Dont worry about your tangents Paul, I appreciate them as much as the rest ( :

I built a pair of transmission lines with Focal drivers 30 years ago. They got better with every component upgrade I made, and I enjoy them more than ever now.

Great video Paul. I'm still rocking my homemade transmission line speakers I designed built around 1980. They are about 2 ft. square and 4 ft. high with a pair of 10" SpeakerLab transmission line drivers in each. You are right about all the internal baffles making for a rigid box, there's almost as much material inside the box as makes up the outside. It was also quite a job tuning the internal passages with batting and adding shaped foam blocks at all the transitions to get rid of reflections. But once finished, I really enjoy the sound. I had to re-foam the woofers about 10 years ago.

Paul, I for 1 absolutely love your ramblings.... ;)

I think one of the key aspects of a transmission line speaker, is that the air inside the line moves back and forth in conjunction with the woofer cone. The air moves rather than just compressing, so to speak. There is sophisticated software that does most of the calculations needed to model the response of a transmission line - one such program is called Hornresp (for Horn Response). A big change in the way that TL speakers are designed, is to locate the woofer at *about* 1/3rd of the way from the closed end - this can make the response of the speaker *much* more even and consistent. The "old" way of doing TL speakers with the woofer right at the closed end, often have significant dips / troughs in the response.

Well done Transmission Line speakers sound really impressive, kinda like a more dynamic and extended closed box, they're awesome.

Several of Arnie Nudell's early Infinity's (ie: 1a monitor) was a transmission line whereby he used only stuffing/damping material only to create the phasing. NO internal baffles at all and it still works properly. I have a working pair, complete with Walsh tweeters and the Port is as far away from the woofer as possible. The in-phasing is done by stuffing the tower cabinet very densely near the port and reduces as you get closer to the 12" woofer. Excellent detailed bass down to 26hz -1db.

Transmission line speakers are known for their flat impedance curve and designs from the 1960s are well known for being able to get serious deep bass from "modest" amplification like those single ended Mullard 3-watt tube amps.

I recently acquired a pair of Transmission Line B&W DM2"s (the original series). As a newbie to Hi-Fi this really helped me understand what exactly is going on inside the cabinets. They sound incredible to my ears. Thanks for this!

The Rega Naos was a floor standing Quarter Wave transmission line design with 8" paper cone midbass. I've measured decent bass output to below 27hz on mine, which is surprising. They are 92db efficient and don't suffer from the upper bass hump and rapid rolloff of reflex loaded designs. Thanks for attempting to describe the concept, Paul

I love my T-line. It’s tuned to 17hz approximately and is compact. Uses 4” pvc tube for maximum energy transfer without internal standing waves.

So far I'm impressed with my DCM time windows. Wife approves of their unique shape and sound. Good way to describe it is you can hear the low notes without the shaking the entire room like a in your face dedicated subwoofer.

Paul, we love the ramble.

I enlisted as a 2E1X3 in the Air Force over a decade ago. You talking about waveguides took me back.

My old roommate was drunk one night when a storm rolled in and he stood out under the street light to see the lightning hitting the pole, right over his lucky drunk noggin. I ran out pulled him in and got him calmed down after one good hit scared the heck out of him, and me!

Love your take on all things audio Paul!

I built a transmission line subwoofer recently. Trust me, once you hear a t-line you won’t want to go back to one-note bass reflex designs (ported).

I could listen to this guy all day long if I'm high knowing he would take me right back in phase so ramble on man

Great video, and love that outro! Those mountains look incredible.

I just discovered this channel and KZfaq keeps recommending and I just keep watching!!! :-0

I built some speakers that use a 15" woofer and have two 4" ports. When it came time to tune the ports, I wound up using PVC pipe and elbows. The ports are about 28" long (I haven't looked at them for years). The cabinet resonance is below the driver resonance.

