Rane AC 22B (1998 version) - Manual (Page 6)

Manual-6
Time Delay Adjustment
Before jumping feet first into the realm of time delay and
how to adjust it, it might help to spend a moment here to
re-affirm why on earth this Delay is really necessary. For a
detailed and enjoyable short course on time delay,
Linkwitz-Riley and other mouth-watering details, we urge
you to pick up a free copy of RaneNote “Linkwitz-Riley
Crossovers”. Ask your dealer, call the factory, or download it
from our web site. In the way of summary, a few words are in
order here to outline the basic effects of time delay in cross-
overs.
Problems pop up when two different speakers emit the
same frequency as occurs in the crossover regions of two,
three, four and five way systems. Because the two drivers are
displaced vertically, cancellation occurs somewhere off-axis
because the sound waves have to travel different distances
from the two speakers and hence, will arrive shifted in phase.
This forms a “lobe” or radiation pattern, bounded on either
side by cancellation lines or axes, which narrow the disper-
sion pattern or listening area of the speaker.
Fig. 2 Corrected In-Phase Axis Response With Electronic Time Delay on
Low Frequency Driver
OPERATING INSTRUCTIONS
Selecting Crossover Frequencies
Most speaker manufacturers supply low and/or high
frequency cut-off points for each driver, especially if these
are supplied in a system. These cut-off frequencies are based
on each driver’s performance at and beyond this point, with a
certain safety margin to accommodate more gentle filter
roll-offs and resultant higher output beyond the recommended
performance range.
The AC 22B utilizes 41-detent crossover Frequency
selectors which are precision potentiometers. The detents
assure consistent accuracy from Channel to Channel and unit
to unit. This is a distinct advantage over the continuously
variable designs using low-tolerance parts, possible knob
misalignment and panel screening variations. Even with 41
choices it is possible that the exact recommended Crossover
Frequency may not fall on one of the detents on the selector.
Not to panic, for these sound reasons:
1. The AC 22B possesses 24 dB/octave roll-off, so the
Crossover points may be set to the nearest detent above or
below the recommended limit with virtually no hazard to
the driver or degradation in sound quality. If extremely
high power levels are expected, it is safer to defer to the
high frequency drivers and shift the Frequency up rather
than down.
2. Detents do not rely on knob alignment, silk-screen accu-
racy, parallax and other variables which erode the accuracy
of continuously variable designs. Chances are that even
careful visual alignment on these will often yield a Fre-
quency error greater than a full detent on the AC 22B.
3. If it is absolutely critical to obtain the exact Crossover
Frequency (Mil Spec., P.A., etc.), the selector can be
positioned between detents if necessary. This of course will
require the aid of a precision signal generator and other
equipment to verify the exact setting.
For best overall system results, try to choose the speaker
components so that each operates well within its recom-
mended limits. This will provide valuable leeway so that you
may move crossover points in order to fine-tune the system,
and will also yield higher system reliability. If at all possible,
beg, borrow or best yet always use some kind of realtime
analyzer to tune your crossover and fine-tune the system for
each different location with an equalizer. Keep reading for
further alignment details.
Fig. 1 In-Phase Axis Response Without Time Delay