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Posts: 5109
Location: Brisbane
Joined: September 25, 1999
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I think the pressure differential is important but I have no idea how important or how to optomise the trap for best results. I suspect there is a relationship between interior volume and flow rate through the insulation.
I don't think shape is likely to be critical though I do think that exposed surface area, ie outside surface area, is an issue and that it also has a relationship to interior volume and flow rate through the insulation.
I just went digging through some old stuff I copied from the net years ago and came up with the following from an older version of Jon's web site. I hope he doesn't mind me posting it here:
"Quick and dirty homemade tube traps
Obtain some sheets of 1" thick rigid high-density fiberglass panels, or better yet, rock wool panels. If the panels are only medium density, double up on them and size accordingly for the inner/outer panels. Determine a size based on an equilateral triangle (side panels of 24" or smaller recommended, make them sub-multiples of the sheet width, e.g.,24",16",12")and once size is determined, cut the panels to size (these can be 8 feet tall if the panels come 8' by 4', but a full 8 feet will probably be too unwieldy). The shape can be a right triangle so as to fit in a corner better, size the panels accordingly. For a full use of a 48" wide panel, 14' on the sides, and 20" across the hypotenuse.
Glue (silicone rubber or liquid nails) these together at the edges forming an equilateral triangle or a right triangle, and cut 3/4" wooden end caps in the appropriate size/shape to cap the ends and glue the triangle of panels to the end caps. To take some of the "edge" off of the acute angles, wrap a single layer of 3/4" minimum loosely spun bonded polyester batting around the fiberglass panels (this also aids HF absorption), and then wrap with fire-retardant treated burlap. If you want some partial reflectance/diffusion, wrap a limp plastic sheet around one corner of the triangle and half way across the two sides.
Either one of these will easily outperform the previously posted cardboard tubes filled with fiberglass and covered with carpet, and at a lower cost,
providing a broadband absorption over a wide and extended LF range."
Jon doesn't seem to have made any comment on how the performance of these traps compares to his version of the round trap but I suspect the "dirty" part of the "quick and dirty" name and the fact that this design is offered as his second option in the document I copied both indicate that the round traps perform better.
David Aiken
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Basically… - David Aiken 13:16:10 09/12/09
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