Hey All,

Does anyone here have experience with this type of design?

Thoughts/Impressions/Comparisons?

thanks,
Jeff

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

Another "built my own" experience here, probably from the early '80s. Mine were a fairly standard 3-way, IIRC the drivers were KEF B139, B110 and T27. Maybe 4 feet tall, 12" wide and 18" deep. A number of my friends built identical speakers after listening to mine, so I guess they sounded pretty good.

Main challenge with transmission lines IIRC is that they have to be quite large relative to the driver size in order to work well, but upside is that you can get smooth & deep bass, better than ported enclosures at the time. I still remember listening to other speakers back than, missing the deeper bass notes, and wondering why more people didn't use TL enclosures (it was another decade before I discovered WAF :)).

My impression is that ported enclosure designs have continued to advance while transmission line designs have not (at least not so much) so I imagine the relative benefits are smaller these days.

In terms of modern speakers, I believe the Salk SongTower's are transmission line. Thought there were a couple of others as well but the names are escaping me at the moment.

EDIT -- that reminds me, one of my friends at the time had some similarly sized/shaped speakers, also with a port at the bottom front, but I don't think I ever bothered to ask if they were bass reflex or TL. His parents had the biggest/fattest cat I had ever seen, and the cat liked to sleep in front of the port on the left hand speaker. When we played music with deep bass (DSOTM was always a favorite) the cat's fur would puff out in time with the music.

So I have done a little searching and found that yes, Salk Sound has a least two models where the TL design is utilized, the Song Tower and Veracity models.
Also found that Atlantic Tech is promoting what they refer to as H-PAS that they indicate is partially a TL design.
I would certainly like to hear a speaker with this design but don't know anyone who has one of these models.
thanks,
Jeff

I'll second PMC as fantastic TL speakers. Spent some time as I auditioned coveting them. Very expensive.

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?

Hi,

I am familiar with the company and know the founder, but I don't have info on his enclosure designs. His speakers used to use large vertical ribbon drivers on top of a bass enclosure, which I think may be the reason he called them a "line source" system.

Alan

When checking the Newform Research website, the narrow vertical ribbon speakers on top of the bass module are still a staple of their design, however, they are offering newer designs where it is a somewhat smaller cabinet, yet, the vertical ribbons are sitting directly in front of the speakers themselves, quite unusual and have never seen anything like this before with any other manufacturer. I can only assume it is attempting to achieve somewhat of a "point source" listening experience along the lines of "Kef" but, using ribbons as the tweeter which are jutting out from the cabinet. Quite pricey, I might add despite the fact that they seem to have recently reverted to the on-line only sales route as well.

It would be interesting to hear what they sound like and despite their reference to a home theater application for their products, they don't offer a center channel model in their product line.