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In Reply to: Can the Ikea Hol be a bass trap if I stuff 2" Owens Corning 705 posted by Lona on February 18, 2007 at 06:41:57:
Hi, 2 questions that I forgot to ask earlier.Usually, bass traps have hard top and bottom, but for something like the Ikea Hol, is it alright for all 6 sides to be covered with fiber glass and polyester batting? I have to make sure it's air tight, right?
Another one, what material should be used for the reflective side of a bass trap. I've read about "plastic sheet", but what exactly is it?
Follow Ups:
I believe that TNT has posted a "project" based on this unit, used without any internal stuffing. This would utilize the reactance of the air trapped in the open squares between the slats.Placing some sound absorbing material inside would probably augment the effectiveness of the unit by itself.
However, note that this would still not be a "true" bass trap, it would be more on the order of a brute force approach similar to the Super Quick & Dirty bass traps, where sheer fiberglass volume does the work.
In that sense, simply buying and using the fiberglass rolls as per my SQ&D recipe
(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.html )would be more cost effective, as then all the money would be spent on the absorbing material, and it's absorbing power would not be altered by a semi-open enclosure.
However, I realize that it is not a trivial thing to create a decent looking bass trap, and so, these Ikea units may be helpful in that regard.
Be aware that if I were going to load the Ikea unit with absorbing material, it would be just as effective to use building grade fiberglass, the 705 would be way more expensive, and may not perform as well.
It might also be helpful to know that filling it with the proper density of polyester fiberfill/batting would also do a good job, and side-step the safety issues of loose glass fibers.
What density of polyester would be best? Probably somewhere on the order of 1.5 to 2.5 lbs. per cu. ft.
. . . . weeks after I had returned them to Home Depot that is.Hukk
Most folks who share their experiences with me regarding the bass traps, do not have problems with either the original bass trap, which involves a lot of handling of the raw fiberglss, or the Super Quick & Dirty traps. But then, most of those folks take normal precautions when working with fiberglass, such as using a mask, putting on old clothes that can be discarded, and that are long sleeve/pants instead of shorts, etc., sealing any leaks in the bags, and so on.It is an unfortunate reality, that most hardware and lumber stores do not treat the bags of fiberglass insulation with any respect, and that they both get punctured, and that they get other dust (wood, tile, carpet, etc.) and debris all over them. Thus, when you purchase such a bag, it could literally be covered with all kinds of allergens and dust, as well as have that same dust etc., come wheezing out of the bag when you set it down.
The thing to do is to be sensible about it, if you suffer from allergies or are sensitive to the possiblility of fiberglass particles, pick out the most intact bags to purchase and take home, wipe them down in the parking lot and seal any leaks or punctures in the bags right there on the lot, before you place them in a plastic trash bag to take home, once you get them home, double check to make sure all leaks have been sealed in the bags, and wipe them down again or blow them off with compressed air, etc., and then wrap the bag with the polyester batting and cloth.
Throw away the trash bag used to transport them. Blow off your skin and clothing with compressed air, take a shower right away, and then wash the clothes separately and immediately, following the normal wash cycle with another one free from soap with the clothes in the washer, and then yet another cycle with no clothes or soap, and air dry the clothes so they do not contaminate the dryer. Or, as suggested above, use old clothes you can dispose of after working with fiberglass.Once the bags of fiberglass are sealed, covered and placed in the room, they should no longer be an issue for almost everyone, except those subject to the most sensitive allergies and problems. Of course, at that point, just walking into the hardware store will be a major problem .....
Hi Jon,
Thank you for your detailed answer.How about my question of having a cubic 6-face bass trap filled with fiber glass instead of the usual cylindrical tube sealed with solid top and solid bottom? For instance, will a 6-face one be more effective than a 4-face cube?
And I am assuming that I try to make them as air tight as possible by applying liquid-nails or some bonding material.
Cheers!
The original DIY bass traqp was modeled after the ASC type bass traps, and it works on a specific principle, that of a pressure differential across an acoustically resistive medium, between an inner air chamber, and the rest of the room.This type of bass absorption is very efficient, makes maximum use of a given amount of acuostic material, and is usually very linear and wideband. It also has certain requirements, such as an air tight seal around that resistive layer, a certain minimumm thickness for a given density, a minimum amount of internal volume to achieve a given amount of LF absorption, etc.
The Super Quick & Dirty bass trap approach is simple and direct: sheer amounts of high density absorbing material, with enough volume to do some good. It is neither efficient nor does it go as deep, but it does do more than a simple 2'X 4' by 2" thick panel stuck in the corner.
The trick here is to get enough material in the corner with enough density, but not too much density.
In both cases, the maximum benefit and the maximum amount of room mode damping will be obtained when the devices/material is in the corners, all the way in the corners as much as possible.
