Transmission line speakers!

Hi group,

I just pulled the trigger on a mint pair of Falcon speakers. They are a transmission line design. I don’t see many speakers using transmission line. Does anyone here have any experience pro or con with this type of design? BTW, I have always liked sealed type speakers over ported speakers!

Thanks much!


I use transmission line speakers rear ported, new production, not a known brand (custom made). They are rather splendid in my opinion for the price point of about $2K (direct selling from the dude who makes them).

96 dB @1w/1m, 26hz - 30khz +/- 2dB.

I didn’t know anything about TM before buying them. There is quite a lot of reading available, some quite technical which is above and beyond that for other configurations.

As to pro/cons - I can hear only pro things, but I’m biased so don’t go there! Enjoy!

[edit - coincidentally, just yesterday I posted a quote from Stereophile which referenced Falcon speakers - that Prima Luna bloke reckoned PL are a good match for Falcons.  He sells PL by the thousands, so read into that what you may! ]

First speakers I built were the Roger Sanders transmission line design published in Speaker Builder magazine back in 1980. Being dirt poor they were built to fit the 10" woofers from my old JBL L26 Jubal speakers. 

These transmission lines were about 14" wide by 20" deep and about 48" tall. This was way before all the speaker building software we take for granted today. A lot of this stuff was worked out pencil and paper. However he did it the same drivers that put out lumpy bass that trailed off below about 60Hz somehow were a lot more flat and extended way down at least an octave lower in the transmission line cabinet.

It is such a winning design I have to think it isn't used more because of size, construction cost, and weight. Mine were twice the size and three times the weight of the JBL, and that was just for the woofer. They were so good however I was able to put some little car speakers on top of them and this combo was actually a pretty normal floor stander size and sounded far, far better than the JBL. 

Again, this was 1980. More than 40 years ago. It will be a travesty of short-sighted cost-cutting if the ones you just bought aren't light years better. And these were already pretty damn good!

Many loudspeakers use transmission line design and you would not know it by looking at it. Many Infinity designs of the 70s were transmission line.

Being dirt poor they were built to fit the 10" woofers from my old JBL L26 Jubal speakers.

JBL L 65 Jubal’s have a 12’’ woofer not 10’’.

Many Infinity designs of the 70s were transmission line.


I'm not familiar with any transmission line speaker Infinity made. Hybrid line source all except the Beta Vs I think. They were a true, line source speakers. The QLS1 was a hybrid too. Maybe you got the nomenclature mixed up.. or I missed something back then. Still have a few Infinities. RS2bs, RS4B, 2 sets of the original Infinitesimals. I've sure worked and owned a lot of them through the years..

Transmission Line Speakers are pretty cool actually. Folded box designs are too.

Fibonacci speakers. :-)


I’ve had custom transmission lines for 32 years. Even if I ever try another pair of speakers at some point, they’ll most likely use a TL. They’re more difficult to build and to get right than many speakers, but when done well, the lack of resonance can be spectacular from the low bass all the up into the midrange....the midrange can be one of the strongest benefits of a TL (lots of variables, obviously).  Add good higher frequency drivers and a well executed crossover, and you have the makings for impressive fidelity that most speakers struggle to match.

ditusa- Yes and the L65 has the 6 in front of the 5 instead of behind it like in the L25. Good catch. Anyway thanks, I was wrong about Jubal don't know where that came from they were L25 Prima. The L26 was the wood cabinet version of the L25. Same speaker, different cabinets. Both had 10" woofers. The L25 is the ugly one you buy when your paper route earnings aren't enough to afford the nice wood one. Thanks for reminding me how much I was willing to sacrifice if it would get me a good stereo. 

People think Tekton are ugly. They have no idea. Bright yellow and orange, ugliest speaker ever.


I'm not familiar with any transmission line speaker Infinity made.

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

I owned TDL large monitors, bought the same model twice, and loved them. Great subterranean bass.

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


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. :-)

Transmission line speakers, Subwoofer and Bookshelf or rear speakers

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.


Infinity Column II Speakers ~~ 5 way 250 Watts RMS

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.

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. 

I had a pair of TylerAcoustics HT2-TL speakers that I could not get any 80hz bass out of, in multiple rooms with multiple front ends.  Beautiful looking speakers, smooth, detailed and refined sound, but my Fritz Carrera BE’s smashed them in bass response.  I was able to get the Carreras to play -3db at 20hz and pretty much flat from 23hz to 100hz.