Very good video. To help understand why ported enclosures work (the output from the port in a properly designed cabinet IS in phase with the main driver cone) is that the extra distance the sound wave has to travel through the transmission line on the reflex side of the wave as the cone is vibrating will delay the arrival of the wave so that it will be in phase with the front portion of the wave coming from the main driver itself when it arrives at the port entrance. The advantage is that you have a much more pronounced bass response. The drawback is that you need a cabinet about 60% larger than a sealed box cabinet to produce the same volume level at the same amplifier power level. Paul is correct that just randomly knocking a hole in the cabinet will likely produce poor results. There are two common ways to achieve a transmission line design. [The technical term is called "bass reflex", btw. Get a copy of Loudspeaker Design Cookbook which describes all of the nuances of building a loudspeaker (including the Thiele and Small parameters). It will also give you an incredible insight into why the actual physics works AND how to build your own like Paul and I and so many others enjoy doing.] Historically, most bass reflex designs used a pipe of some sort to create the transmission line. The length and diameter would depend on the Q of the main speaker cone, the desired peak response frequency, the size of the cabinet, etc. (I used on my most recent design 3" x 4" PVC pipe from Home Depot. A better choice would actually be heavy duty cardboard since it is less likely to vibrate or "ring" if not thoroughly glued in place. Do NOT under any conditions use anything metallic!) If you use the cabinet itself to create the transmission line, you need to design tunnels or corridors to allow the wave to progress through the cabinet. Paul is 100% correct. This is very difficult to get right and, while I am good with pipe bass reflex designs, I am still a student with this method. The most famous product out there that uses this technique is, of course, the Bose Wave Radio. the "Wave" has nothing to do with the radio part. It has to do with reproducing very good bass response in a small enclosure. Very good design and they sold millions of them. If you take one apart (there probably are videos here that show this), you get to see what a transmission line enclosure looks like. There are several software applications out there to help you design and you can get speaker components from Parts Express which has a full library of loudspeaker designs you can try. I could drop $20,000 if I built just a few of their higher end models. :)

I built a pair transmission line speakers in 1999. They perform magnificent. Cheers from Indonesia

I made a transmission line box for a pair of 12" subwoofers. Damn that was a clean sounding box. It had a very flat frequency response from around 20 Hz all the way up to around 55 Hz However, it did lack the punchy sound you would normally get out of a standard tube, L or U-shaped slot-ported box. In my experience, the transmission lines are much like sealed enclosures with a slightly narrower band, but more output. Still, they are amazing for SQ builds I've heard most of the port types in action, and I can say that there are pros and cons for all. Tube (aeroports): Easiest to install and tune, but they are more susceptible to port-noise. This can be mitigated by using flanges. Port-hole: It is as it sounds like, just a hole in the box. These have a very high tuning, and does not sound good at all. Slot-port (straight): A great way to add some tuning to the box. Straight slot-ports are very similar to tubes, but less susceptible to port noise. L-port: Slot-port design, commonly used in car stereo, this port design is easy to make and install, and it adds a little bit of bracing to the box. U-port: A longer version of the L-port, it sounds a lot more like a transmission line due to the added length. This is more cumbersome to assemble correctly, but it makes up for it with a wider frequency band and additional bracing. Bandpass (4th order): Sealed and ported at the same time. These has a narrow frequency band, but has high output, and work great for SPL. Bandpass (6th order): Internal ported enclosure within a larger ported chamber. These boxes has the highest output, but they are very hard to get correctly tuned. These are the kind of boxes commonly seen in wall builds, or competitions. Horn-loaded enclosure: These enclosures are great for amplifying the output of a certain frequency to an incredible level. The compression chamber is small, and the port gets progressively wider the longer it is. This is more common in professional audio. The length of the horn determines the tuning frequency. Horn loaded enclosures can become very large, especially if you want a subsonic horn for a home-theatre install.

(Sorry guys, wasn't done yet) As I was trying to comment, the original acoustic labyrinth had an open enclosure at the top, where the opening, behind the woofer fed into a series of equidistant slats which went back and forth until finally venting into a rectangular port facing in the same direction as the woofer. The dimensions of the acoustic line (port opening) were roughly equal to the surface area of the woofer, and the length of the Labyrinth was usually equal to one quarter the wavelength of the tuning frequency (9ft for approx 33hz). The final enclosure is somewhat proportional to a tower loudspeaker, only somewhat larger. All I can say, is that the results of this effort are astounding, I personally have never heard bass this low on any system before or since. As far a I know there was no stuffing in the line, but the bass response (even with the 90 degree elbows in the line) was intense!!!

