Ah thanks! Arendal are TL? I feel like a dummy. Guess I need to study more.
No, Arendal are sealed, with complex DSP. The advantage is a small box, but that makes them really inefficient and power hungry.
A TL is a modified Gedeckt organ pipe. It is a stopped pipe and closed at one end with the port at the other. Placement of the diver is critical so as not to excite the odd harmonics. The pipe is critically damped, but with output preserved, but the damping is aperiodic, which means it is critically damped and non resonant.
They are very efficient, do not take gobs of power, and the pressure towards to closed end is very high, so driver excursion is really well controlled. So you can get room shaking bass, but the drivers seem to be barely moving. I have designed dual TLs, which have fundamentals an octave apart. As far as I know, I am the only person other then the late John Wright of TDL to have designed dual TLs and he only designed one.
The design parameters were very hit and miss until George Augspurger published the correct mathematical model in the AES journal in 2000. He subsequently developed a software design program. George is one of the great audio engineers of the last 70 years or more. He is now well into his nineties. He gave me the privilege of keeping his design program available to designers.
You can download it from my website. The only major TL manufacturer is PMC. However in my view their designs are not optimal. The problem with TLs, is that they are large, and the carpentry somewhat complex.
These are my front three active TLs, the right and left are dual lines. They are truly full range and no extra sub is required. The design is fully integrated for HT with my custom electronics.
