Upon viewing a cross-section of the AT-1’s cabinet, a long-time audio fan would instantly call the design a transmission line (see diagram). Transmission-line bass loading has enjoyed an on-again, off-again history, popularized in some high-end British loudspeakers back in the ’60s. A few American manufacturers also gave it a go over the years. When properly designed, it offers purported benefits, including extended and free-breathing bass.
But an acoustic transmission-line design required a large, complex, and expensive enclosure, with line resonances that could be difficult to control. The design of the line and the optimum box stuffing were never characterized with the mathematical rigor that made other types of enclosure designs far more commercially practical.
When I looked at a cutaway diagram of H-PAS (slicing the box in half to have a look wasn’t in the cards), I saw the H-PAS as a short transmission line with a significant twist. At or near the exit of the line, there’s a port into a separate, sealed chamber. Atlantic claims that this chamber is tuned to dampen resonances within the line before they can exit the port and color the sound. According to Atlantic, the trusses with the holes in them behind the drivers provide bracing within the cabi- net to dampen vibration but without reducing airflow, which is critical in maintaining the air pressure within the cabinet in this design.
This is all fine and dandy, but a huge number of variables are involved. To attempt to account for all of them in a build-try-rinse-repeat mode would more likely lead to a flight over the cuckoo’s nest than to a great speaker system. The genius in the H-PAS design is the development of a set of differential equations that takes all the important factors into account. Atlantic’s Boaz Shalev showed me some of the equations, developed together with consultant
Martin King, who has been researching transmission line design for years.
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http://www.soundandvision.com/content/atlantic-technology-1-loudspeaker-way-we-are#efpFQTHJ52gdFcYh.99