The digressions are great!

Nice one Paul, you taught a Portuguese speakers something he didn't know about Port. :)

Although the "pipe" part of a port does help reducing wind noise compared to a hole, that's not what it's for. In a ported speaker the air inside the box acts like a spring and the air inside the port acts like a mass that is attached to this spring. This mass-spring system acts like a Helmholtz resonator at low frequencies, meaning that the air inside the port resonates with the movement of the speaker cone. This means the speaker cone and the air in the port are in phase, that means when the cone moves forward, so does the air inside the port, which means that the port makes the speaker louder. The reason a port needs to be a tunnel rather than a hole, is that a hole doesn't contain any (or just a very small) volume of air, which means there's no mass, so the resonance won't occur, or at least not at the right frequencies, which means the port will not be a bass port, it will just be a hole that lets back radiation from the cone escape. Also, designing a ported box involves quite a number of complex calculations to figure out what the size of the port needs to be, where it needs to go, what the shape needs to be etc. It's far more than just drilling a hole in a box and calling it a day. I fully agree that many ported speakers are poorly designed and don't sound great, but they can sound great if they are designed with care, which again, isn't an easy task.

Hi Paul, thanks for explaining transmission line, do you think if it possible to use same theory to build a TL box with micro speakers which same speakers in iPhone. To make a small device with iPhone speakers but with more extra bass power. You can put it near your ears but still open ears.

I've made two t-line boxes for my 12s. Good quality tones. However, I think it loses some on being punchy. Also, hard to heard if your sub is distorting. There are some numbers to crunch though. The last one I made has a piece of plexiglass at a 45 degree angle in-between the back of the sub and the port. Wow.

This makes me really want a transmission line box

T-Limes (when designed and built right) can be the best performing (over wide and diggin double deep) designs. It was secret for a long time to figure it out but there’s a super simple formula that we always follow and it turns out so well. I even took Paul Carmody’s “Speedster” build and did them in T-Line and they dig so damn deep and flat it’s crazy good.

Great video, Paul.

I am just finishing the veneer on my first speaker build. It is a MTM transmission line design from the well known parts place. I should have it working within the week!

Paul, ported boxes are not just about poking a hole in a box, they have tuned pipes inside, designed with calculations including the internal cabinet volume, woofer diameter, excursion, resonant frequency etc:)

TL speakers are the best at reproducing real-time low frequencies for a passive system in my experience. They are expensive to build because of the extra cabinetry involved but they are worth the effort for the DIY crowd. There are lots of great plans available which pair proven cabinet design with readily available drivers. There are few if any DIY speaker projects that will yield the outstanding results of a proper TL design. Beyond that, servo-controlled subwoofers are the way to go, hands down.

Question: Paul, if a TL delays the wave at a resonant frequency, you can extend the bass -- but would this not smear the timing significantly?

See IMF tls 80 transmission lines circa 1970s. Good video with interesting sound effects.

I developed about 4 types of TLs. First was totally apparent and in mono - just set open type speaker box at furniture in corner of room and sealed around so that low had only one way out - down to the floor under the furniture. I noticed it was something I never thought before. Then after 15 years were my premeditated constructions - big one - made 3 stereo sets and two smaller - actually first smaller was a prototype of second smaller which I made in two stereo sets. . Small means 130 cm high. If one likes strong very low bass it is unbeatable. It can shake floors down and travel across street with no much power. . . Its strong side is little coloring in upper range so it is good for real sound.But it's known disadvantage is narrow minimum in working range which takes a hard to fill.. I developed unique solution within my also unique construction allowing me to damp independent 4 parallel chambers similar to pipe organs mixing its resonance into that minimum. Basic bass was calculated at 30 Hz and it is pushing max at 35 Hz. Took me next 20 years before I made something another.

I speak Portuguese fluently. Glad to know there is someone else that speaks it!

i have a route 2 times a week in boulder picking up donations for vietnam vets , i usually have a pick up right next door to your house!! also yes the thunder storms get wild in boulder!!

