9. Logitech Z-640

The Z-640s are the successors to the Z-540s in a 5.1 version. They use exactly the same design as their predecessors, both for the woofer and the satellite speakers. The wider central channel is positioned horizontally. It is interesting to note that this additional width is actually due only to the spacing of the control knobs. In fact, if you remove the front grille, you can see that the central channel has only one driver, the same as that used by the satellites. You will also note that the cabinet is quite large in comparison to that of the 251s, and that it incorporates an 8" driver, as opposed to a 5.25" driver in the 251s, for example. It is also amusing to note that the external look of the cabinet, with its silver trim, might lead you to believe that the driver is much bigger than it actually is. As for power, the statistics have barely increased in relation to the Z-540 - 5 x 5.5 watts RMS for the satellites and central channel, and 23.5 watts RMS for the woofer. Logitech claims a bandwidth of 35 Hz through 20 KHz with a noise-to-signal ratio of better than 75 dB. The control buttons are fairly comprehensive, consisting of an on/ off button, a slider for the general volume, one for the level of the central sound, another for back/ front level, and a Matrix button to activate the M3D. What is lacking, however, is some sort of adjustment for the bass and treble, and that's a pity. The central channel also has a headphone socket.

The M3D, or Matrix Surround Sound, is a system that in theory makes it possible for a sound card with only one stereo output to produce high-quality 3D surround sound, by channeling atmospheric and ambient sound to the rear satellites. We don't think this system is massively useful. In fact, none of the recent sound cards or integrated chipsets have a single output, and the 3D sound technologies currently being developed by Sensaura or Creative Labs make it possible to reproduce 3D sound much more convincingly, using only two speakers.