Transmission line speakers explained

[@oliverbeard7912]

The phase is inverted 180 degrees before exiting the port,so is in phase.Below resonance where the air pressure within the box is unable to react against the pressure within the port,it just effectively becomes a hole and phase cancellation then sets in.This is the reason for the greater 24db/octave roll off because the wave exiting the port then cancels out with the one emanating from the front from the main driver. In T lines the rear wave is shifted a quarter of the wavelength, so is effectively a phase shift rather than an inversion. A well designed transmission line can have lower group delay than a port and a passive radiator design while allowing for lower extension. It's also better at dealing with standing waves behind the main driver,which can be a problem with the other enclosure types and can act as a quite effective brace for the box too.Lawrence Dickie of Vivid audio has done some great work in dealing with the rear wave problem in his designs. In my own home brew speakers i use a sealed acoustic suspension with a low Q alignment. This is the tightest transient wise and the slow roll off coupled with room gain means that a low extension is obtainable aswell as razor sharp transients. There are pros and cons for all of the enclosure types.

[@carlstineman274]

The back wave is generated a half cycle behind the front wave then is delayed another half cycle by the transmission line so it exits the speaker a full cycle behind the front wave making it additive.

[@glenncurry3041]

@@carlstineman274 Explain how a single driver/ surface ... can produce a back wave at a time delayed from the front wave. The back is not delayed, "a half cycle behind". It is just the opposite change in air pressure. When compression on one side, ratification on the other. But yes the transmission line does delay that pressure change from exiting the cabinet. as to at what phase/ timing relationship depends on the frequency.

[@subdynoman]

best reply ever, why dont you have anything on your channel? where are all you audio people at when i need you???

[@chrisborak2200]

​@@glenncurry3041 Not sure if you're trying to be sarcastic. It's very obvious he means the phase if flipped.

[@Bassotronics]

All my current subwoofer enclosures are all T-lines. Especially tubed style T-lines. Solid down to the teens.

[@stefanblutke8053]

Another example how talented Paul is in teaching/explaining of complex stuff. Being a technics/Math teacher I both- value as well as admire his skills

[@x-techgaming]

Too bad he doesn't do actual, short lectures, offering a complete course/understanding of, say, everything involved with a 2-way dynamic speaker, or 3-way ribbon speaker. But he did say in this video, "I am no speaker expert" :o

[@cunawarit]

Great video! It's refreshing to hear you discuss these concepts and introduce them to a wider audience. One of the best examples of what's possible with transmission line technology is found in the Bose Wave systems. These compact all-in-one units use long transmission lines to produce deep bass from relatively small speakers. Similarly, some modern soundbars incorporate this technology to achieve impressive low-frequency performance for their size.

[@mattuw82]

Chris needs to make some videos! He knows by far the most about speakers of anyone I've ever seen on KZbin.

[@67daltonknox]

45 years ago, I built a pair of transmission line speakers based on the AR Bailey design using KEF speakers and Coles supertweeters. The line is tuned for 20Hz. I still have them hooked up to my television where they have a much cleaner sound than those in the TV.

[@The4Crawler]

I built my TL speakers about that long ago and they're still going strong. I had to re-foam the woofers about 20 years ago. I used a TL design paper and 4 - 10" long throw drivers (2 per box) from Speaker Lab in Seattle, WA. Hand wound crossover coils with dome mid-range and dome tweeters. Spent a long weekend tuning the line using an o-scope and signal generator I borrowed from work. I think I needed 4 sheets of 3/4" particle board for the build, and that was my wish list for Christmas that year. I cut all the wood at my parents house, drove back to my apartment and then assembled the speakers there.

[@stimpy1226]

I met Bud Fried once at an Audio Salon in Ridgewood New Jersey. I won’t say he was nice he was too focused on how wonderful his speakers were so I didn’t stay very long to listen to his pontifications. I should’ve stuck around because I just learned a lot Paul from your description.

