Drooping Didgeridoo

Fostex FE 127
<clik any image for a larger one>

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....

    1/4 wavefor Fostex FE 127 70 Hz Fs as published


  closed end to flange of tee


  open end to flange of elbow



  radii of Tee and Elbow flange end to flange end


  total pipe length


  Driver from the closed end (39%)

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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