Transmission Line Bass

As a long time proponent of good bass without subs, I like tinkering with different ways of approching the age old problem of recreating all energy below 100Hz.
Seriously, if you look at loudspeaker responses, everything seems goes to hell just below that point, swinging wildly in output response, almost independent of many of the typical factors that would be indicators of performance.
So, the question.
Who among us has had extensive Transmission Line Bass Experience in listening, (like me with the IMF's in days gone by, with Bud Fried being a wonderful mentor to me).
In Jim Thiel's lab, one time he told me 'candidly' that Transmission Line Designs 'in theory' don't work. (Another discussion for another time). But he, like me was a bass freak of the first order, loving a rich full bottom end, hence some of his equalized designs early on. They were an all out attempt to bend the laws of physics.
So, what do we think of Transmission Line bass--so, if you're familiar with the sonics though actual listening, and can express first hand opinions let us hear your impressions of the differences between ported, passive radiators and transmission.

Thanks in advance...

I am a fan and, although I have not built anything recently, I have built a few TLs that have been entirely convincing. The IMFs (the ones built in England by John Wright) were my inspiration.

I'd rather hear about the other discussion now:-).
Jump right in.
In the late 70's I built a pair of Frieds 12" subs, I think they were called the OM12 or OM2's. Can't remember. I thought the bass was very realistic sounding. Deep bass sounded like real instruments. The only problem was it was a little slow so probably not suitable for todays speakers.

Heard the Intersound speakers at the RMAF, I think he uses a 10" transmission like below the electrostatic. Sounded really good, so there must be potential.

Not extensive experience...............intensive however.
I have had a pair of Meadowlark Blue heron 2's for over 4 years now. They are time coherent, use first-order crossovers, and are transmission-line-loaded bass. I am not skilled in the art of audiophile bs and I have not owned that many speakers. I can tell you the subtlety and nuance these speakers offer are amazing to me. The placement and clarity of instruments and voices, the decay of notes and the general sense of presence can transport me or punch me in the gut. I am still surprised by their sound. Too bad they went out of business.
Anybody familiar with the PMC versions of the transmission line? FB1?
You lost me, I had to reread my post...your talking about Jim Thiel's comments, right?
He's not the only person to take exception to the efficacy of the TL in loudspeakers, as I understand it. (One reason for the post actually).
Reading a bit, I hear things such as, "Since a bass wave that we're talking about is longer than the line itself, how can this work...." being one of the more popular nay sayer comments.
Then, I read again, as it's been years since I did so with enough interest to remember such...that the wool, (that Bud Fried used) and I prefer for sound dampening in speakers, causes the speed of the bass to change internally to approxiamately (too many factors to be specific), 85% of it's original speed, and that depending on the methods used, the bass tone is 'tricked' (not my words) into thinking the line is actually longer than it is, by an amount of distance which is significant.
Now you see why I posed the question.
I'm about to use a TL in a simple form, and compare it to just ported bass, in a bookshelf--and I'll be happy to pass on my subjective impressions of the quality of bass. (May take a little while).
So, I'd like to hear more of your opinions about the qualitative, (subjective of course)differences.
I do remember my IMF's having some of the most 'musical' bass I'd ever heard...especially given the cabinet size of the speaker I was listening to.

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.

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 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.


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.
You've stated the very thing that makes this whole debate an ongoing one...
Just wondering, as a 50Hz tone is 25', how would that be possible? (To build a T Line as long as a bass wave). A 25Hz 50'...and so on. This is what Jim Thiel was referring to--whether valid or not, with regard to our ability to build such a device. (I refuse to discuss most theory, as people ususally know, myself included, just enough to argue not convince). What is everyone else missing?
PMC are worth every dime"""USED $$""" but the MRSP is absolutely outrages.
I have heard very good bass all types of inclosures, including Transmission Lines, as it has been alluded to here already, the line can be quite long and quite frankly, the transmission line enclosure is the toughest to get right. I believe that is the single reason that you don't see alot of transmission lines, but done right, they drive the speaker down...down quite well. This design allows us to get deep bass from smaller drivers.
It is also very difficult to get a great driver that will do very well in a sealed box, but when done correctly, I still prefer a sealed box bass with the proper finished qtc.
Again, "when done correctly" Good Listening, Tim
It seems to me that though it might be possible to build a TL with the necessary dimensions, with or without "stuffing tricks", for most of us, it would be impractical to house, and even more difficult to market. Of course all designs necessitate compromise, and I suppose one could get some measure of the benefits of a TL in a more manageable package.
I have yet to hear a speaker that uses a transmission line enclosure reproduce natural sounding bass. I do think that TL's can produce deep and powerful bass when done correctly, but something about a TL system simply does not sound "right" to me. My current speakers use an aperiodic vent which, it seems, is pretty rare. They produce the most natural bass I've ever heard.
what about the acoustic zen adagios? Are these true T-lines?
Its tough for most people to separate what sounds correct, from what sounds like the thing that they're most used to hearing.
While designing, a tragic error can be to use a previous model, OR another speaker as a reference--don't get me wrong, it's almost impossible not to. However, as Michael Keaton said in Multiplicity, 'a copy of a copy of a copy is just not rignt.' Therin lies the danger. I had to, since I didn't happen to have a live band here, use a speaker, and I used the Sound Lab A-1--and its no surprise that my loudspeakers sound was natural, flat, while still musical, as the Sound Labs sort of set the bar in those areas.
However at some point you have to, in your mind's eye, still be able to hear/know what that bass being bowed or plucked, really sounds like, and have a really good sonic memory. All this is my way of asking, 'Does it sound like music, or what you're used to hearing from speakers'...and THAT is a distinction with a difference to me.
Then there's the 'Transmission Line Bass' has its unique sound,' camp. I agree, and I like that sound, and think that in some ways its more natural sounding.
The funny part about bass is that, bass gets its character from the midrange--2,3,4,5 and more octaves above the dominant tone that's expressed by the instrument.
When a double bass's open E string is plucked and 41.6Hz is put out there, it's really 83. whaever, then 166.whatever Hz and 332.Hz then 664Hz thats giving it so much of its tonality. Bass is curiously, or maybe not curiously the most complex aspect of music--partly because it's centered in our human hearing curves center--kind of.
Whatever, just rambling now.
More thoughts...your input(s) have been great!