[@nick_yt23]

Transmission lines and open baffles have the most open and unmuffled sound and the best and most glorious sound stage in my subjective perception .

[@5starmaniac]

Well..Have you heard any of the best sealed ones..? Like YG acoustics, Magico.. ?

[@shipsahoy1793]

@@5starmaniac there's nothing quite like a large high-quality sealed design imho; my personal favorite 4sound certain lol

[@5starmaniac]

@@shipsahoy1793 Agree 100%

[@A-gks]

Yeah sealed speakers easily beat any of your transmission lines and open baffles

[@SastusBulbas1]

I loved transmition lines, as a young guy the IMF occasionally showed up, but in poor condition, and back then spares were rare. I ended up with the HiFi Answers transmition line speaker, based I think on Cambridge Audio R50? Anyway, these were huge, ugly, caulk used in places, and a proper DIY job, original B139/B110 etc. They worked well, went low, but I sold them to a friend. I then ended up with Nightingale Audio NM1, with the later B139, Peerless mid, Isophon tweeter, external crossover, they looked much nicer, and had a cleaner more open sound, with a lovely tight low bass in a shallow TL cabinet, I spent some time with those, hoping to get mint large IMF, but ended up with Kef 105.4. I was very dissapointed with the loss of low low end, but man that speaker was just in another league with the quality and ability to just not be noticed. Soundstage, layering, depth, width, this was all new to me. I still ponder the old IMF's, but at the end of my teenage years I ended up with the Kef 107, coupled cavity, -2db at 18hz, and was getting usable low end response far lower, I think around -6db at 13hz. But with imaging and a speaker that simply disappeared, a trick the Kef 105 and upwards managed superbly, that sadly the larger box speakers failed at. Over the years I tried other speakers, I still love large speakers, and that old style, I certainly would love to revisit transmition lines, and would certainly entertain the large IMF.

[@stevesmyth4982]

The t-linespeakers site has a dual B139 enclosure that's 6 x 2 x 2 (feet) and has two folded and tapered lines. The Falcon Acoustics uprated B139 works very well in the enclosure and crossed over at 80 Hz makes a perfect partner for the old Quad ESL 57s.

[@gtrguyinaz]

Arnie at Infinity designed the. WTLC speaker. I owned them and they were great… they also employed a Walsh tweeter and a rear firing mid tweet…

[@JohnMoog-ug6bk]

Fried R-4s were my first high-end speakers - very fond memories

[@bryanwilliams3665]

Transmission line are fantastic when implemented properly..They aren't a mainstream design simply because not many speaker manufacturers know how to build a good one. Ascension Loudspeakers (Adelaide Australia) ultilise the technology on all their speakers pretty much.. Fantastic Speakers using SB Acoustics Drivers. That builder has mastered the difficult art that is the Transmission Line.

[@joelowens5211]

Bose used the labyrinth model also. We had a transmission line in a our car audio system back in the day. The box was bigger and a lot of work internally to build it out. It would push out an incredible amount of sound with volume. It would miss some on the separation of notes and impact. Sealed boxes can have a nice tight sound for impact. Harder to get real deepness out of them though. No box and no speaker is perfect again it comes down to taste. Some of the tightest 15's I heard was when I owned the Klipschorn flagship corner horn speakers.

[@abbywallace5154]

What a great explanation. Like a maze for the back of the speaker. Seriously awesome

[@CashGravel]

owned the meadowlark kestral 2 yrs ago and was highly impressed w the bass from the 6in? scan speaker woofer. the thing played super low and clean. using a smaller driver is when they really come into their own imo.

