Greetings people, What are the arguments, pro and con, for transmission line speakers that: have channels with parallel walls, and those that progressively get wider, as in a horn? I want to do a build with plans that show parallel walls, where I can alter them to create an ever widening channel within the same size container. I am a newbie in this area of DIY speakers, and am sure there are opposing views.
Transmission lines can be very satisfying... As koss_amojan explained in the past there has been a great deal of guess work... Maybe 20 years or so ago the math was fairly well proven based on figuring line length based on the cone size and what it takes to get a quarter wavelength of acoustic standing wave inside of the transmission line. It isn't typically for the beginner. If you insist on a transmission line, I would highly recommend that you consider finding a proven kit and starting there. If you'd like to create an all new design of a transmission horn or something, that would be great, we are always arguing within the forum that there isn't real growth in speaker technology, maybe you can give us all something to talk about.
A speaker with well-designed transmission-line woofer loading is the ESS Transtatic I, from the very-early 70's (I first saw and heard it in 1971). The woofer in that speaker was the famous KEF B139, a great driver for it's time (David Wilson used two of them as the mid-bass driver in his WAMM loudspeaker).
The reason ESS ended up being the manufacturer of the Heil AMT speaker is that Dr. Heil had heard the Transtatic, and wanted to use the B139 in the speaker he was designing. He came into the hi-fi specialty shop in San Jose that was an ESS retailer, TV-Audio Center, Inc. (where I heard the speaker, and where legendary High End retailer John Garland worker at the time), to find out where he could buy some of the drivers. They put him in contact with ESS, and the rest is history. I have a pair of Transtatics; if you're anywhere close to the Portland, Oregon area, come on by!
@roberjerman "Take a look at some of the old IMF’s (U.K.) and how they built their trans lines. TSL - 80’s. I’d just copy them!
That’s excellent advice. Bud (Irving M Fried / IMF) was a mentor of mine, and one of the most interesting and unique people in audio history. I have his own personal O subwoofers as part of his Valhalla (pyramidal C satellites with true transmission line midrange + TL subs) System that he gave me shortly before he passed on. Large, but manageable and not overly large cabinets, they would fit into most rooms that have mid - large sized loudspeakers. I have the plans for the O and D subwoofers around somewhere that I might be able to scare up if you’re that interested, they’re somewhere around 39" tall X 13" wide X 27" deep. He also produced even larger SM and the H (coffin) subwoofers, and I used to know where to find them on the web. There’s nothing about the design that any reasonable DIYer or someone with decent woodworking skills couldn’t handle. You can stuff (not overstuff) them with the ubiquitous open cell foam, though people also use a lot of other (wool, fiberglass, cotton or polyester batting) materials. I can scare the pants off most (literally) people, including myself, with a Dynaco ST70, though hefty solid state amps would obviously put out a lot more low-end grunt.
True transmission lines (TL) handily outperform both bass reflex / ported and sealed and aperiodic bass loading configurations. You get an incredible sense of the music (many use the term tuneful) compared with ported speakers, which was Bud’s (he also produced a poor man’s TL called the Line Tunnel which was a stuffed ported speaker used in many of the products, along with aperiodic loading in the Beta) motivation for using them. I’m not one who uses the "one note bass" description of ported loudspeakers, but I understand what people mean. The description I feel when comparing them is that ported speakers sound tremendously dirty and distorted next to a TL. They also portray a lot less sense of the box or restraint than sealed designs. It’s one of those things you don’t realize until you hear it in comparison to the other methodologies, and then you don’t forget it. I’ve heard so many people downplay the advantages of TL, but I think it’s simply a function of not actually experiencing it themselves, and underestimating it. I often wonder why more companies don’t sell such designs. That said, I don’t want to imply it’s something magical, mystical, or otherworldly, as it simply isn’t. But well-implemented TL is better than the other alignments. The downsides of transmission lines are the the added complexity, cost of construction, and people not really understanding them which others have raised, along with reduced efficiency compared with ported speakers.
As great as TL is for bass, it’s all the more advantageous for midrange loading. Bud and I often discussed how the music just flies out of the speakers in a way one likely never experienced otherwise
I am a woodworker who builds one-of-a-kind, exotic, high-end furniture. I think I'd like to see those plans...if it's not too much of a hassle to find them. And thanks for the info. It's invaluable.