How do you determine the size of a transmission line speaker, and how to qualify a speaker for their use in a transmission line? And in a transmission line speaker, by keeping the pressure wave of the woofer in phase with the woofer's positive wave, or forward movement, doesn't the resulting wave of the port fall out of time with the positive wave of the woofer. In other words, when a positive impulse reaches the woofer the in phase of the port will follow or lag behind that of the woofer, causing distortion? Is that audible at the lowest frequencies?

Great video, very informative. I was wondering what a transmission line speaker was and your explanation was clear. Your tangent on the speed of sound and thunder did lead a little bit to be desired. Planes avoid going near the speed of sound because the pressure waves start building up as you near the speed of sound and put extreme stress on the leading edges of the frame. And the thunder clap isn't exactly a sonic boom, but more of the largest subwoofer in the world - the lightning creates a shockwave by heating up the air quickly and powerfully. And the rumbles that follow it is the air vibrating after the bolt. So it's more like a speaker than we thought! Crazy, eh?

I love the tangents!Transmission line is a good choice for DIY imo, though don't try and design it yourself unless you really know what you're doing. You get a very solid box, and the carpentry that is so expensive for a company to make and ship is not much of an issue. IPL acoustics in UK produce highly regarded kits, and Troels Gravsen has some awesome designs on 'DIY speakers' with parts kits sold through Janzen audio. Both these are super helpful.

Paul - lovely explanation, as always! Been to Ft Collins and Thomson Canyon and I can relate to the lightning shows over there! Btw, are those speakers GoldenEar AONs on the top shelf behind you?

The speed of sound changes significantly base on altitude, the barometric pressure at that moment in time, and temperature; all impact air density hence very the speed of sound. So for transmission line speakers do they automatically adjust the baffle length based on barometric pressure to they stay in tune?? You live in Boulder Colorado, I live in Colorado. The speed of sound is different gear then at sea level, and changes based on temperature and the weather (barometric pressure that moment in time)

A well done rear port can be in phase too, however it requires the speaker to be properly aligned with the wall behind it, and the room acoustics to be right. But most people don't have that flexability of placement, which is where a transmission line will be better it removes the room acoustics from the play...as far as phase goes.

Rambling is good!

The result of a close lightning strike is a simultaneous flash and boom. I refer to it as a FLABOOM! It is the compression wave caused by the flash heating of the air by the lightning bolt, rather than the fact that the bolt propagates faster than the speed of sound, that I believe causes the boom. The first pair of audiophile speakers that I encountered were of the transmission line type, way back in the early 1960's. They were almost as large as refrigerators and were home built. A tube pre-amp and separate tube amplifiers were of course used to drive them. I was impressed, but as a teenage kid, they were beyond my budget.

As far as I'm aware a transmission line works as a IB enclosure down to the line length frequency, with the rear wave being absorbed completely but not reducing efficiency by adding an extra spring like a sealed box does. Below the line length frequency you get a boost from the low frequencies exiting the box 90 degrees out of phase

Would a Transition line enclosure improve transient response over regular ported enclosure?

A R Bailey of the class A transistor amp circuit design fame also worked out the math for transmission line speakers.

I am making a classic /straight T-line with a 12" woofer. The cabinet/waveguide is now at 240 lenght and is around 155 liters. Someone i know say i should try to make the T-line closer to VAS of the driver(85 Liter) Should i worry about VAS when making a classic T-line? I dont se how since the line area should equal or exceed slighty the cone area of the driver used and the line length should be 1/4 wavelength tuned to the resonant frequency of the chosen speaker. Can someone help me out? Thx

I built non-ported boxes for the trunk of my car. I enjoy the nice range of bass that they provide rather than the one note wonders that people like to rattle the neighborhood with. I don't show off my visibly vibrating boot lid although I could if I wanted to. A good romp on the pipe organ blurs my rear view mirror though.

Is the Voigt pipe/tapered tube considered a type of transmission line? Voigt pipes seemed simpler to build, albeit taller. Is one more efficient than the other as a design?

Thunderstorms at night scare the hell out of me. When I was kid near Blairstown NJ I survived a tornado at night.

Best port I've heard is the one on the KEF LS50, made them seem like they were defying the laws of physics at times.

