@Yossi:
If you are ONLY measuring two Beolab 50s, then it doesn’t matter where you measure from, since the software is calculating the difference between the two. For example, if you tell the software that one loudspeaker is 1.5 m away and the other is 1.75 m away, you get the same result as if you said 0.0 m and 0.25 m. The DSP is finding the closest of the two loudspeakers and delaying it by the difference.
HOWEVER, if you have a mixed system, then you need to be a little more careful – or be willing to make changes based on how it sounds rather than what your laser says. The acoustic centre of a Beolab 50 is closer to the tweeter than the midranges or speaker grille. So, measuring from the tweeter (or the middle of the circle at the top of the speaker if it’s closed) will deliver a closer better result. But the distance value can really be considered to be a quick, but slightly imprecise setup that can, in most cases, be tweaked to sound “better” to the listener.
As for your nose, since the distance is imprecise (my definition of “precise” when setting up loudspeakers means millimetre-scale) then measuring from your nose is good enough (that also what I do…). However, if you’re going to be as geeky as possible, you should measure from the centre of where your head would be. Unfortunately, your ears are about 7 cm away from that point, but it’s the best you can do…
Cheers
-geoff
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