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Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ. |
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Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ. |
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In Reply to: Thank you very much and one last question! posted by Lona on February 19, 2007 at 01:18:31:
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.
Jon Risch
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Follow Ups
- Re: Thank you very much and one last question! - Jon Risch 20:07:51 02/22/07 (0)
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