[@johnmarchington3146]

Many decades ago, I was friendly with someone who was the woodwork instructor at a school and one Saturday morning we found ourselves in the woodworking room, cutting up timber for building two transmission line enclosures for the Bailey design, in which KEF B139's woofers would eventually be fitted. It was extremely successful and the bass was both clean and extended

[@davidcooper5442]

I have built a couple of True Dr Bailey Fully Damped TL speakers. You get an extra octave below FS of the driver but you lose sensitivity and they need decent power to drive the line. But done right they can be superb. The other problem is that they need large cabinets with a complicated internal structure to create the line.

[@JonAnderhub]

IF the low frequency coming from a woofer was a sine wave at a specific frequency then perhaps the sound coming from a passive radiator or a port would be okay BUT because a woofer or sub woofer is typically not playing a sine wave at a specific frequency and is more likely playing a multitude of frequencies the delay caused by both transmission AND passive radiators IS NOT "in phase" with the signal that is being delivered by the woofer. The end result of this is the muddying up of the overall bass response of the speakers as the passive radiators or transmission port deliver delayed signals at the same time the low frequency driver is delivering an entirely different signal. People often mistake the delivery of "more" bass as "better" bass when, in fact, the bass is actually worse due to loss of clear transients and the addition of added harmonics and distortions caused by the delayed signal from the passive radiator(s) or transmission port.

[@sudd3660]

you can put any kind of hole in a box(passive radiator included or flappy hole as i call it). but do give us sealed options too, a pure sound quality first cabinet. bass if for the subwoofer. and as paul mention, one cycle behind or in phase if we please can get delay for the main speakers.

[@glenncurry3041]

So transmission line design has become a popular topic? Was just discussing this in another vid thread. Transmission line design is kind of like a reverse horn system. Instead of using a horn in front to load the driver's front wave to, a tunnel/ horn is behind the driver to control the back wave. The wave from the back of the driver is loaded into a path who's length and size controls the air pressures release into the room. Like a ported speaker but with additional time delay and more tuning. Because of the length of the transmission tunnel, it's output is delayed in time from the front wave. Thus the extra energy/ extended bass is because of the time delay/ smear.

[@tutnallman]

I still use a pair of transmission lines i built 50 years ago, recent crossover upgrade has brought them back into favour. Too big for the house (any house probably) they reside in my workshop about 9 metres apart. Originally built to reproduce church organ music , The bass of an eagles recording can only be described as bathing in warm melted butter.

[@geoff37s38]

I built TL speakers 40 years ago based on a design by Dr. A R Bailey. I used KEF drivers and long fibre wool filling. They sounded excellent but not very efficient. The transmission line absorbs most of the energy from the rear of the driver and does not cause undesirable back pressure or resonances. Not much output reaches the port, only very low frequencies. Large boxes and a bit difficult to make, but worth the effort.

[@societyofhighendaudio]

I've got a pair small 2 way passive radiator with a 6" woofer and 1" tweeter .It's a wharfdale Glendale abr. I miss it

[@razzman2987]

My 2nd set speakers where the IMF LS80 I loved that sound

[@spentron1]

Also has possible advantages for midrange. As an amateur designer a TL seems more of interest for a midrange driver. See also sealed lines.

[@paulchristman5875]

I have loved passive radiator designs from way back in the 70's. They work well. Just about every cheapy, portable little stereo these days are all using passive radiators. Why? Enhanced bass with little space. Thanks Paul ❤

[@DanielWilliams-l7j]

DCM Time Windows are a great example.

[@subdynoman]

i got 2 inch tangband subs (yes 2 inch subwoofers) doing 18hz that is audible. I placed some TP so you can visually see how much displacement there is. No magic, just good air matching.

[@Jorge-Fernandez-Lopez]

Many sealed subs are probably "cleaner", speakers with less (and even) bass output might "sound cleaner", while most rooms mess with the bass frequencies. The sitting position, the room and the fake bass traps are probably the biggest problem

[@tuathadedanann195]

I got my PMC XBD-Active flat down to 8 hz.

