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Just to say I did it;
I made a set of folded quarter wave pipes, again from 4" ABS. I placed the baffle
on one of the straight through ends of a Tee. An elbow was placed on the opposite
end of the straight part of the Tee connecting to a straight piece of pipe to form
the open end of the enclosure. The remaining (perpendicular) Tee connection was used
for the closed section of the line. This was formed by another piece of pipe closed
at one end by a pipe cap. I managed some taper in the closed section of the line
by, again, inserting a tapered 2x4 this time with the thick end at the closed end.
I've not included dimensions for the pipes as I have noticed that not all ABS couplers
are created equally. Elbow radii in 4 inch stock can vary from 200 to 240 mm depending
on manufacturer. I like BOW couplers available at Canadian Tire because they have
the least "kink" in the turn. They are about 240 mm center of radius end
to end. I am also very unsure of the math on these pipes. I find T-Line theory much
less confusing than what is available for FQW Tubes. In the event, I made a SWAG
calculation (scientific wild ass guess) and came up with....
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1/4
wavefor Fostex FE 127 70 Hz Fs as published |
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360mm
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closed end to flange of
tee |
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440mm
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open end to flange of
elbow |
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radii of Tee and Elbow
flange end to flange end |
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1280mm
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total pipe length |
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500mm
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Driver from the closed
end (39%) |
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Perhaps this is a bit long for a proper 1/4 wave match but
given that there is no flare on the open end I thought a little more volume and length
wouldn't hurt.
The sound? My friends think this configuration sounds most like a commercial product;
I think it is over stuffed. I haven't had time to tune this one properly, line lengths
and all but will let you know if I find a magic formula.
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