Transmission line speakers!

Infinity Column and Column II, QLS-1, Quantum-2, 1001A, to name a few.

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None of them were. They were Line Source. QLS. Quantum Line Source.

They were a hybrid at that. Then only the QLS1, kinda. It wasn’t a true LS speaker not TL. It was a big ol box.. That’s it..

A transmission line uses an internal partition to lengthen the path from the rear of the driver, to the port. The sound is transmitted through the length of the path and in doing so tunes the box.

There are no folds, much less bracing in any of the Infinity boxes. Just a big ol box, nothing fancy at all.. Veneers. :-)

This is the inside of a transmission line.

You can see the mids and tweeter would have to be an enclosed design to share the same baffle and port for tuning. That hole in the back, I’m sure that is for the binding post. The space on top is tuning the box, adding bracing and reducing resonance issues with the long section of the throat. The long run in the back we use to put shag carpet.. Now NoRez on the back only. Maybe 10" of the port exit.

Every corner would need batting. This is a serious build, they did a good job smoothing the throat. See how they rounded the corners. They are not just left square. Double front and bottom it looks like, too.

Regards

They use a passive radiator on the bottom to tune to box.. Still a port.. I've tuned these with putty, add and subtract the mass on the bottom.. Quite effective per room and amp.. (Q)uality tuning.

My Infinity Monitor IIa’s are transmission line. I bought them new in 1977 and still play them daily. They are rated flat down to 22hz and have the best bass performance (ie, most pleasing to me) of any speaker I have had - including my Von Schweikert VR4-III’s, which are also transmission line (per Albert Von Schweikert).

Some of Rega’s  speakers are purportedly TL.

That’s a really impressive TL cabinet oldhvymec.

Transmission line woofer enclosures are a way of effectively doubling the size of the woofer by turning it's back wave around and getting it to come out in phase with the front wave at the "right" frequencies. It is a very difficult design to get right and requires a lot of trial and error fiddling. It is best to keep the woofer under 200 Hz or too much coloration will get into the midrange. Done right it can make a smallish loudspeaker much more powerful. The best one I have heard is in Roger Sander's Model 10 ESL. He bi amps them and uses a dBx Driverack as a crossover.