In a PMC ATL (Advanced Transmission Line) enclosure, the bass driver is placed at one end of a long tunnel (the transmission line), which is heavily damped with absorbent acoustic material. This material is specified to absorb the upper bass and higher frequencies that radiate from the rear of the bass driver.

The lowest frequencies, which remain in phase, then emerge from the large vent at the end of the line, which essentially acts as a second driver. One advantage to this approach is that the air pressure loading the main driver is maintained, thus controlling the driver over a wide frequency range, which in turn significantly reduces distortion. A spin-off from the lack of distortion is that the upper bass and midrange detail is not masked by harmonic distortion residing in the very low frequencies. The result is PMC’s characteristic transparent midrange and fast, attacking bass notes, all reproduced with outstanding clarity.

A further advantage of the transmission line approach is a cabinet that produces a higher volume and greater bass extension than a ported or sealed design of a similar size, even if identical drivers were used. Moreover, as the loading on the main driver is maintained at all volumes, the frequency response also remains consistent regardless of listening level.

Casual late night listening or analytical studio sessions can be conducted without the need for high volumes to achieve maximum bass response. A characteristic that is especially suited to both the home enthusiast and recording professional alike.