I've always found transmission lines intriguing, not only because of their attributes, but also because for so long their design was cloaked in mystery and conjecture, rules of thumb, and sometimes outright bunk. The recent works of Martin King and Augspurger, among others, have removed the veil on proper design-or at least made it somewhat more transparent.
Although their design process can be tricky, transmission lines provide an alternative solution to some basic acoustical challenges. Half of a driver's acoustic energy radiates from the back of the cone. In a sealed design, an attempt is made to dissipate this unwanted energy by absorbing it in stuffing, but in many cases a significant amount of energy reenters the cone- delayed in time, and revealed as response peaks due to internal standing waves. All of these effects cause distortion of the original signal.
A transmission line functions by using this wasted and unwanted acoustic energy in a positive manner. By encouraging standing waves of a single low frequency, and providing an opening (or terminus) out of which these standing waves can escape, the bass response of the driver can be extended. At the same time, the transmission line reduces the energy that reenters the cone and causes distortion. I chose the classic tapered transmission line for the TriTrix design for its characteristic nearly linear impedance, uncolored sound, good bass extension, and simplicity of construction.
One objective was to keep the enclosure volume as small and compact as possible. I used Martin King's "Classic Transmission Line Enclosure Alignment Tables" to design the enclosure, and verified it using his MathCad computer models.
A significant advantage of all the TriTrix designs is their relatively small enclosure volume requirement, no matter which version. For the sealed alternative, the external dimensions are a diminutive 20" x 6-1/4" x 8- 1/4" deep, and the max SPL models at in excess of 104 dB. Likewise, the TriTrix in a vented enclosure also lends itself to smaller volume of 19 liters, with an f3 in the low to mid fifties and an f10 right at 40 Hz.