I have a transmission line speaker built by Serious Stereo which uses the Altec 604 duplex driver and 2 bottom vents. I must say that the bass is much better than the other ported speakers I have had in the past. It goes down into the mid 20hz before starting to roll off. It is very tight and nuanced. The downside is that the enclosure is 11 cubic feet so the speaker has a rather low WAF.
I have Fried Studio 7's. I love the transmission line bass. It just sounds more authentic, not bloated or artificial in any way. Some here cite size as limiter and my Fried's are pretty substantial, but you can get good TL bass with smaller enclosures and folding of the transmission line. Another plus for TL enclosures, is because the internal transmission line construction naturally lends itself to a stiffer cabinet.

I own or have owned 2 TL systems. Both produce bass of very high caliber IMO. The speakers are the Intuitive Design Summit (no longer own) and the Fried C3/L monitors with Fried D2 subs currently in a second system. Both the C3/L and the D2 are TL loaded. I found the bass of both speaker systems to have excellent pitch definition as well as proper weight. I don't hear bloat or overhang with the Fried's or the Summits. Both systems are very dynamic. I do not know if the TL loading plays a part in that or not, but to my ears they sound very natural and convincing thru out the bass.
You do know I wasn't saying that emperically, you didn't reference live music, right? It's just that very few people really have that inner reference, and sonic memory. I liken it to perfect pitch, or relative pitch...rare and unusual talent. I'm fortunate, in that I can hear, and remember...your comments are far from being unusual, hence the question. Its not a 'mild' complaint, almost a 'love it or hate it', kind of thing, so far, and you expressed a very valid, "I don't like it", which should probably should be, "I don't like WHAT I've heard SO FAR." I personally LOVED it, and was a little disappointed in the electronic sound of the equalized THIEL 03as that replaced my beloved IMF's, back in the day. I became accustomed to it, sort of like having a wife who smokes--you learn to look past it, I suppose. Older now, I have a smaller window of 'looking past', and want to really do it right.
My LSA's have good bass, and with the mosterous Air Core's that we used, and great caps, very tuneful. But, I want to move to the 'next and better thing'.
I'll tell you what's how 'right' the bass on the A-1 Sound Labs was--no cabinet noises, obviously, perfect phase, perfect time alignment--and it just sounded right. Maybe I want an electrostatic with that kind of bass response...I DID love it. They are so damn underrated in EVERY WAY!

See, your comments are very 'spot on' as to what I experienced. See Dodge, another, like it to offset. This is what's maddening.

I enjoy listening to
Clements RT-7
with its version of transmission line bass and ribbon tweeter.
Sounds very satisfying over a few decades.
Positively thrilling on good recordings of music from challenging opera and organ right on down down to solo vocalist, piano or violin.
I also go to a lot of live performances.
A home system properly reproducing a great recording is not usually able to reproduce what I actually hear (or, heard) in the audience at live performance. Still, we all can know and enjoy great sound when we hear it in the home setting.
Hearing pitch accurate, musical TL bass that subjectively "keeps up" with a ribbon tweeter is a speaker designer feat, for sure.
Congratulations to Philip R. Clements. He is worthy of mention in the same breath with other elite speaker designers.
Clements 207 D I's and a pair of 107 D I's outstanding clean bass.
I think that the most important improvement in the bass when using a Transmission Line is not so much the depth of the bass but the quality.. I attribute that to the face that the rear waves off the back of the driver is not just absorbed by the MDF (in most speakers) but rather has an outlet. This must reduce the resonance considerably. I remember when I built the Fried's using Bud's 12" driver I asked him if it would be better to use MDF the the plywood in his plans, (they were do it yourself) speakers. He told me that he didn't feel any resonance in his cabinets that were made from plywood.

