Differences Between Folded Horn Speakers and Transmission Line Speakers
I've been looking at various DIY speaker builds and came across a folder horn speaker and I've also seen transmission line speakers. I've tried to google the differences in the two, as they look similar, but I suspect that there are differences. The only visual difference that I've noticed (I've only seen one folded horn, so the comparison pool is very small) is that the folded horn seem to have a larger opening than the transmission line speakers. Maybe it's just the one speaker that I saw, so I don't know that would always be the case. I'm hoping someone on the forum is much more knowledgeable about these things than I am.
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...) |
