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Old 7th September 2002, 01:51 AM   #1
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Default Tube traps ?

Does anyone have any experience building tube traps with fiberglass tubes. I saw one good article on this where the
author says to leave the center of the tube hollow but I wonder
if it would be better to stuff the center with fiberglass.

Thanks in advance,


bob12345678 AKA Woody
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Old 10th September 2002, 05:48 PM   #2
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I've stuffed with Dacron, it's easier on your skin and lungs and can be teased out so it is less dense. Works fine. Get a copy of an acoustics handbook and design for the frequency of interest.

cyclotronguy
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Old 10th September 2002, 09:15 PM   #3
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Thanks for the feedback but I still want to know if the designe
using a hollow unstuffed fiberglass tube is as effective as those
that are stuffed.


Regards

bob12345678
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Old 10th September 2002, 09:48 PM   #4
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Maybe Bill could be of help. If not, why not experiment yourself? Fiber glass or Dacron is pretty cheap. Actually that would be the best way to learn.
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Old 10th September 2002, 09:56 PM   #5
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Bill can help this much.

<a href="http://www.audiophilia.com/hardware/tubetrap.htm">ASC Link (the tube trap people)</a>

Art Noxon, who designs this stuff knows what he's doing.
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Old 10th September 2002, 11:42 PM   #6
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Jon Risch's Acoustic Treatments page.

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Old 11th September 2002, 12:19 AM   #7
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Thanks for the feedback. I will be looking those web pages over.

Regards,

bob12345678
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Old 12th September 2002, 11:58 AM   #8
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Hi all!

I built a handful of DIY tube traps according to Jon Risch's recipe (i. e., fiberglass around a cylinder of metal mesh, with metal mesh and polyester batting around it all) and I can hear a quite clear difference in the acoustics of my living room.

They were not that easy to make, and I think I compressed the fiberglass too much in order to get the optimum absorption, but... in fact I want to have more of them.

I also had some very valuable mail correspondance with Mr. Risch, here it comes!

Best wishes
Mattias, Gothenburg, Sweden


-------------snip-----------------------------------

From: Jon Risch <jrisch@strato.net>
> Mattias Rickardsson wrote:
>
> How important is the density of the fiberglass?
>
> I guess (If I've got things right) that it's the air pumped in and out of
> the bass traps that loses it's energy due to friction in the fiberglass,
> and then it should behave differently depending on its density. And when
> you roll it around the tube, it can get even more compact than it was
> before.

My DIY note has the optimized amount and density via the construction details.

See:
http://members.xoom.com/Jon_Risch/a1.htm

I have tested the recipe, and it comapres very favorable to the retail ASC
devices, at least as good, perhaps better.

> Another question: ASC tube traps have middle walls to remove standing
> waves. Is this really a problem?

AS for the internal divider, the middel circle I speake of provides this, and
yes, it helps, as well as streengthens the device, and helps keep air leaks
from impactinf performance as much.

Jon Risch


From: Jon Risch <jrisch@strato.net>

> I've finally started getting the ingredients of some DIY tube traps.
> (They'll be 30 cm inner / 41 cm outer diameter, 1 m high, 17 cm thick
> glass fiber, very stable wire net, and quite thin polyester batting.
> I start making 3 of them, and an additional 2 of half the height.)
>
> However, there are two details which I'm not sure of:
>
> 1) The plastic film. I'm not sure how limp or stiff it should be compared
> to, for instance, ordinary plastic bags. And does that really matter? I
> guess almost no air travels through the tube on this side, so I'm not sure
> what difference a stiffer or limper film would make.

Early on, when I wrote the DIY note, I was convinced that the plastic had tobe super
limp, that is, not stiff. This turned out to be not the case, and any plastic sheet
will be fine.

> 2) The "Liquid Nails". This sounds like a brand name to me, and my guess
> is that it is some kind of hot melt glue. But maybe not. Anyway, both me
> and my helpful dad (who builds houses daily) are somewhat sceptical to how
> the fluffy glass fiber would work together with such stuff. Maybe I
> misunderstood the description? Maybe we should use a broad adhesive tape
> on the outside to get rid of leaks? Well, I thought I'd better ask. :-)
> I guess it would be best if the glass fiber would be glued as much as
> possible to the outer edges, but I haven't found a good way yet.

Liquid Nails is a conztruction adhesive, that has a LOT of solvent in it, and when
it dries, it is like a hard plastic. Silicone rubber can be used, or other
adhesives.

The idea is to squirt some into the seams, and around the edges, enough so that any
gaps are bonded together to provide the "air seal".

Jon Risch


From: Jon Risch <jrisch@strato.net>

> we made five tube traps last weekend.
>
> 41 cm outer, 30 cm inner diameter, 1 m in height, with a stable wire fence
> with holes of only 2 cm. I believe we used rockwool, not glass fiber, and
> I think it has a density of 30 kg/m3. What's your spontaneous reaction to
> that?

