
The twin speaker units in the sub-bass enclosure - which is as large as a small, black paper basket - are mounted face-to-face in an isobaric arrangement. Isobaric, or constant pressure, speaker systems are designed to increase the bass range in a given size of cabinet, by using two speakers rather than one. By mounting them one behind the other to create a constant-pressure zone between them, they should gain an increased bass range of up to an extra half-octave, compared with single-speaker designs.
The strange thing here is that whereas most isobaric arrangements put the speakers one behind the other in cone-to-magnet or magnet-to-magnet designs, Altec Lansing mounts them vertically, cone-to-cone, so the sound emanates from the back of the cones. You would think the structure of each speaker - the frame holding the cone in place - might obstruct the sound coming from its back. In practice, the 24W sub-bass unit works very well, giving a strong bass line to music and an impressive punch to explosions in movies and games.
The two 11W satellites are mounted on cast metal stands and include both 40mm mid-range and 18mm high-frequency drivers, which play through thin, black-metal meshes. These complement the bass unit well, adding a good level of detail to speech, singing and treble instruments. They don't quite have the presence of systems like the Acoustic Energy Aego-M, but they're less than half the price of these, our current favourite PC speakers.
Controls of the FX4021 can be operated from the wired control pod or a wireless remote and the control pod enables you to plug a media player, such as an iPod, into the speakers without disturbing the connection from your PC. Control involves selecting a setting - volume, tone or the stereo image controlled by Altec Lansing's SFX software - and adjusting the level with a digital click-wheel. This is a logical technique and works well to tweak sound characteristics when switching between sources.