Amazing.

I'm lucky to have inherited my fathers pair of IMF TLS50s that I grew up listening to as a little boy in the 70's and teenager in the 80's. They have a big sound for the relatively small woofer size.

Love a good flange!

Just got myself a mint pair of TDL Studio1's with the recessed drivers, a contender for the best pound for pound speaker ever made IMHO.

Actually all ports are in phase within the freq they are tuned for. The air starts moving in sync. But it is when it rolls off the air starts to move out of phase. Just saw a video demonstrating this very well.

I use a pair of TDL Studio 1 TL's in my man cave, which measures about 3.5m x 4.5m. They fire across the room at my listening seat on the end of Audiolab mono-block amps, a very happy marriage. The best thing about them, is the way they do not loose bass weight when the volume is low, my wife goes to bed quite early so a lot of time is spent listening like this. Even the Tannoy DC3000's in the living room, probably my favourite speaker of all time, have a threshold volume, below which point the bass is lost.

Hi, I believe the best speakers are sealed box designs as they let the actual drivers do the work they are supposed to, as long as the drivers are of sufficient quality? Do you agree with my opinion?

Hi Paul. Nice description there. I have some huge Leak 2075's from the 70's that Leak described as transmission ABSORBER as opposed to LINE and their bass is amazing but without overhang from their 15" bass units. I guess they would cost a lot of money to manufacture these days. Also remember the big TDL Ref TL Monitors from the early 90's. Chris from the UK

Oh, well. When I saw the subject I honestly expected a discussion of Lincoln Walsh's patented Transmission Line drivers. I was disappointed when it was only a discussion of yet another ported box - one with a long, wiggly port tube. Would you like to possibly discuss the design of the Walsh Transmission Line Speaker? I've really liked those I've heard.

And the internal baffles should be thin not thick so you can get more in the cabinet what will lower it's output frequency by cancellation diffraction the angle of the internal baffles has a bearing on frequency as well a narrowing to the output end will give you a more punches sound and vice a versa and the type of filling has a big bearing.

Your physique is awe inspiring paul. How much do you bench? And whats your regime for maintaining your 6-pac?

Hello Paul!!! May you demonstrate how to calculate a LT Speaker? Thanks.

I have PMC speakers. they use transmission lines. best speakers ive ever had/heard. soooo clean

Interesting subject Paul can't help but think as if ported speakers can sound boomy,blurred by making transmission although better there must be even greater time delay in bass output although in phase.

I' d like to see a video of your thunderstorms.

Paul nice job as always ( And PLEASE Ramble as much as you want cause your a RAMBLER BUDDY and that's a good thing )....

Great TL speakers : TDL all models, B&W P4 (from 90's) and PMC from all times, all models etc.

The sound exiting the port behind the woofer is in phase with the sound from the woofer only at one frequency [ at some other frequencies cancellation occurs ]. Also the port behaves like an organ pipe at certain frequencies, resulting in peaks and dips in the bass. This requires that the port be filled with damping material which limits the output at the desired low frequencies. These are some of the serious problems that one encounters with transmission lines. Notice that there are not many of them around.

If you live in the UK have a look at ipl acoustics great transmission line speakers

Yes, we speak Portuguese! 😁

The German speaker builder T & A build speakers using the transmission concept. They sound very nice and are expensive!

I am waiting for you to tell us that your company finally has speakers we can buy. I'd love to meet you and buy my audio system from you. (not that I am loaded with money) mind you. Thank you so much for all the education.

Ok, ported enclousures work on the Hermoltz resonator principle. The air in the port moves in phase with the driver down to the tuning frequency and then starts going out of phase thus the need for subsonic filter. Transmission line enclousures arent popular for their big size compared to efficiency. You can put multiple drivers in for relatively same size box in a ported config for far more output. They also dont have good transient responce because theres no trapped air behind to help the driver suspension and amplifier damping.

thank you

Isn't the Bose table top stuff wave-guide meaning they are using a transmission line?

Big con is that the boxes are much bigger than normal ported boxes due to the length and diameter of the port. Biggest pro is that it is probably the best sounding a particular sub can ever sound (clean and deep).

