(Proposed) Recycled
Transmission Line Subwoofer


Two 12" drivers -- from a set of garage sale speakers -- resurrounded. 1" & 1/2" MDF/Melamine left over from old desks when an architectural client got new furniture.

The Theory

The two 12" drivers are loaded push-push into a tapered T-Line. Push-push practically eliminates much of the mechanical loading the speaker would normally put into the enclosure. A T-Line since I feel it probably is the best enclosure to mitigate the quality (lack thereof) of the drivers -- and besides after building tlines at university it appeals to me.

Intended to be a transitory woofer for a pair of Accoustat 2s (scheduled for "detailing" themselves) and then in more permanent duty as woofers for a pair of PSB Alphas (themselves free of any cost)

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  • The Woofer is driven in stereo w an active crossover (~100 - 125 Hz/24 db/octave -- Hafler DH220). Mechanical effects will make it effectively mono much like a dual-coil woofer. The side-firing arrangement should still allow some higher frequency stereo information to be retained.
  • With the els units a passive 1st order high-level hi-pass filter may be used to reduce the electronics the signal has to pass-thru. (ELSs driven by a pair of NAIM 160s)
  • Enclosure built of, and designed around the scrap desk-parts.
  • The enclosure is somewhat of a comprimise in that the beginning part of the line has a cross-sectional area is only 117% Sd of the two drivers, tapering to 84%. It is my hope that the loading of the drivers will make them act as if the Sd of the driver assembly is the "mouth area" that loads into the line. When I actually start building it, this last will get subjected to actual testing.
  • line length is ~116 inches (w 6" of end correction) or a 1/4 wavelength of ~30 Hz. The woofers have an Fs of 19 Hz so a speed of sound reduction to about 65% will be required for proper tuning.
  • The woofers are going to be mechnically coupled at the rims using ready-rod bolts.
  • I want to treat the paper-cone woofers with some plastic of some sort to lower the fs and more importantly to reduce reflections back thru the cone.

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