[@georgekost7967]

Paul.. it's a half cycle, right ?(to get the transmission line delayed signal from the back of the woofer to align with the non-delayed front wave)

[@serpex77]

Hello Paul . Greetings from Romania. I have a question for you . I have just encountered a change of paradigm in speaker design, the new Fourier Transform Speaker design. They look so complicated with a lot of cables and amplifiers, and I have read the description but I am still confused. The builder claims that the sound is much more accurate to the instrument because they do not propagate the sound forward as a normal speaker , but in surround as an instrument does . Can you explain please how they work, and if they really are revolutionary ? The only video about it is on the Audiophile Junky channel on youtube. I've also noticed some subwoofers next to the speakers but I am not sure if they are a part of the system or not. Thank you so much for your time and I look forward to your answer. Bye!

[@chrisborak2200]

Passive radiators are out of phase exactly like a port. They move out when the back of the driver moves in, hence 180deg out of phase.

[@rrd1975]

I have both sealed box and ported speaker designs, and a well engineered ported loudspeaker gives up little or nothing to a great acoustic suspension or sealed box speaker. I want accurate and powerful bass and have experienced it from ported and sealed boxes, but I've never owned a transmission line loudspeaker.

[@Gary_Hun]

As far as i see it, the maze is essentially for suppressing the other side's energy. So air although travels, letting the speaker travel freely, but actual sound from the back is negligible and does not interfere with the front / actual speaker sound. This phase thing is fishy to me, i mean, probably it works to an extent. But i would think only around a very specific frequency, no? What about the other frequencies where the out of phase problem once again arises?

[@MrBravo143]

As a PMC transmission line speaker owner, I find that the TL design has a cleaner mid compared to most of the other designs.

[@tristanjones7735]

It's actually more an issue of tuning. A TL speaker will sound better than a passive radiator IF it is tuned correctly. How often are TL speakers tuned correctly? Never. It is near impossible to make an actual TL speaker. Not only does a TL speaker need to be designed for your specific altitude, but it's also humidity and temperature dependent as well. But wait, it gets better. The frequency of interest has to be the ONLY frequency that comes out of the port. You have to absorb all other frequencies. Otherwise they will form a comb filter with your speaker driver output. If you want to go through all the hell of trying to control your physical world in order to make a TL speaker work properly, then go for it. For everyone else, a passive radiator will sound better.

[@ThinkingBetter]

Yes actually I prefer bass from a closed box even it takes a bigger driver and more volume to get good SPL and low frequency. I have a couple of servo subwoofers with closed box from Velodyne that I’ve reworked and I love their very low distortion, flat frequency response and short decay. A passive radiator adds another moving part that has a resonance frequency, motion linearity and decay to it.

[@shipsahoy1793]

I agree Paul. I'm not a fan of ported speakers either, although proper designed ported speakers and properly designed transmission line speakers aren't that bad. Personally, I prefer a well-designed sealed acoustic suspension or well-designed passive radiator system.

[@glenncurry3041]

Yes, any time the rear wave from the driver is released there will be a time delay and all the extra energy will yes produce additional SPL but as a blur because of the delay. Laws of physics!

[@laszlobarchet2646]

It's confusing. Different frequencies mean different wave lenght. The "maze" lenght is definitely fix. How is it possible that on every frequency the port output will be in phase?

[@L.Scott_Music]

Kali Audio has a port design that doesn't chuff. Have you looked into that? Also, how does a passive system keep one cycle behind at different frequencies?

[@glenncurry3041]

It doesn't! All delays are time consistent, not frequency dependent. Which means the timing cycle alignment is based on frequency to path delay. It is one or half cycle behind at a given frequency and no others.

[@stimpy1226]

I met Bud Fried once at an Audio Salon in Ridgewood New Jersey. I won’t say he was nice he was too focused on how wonderful his speakers were so I didn’t stay very long to listen to his pontifications.

