Transmission Line Bass

intersting comment about the wool. Pat McGinty of Meadowlark used 5/8" wool felt in his front bass firing ports. he also tuned each speaker's ports with instrumentation as the final step before shipping.

the most satisfying bass performance I've heard is from my vintage 1975 Infinity Monitor IIa's. The bass is deep and full without being overwhelming. They are rated flat to 22hz. I still have those speakers but also now have Von Schweikert VR4genIII's which are also said to be TL's. I like them top to bottom, though the bass isn't as full as the monitor IIa's I believe it's more of a room issue than the speaker.

Larry,

I can give you lots of first hand experience with quarter-wave TLs. My father and I first began to experiment with them back in the late 50s (wow, I'm getting old) and were completely taken with the inherent low frequency extension and lack of boomy resonance, although we were admittedly "guessing" at the optimum dimensions (cross-section of the line)and usually wound up with refrigerator-sized cabinets Over the years I've built about a dozen differnt designs, each one improving on the last (lessons learned)and reduced in size.

Fast forward 50+ years. While browsing the Parts Express site I came across a link to a website by Martin J. King www.quarter-wave.com and was blown away by all the research and modeling this guy has done on TLs, especially the utilization of a tapered line and variable density stuffing (Acousta Stuff)which results in a dramatically smaller enclosure. It was the first time I'd ever seen a mathematical expression of TL characteristics---which takes some time to understand but really explains the physics of this concept. He has also reduced all the calculations to easy to use tables for the DIYer.

With this inspiration, I got out the drawing board and saws and put together a sub using a PE / Dayton 12" reference series woofer and modest 240W plate amp. In a word, I was stunned with the results.

Based on this success, I have gone on to build what I call an "Uber Woofer" using a 15" PE/ Dayton reference series woofer and PE's 1,000W external sub amp. While the cabinet is a bit larger (tuned to 17 Hz, which increased the line length), it still passes the wife approval factor (WAF) where I have it positioned in a corner of our theater room. Cabinet dimensions are 65.5H x 20.5W x 16D, it sits on 3" roller wheels, and the woofer is down-firing.
Awesome does not begin to describe the flat response and LF extension it generates, and transient response is completely satisfactory (to my ears).

If you're a real bass afficionado, this is the only way to go. I built it for about $800 and it blows away anthing I've heard under $5K (yes, I listened to most of the high end subs at the recent RMAF).

If you'd like more info, feel free to contact me, but I really suggest that you first take the time to study and understand Mr. King's website. I think he's probably done more research on TLs than any of the loudspeaker manufacturers mentioned in this thread (including Mr. Theil, GRHS).

BTW, if you're wondering why none of the name brand manufacturers have pushed TLs, it's not because of their lack of transient responese, its due to the much higher construction, packaging and shipping costs compared to the contemporary sealed / vented "boomboxes" (which they can sell at higher margins).

You can make the T line as long as bass wave.

Unless the bass is generated adjacent to the wall, in-room cancellations will create the swing in FR you cite in your OP. So....either find a loudspeaker designed for use against a wall, correct bass response with a room correction device (e.g. Audyssey), or drop the objection to subwoofers.

Marty

That said, good luck with the TL hunt - I do like some of these designs, particularly the aforementioned IMF and Fried. Alas, the listening room is a cruel mistress.