Transmission line speakers!

@roxy54

bkeske,

I don’t think that Vandersteen ever called any of his speakers transmission lines, and having a slot vent doesn’t make them one.

Sure they have. It’s right on their web site, and in many reviews of the 1C’s over the years as well.

From Vandersteen’s web site regarding the current 1C’s (the basic design has not changed), and also include a ‘cut-thru’ photo as well, albeit not very detailed :

The Model 1Ci’s transmission-line port extends bass response while operating much closer to the ideal than any of the more conventional ported or passive designs.

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.