[@navinadv]

@Paulmcgowanpsaudio why is the bass from a passive radiator one cycle behind? Does that mean that the bass from a bass reflex tube is also 1 cycle behind? I thought passive radiators and bass reflex tubes had the same delay only that one was cheaper to produce and had chuffing and challenges in length while the other was more expensive because a PR is effectively a woofer minus the magnet and voice coil.

[@glenncurry3041]

It is better to think of the output from any kind of cabinet opening being a time not cycle shift. The time between the energy at the back of the driver and it's existing the cabinet will be constant. So will only be at specific "phase" relationships when that time delay matches or is harmonically related to the wavelength. So when a signal is not wavelength/ time locked, IOW different frequencies, the "phase" relationship is not constant.

[@johnstone7697]

Probably the most successful commercial TL speakers made were the old IMF/TDL models from the 70s and early 80s. They were big, heavy, had a lot of low end for their day, but weren't all that well defined and had poor power handling. I owned a few pair of them and enjoyed them, but ultimately moved on to more conventional designs that performed better. My understanding is that a pure TL would be closed at its end, ultimately absorbing all the rear energy from the woofer. But these had a large port and you could certainly hear bass coming from it. So I guess they were a kind of hybrid. With active, DSP controlled subs, I see no purpose for TL's in modern loudspeaker design.

[@Oystein87]

It's actually not out of phase when it comes put of the bassreflex port...

[@marcelorizzi276]

People in general, including designers, always search for bass energy created by sustained tones, rrrrrrrrrrrrr. What helps you feel the most real illusion on reproduced audio? Transients and Dynamics, thays why many little 2 ways are praised on the ported side, but truth comes in sealed boxes, open baffles and planars. As an old Hales mug use to say: death before bass-reflex....

[@paulgaerisch]

I thought years ago a company called Electro-Voice used a passive radiator to increase its bass response.

[@glenncurry3041]

EV was big into horns.

[@paulgaerisch]

@ I think it’s Klipsch that still uses horns.

[@shipsahoy1793]

Good morning Mr. Phelps, your mission should you decide to accept it, is to listen to your tunes on these new transmission line speakers from the IMF .. hopefully they won't self-destruct in under a billion seconds... (32+ yrs) Good luck Jim..

[@ryanschipp8513]

I've owned countless speakers with ports in the front and in the back. Never heard one that has chuffed. Paul referencing speakers that have a port will chuff is a bunch of malarkey. Also, I have an Anthony Gallo Classico speaker that has a transmission line and the port is in the back so the port isn't always in the front as Paul references

[@geirzzzzzzz]

How can the passive radiator (or transmission line) be «one cycle behind»? The frequencies in the base part of the sound may consist of multiple frequencies/soundwaves. How can each of these individual soundwaves all be delayed «one cycle» when they all have different cycles/frequencies/wavelengths? Please explain, someone.

[@janinapalmer8368]

The idea of the transmission line speaker is to absorb all the rear energy from the speaker ... it's a long tapered duct starting with a throat area equal to or larger than the bass speakers cone area. The length of the transmission line is usually calculated to be a quarter of the wavelength of the speaker's free air resonance. The taper of the line ensures no resonances and this line is stuffed with varying densities of long fibre wool or earth wool ... Unfortunately they are a labour of love and you must expect to do a lot of experimenting before you get it all right . One thing you will notice is the flat impedance curve at the LF end of the audio sweep. Rather similar to an aperiodic enclosure ...

[@IanKnight40]

Passive radiators also don't suffer the comb filtering of the transmission lines at the 2nd and 3rd harmonics of the fundamental. Passive radiators are better understood these days, a far cry from the so called drone cones of yesteryear. Cheers Ian.

[@Exgol2005]

I have BRX and PMC. BRX comes on top many times

[@glenncurry3041]

Imagine if every frequency from every driver was released into the room twice, the 2nd time a cycle behind.

