Differences Between Folded Horn Speakers and Transmission Line Speakers

Quarter wave back loaded horns have a constantly expanding cross section to the folded horn.  That expansion prevents standing waves from developing in the horn.  A transmission line has a more constant cross section and has to have a lot of damping material in it to reduce standing waves.  This damping greatly reduces the amount of acoustic energy that back wave can contribute to the sound, hence the much lower efficiency of transmission lines.  But, it is a much harder trick to make that back horn have the properly expanding size and the opening has to be quite large.

@larryi Thanks. I could kind of see it, but I wasn't sure if it was just the one folded horn I had seen or it it was generally the case. I definitely didn't know the reason for the shape of the folded horn.

Additionally, how would you compare the sound of the folder horn verses the transmission line speakers? I haven't heard the TL myself, but I understand that they are very good at producing the lower frequency range. Like I said, I know nothing about folded horn or how they sound.

Thanks.

The transmission line speakers I heard had very tight bass and sounded quite good.  They were also reasonably compact and did not require a lot of depth.  The various folded horns, like the Tannoy speakers, sound really good, although the bass did not go extremely deep in frequency, and most were quite lively sounding.  In recent years, I’ve heard single- driver backloaded horns systems, like those from Charney Audio, that blew me away because they sounded so lively, rich, and smooth—so much more complete and free from peakiness than most other single driver systems.  The Charney speakers were compact in width and height, but were quite deep to allow for the back horn.  A big plus with backloaded horns is that the high efficiency allows for use of low-powered tube amps thst are my favorite amps.

Sounds nice. I might have to try a pair; one of each type. Thanks for the info. 

I may not be entirely correct here, but I think of folded horns as horns and TL as competitors to the ported enclosure.  That is, horns gain efficiency through the improved impedance match of the driver to the air via the horn.

The TL however AFAIK has similar efficiencies in the high frequencies of a sealed or ported speaker, it’s the deeper and more extended bass that make them worthwhile. 

I'm sure others will correct me.

With horn compression drivers, typically used for midrange and high frequency drivers, air is confined in a chamber and this does effectively increase impedance to allow for a better coupling of the driver to the air.  This certainly does improve efficiency greatly.  With woofers with a back-loaded horn, there may be some such impedance improvement, but, the biggest improvement comes from not trying to dissipate this back wave, rather, to lengthen its path so that the backwave, which starts out inverted in phase with the front wave, is now in phase and augments the front going wave.  Transmission lines are more in the business of dissipating the back wave energy at higher frequencies through use of damping material lining the tunnel.

@larryi - The OP asked about a folded horn, which is different than a back-loaded horn.  The typical example is a Klipsch corner horn or La Scala.

As their name implies, they are horns... but the folding reduces the floor space.  They fire into the horn, and the rear is a sealed space.

+1 @erik_squires on the Transmission Line being competition to the usual front, rear or bottom ports.  All extend bass.  I learned a lot looking at PMC speakers about Transmission Line.  They are touted as being tighter, less bloated bass compared to some ports.  Additionally, they allow placement of the speakers closer to the rear wall.  PMC seems to specialize in transmission Line bass.  I am a horn dummy though.

Optimal positioning of a speaker for optimal soundfield, imaging, etc is never usually the optimal spot for low bass... hence the need for installing subs at the right spots (whether some speaker was full range or not didn’t matter)

Hence, the focus on a transmission line speaker design is usually a lost cause... a vestigial idea from a time when high quality subs weren’t really a thing.

a) DIY some high efficiency horn speaker with all the merits of such and put it at the right spot. 

b) DIY a ’transmission line subwoofer’ and put it at the right spot,

(win win...)

Thanks all for the input. This gives me more to look into and consider. The whole subject of speaker design is very interesting.

@erik_squires Wrote:

  it’s the deeper and more extended bass that make them worthwhile. 

I agree!

Transmission line speakers achieve more extended bass at the expense of efficiency. I prefer horns or tuned ports. 

A great place to stop in and ask builders is diyaudio.com

Horns and transmission lines are completely different. Horns are a way to maximize the efficiency of a driver. A transmission line is a way to dissipate the back wave of a driver with minimal reflection back to the driver and they tend to be inefficient. Traditionally transmission lines are open at the end which if tuned properly can add bass extension similarly to a bass reflex. But they can be used closed to simply absorb the back wave.

TLs tend to sound better than ports, but the bass is still not on par with the best sealed enclosures IMO. What we are discussing is tighter bass, not so much lower bass. Ports and some TLs have the tendency to sound as if they have lower bass, but the bass present can be a bit confused and tubby. That ported sound is especially apparent in smaller ported speakers. I dont like it as a whole.