I had a pair of Clements Audio RT-7 that I used for years. Great speaker. 2-Way with a true ribbon tweeter and a small transmission-line loaded woofer. Narrow baffle. Nice sounding speaker. I auditioned it against a comparably sized and priced Ohm Omni speaker at the time and chose the Clements.

I may still be using them today if the cosmetic/aesthetic were better. The early RT-7s had a foam wrap around the whole column and the column simply sat in a base. The speaker column had a beveled edge on the bottom and the base had an opposite beveled edge to accept the speaker column. Wasn't particularly stable or instill a great amount of confidence in the junction between speaker column and base.

Later versions of the Clements Audio RT-7 did away with the column/base setup and also changed the finish from a foam wrap to finished hardwood veneer. 

Transmission lines are still ported speakers, although when properly designed tend to sound a bit better. Still nothing compares to a properly designed acoustic suspension design to my ears. 

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I also had a pair of Fried transmission-line speakers. Can't remember which model, but if I recall, they has some kind of cross-connectivity like Polk SDA. I could be wrong about that. I didn't have them for very long, and it was probably about 20 years ago.

None of them were. 

Infinity made the claim, not me. Oh, I guess I did...but I was referring to the Infinity's claim. I know they aren't a true labyrinth design but they stuffed the cabinet with absorbent material and lowered the port resonance. Maybe it was just fancy sales writers but they made the claim.  

My Infinity Monitor IIa’s are transmission line.

One of my favorites, only to be replaced by my Reference Standard 2.5s which I kept for many years.


This is the only one that I could find. A wave transmission line. I would have to take the driver out and look. Simple as that. 

I don't see a fixed throat for the exit port. I guess the hole in the back is the port?

They may use TL tech but in the stricter sense of a TL speaker design, not so much. It's like calling a QLS1 a Line source when the only one they ever produced was the IRS Beta V. Everything was not quite the same or a hybrid of some kind.

As far as deep bass, TL make good bass, the problem is like any speaker that has bass in the same box as the monitor section, timing is the issue. With TL designs it's even worse.. One driver doing double duty.. the back wave is slower.

As far as ports, I haven't used fixed ports in 40 years.. Passive Radiator, OB, or IB but fixed ports are Worthless..


@russ69  and All,

As I've said, I've owned a couple of different TL speakers. I enjoyed the Clements Audio RT-7 for many years, the Fried for less. However, for the last few years I've been using a pair of sealed enclosures - Infinity RS1.5s. They are a great fit in my room and sound fantastic. Better still, I only paid $264 on eBay and picked them up from the seller as I was driving through his area on a ski trip a few years ago. I love the sound of vintage Infinity speakers! I've even bought a pair of professionally re-foamed Watkins Woofers for them. Paid almost as much for the pair of woofers as I did for the pair of speakers.

Would love to have a pair of RS2.5, 4.5 or IRS, but I don't think I have enough space for them.

Many of the Salk loudspeakers are transmission are the new Philharmonic Audio towers.

When executed properly, the bass will usually go pretty deep and with good tone.

Another advantage is the roll off is such that they are easy to blend with sealed subwoofers.

@oldhvymec , I used to have a pair of those WTLC's.....long ago, far away...

The only objection, which took awhile to comprehend as to Why. was the Walsh supertweet on top, often referred to as the 'ice cream cone'...

Having corresponded with the one who worked on the prototypes literally on the kitchen table when @ Infinity, they were a bit of a lark.  Inf. had an agreement with Ohm of that era to use the concept...

My biggest observation/objection is the the cone is upside down; given the height, the Walsh only came into play when you sat on the floor about 6~8' away.  And, even then, the top corners of the TL cabinet appeared to 'get in the way'....

'Space and spacing finicky', and could have used a sub.  An active xover and tri-amping  as well, not practical at the time.

Pleasant until 'pushed', then over it's head so to speak. Replaced w/ESS AMT 1B's.

One of the reasons I play with Walsh drivers, tho'....with a somewhat different approach.... ;)

Thanks for the memory lane pic....*S*

Happy Post-New Year to you 'n all y'all...

*sigh* "It's the end of the 'bot jokes as we knew them, and I feel defined..." *L* least the veneer on that pair is just as bland as what was on my pair....

