Transmission line (TL) loudspeakers are a rare bird today in a speaker universe dominated by bass reflex designs. There are two main reasons for this, aside from cost. First, there is no complete electro-acoustical model that can be readily used to investigate alignment options for a particular woofer. The models that do exist are either incomplete or too simplistic and therefore insufficiently accurate for practical applications. On the other hand Thiele-Small parameter based closed and vented box design software is routine stuff. Thus, a successful TL is typically the result of empirical investigation. Second, a bass reflex design is far more compact for a given bass cutoff frequency relative to a TL, and of course, less volume translates to a lower enclosure cost.
I am currently reviewing the Acoustic Zen Technologies Crescendo loudspeaker, a classic TL done right. This three-way design has been sounding spectacular at Shows, especially when driven by the Triode Corporation M845 mono blocks. And I’m happy to report that it’s off to a fabulous start in my listening room… stay tuned for a full review.