Crane Song AVOCET II - Manual (Page 44)

More Refinement
Fine tuning the stereo separation (space between the woofers)
If you have stereo subwoofers, their left-right separation must be adjusted. Play
Spanish Harlem .
Listen to the sound of the bass with the subs off. It should be perfectly centered as a phantom image
and and its apparent distance from the listener should subtend a line between the satellites. If it is not
perfectly centered or its image is vague, the satellites are too far apart. Now add the subwoofers. The
bass should not move forward or backward, and its image should not get wider or vaguer. Adjust the
physical separation of the subwoofers until the bass image width is not disturbed when they are
turned on. This “integrates” the system. Go back to step one, recheck the amplitude and phase
settings for the new woofer position. Everything is now spot on.
Congratulations, you’ve just aligned a world-class reproduction system! A subwoofer should not call
attention to itself, either by location or amplitude. When you play music, the combination of the sub
and mains will sound like a single, seamless source.
Now, after logging your settings, sit back, listen and enjoy. You’ve earned the time off. Don’t let anyone
touch those hard-earned adjustments, for you can be confident that they are about as good as they’re
going to get. Play several of your favorite recordings, and listen to the bass. The bass on the best
recordings will be acceptable on your reference system; the worst recordings will have too much or
too little bass. Now you can be reasonably sure the problem is in the recording, not your room or
woofers. What a nice feeling!
How The Pitch Detection Method Works
The 1/3 octave pink noise signal (or the multitone test signal) contains a narrow band of frequencies,
whose dominant level is at the center of the band. Thus, you perceive a “pitch” to the signal. When
you add a second loudspeaker driver (the subwoofer) driven by the same signal, if the woofer’s output
does not exactly match the level and distribution of frequencies produced by the main loudspeaker,
there will be a shift in the dominance of the multifrequencies, either towards the high end of the band
or the low end, perceived as a pitch shift. When the two signals are well-matched in level, freqeuency
distribution and phase, you will hear a delicate increase in level, but no change inpitch. By simple
comparative listening, taking the woofer in and out of the circuit, you have confirmed that your drivers
are matched at the crossover frequency, and that the wavefronts of your main speakers and subs are
aligned at the critical crossover frequency.
Of course, we’re making certain assumptions...that:
· your satellite system is well designed, linear and rolls off below some defined frequency.
· your subwoofer system is linear and rolls off above some defined frequency.
· the slopes of the two rolloffs are compatible and will integrate.
Your degree of success depends on how closely the two systems meet those requirements.
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