by Ethan Winer:
QB Hi Mike,
I've measured my room
Just curious, but how did you do that? What analyzer or software did you use?
I used a self contained sound meter - from Tandy - Radio Shack in USA - some years back. I mounted it in my usual listening position, I have a CD made by Alan Parsons - engineer on Pink Floyd's Dark Side of the Moon. On the CD, as well as other stuff, are 1/3 octave pink noise tracks. I set up the 1K to read 0dB on my mixer, and turned the main amp to a reasonable level - not loud, not quiet - 80dB reading on the meter - about 4 ft away from eack loudspeaker. Then I played each band in turn and wrote down the dB reading. I had to choose some different ranges on the meter where it was too loud or soft. It was set to C weighting. I think it was C - the notes said this was a better approximation of our hearing.
I am considering making two ceiling mounted traps
You'll need a lot more than that to make a meaningful improvement! If you look at my plans article you'll see it recommends basically going around the entire room. At the minimum you should have one of each trap type - high-bass and low-bass - in each regular corner, and then also line the rear wall.
I should have described my room so far. It is unfortunately nearly a cube: W & D 9ft, height sloping from 7ft 8ins to about 7ft 5ins. It is a dormer so most of it sticks out above the roof line. It is mostly wood studding (4in x 2in) filled with Rockwool RW4, and plasterboarded with two thicknesses, plus skim.
Across the rear wall facing the speakers I have screens - pretty much floor to ceiling - which I use when recording. They have steel feet, and clip together. They are made from 2in x 1in timber round the edges, and filled with (yup, you guessed it) Rockwool RW4! This is covered with a thin white polythene - *very* easy to put your finger through it - to hold in the fibres, and a cloth covering. When mixing these panels cover the rear wall, and rest on it, held loosely by clips at the top.
I also have about 10 purpose made foam acoustic panels which help the highs and mids. No flutter problems.
So the bass traps I'm considering are in addition to the function of the rooms walls which must help. There is little room for more unfortunately, although I could add one in each rear corner on the ceiling.
ply panel : 11mm
airspace : 1 inch
I'm not fluid with metric, but if those dimensions are close to what my plans call for you'll be fine.
The ply is just under half an inch. I read somewhere but now can't find it that 3/8 would work around 70Hz, and I need to go a bit lower to tame the really big 63Hz peak.
You say above to use 4 high bass traps but my room plot shows a dip in this band, so . . ?
back panel? I have some 1/2" mdf or would chipboard 15mm do?
When I've made back panels they were heavy MDF and also had crossbars screwed and glued every two feet. This type of trap is meant to go on a wall. You can make a back, but it must be very rigid.
I could make the box 8" deep <
No, make them the same depth as shown in my article.
Ethan QB QUOTE
_________________________
from Mike Levon :::::::::::::::::::::::::::::::::::::::::::::::::: HOLYGROUND RECORDS http://www.holyground.co.uk England's first independent label 1970's Bill Nelson ELECTROTYPE ::::::::::::::::::::::::::::::::::::::::::::::::::
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#1647785 - 04/20/04 02:04 PM
Re: Bass traps with Rockwool RW4 (in UK)
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Ethan Winer
MP Hall of Fame Member
Registered: 06/12/00
Posts: 5405
Loc: New Milford, CT, USA
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Mike,
> 1/3 octave pink noise tracks <
Using 1/3 octave pink noise at low frequencies is about equal to throwing darts at a piece of graph paper and then connecting the dots - that is, the information is all but useless.
> When mixing these panels cover the rear wall <
Okay,that's a good start.
> I also have about 10 purpose made foam acoustic panels which help the highs and mids. No flutter problems. <
Unless you wad them up in the corners they won't do much at low frequencies.
> The ply is just under half an inch <
To tell you the truth, in a room that size you'll do just as well to make more fiberglass panels, but make them very thick and put them in every available corner.
> You say above to use 4 high bass traps but my room plot shows a dip in this band <
Bass traps flatten the response. Lots of rooms have big dips, and those too are solved by bass traps.
--Ethan
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