Originally Posted By: alan
Hi Strider53,

Yes, decades ago, in the early 1970s, I built two large transmission line passive subwoofers based on a design marketed by IMF (Irving M. Fried). The enclosure was coffin-like and stood about chest height, with the KEF bass driver facing upwards. The target low frequency I was after was below 20 Hz, which required a long transmission line, and the enclosure was stuffed with wedges of porous foam that in effect created an acoustic wave guide of infinite lenght (in theory).

They worked well but were very insensitive and required a large power amplifier to drive them. I had paired them with a pair of Rogers LS-35A mini-monitors (the so-called "BBC monitor"), which handled the midrange and treble frequencies.

In retrospect, the bass was very deep and seemed undistorted, but I do not think the quality of the bass was superior to, say, an Axiom EP-500 active subwoofer, which is what I've been using for some years. I'm entirely satisfied with the quality and quantity of bass that I get from Axiom's EP-500.

Transmission-line enclosures went out of fashion as powered subwoofers became more popular. The only company I'm aware of that still markets full-range speaker systems utilizing transmission-line enclosures is PMC, a British line of quite good but expensive loudspeakers.

There is a decent article on the theory of transmission line enclosures at Wikipedia: http://en.wikipedia.org/wiki/Acoustic_transmission_line

Regards,
Alan



Hi Allan:

I just wondered if the speakers that the boutique company, (that, no doubt, you are familiar with), "Newform Research" builds, located in Midland, Ontario, that they describe as a "Line Source" design, has any resemblance at all to the Transmission Line concept?