[@paulapplewhite6135]

Surely, if the signal is one cycle behind at one frequency, the signal is likely to be half, or quarter of a cycle behind at another frequency? This has always puzzled me 🤔

[@glenncurry3041]

And fractional values in between. e.g. if the port/ TL... is tuned for 20hz, a 25hz signal will will move between comb filtering timing relationships. Not stay constant at one cycle, half cycle, 245°, ...

[@proffessasvids]

The port output on a bass reflex is a half cycle behind the fundamental.. its a half-wave inverter at tuning. A passive rad is exactly the same as a bass reflex but it prevents pipe resonances and turbulence. Sealed boxes have box resonances and a roll off in the low end. Transmission lines are a quarter wave behind at the lowest tone, they maintain the wave front throughout the line (a bass reflex is a reactive bludgeon tool), a well designed TL will maintain a more even FR with regard to input voltage level, TLs are more efficient than vented (iron law volume aspect). Only issues are they must be used in a multi way speaker as the midrange becomes choppy and that they are massive and heavy. In today's levels of power and dsp usage.. eq can easily be applied to correct a sealed or passive rad setup to sound equally as good as a TL.... but that's cheating xx

[@glenncurry3041]

"The port output on a bass reflex is a half cycle behind the fundamental" at only one frequency. All others are moving targets.

[@jaakimheinola8705]

I agree with you that transmission line should be used only for low frequencies. My current setup of two channels is perfect example of that, there is two TL 8 inch woofers per speaker, they are full active four way and TL has 100 Hz low pass active filter. Then sealed midwoofer plays low mid area. I am pleased with extension and quality. Cabinets are pretty complicated tho.

[@PlatinumMastering]

Bose speakers have transmission lines and also passive radiators 😅

[@CycloneCyd]

1 cycle behind❓ 1/2 (half) a cycle, surely❓

[@glenncurry3041]

Frequency dependent.

[@stevenholquin2127]

At My Age It’s All Academic …..Paul Looks 👀 Well Rested Yet It’s Night Night For Me

[@johnlastname2895]

I have transmission lines in my truck

[@gotham61]

IMF = Irving (Bud) M Fried.

[@RickMahoney2013]

I had a 5 speed transmission in my 1970 396 Chevy.

[@chrisblock6697]

Hopefully you weren't a cycle behind at the line.

[@glenncurry3041]

@@chrisblock6697 Could you keep it in a straight line? Those tended to not have Positraction.

[@jondu-sud274]

Ah ! So that’s what it is all about......can you hear my penny drop

[@unclewilbur8976]

Paul, your video is early. I thought we were on a 2 am schedule. ¯\_(ツ)_/¯

[@Bassotronics]

Daylight Savings Time Applied

[@unclewilbur8976]

@Bassotronics Thanks. Ironically, just seconds before your comment appeared, I looked at my clock on the wall, then the time difference on my phone. And realized daylight savings time had tricked me again!!! We should cancel daylight savings time! Anyway, thanks for clearing this for me.

[@shipsahoy1793]

I agree Paul. I'm not a fan of ported speakers either, although proper designed ported speakers and properly designed transmission line speakers aren't that bad. Personally, I prefer a well-designed sealed acoustic suspension or well-designed passive radiator system.

[@glenncurry3041]

If drivers in a box, Acoustic (Bullshit) suspension all the way! But I prefer panels.

[@shipsahoy1793]

@ well I thought we were talking about boxes, I apologize lol

[@markjohnathanappleton8642]

transmission line ,are not that popular ,due to the cost of the cabinets

[@shipsahoy1793]

@ It seems to me that all the speaker designs, when designed well, end up being pricey.. I think the cheapest design is probably a two-way bookshelf(?) speaker that's not too big and not too small, with all its components chosen carefully ..probably a sweet spot where a ported speaker of a certain size is the cheapest option, and will most certainly be of low sensitivity & hampered efficiency..😉 although some people will prefer them anyhoo..😂