My recipe was designed with 6 to 6 1/2" (15.25 cM to 16.5 cm) thick fiberglass compressed
down to approx. 1 7/8" (4.75 cm). Uncompressed building fiberglass runs about 0.5-0.6 lbs
per cubic foot, or about 8.8 kg/m3 uncompressed. After compression, it would be about 32
kg/m3, so your figure sound right if that is AFTER compression.

> I was planning on using 17 cm thick insulation, but that seemed far too
> tough to press together, so we used 14,5 cm instead. The rockwool still
> seems very tight. I wonder if it's too much stuffed in there... Is the
> density extremely critical?
>
> One thought I had was that one might be able to reduce the effective
> density by piercing tiny holes half through the insulation with a small
> nail or thick needle. But I don't know if that's a good idea...

No, NOT a good idea. The idea is to create a resistive layer the pressure waves must pass
through, and dissipate energy.

> I put some loose rockwool pieces into some of the tubes as well, and I
> think I can actually hear the difference by knocking on them. The ones
> without this loose wool makes more of a tone when knocked.
>
> The result?
>
> Well, I put them in the room corners and with the first sounds I listened
> to, I got really worried because I didn't notice any change. It was dark
> electro with up-front bass drums that really excites the room modes. And
> with the tube traps, I still felt the room very boomy.
>
> But then, when I listened to something with less prominent bass drums and
> more bass lines, I heard much more details than before. What a relief!
>
> Bass notes begin and end more suddenly than before, and are more easy to
> follow. As expected. Much new information is revealed. But I really
> expected the room modes to be much less noticeable. The bass still booms
> in the corners and disappears a lot in the centre.
>
> Another thing:
> Now when my tube traps are 1 m high and I normally have my ears higher
> than the top of the traps, does that matter? Or is the (e.g. diffusing)
> effect greater when they are at the same height as your ears?

The plastic sheet side can help with diffussion, anbd doe snto have to be at ear height to
do so, however, the portion of the corner they do not cover will not be diffussed, so
having a pair in the front corners can definitely help in this regard.

> > Early on, when I wrote the DIY note, I was convinced that the plastic had tobe super
> > limp, that is, not stiff. This turned out to be not the case, and any plastic sheet
> > will be fine.
>
> In the picture of the ASC Tube Trap at www.tubetrap.com, it looks like the
> film is perforated with holes. I guess the bass absorption is worse
> without the holes?

They now use a perforated metal sheet.

> > The idea is to squirt some into the seams, and around the edges, enough so that any
> > gaps are bonded together to provide the "air seal".
>
> Our rockwool got quite tight, so now I feel no need for that extra air
> seal. Instead I think it got even tighter at the seam... I would guess the
> performance then is reduced at the seam. Should I then place the tubes
> with such a seam in any particular direction, or is it completely
> omnidirectional?

I recommend the seam be the side where the plastic sheet is placed, so as to avoid any
unintended reflectance from there.

Jon Risch


From: Jon Risch <jrisch@strato.net>

> > My recipe was designed with 6 to 6 1/2" (15.25 cM to 16.5 cm) thick fiberglass compressed
> > down to approx. 1 7/8" (4.75 cm). Uncompressed building fiberglass runs about 0.5-0.6 lbs
> > per cubic foot, or about 8.8 kg/m3 uncompressed. After compression, it would be about 32
> > kg/m3, so your figure sound right if that is AFTER compression.
>
> No, I'm afraid that is the density BEFORE compression. Now, after compression, it's 60 kg/m3. Two questions arise:
>
> a) Should rockwool have the same density as glass fiber in a tube trap?

Yes, although it deos seem to work OK to higher densities than fiberglass does, you may be getting away with this due to the rockwool.

> b) How much does the performance suffer when the density is doubled?

With the rock wool, hard to tell. When folks built some of my trap with the wrong density material, or compressed too much, the traps were
only about 70% as effective as properly built ones, based on some early measurements I did when I was designing them.

> I think it would be possible to pinch through the wire fence and remove maybe 20% of the wool, if one thinks that would improve things.

Naw, just likely to cause problems: leaks, etc. If you build any more, try to use less dense material, from my own experiences, with
materiola that is ALREADY at the "proepr" density, it does NOT seem to work as well, I don;t exactly know why, but for whatever reason,
there seems to be a need for some minimal amount of compression taking place, and the end reuslt density works better if it started out
much less than the final amount.

Jon Risch

-------------snip-----------------------------------
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Old 13th September 2002, 06:45 PM   #9
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I believe you will find that the basis for Art Noxon's
patent on Tube Traps is the holes in the plastic film,
which allow the bass to through the fiberglass into
the interior, but tends to reflect the mid and high end,
acting more as a diffusor than an absorber.

The act of passing through the dense fiberglass is the
resistive absorption part of the effect, and I don't think
there is significant value to internal stuffing, in fact it
might be detrimental if overdone.

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