Arnie liked being 'cutting edge', but apparently had issues over spending for it...


"All of My 'ports' are fixed....and a good thing, too...." *L* ;)

Spouse claims I talk out of my 'stern' port, but I point out it's kinda' 'one note'... which, "Precisely!" is the refrain.....;)

Your results likely vary, to some degree....

@roxy54 not to nitpick but the oval KEF bass driver is the B-139. I worked at a KEF dealer and we had a speaker business as well w subcontract EE help and our own FFT and importantly ears to custom design transmission line  ( and other alignments ). The B-139 was a favorite for that duty as every TL requires “ trimming “ and KEF drivers had “ pretty tight “ tolerances for the day. We did a few B-200 in a TL and the Infinity Watkins 10” worked well in a “ poor mans HQD ala Levinson / Quad ESL system. We also carried Infinity ;-) no comment but sometimes advertisements get out in front of reality..but i confess to NOT dissembling every model, we had them all except IRS. Another dealer i worked at carried Freid / IMF and for tge $ or £ those were some impressive boxes…. fun thread…

Now, there are some advantages to a tapered TL alignment for the B-110 driver…ala KEF Cantata as i recall but…2 lazy to go look at the  B-110 file… a great mid for sure

@asvjerry i have the same one note problem, play a B e a n Flat…or so the War Dept. says…

On further review of the infinity marketing material that led me to think the monitor ilia is transmission line - it actually says that they “pack the other Enclosure with uniquely configured material that further damps the woofer and creates a transmission line load”.


I think the real magic is in the woofer itself which has damping material applied to the cone which stiffens it.  

they still produce glorious deep, deep bass, however it’s done.

My Vandersteen 1C’s are transmission line. The ‘port’ is a wide thin opening at the rear bottom. Now used in my bedroom system. Was laying in bed streaming last night before going to sleep, and never ceases to amaze the *quality* of bass those speakers are capable of. Are they as good as my 2CE Sigs or Treo’s in quantity of bass? No, but pretty good for what they are.

tomic601....and Beano won’t stop it!

Real drag for us refried fans...having to stay downwind to download, degauss, denigrate the local atmosphere....not to mention the potential of cheek chunks...

(I know... "Too much information, runnin’ through my head..." Thanks, Sting....*G*)

*sigh* 6’o1, half dozen of the other.... ;)

@reubent , never heard or heard of the Clements RT7’s. but a quick drill-about brought up a look@.....👍 Taller ribbon versions of that sort seem to present a nice stage, I’ve a smaller bookshelf pair that mate nicely with the home flat screen. Part of a small Philips set bought to ’fill in the blank’ awhile back.

One CN vendor ( has tweaked my interest with theirs, but never pulled the itchy trigger of mine to try. Never read any comments here, but would expect the HF drivers to respond nicely. That, and not being a dipole would be an attraction for the room(s) not suited for such.... If any have any thoughts upon, would be of interest perhaps...

Seems to be TL cabs beneath, but could be wrong.....*horrors* Me, Wrong?!

Yeah, weakly....*L*


My Shahinian's were transmission line, as were my TDLs. I think PWK's folded horn was an extension of the principal.

Many of the speakers that Dale Pitcher designed utilized transmission lines. He was responsible for the Essence, Intuitive Design, and Mosaic Acoustics line ups. 

A lot of Mark Audio full range drivers use Mass Loaded Transmission Line (MLTL) speaker enclosure designs to optimize their bass response. They are modern designs that more resemble bass reflex boxes in appearance with a duct at the bottom of the cabinet.


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


The Khorns were nothing like a transmission line, they were just a horn loaded bass driver.

I started designing Transmission line speakers in the mid '70's. They can be real good for the money. These days I use a ported cabinet design because you can get a better final performance curve.

I own T+A Criterion 2100 TL speakers.  I believe all the T+A Criterion speakers are transmission line.    Very deep, natural and linear sounding bass for midsized floorstanding speakers.  Never boomy, even in my room with hardwood floors. 

If they are in your price range, I'd take a listen.  I think they have one of the best transmission line designs. 





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.

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.  


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. 



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.

I think PWK’s folded horn was an extension of the principal.

I think it is the opposite, the transmission line is using a quasi folded horn principal with a port. Whereas a true folded horn will exit the air in the woofer chamber out the mouth of the horn (no port). I could be wrong...