Anyone who is interested in loudspeaker design should IMHO seek out and read Gilbert Briggs books on loudspeaker design.Regarding transmission line loudspeakers I think the dimensions of the line should be calculated from the size of the drive unit and the length of the line should be a 1/4 of the drivers resonant frequency?

In '79 I built a modification of the Bailey cabinet design, each populated with 3 KEF speakers, a Coles super-tweeter and a Falcon crossover. They have been dragged all over the country in the intervening years and look a bit shabby so at the request of my partner, I considered a replacement. After reading many good reviews of a direct seller's floor stander, I got a pair. Mistake. In that room they can't hold a candle to the old ones... simply not as musical. Next time I think about it, it will have to be something I can audition first.

I have Rega Kyte speakers. The port is a triangle on the front upper left side. They are not symmetrical. Both speakers have the ports on the upper left side, beside the tweeter. Don't know if this qualifies as a transmission line speaker. For the price they are amazing. But they have no low end bass. Of course you can add a subwoofer. but you need an accurate one. I blew one of the tweeters. Bu instead of repairing them I bought an extra pair for just $30. They cost around $300 new in the nineties. A forgotten classic.

cool stuff

A competently designed TL also has an essentially flat impedance curve throughout its bandwidth. Makes for better interface with the amplifier. There is ample literature available for the speaker builder. The TL produces the best bass response from conventional means of woofer tuning. Bob Carver gets prodigious bass from Non-conventional woofer design.

The real reason for a ported enclosure is reduction in size compared to a sealed cabinet. The port is used to tune the cabinet to a resonant frequency so the cabinet starts to produce bass at the lower "usefulness"of the bass driver.

I own a pair of Polk Signature Reference Series SDA speakers which I purchased new in 1987. The enclosures are 66in high x 22inches wide. Each enclosure has 8x 6.5" drivers plus one 15" passive bass radiator plus 4 x 1" tweeters. Mathew Polk does not specify which type of enclosure design is used. The bass response is quite impressive, according to Stereo Review Magazine: +/- 4.5dB from 20 to 20,000 Hz with the output dropping to -7dB@12Hz, while distortion was measured as .7% between 70 and 20Hz with an output of 90dB. I love these speakers so much that I will not part with them, ever! Does anybody know what type of enclosure design these are? Thank you.

T-line boxes are also much bigger.. I can't imagine trying to build a 1/2 wave box. Even a 1/4 wave for 10" woofer is big. But I kinda want to do that now..

Fried used to make Transmission line speakers.

How can they be in-phase for every frequency?

A Tline may not be so easy to build but it's worth the time and money if you have a good quality speaker and want to get the best quality sound

Could we compare transmission line speakers with folded horn speakers like the Voice of the Theater?

Thank you for yet one more educational video, Paul! My hat is off to you on behalf of all the subscribers of your channel! Personally, I am in search of a pair of speakers which would produce good sound-stage and a definite separation of instruments and singers. Primarily they need to be true to the live, uncolored, un-modified recordings of acoustic instruments and voices. I am one of those nuts who enjoy hearing pages turning by members of the orchestra and of the swish of their clothes. Can you please suggest a pair of sealed or front-ported floor-standers for a medium size room? I can spend about $5,000 for a truly great pair of such speakers.

PMC uses TL design on both their pro-audio and audiophile speakers.

I built a pair of transmission line speakers based on he design of Dr Bailey from 1969 ? I think. He used triangular pipes to make the cabinets more rigid. IMF, a British company also used a transmission line but with flat panels. The most popular bass driver was the Keff B139. The one advantage of those designs was the greatly extended bass they produced. I still have a pair of Keff B139's in their original boxes and when I can find a cabinet maker I will get them to build me a pair based on the original Dr Bailey design. I used Rogers LS3s for the upper frequencies.

Please, I could generate the subtitles in a manual way since in that way when translating them into Spanish they are perfect saludos desde argentina

A nice relatable ballpark number for the speed of sound 1'/ms or 761mph (1,225km/h) at sea level, and 660mph (1,062 km/h) at the tropopause where most jets fly....Should a port be at the front, back , or side of a speaker? Or does it make a difference?