Bookshelf Speaker Reviews

H-PAS stands for Hybrid Pressure Acceleration System. How does it work? The 5.25-inch woofer’s backwave embarks on an extraordinary journey as it is captured, pressurized, and accelerated through a cascade of structures. Starting with a small woofer is part of the plan, and it does more than just save space. According to Atlantic Technology, the lighter woofer ultimately delivers better transient response and more detailed bass at the same low frequencies that normally require a larger woofer to achieve. Another benefit: Since the system inherently results in high sound-pressure levels (SPL) and low distortion, it is said to negate the need for high-power amplification normally required to get big bass from a small driver.

Let’s pretend you’re a backwave coming off the AT-2’s woofer and the AT-2 enclosure is the acoustic equivalent of a luxury spa. Here is what happens to you:

The woofer expels you into a heavily damped lobby, which acts similar to an acoustic suspension chamber to provide some degree of driver control. Heading to the gym for a workout, you’re whooshed through a multi-segmented chamber that narrows like an inverse horn, which pressurizes and accelerates you for greater output.

But it’s been a tumultuous travel day, and you’re still frazzled, so you pass by the bass trap, which strives to peel off harmonic distortion and leave it behind in the equivalent of your post-workout massage. Finally, you dress up for the evening and go out on the town through a baffle slot at the bottom of the speaker that outwardly resembles both a horn and a port. By this time you’re a lean, mean, bass wave—ready to take on Charles Mingus.

Keeping with this analogy, the Atlantic Technology team read the description above and added the following: “AT has developed a sophisticated mathematical model that describes and predicts every aspect of H-PAS behavior. Every angle, internal dimension, chamber volume, and driver parameter is fed into the formula. This mathematical model is like a personal trainer with advanced graduate degrees in nutrition and anatomy/physiology. To you, it may seem as if you’re just working out at the gym. But in reality, every move, every exercise, every gram of protein you consume has a specific purpose toward a precise outcome. And so it is with H-PAS, and its internal puzzle of chambers, partitions, and angles. It is all there for a reason, all very intentional and calculated.”

This cutaway diagram shows generally how H-PAS works in the AT-2. Although this is a 2D drawing that only shows top-to-bottom airflow, the chambers actually work in three dimensions, and the width and diameters of the openings and angles vary side to side as well. To assist in the design of H-PAS speakers, AT has developed a sophisticated, predictive algorithm that allows its engineers to hold any one variable constant (i.e. desired low frequency -3 dB point, driver size/parameters, system sensitivity, cabinet volume) and determine the other values based on the held variable. (The diagram is strictly representational, and no measurements or dimensional relationships among the components and chambers should be inferred.)