3. Test Methods, Continued

All the tests were run in conditions similar to those found in real life: satellites on a desk and the subwoofer on the floor. The results therefore correspond to what you would actually get with a properly installed system.

For the subjective tests, we used a PC with a Creative Audigy 2 ZS Platinum Pro sound card. You could hardly find a better source for this sort of sound system! We played different sorts of music to get a good idea of sound quality and defects in the main pitches. The supports were DVD Audio and CD Audio.

We rounded off the tests by seeing what was the highest sound level we could reach without any audible distortion. To do so, we developed a custom measurement signal from three sources of pink noise encoded in stereo (right, left, center). The signal was strongly filtered in the sub-bass range (practically absent from most kinds of music) and lightly filtered in low-pass from 500 Hz (-3 dB) in relation to the broadband pink noise.

This third octave analysis of our test signal shows exactly how the frequencies sent to the speakers are distributed.

The crest factor is 12 dB. We did not try to reach the top level but stuck to the reality of the music reproduction it is supposed to simulate, though with a constant signal to obtain a reliable rating. The signal is of course random, like any pink noise (the basic signal).

This 3D spectrum analysis (sound level, frequency and time out of 5.5 s) gives an idea of what our signal is like.

Sound levels were measured at 1 meter from the speakers installed in a typical way (satellites on a desk and the subwoofer on the floor) using a sound level meter with a resolution of 0.1 dB SPL and configured with a standard "Long" response time to obtain a stable value representative of the mean level obtained. The resulting value is of course in dB SPL (Sound Pressure Level) without weighting, as it should be for the sound ratings of broadband noise. But don't forget that this is a comparative test so the value is not absolute: in other conditions, these systems would produce different sound level ratings.

The sound level obtained in dB SPL "L" (Linear) as seen on the screen of our meter.