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In Reply to: DIY Tube Trap - does it have to be rounded and use fibreglass? posted by Champion on December 19, 2006 at 14:07:48:
Does it have to be round? - No, but round offers a number of advantages. The proper tube trap has to be pretty well sealed so that the only air entry/exit is through the insulation so you don't want gaps. Round allows you to wrap the insulation around the core and that usually means that any joins are covered by more insulation which is a plus. It's also more structurally sound. Square tends not to be as sound and you tend to but insulation batts up against each other at the corners and that provides a potential air gap.Does it have to be fibreglass? - No. You can use polyester. Just ensure the density of the compressed insulation is around the 2 lb/cu ft mark.
Does the centre have to be empty?:
Answer 1 - Yes, for the ASC type tube trap design. The vacant centre acts as an air resorvoir and air bleeds into it when the room is pressurised and bleeds from it as the pressure in the room rarefies. That air movement helps to equalise air pressure in the high pressure zones where this trap is most effective.
Answer 2 - No. Take a look at Jon Risch's quick and dirty bass trap design. Simply compressing a solid 'block' of insulation and wrapping it will work fine through a brute force approach but won't be as effective as the proper tube trap. My traps, which I based on Jon's quick and dirty design, are simply a pile of polyester batts encased in a wire mesh cage that compresses them to the right density. The wire mesh is wrapped in a thin sheet of polyester batting and then covered in burlap. They work fine but I think the tube trap design with the hollow core would be more effective.
Follow Ups:
Thanks alot David for your detailed explanation. What I planned to do was to build a wooden frame (like a four pole stands) and wrap the 'stand' with fabric and stuff polyester in it. Then I can put pot plant etc on top.
Here's another option that folks seem to think works quite well:
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Yes, it CAN work, but there needs to be enough absorbing material of a high enough density, or it will not do as much as it should or could.See:
the original post where I reveal the latest Super Quick & Dirty easy bass traps recipe:
http://www.audioasylum.com/audio/tweaks/messages/15737.html
and petew's post where he goes into detail on what he did.
http://www.AudioAsylum.com/audio/general/messages/70817.htmlThe SQ&D versions are approx. 80% the effectivenes of the full blown ASC style ones that are hollow, and a LOT easier to build. However, they use more raw fiberglass, and cost more to make over all. If you take fiberglass, or ppolyester, that has been left to "unroll" and fluff up, and then merely place some of this inside a frame with cloth covering, the amount of fiberglass will not be enough, nor will the density be high enough, to absorb much bass.
Ordinary building grade fiberglass tends to run around 0.5 lbs/cubic foot, while the same fiberglass still in the roll as it comes from the supplier is at a density approx. 3-5 times higher, and thus has a greater capability to absorb bas energy. The SQ&D is literally a brute force method of bass absorption, while the ASC style is the fineese method.
The ASC style "hollow-in-the-middle" type traps make maximum effective use of the materials, using less fiberglass and getting superior results, but in order for them to work, the frames and the construction must be correct, see:
Common Problems In DIY Bass Trap Construction:
http://www.AudioAsylum.com/audio/tweaks/messages/29191.htmlMy DIY Acoustric info is at:
http://www.geocities.com/jonrisch/a.htm
Good luck!
Jon Risch
Hi Jon, thanks for chipping in. While you are here, have you gone any further on the room lens design? i.e. actually testing it? That looks like an interesting one. If I am going to build the bass trap and put them at the corners, can I build the lens with solid wood to just use them as diffusor to treat the reflection point? I really like the idea of treating first reflection point without absorbing high/midrange.
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