I have built a number of transmission lines. Generally, I’ve set the line length to be 1/4 of the wavelength of the lowest frequency but assume that the packing effectively reduces the speed of sound by 1/2 (most likely because of the packing (I use polypropylene.) The line tapers from 1.25 x the driver’s piston area to the piston area at the rear or bottom exit. Try to find an efficient, high power-handling driver to use. I like 8" drivers that can handle at least 100W continuous and have SPLs at least 92dB and around 0.3 Qts. They are very smooth down to very low frequencies. My current LF speakers are rolled off below 25Hz because the go down much lower and that information is just noise, can't be heard, and only shakes stuff around.
@trelja said: "True transmission lines (TL) handily outperform both bass reflex / ported and sealed and aperiodic bass loading configurations."
I agree that good transmission lines sound wonderful, and have greater potential than either reflex or sealed or aperiodic boxes. As a manufacturer, with enclosure cost being the dominant cost, I believe that I can offer more bang for the buck with a good reflex box.
Going back to my DIY days, one issue that I ran into with transmission lines is the one-wavelength cancellation dip. At the frequency where the path length is equal to one wavelength, the backwave energy emerging from the open terminus is 180 degrees out-of-phase with the energy coming from the front of the cone. The two are physically close enough that significant cancellation occurs. I could hear the dip before I figured out what was causing it. You can see it in anechoic measurements of transmission line speakers:
The dip is probably not as bad in the power response (summed omnidirectional response) but it will still be present. Fortunately dips look much worse on paper than they actually sound - the ear is pretty good at ignoring them.
There are techniques for mitigating the dip (positioning the woofer partway down the line, using very dense stuffing, building a Helmholtz absorber into the line), but like practically everything else in speaker design, they involve tradeoffs.
From your experience, do you have any comments on the one-wavelength dip? Did Bud Fried do anything in particular to mitigate it?
Trelja again: "As great as TL is for bass, it’s all the more advantageous for midrange loading."
Again, I agree. I think the transmission line acts like a "trap" for the backwave midrange energy, so that very little of it reflects back into the cone.
I had an article published in SpeakerBuilder magazine back in 1986 that used transmission line loading for the two 7" midwoofers and for the 30" tall ribbon they were mated with. Over the years several people have told me they tried various enclosure designs for the same ribbon and my "W-shaped" transmission line geometry worked the best.
I still think about doing a transmission line "satellite" speaker that would be augmented south of 80 Hz by a distributed multisub system, since I believe the room effects are the biggest issue in the bottom two octaves. This would let me use a smaller transmission line box (less costly) and would take advantage of its superior midrange potential (which is imo its biggest benefit). Maybe one of these days.
What I have found with reflex boxes, and this is somewhat counter-intuitive, is that placing the ports right smack behind the woofer cone results in better midrange than from a sealed box. I think this is because the (flared) ports act like traps and remove at least some of the midrange energy that would otherwise reflect back into the cone. So this is perhaps a crude first approximation of one of the benefits of a good transmission line. On these speakers I include a reduced-level rear-firing tweeter to combine with the port-escape midrange energy, to correct the spectral balance of the reflections.
Wow! Excellent info! (especially for the uninformed). Thanks, people. I was intending to use an 8" full-spectrum speaker of quality (and cost). I will stick to a known plan for the box until I get more knowledge.
@sound22card, I sent you a PM so I can forward you the Fried D subwoofer plans. This TL cabinet is 36H X 15.75X X 15D, and used an 8" driver. Personally, I find it a much bigger step back from my O subs with their 10" driver than I or most would have expected, but I can't find the paperwork on that right now. The benefit of the D subwoofer is that it mates perfectly (in width) with the C (pyramidal) Series satellites that sit on them to form the Valhalla System. Think along the lines of the Wilson WATT/Puppy aesthetic. But it will at least give you a look at one of the more highly regarded TL cabinets produced. Fried sold a pretty good number of D subs, and very few O subs. The IMF Electronics site used to carry a wealth of information on many of the IMF / Fried products, including these, but the content doesn't seem to come up right now. Hopefully, it's not lost, as there is a treasure trove of documentation there.
@areed622 "I like 8" drivers that can handle at least 100W continuous and have SPLs at least 92dB and around 0.3 Qts."
