Atlantic Technology AT-1 loudspeaker
It was the 2010 Consumer Electronics Show, and JA and I were nearing the end of a dog-and-pony act expertly presented by Atlantic Technology's president, Peter Tribeman, touting a prototype of his company's new loudspeaker, the AT-1. JA and I had just heard about the finer points of the AT-1's new bass-venting technology, the Hybrid-Pressure Acceleration System (H-PAS), which was supposed to combine all the benefits and qualities of a transmission-line enclosure, horn loading, and sealed and ported designs. At the time, I didn't care if it combined all of the qualities of Kim Kardashian, Sacagawea, Joan of Arc, and Marie CurieI was just thrilled that the AT-1s were sounding so good in a partitioned ballroom.
Another elbow to the ribs: "I want to hear those kick drums from 'Fit Song' on this system," JA muttered.
To avoid more bruising to my midsection, I politely raised my hand, asked if we could hear a track from my CD, and was kindly obliged. Tribeman even handed me the remote control. I turned the system up to levels you're not really supposed to reach at a hi-fi show.
The room went quiet as the unassuming black towers of the AT-1s took on "Fit Song." Each kick-drum sample hit the assembled crowd in the gut with a speed and a weight I hadn't heard in that entire CES. Jaws dropped all over the room, at the sound of the AT-1s and at how frickin' awesome this music is. At the song's abrupt end, the listeners almost applauded. When Tribeman told us that we were listening to a speaker that would cost somewhere between $2000 and $3000/pair, I knew I had to get review samples as soon as the model was put into production.
The technology inside the AT-1's H-PAS enclosure isn't new, but its application is. I asked Peter Tribeman about the enclosure's pedigree and development:
"H-PAS is based upon earlier work originally introduced by acoustician Philip Clements. In those days Phil was looking for ways to acoustically eliminate some distortion byproducts for his newly developed vented speaker designs. He discovered by accident that as he adjusted the relative lengths and angles of his internal chambers with small changes, the bass extension and intensity of the low-frequency output from the vent was dramatically improved. Phil realized at that point that he could achieve incredible bass response with high efficiency and low distortion in 'normal'-size speaker cabinets. By trial and error and constant experiments, Phil made up the rules of this newly discovered technology. Three decades later, we approached Phil with some proposals as to how to make some of those designs in a much smaller footprint. Both Atlantic and Phil brought computers, mathematicians, and sophisticated algorithms to the table to apply up-to-date science to solve the mysteries of his early work in speaker fluid dynamics. From this collaborative effort came what is now known as H-PAS, and our first product with this technology, the AT-1."
The AT-1 looks like a typical two-way, floorstanding speaker with a 1.1" silk-dome tweeter nestled between two 5.25" woofers with graphite-loaded homopolymer cones. Inside, however, things look a bit unusual. Glance at the cutaway diagram provided by Atlantic Technology and you get the impression that the AT-1 looks essentially like a modified transmission-line design. But according to Steve Feinstein, Atlantic's director of marketing and product development, that appearance is misleading:
"Because of the way the internal chambers work, the AT-1 really combines the essential operational characteristics of four different speaker technologies into one product: The top chamber exerts the driver control on the woofers' cones like a sealed design; the long, multi-segment internal chamber, which becomes narrower and narrower, is like an inverted horn, increasing sensitivity; the internal 'bass trap' portion, which literally 'peels off' the bass wave's harmonic-distortion products (based on that chamber and its opening's dimensional relationship to the harmonic frequencies in the bass region), is transmission line-like in its effect; and, finally, the vent opening, which acts like a horn (because of the internal wave-compressing 'plates' that are employed at that point) and also like a reflex vent. We're getting the benefits of all four types."
A benefit of the H-PAS topology is that it allows the designer to use smaller, quicker woofers without sacrificing low-bass extension. The AT-1's 3dB bass-rolloff point is specified at a low 29Hzpretty darned good for a pair of 5.25" cones. The speaker also boasts a sensitivity of 89dB, which is nearly unheard of for small drivers capable of such low bass.
The AT-1's woofers are crossed over to its 1.1" silk-dome tweeter at 2kHz, the tweeter seeing a third-order slope and the woofer a second-order handoff. While many two-way designs cross over at higher frequencies, the AT-1's 2kHz crossover ensures a more even dispersion pattern at the top of the woofers' passband and better integration with the tweeter. However, the lower the crossover frequency, the more energy a small tweeter is asked to produce, and the greater chance it has of overheating or running out of excursion capability.