Of course I ignored him, who wouldn't, he was just an old man, and I was young and much smarter then he was... then the wisdom of his choice came to light when I had to carry the speakers up stairs from my shop in the basement.

Larry lets us know how your experiment goes.

Sounds Real Audio
Can you spot the problem with transmission lines...?

The advantage is managing the phase from the back wave to reinforce or null at specific frequencies.

Traditionally, a transmission line is tapered and "stuffed" which absorbs some energy, lowers Q, and reduces bass extension. Been playing around with another idea that takes advantage of the difference between slow air movement and fast sound travel but, as yet, untested. Expect complications.
Any reports on the Salk Veracity HT1-TL or HT2-TL?
I believe TL designates "transmission line" models.
PMC is an excellent example of a well designed TL.
there is a really good white paper on the wisdom audio site. They are using "regenerative" transmission lines in all of their woofers - and they are the best, most musical subs I've heard.
go to audio circle big fan club of salks over there
I have a pair Intuitive Design Summits, like Csmgolf had.

Not to complicate matters, but they are referred to as a triangular transmission line design by Dale Pitcher.

The lower cabinets have three tubes running from top to bottom inside (in a triangular position) which contain some kind of fluid (I don't know what the fluid really is)

The lower cabinets themselves are also fillable (more or less) to help achieve proper bass response in accordance to room size.

The energy from the top cabinets is transmitted via Stillpoints to the postions of the tubes in the lower cabinets.

A very effective design, I sold my pair of subs after hearing these.
only if you listen at high levels...

+ great speed & coherence with 2 Ways (PMC GB1 / DB1)
+ great PRAT at high levels

- unnatural bass
- bass volume much lower than mids volume

dont care for the 3-way designs (PMC).
Check out the Stromberg Carlson 340 radio (1939) with Acoustical Labyrinth. the first transmission line?
Would the Dali Megalines produce the kind of bass you are looking for?
I run soundlab m2's and the bass they produce in my system sound quite good,I listen to jazz,choir with organ(cante domino on Proprius great organ),vocals and even pink floyd drops in now and then.
I don't think I have ever listened to a transmission line speaker but this is quite a interesting thread.
I've had a few TL speakers (dcm,Freid & TDL),and the main draw with all of them was base performance. For me, TL systems seem to just sound "right". I'm not sure if they are really better, but they sure seemed to go lower than their little woofers had any right to!
I think the appeal of Transmission lines was (when done properly) was they did not have peaky low end boost as so many short port speakers offered at the same time. There were a lot of crappy cone speakers around when Freid was hot in the late 70s. Really nice extended lows from very small drive units. However, the TL vs port is a bit unfair, like comparing apples to oranges. A transmission line is BIG, and even a long port speaker was much more compact and workable into a room. Most purchasers would not be comparing a TL to the more compact monitor for a host of (non audio) reasons. A Dahlquist DQ10 was easier to work into a room than a big tall wide top of the line Freid..

My DCM TF700s go much lower than DQ10s ever could, and with a much smaller foot print. They are about the same size as DQ20s, but have better low end than those as well. I'm not sure I'd be so quick to dismiss TL speakers as overly big for their base response.
I don't think TL speakers are overly big, that was not my point. My comment was the TL is not free of cost to the consumer; there is a size "price" for a long transmission line (even folded as much as possible).
I would still tend to disagree with your assertion that TL speakers shouldn't be compared to ported. Since small and large speakers, with deep, and not so deep base, have been offered in both designs... as well as sealed & infinite baffle, for that matter. I think most people look for the best compromise between price, sound, and size.

Since there are small speakers made with each of these base systems the listener has to choose based on those three criteria, even if they are looking for a small speaker. The only base system I'd categorically eliminate from their choices would be horn loaded... even a "folded" horn loaded design would not be competent for a small, say "bookshelf" speaker.

Fried, DCM, and others, have offered true bookshelf sized speakers over the years, that benefited from TL porting. Of course, due to their size (and subsequent TL length), they didn't go super low, but then again neither did their Vented, or sealed counterparts.

I guess I cannot disagree with the way you say it. But you have to agree there are quite a few larger TL speakers and not so many little ones! TL and ported certainly can and should be compared and they are.
"everything seems goes to hell just below that point," (100 Hz).

That doesn't happen with Maggies, which is why their bass is a lot "better" than you would expect from the specs. My MG1.6 go silent at 40 Hz, but above that the rolloff is perfectly smooth. Lots of music can do without 40Hz and down.

PS:I do have subwoofers for when I need them.