Rane AC 23B (2003 version) - Manual (Page 13)

Manual-
Time Delay Adjustment Using
Realtime Analyzer & Pink Noise
This method outlines the use of a realtime analyzer, pink
noise generator and flat response microphone to set crossover
time delay. Some references will be made to the Rane RA 30
realtime analyzer for those with the intelligence and good taste
to use one of these regularly. The procedure applies to virtually
any analyzer system. We recommend using a 1/3 or 2/3 octave
analyzer as either of these is more likely to match your specific
crossover points than a one-octave analyzer. And it is important
to match the analyzer to the crossover point as closely as possible
for proper phase alignment, otherwise the analyzer readings may
be misleading.
STEP BY STEP PROCEDURE
A 3-Way mode consisting of High, Mid and Low drivers is
used here as an example. For other configurations, use the same
procedure starting with the highest crossover point and repeating
steps 2 through 5 for each lower crossover point. NOTE: If you
are running two separate channels on the crossover, tune up only one
channel at a time, using the same procedure for both.
1. Place the analyzer mic about 15 feet in front of the speaker
stack and at a height about midway between the high and mid
drivers. Turn all crossover LEVEL controls fully down.
2. Connect the pink noise source to the crossover INPUT (or
mixer or wherever is convenient). Turn up the crossover MAS-
TER LEVEL control and the MID OUT control until noise
is heard only from the mid driver at a comfortable volume.
3. With a healthy but not uncomfortable volume of noise from
the mid driver, set the analyzer DISPLAY LEVEL control so
the LED’s corresponding to the high crossover frequency are
reading 0 dB (this would be a green LED at the crossover fre-
quency with any of the Rane analyzers). For example, if your
high crossover frequency is 2 kHz, set the RA 30 in the ±1
dB mode and then adjust the RTA LEVEL control until the
green LED is lit in the 2 kHz band. There...easy.
4. Press in the MID MUTE switch on the crossover so the tone
is removed from the mid driver. Without re-adjusting either the
meter or the crossover Input or Mid Level controls, turn up the
HIGH LEVEL control until the tone coming from the high
driver reads 0 dB (a green LED at the crossover frequency).
5. Now release the MID MUTE switch on the crossover so that
pink noise is heard from both the high and mid drivers. Switch
the display sensitivity to ±3 dB on Rane analyzers (not neces-
sary with full scale analyzers) and observe the display reading
at the crossover frequency:
i. If the display shows a +3 dB reading, then the drivers are
properly phase aligned and no delay is necessary; leave the
MID DELAY control at minimum.
ii. If the display shows less than +3 dB reading, slowly turn up
the MID DELAY control on the crossover until the display
shows +3 dB. Now the drivers are electronically phase
aligned. The Delay control should be left in this position
unless the speaker system is physically altered.
iii. If the MID DELAY control is all the way up and you still
do not have a +3 dB (red) reading, you will have to physi-
cally move the high driver farther forward until the display
shows +3 dB (red). The amount of displacement correction
available from the Delay depends on the actual crossover
frequency: the higher the frequency, the less amount of cor-
rection capability. If the drivers are built into a single cabi-
net and/or it is impossible to change relative positions, then
you will have to obtain additional external delay to achieve
proper phase alignment. such as the Rane AD 22B.
iv. If turning the MID DELAY control up makes the display
reading decrease instead of increase, this means that the high
driver is actually in front of the mid driver; adding delay
to the mid driver only worsens the situation. There are a
couple of ways to deal with this:
a. Try to move the high driver back as far as possible without
losing stability in balancing the speaker stack. You may
want to raise it up as well to restore dispersion close to
the stack. If you cannot move the high driver, then you
will have to use an additional delay source to align the
high and mid drivers. The built-in delay system in the
AC 23B is designed to accommodate the majority of
common speaker configurations; if you encounter confu-
sion or difficulty with your particular system, it is best to
consult your dealer or the Rane factory for assistance.
b. If this decrease in the display due to the DELAY control
occurs at a low frequency crossover point below about
150 Hz, set the DELAY control to minimum and leave it
there. Frequencies below 150 Hz are actually omnidirec-
tional, so that phase misalignment is virtually inaudible
below this point. Subwoofers will often possess long
folded or straight horns, resulting in the diaphragm being
well behind the rest of the stack. Most authorities agree
that phase alignment of subwoofers is unnecessary.
6. Lower the microphone until it is vertically midway between
the mid and low drivers. Repeat steps 2 through 5, using the
crossover LEVEL control, MUTE switch and next DELAY
control. You may start each series of steps 2 through 5 at a
different volume as necessary—but once the Levels are set in
step 3 do not alter these until step 5 is completed. Once all of
the crossover DELAY controls are set, then adjust the output
LEVEL controls as outlined on page Manual-14.