Transmission line speakers!

I'm another fan of the acoustic suspension approach.  It's been ~50 years since I read the Thiele-Small papers, so please correct me if I'm wrong.  IIRC, ideal porting only extends linear bass response for something like 1/3 octave - 2 or 3 notes.  Below that, it drops off at 12 db/octave, while an AS design rolls off at 6 db/octave.  In addition to the rapid roll-off, ported designs also unload completely at their resonant frequency, resulting in wild, undamped woofer oscillation.  A TL is a modified port design.  Creating a longer, damped path to the port ameliorates some of the problems with ports at a significant increase in cabinet complexity and cost.

I am intrigued by passive radiators, which allow the use of the woofer back wave without unloading the woofer, but have never owned any.

https://www.xlrtechs.com/dbkeele.com/papers.htm

I own T+A Criterion 2100 TL speakers

Now those are true TL speakers.

In the late 70's I owned Infinity Monitor Jr.'s; they had varying densities of cotton batting inside the cabinet and Infinity called them a TL design.  I always felt they were stretching the TL definition and that they were actually just another vented cabinet design.  IMF's were the TL standard back then.  

mrmichaelp

Those are beautiful speakers... impressive

I had  pair of Spendor D7 which uses a quasi-transmission line bottom firing port.  The bass and sub-bass was so deep and effortless, a speaker with very special bass.  It improves the efficiency of bass response and makes them easier to position. 

My issue with the Spendors is that they were voiced nearly flat without the usual midbass bump.  Otherwise they would have been perfect. 

T-line designs have the potential to be outstanding.  Application is unfortunately not consistent. 

bkeske,

I'm not sure of how a transmission line port differs from any other port, but that is only part of what a transmission line is. It should include a long folded labyrinth from that rear of the bass driver to the port. I would like to hear from others more knowledgeable than myself here as to whether they consider this a transmission line.