You included an incredibly important detail when mentioning the Qts. Bud Fried considered it critical importance to select a driver with as low a Qts specification as possible. Over the years, I've learned that's exactly opposite of most opinions I find in the internet discussions, which recommend the opposite. Bud even replaced the 10" drivers in his subs, and when he handed me a cardboard box, he explained these were the original drivers, but he was able to have Gefco make him a special pair with an even lower Qts, and those were the ones in the cabinets. I can tell you from my Fried O subwoofers, they really bring the thunder, and apart from being a bit larger than most folks feel comfortable with, have no real weaknesses. As I said, even when I know what's coming, for whatever reason my body will still (involuntarily) flinch when certain notes get played.
@audiokinesis, my hat's off to you, Duke. You REALLY understand TL!
Thank you very much, @trelja. I made a lot of sawdust trying out different transmission line ideas in the late 70’s and 80’s.
You wrote:
"Bud Fried considered it critical importance to select a driver with as low a Qts specification as possible. Over the years, I’ve learned that’s exactly opposite of most opinions I find in the internet discussions, which recommend the opposite."
Must admit that I had better results with medium to high Qts woofers in transmission lines, but then I’m no Bud Fried!
Can you reveal anything else about what parameters Bud looked for? I used KEF B-139’s in most of my sixty-something transmission lines, but I’m sure the over-the-counter version’s parameters were not ideal. It’s x-lim was rather modest, as I found out the hard way.
I would love to know how to use a low Qts woofer in a transmission line. Low Qts = high motor strength = good midrange articulation, in general.
If you don’t think it would violate any confidentialities, I would be very interested in the plans for the D that you mentioned. I’d love to peek under the hood and see what the master did.
There is more bad information about TL's on the Internet than accurate information. The methods on my site have been used to design many TLs (100's probably) that have performed as predicted. The methods have been used by Salk Sound, Dennis Murphy, and a few other commercial TL manufacturers.
Thank you, Duke. Your experience with TL seems to mirror what I’ve read from most people apart from Bud.
Nothing proprietary at this point, most people don’t even remember who Bud Fried was. Anyway, I saw (Salk?) has been trying to resurrect the Fried name, but the products are far different than what Bud used to build. I can send you the plans for the C/6 satellites and D2 subwoofers. You can also have the crossover values from Bud’s C sats, if you want. I’m not sure if you feel comfortable with series crossovers, but even though most implement them as first order, you can alter a value called Zeta (ratio of cap to coil) to produce a steeper or more shallow rolloff than 6 dB/octave. 6 dB/octave has a Zeta value of 1.0, lower (say 0.8) values sound more forward and have a sharper rolloff, higher values (like 1.2) sound more relaxed and liquid and have a slower rolloff. Bud didn’t actually know Zeta per se, but it seemed he understood it from a practical means in terms of varying the cap to coil ratio. Bud’s crossovers are somewhat less than 1.0, and sound a bit more forward than I personally prefer.
I’ve met and received emails from more people over the years than I can remember, all with great stories about him. Most of them focus on either him writing 3 and 4 page handwritten letters to them multiple times in response to their letters or spending a couple of hours on the phone providing the same insight for those willing to pay for the call in the age of expensive long distance service. John Rutan of AudioConnection who often posts here loves to do a Bud Fried imitation that’s just like The Frog from Courageous Cat and Minute Mouse. Most don’t know Bud introduced Lowthers, Quads, Decca cartridges, Dynaudio / ScanSpeak, and other European products to America, quite impressive. I think there will never be another manufacturer like Bud.
Bud claimed to have had a real BAD experience with Focal. You may know he had a fondness for Europe coming out of his WWII service, and spent 1/4 - 1/3 of the year there. His side of the story is he went in pretty heavy with their impressive looking drivers in the early 90s, but told me the product received didn’t come close to what the product literature specified. They disagreed. While on one of his many travels through France, he claimed to have dropped in on them, and demanded a set of measurements be run in front of him to see who was right. Upon returning back home, no Fried ever used another Focal.
He wound up with Gefco for midrange and woofers, of Chicago, who are no longer in business. He claimed they produced the best drivers he ever used. They weren’t pretty (paper cones, stamped steel baskets) or seemingly advanced, but they made him happy. His own personal speakers use them, though a bit hot rodded. You can still find a few on eBay and the like. I have some, as well. For tweeters, he preferred the Hiquphon, and they’ve long featured him in their advertising. I agree they make good tweeters, but don’t think it’s wise in going with a tiny one man operation in Denmark that could ease to exist any day.