@erik_squires i recently started spending time at diyaudio.com. However, it's been trying to learn the electronics side of audio and not on the speaker side of things. 

Hearing the TLS80 transmission line speakers from IMF are what started me on my audiophile journey.  Hearing Klipschorns made want to leave the room.

OP:  go over to the Multi-way speaker forum and you'll find lots of helpful and knowledgeable people with very strong opinions to share. :)

Will do. 

I heard the PMC Transmission Line Speakers at CAF 2023 powered with an Advance Paris Integrated amplifier and it did sound remarkably clear to my untrained ears.    However, any speaker that has ports down low against the floor worries me about critters getting inside. 

https://pmc-speakers.com/technology/atl/

Ported speakers tend to require more experimentation to get setup optimized than sealed speakers.  The payoff, if you can find a good placemeny, is higher efficiency.  This IS a big deal to those who like low powered amps (like me).  I have a local dealer that makes sealed box high efficiency speakers with compression driver midranges.  But, the speakers are quite large in size, and even though their custom woofers are 18” in diameter, they don’t go extremely low (tradeoffs are inescapable).

My next speakers are DIY, Frugel-Horn Joan with Mark Audio MA-200 drivers in the gold color(looks more like copper)

No crossovers, single 8" full range driver, combination of transmission line and rear horn loaded. Excellent reviews of the Mk3 and XL versions, have not seen one on the bigger units with the larger drivers I am building.

Goal is no sub(s), low power amp, low weight, great full sound.

I am likely to build several types of speakers to get the best I can out of the not so easy to tame full time RV we live in.

Rick

@raam Good luck with the speaker build. Please, let us know how it goes. To have to fit it in an RV is a heck of a constraint. 

Thanks:)

I have done a ton of work to be able just to have a decent space to setup a good system. I added 1.5 ft to the length of the RV which has 8 ft ceilings and 8ft wide, 5ft deep until it hits the slide outs on each side then 12.5 ft wide but one side is cabinets with counter top and other side is wood stove, book shelves and Ekornes couch facing the speakers which are 8 ft from the couch and face of them can be as far as 36" from the rear wall but only 12" from the side walls. The speakers are on each side of the 24" D by 54" wide desk that is very solid and has a 2cm Brazilian green soapstone top, like the 8 ft wide kitchen lower cabs, wife's 54" wide stand up desk and 5ft island. The sides are not even near to being equal so there will be some figuring out to do decent acoustic treatments. Some will have to be moveable for critical listening, if such a thing works out.

Rick

The speakers will be around 26" from face to rear wall and 8" to side walls most of the time. The design is intended to be close to the rear wall, corner located, etc so might be better in this position, just able to move them around a bit more if needed.

I have never really cared for ported speaker bass, but love the bass from my PMC's. Remarkable given the driver and cabinet size. One guy's opinion.

https://live.staticflickr.com/65535/54276973197_80d2b5de32_w_d.jpg

@dynamiclinearity Yes my DCM Time Frame 2000s are TL terminated on the front with two ports, possibly one for each 8" woofer.  The pair dig So Deep even in my apartment.  In my old house with a high roof and big room I liked nothing more than to Turn IT Up leave the room and revel in the low end power!  My first REW 20-20000 sweep was Joyous.  Just a blast off from the first tone, fabric on the two ports lifting 2 inches.

No subwoofer or center channel need apply; just two perfect speakers for me.

Happy Listening!

guscreek; actually your DCMs are not transmission lines. It's a common mistake. Infinity did it on the 2000 model. They are stuffed ports, also known a variovents. It is a good way to get tight bass. The best known example was probably the best selling audiophile speaker of all time, the Dynaco A25.

Hello mcraghead. Transmission lines taper from larger to smaller while horns taper from smaller to wider, the opposite. There are mathematics dictating the rate of taper. The transmission line loads the rear of the speaker, and tends to damp resonances. Horns allow the speaker's cone to move freely, very effectively coupled to the room. Several companies produce transmission lines without talking much about them. The foremost advocate of transmission lines, Bud Fried, produced speakers which have been copied by others who have been successful at selling them. I encourage you to build a transmission line enclosure. Be very careful to get the dimensions right and be sure to choose the right driver. The narrow front, deep cabinet using multiple small diameter woofers is ideal for a transmission line. The design is more difficult to build than an bass reflex cabinet, but the effort will be worth it. A sealed enclosure of the right dimensions, paired with the right driver, can be very easy to make and quite effective. Enjoy the music.