If you stuff a solid cube into the corner, you only end up with 3 "exposed" faces, yet it will still provide maximum effectiveness, and this would be an example of a SQ&D type trap.
A cylinder all the way into the corner ends up presenting more surface area to the room, but if it were solid and the volume of the material was the same as the amount of material in the cube, it would end up performing very similar. If the cylindrical shape was that of a 'hollow' bass trap, ala my original DIY traps/ASC traps, then the cylinder will perform better than just three exposed sides.IF a cube (or rectangle) could be made as rigid as a tensioned cylindrical shape, it would IN THEORY, be able to provide slightly more damping of the room modes, due to a greater surface area provided of the resistive layer, and the greater internal volume the cube/rectangle would provide compared to the cylinder. The sides against the corner walls could be spaced a few inches away from the walls, allowing all of the "extra" surface to be exposed. This would also require some sort of "feet" to space the bottom surface up off the floor.
But unless the sides were truly as rigid or more rigid, than the cylinder, which is highly unlikely, even with heroic efforts to buttress the frame and side walls, then the cube/rectangle would end up performing below the level of a similarly sized cylinder.
I have tried to build a squared-off cylinder, and found that the side walls (I used a solid top and bottom) just can not be made stiff enough, the fiberglass is not optimally compressed, and the non-uniformity of the compression causes less than optimal resistive properties for the resistive layer.
If you were to actualy build a cylindrical trap with the inner and outer layer of animal fencing, it would all become clear to you, the stiffness inherent in the cylindrical tensioning of the two layers, the much more even compression of the fiberglass, and the even amount of compression from top edge to the middle to the bottom edge is far superior to the flimsy drum-heading and collapsing of a straight side wall.
Attempts to buttress the side walls of a cubic/rect. shape with extensive framing and braces were futile, because you had to build TWO sets of frames/braces, one for the inside, and one for the outside.
On the outside, you were constantly fighting the 'push' of the fiberglass outward, making it necessary to 'hinge' each side wall, and make the final compression via 'closing' the hinged side shut. Invariably, the sides bulged, relieving a large protion of the compression needed. Trying to compensate by making the spacing even smaller between the inner and outer layers of fencing did not help much, the center 'pushed out' even harder, and the edges got compressed too much. Because of the low compression in the middle/center of each side wall, the amount of acoustic resistance was not close enough to optimal, performance suffered.On the cylindrical construction, the inner lining of animal fencing is butressed by the top, bottom, and middle wooden discs, while the outside layer of animal fencing is held against the tension of the fiberglass being compressed by tension, ratcheting the outer fencing closer and closer together to bring the fiberglass into compression. The tension and compression are 'spread out' over the entire surface of the cylinder, and so, the animal fencing, even though a bit 'flimsy' by itself, becomes able to support an even and consistent amount of fairly high compression on the fiberglass.
I hope this makes it clearer as to why it would be futile to worry about maximizing surface area for a "brute force" SQ&D type trap, and that it just doesn't work well for the pressure differential traps due to the real world limits of the frame and constraint materials.
Absorption requires the absorptive surface to be in contact with the air and sound waves.Let's say you make a cube shaped bass trap which measures 4' on each side. All 6 sides are fibreglass. If you raise it up above the floor on narrow legs, you have a 6 sided trap. If you sit it directly on the floor, one surface loses that air/sound wave contact so you effectively have a 5-sided trap. You may get a little benefit from having the 6th surface on the inside but it won't be anywhere near as much as you lose by sitting it directly on the floor and losing an outside surface. If you stack another bass trap of equal dimensions on top of the first one, the first one now becomes a 4-sided trap and the top one is a 5-sided trap. If you have 8' ceilings and the top surface of the top one is in contact with the ceiling, you have two 4-sided traps. So, if you go floor to ceiling with the traps, effectively there will be minimal difference between using 4- and 6-sided traps.
Effectiveness depends on outside exposed absorptive area and on other factors as well. In the above example, one 5-sided trap, or even one 6-sided trap will not be as effective as two 4-sided traps of the same dimensions. If you're going to stack traps, use something solid for the top and bottom plates with some sort of internal structure between the plates so that they can be load bearing.
Even if you don't intend stacking traps, I'd be inclined to go for traps with solid top and bottom plates and an internal structure so that you have the option of stacking them later on if you choose.
Hi, are you planning to just put the a layer of fibreglass on the inner surface or are you planning to fill it up? From my understanding if you only put a layer on the surface then yes, you need it to be airtight. But I am not sure how you can do it easily. If you stuffing it full then it is the density/amount of the fibreglass that counts.I believe 6 surface is better than 4 surface. But I may be wrong.
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