Obviously, Bud also believed in series crossovers, which he felt were the most important of the three things he believed in - the other two being TL and low Qts drivers. He didn’t develop the technology, and claimed to happen upon it during one of his meetings with Dynaudio. He was an intensely curious and outgoing person, and asked what the two sets of crossovers were, and what I’m certain was enough follow up questions to represent an actual conversation. Based on his account, they explained one set was a parallel network and the other series. He said, what’s the difference? Their answer, well, the series crossovers work and sound better (I realize that’s a subjective statement). Of course, next question, then why don’t you use them? Answer, everyone feels they’re too unusual. As for me, it took a while to get my head around them, as they seem exactly backwards with the coil seemingly on the tweeter leg and cap on the woofer leg. One day a light went off in my head, and they seemed simple and obvious. The signal either goes to the coil or the tweeter, and the cap or the woofer - ah, makes sense...
@trelja In addition to big, very LF TLs, I built a series of small TLs using 4" LF drivers. The first iteration used a higher Q driver that refused to deliver the calculated 56kHz roll-off until a bit of putty was added to the driver dust cap. The weight of the putty was calculated to drop the Q to be ≤ the .3 . This worked and effectively supported the benefits of a low Qts. That said, I am currently running a pair of big TLs that work down to 17Hz using Focal kevlar drivers with Qs around .55 but these are bi-amped and DSP controlled and never worked properly using passive second order x-overs without bottom-end compensation.
I would love to see plans for the D and C, and the C's crossover!!
Yeah
the series crossover is a strange beast at first glance! Instead of
blocking the lows from reaching the tweeter and the highs from reaching
the woofer, the lows go AROUND the tweeter and the highs go AROUND the
woofer. So the specific filtering for each driver is actually in PARALLEL with that driver, but the components are all inter-dependent so it's really all one big filter instead of a highpass filter + a lowpass filter.
My
recollection from experimenting with series crossovers many years ago
is that you need to start out with drivers that have a smooth
response with equal overlap on both sides of the crossover frequency. I
used a Hiquphon tweeter, probably tried several midwoofers but don't
remember which ones. I got better results (to my ears) with parallel
crossovers using filters that had some electrical asymmetry, so I don't
think my midwoofers were a good match for the Hiquphons. I
do remember adjusting the L & C ratio but thought that was
just varying the amount of ovelap in the crossover region and didn't realize it was varying the
slope as well. I didn't have decent measuring equipment back then (in
my amateur days).
Some
pretty serious EQ is needed for my constant-directivity horns, as
without a crossover their response trends roughly -6 dB per octave from
about 1.5 kHz on up. (This is true both on-axis and off-axis, unlike
with direct radiators, so when we fix the on-axis response we have also
fixed the off-axis response - which imo is a very good thing). So in
this case an electrically asymmetrical crossover is needed to achieve
approximate acoustic symmetry, and I don't think that can be done with a
series crossover because the filter is one inter-dependent thing
instead of being separate lowpass and highpass sections, but I'll take another
look.
Did Bud have designs where he went for time coherence (first order crossovers + lining up the arrival times?)
Can you tell me anything about the Qts range Bud preferred?
Thank you Trelja and Duke for sharing the TL info and the stories about Bud. i agree completely with Trelja’s description of the sound of TL bass compared to vented or sealed cabinets. I also agree with Duke’s description of the dip in response caused by out-of-phase cancellation. The foam damping inside the TL helps to reduce the severity of the dip but it’s hard to ignore it once heard.
I built a number of TL woofer systems in my younger days including the Fried H. The most successful was a Fried O cabinet with a KEF B139 woofer and a Fried H satellite on top. My brother still has this system and it continues to sound very nice some 35 years after I built it. I also have several lengthy typed letters from Bud responding to my inquiries about his speakers. He impressed me as a true gentleman.
This is a wonderful sub-forum, and thank all of you for your valuable contributions. Curiosity drives me to build my own TL enclosures, and I looked at a nice unit by Steve Deckert that I can probably build relatively easy. http://www.decware.com/newsite/DNA2.html Unfortunately, I asked to buy plans and Decware won't sell them to me. Sarah Richardson, his polite assistant told me "The DNA2 is new to our speaker line so we don’t have any build plans
yet. Hopefully in the future but time will tell. Thank you for your
inquiry!
" So perhaps the DNA2 is currently built from memory. Can one of you fine fellows point me at a similar sized TL design that does have a schematic I can purchase :) ?
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