(click to enlarge)
Assembling the cabinet from MDF:
Stuffing the transmission line with Polyfil
The woofer cabinet is a quarter-wave transmission line tuned to 30hz. That is; the line is 1/4 the length of a 30 hz sound wave. The line is stuffed with polyfil (pillow stuffing) to a starting density of 0.5 lbs/ft3. The shorter wavelengths are absorbed by the stuffing while the longer waves are slowed to exit the port in-phase and support the low-bass. The tonal quality can be fine tuned by adding stuffing to tamp down any "booming" or removing stuffing to liven up the tone if it sounds muffled. The single-fold line is 9 ft long and tapered, using Roger Sanders' generic "Cookbook" section-area formula: Area at the front of the line is 125% of the woofer's driven area and tapers to 100% of the woofers' driven area at the port end. A properly designed transmission line bass box has almost no resonances, superb transient response, and can play about 1/2 octave lower than other box types. These characteristics make TL's a good choice for hybrid-bass ESL's. Their large volume, complexity and expense is probably why we don't see more commercial TL speakers.
Gluing the 5mm oak plywood sheathing onto the frame rails:
The grills attach to the speakers magnetically, using
hidden grill magnets from Parts Express-- very slick.
Assembling the stat frame to the woofer cabinet:
Cabinet ready for the oak frame facings and trim:
The cabinets are made from 3/4" MDF with 5mm red oak plywood sheathing and trimmed with solid red oak. These cabinets were very time-consuming to build but the results are equally pleasing. I have a full drawing in DeltaCad and DFX formats which I will gladly share-- just email me: email@example.com
Completed beam-splitter cabinets ready for the stat panels and woofers: