Rane AC 22B (2003 version) - Manual (Page 10)

Manual-
cabinet and/or it is impossible to change relative positions,
then you will have to obtain additional external delay to
achieve proper phase alignment.
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 then 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 obtain an additional delay source to align
the high and mid drivers, such as the Rane AD 22B. The
built-in Delay system in the AC 22B is designed to ac-
commodate the majority of common speaker configura-
tions; if you encounter confusion 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 om-
nidirectional, 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.
Otherwise you will have to obtain additional delay equip-
ment to align these to the rest of the system.
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, adjust the output
LEVEL controls as outlined in the Setting Levels Section on
page Manual-12.
Time Delay Adjustment Using SPL
Meter and Tone Generator
Now that good quality realtime analyzers are becoming more
affordable and easier to use, there are few reasons why one of
these should not be regularly used in any sound system. If an
analyzer is simply not available or for some reason inappropriate,
an accurate Delay setting can be obtained by using a straightfor-
ward SPL meter (obtainable at most local electronics stores, the
best is the Rane RA 30) and some kind of variable tone genera-
tor.
In order to exclude the effect of room acoustics and imper-
fect driver response, only the crossover frequencies are to be
emitted (one at a time) by the tone generator. First, the highest
crossover frequency is run through the crossover and each of the
two speakers sharing the crossover point is set separately to an
arbitrary 0 dB level on the SPL meter. When both drivers emit
the crossover tone simultaneously, the combined response should
read +3 dB higher on the meter. If the drivers are not phase
aligned, some cancellation will occur on-axis, resulting in a
combined response less than +3 dB. Turning the DELAY control
up causes the lower frequency driver to electronically move back-
ward until the SPL meter reads +3 dB; then the two drivers are
electronically aligned and the on-axis cancellation is eliminated
(see Figure 2 on page 6). This procedure is then repeated for the
next lower crossover point(s).
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 repeat
steps 2 through 5 for each lower crossover point.
1. Set the tone generator to the highest crossover frequency and
plug it into the Input of the crossover. Turn all crossover
LEVEL controls fully down.
2. Position the SPL meter (microphone) about 15 feet in front of
the speakers and at a height about midway between the high
and mid drivers. It is very important that the meter remain in
exactly the same position throughout the test, so affix it to a
mic stand, small tree or other stable object. Set the switches
on the SPL meter to C-weighting, slow. Be sure to minimize
background noise (air conditioners, fans, traffic, wild animals,
etc.) as these will effect the meter reading.
3. Slowly turn up both the crossover MASTER and MID LEV-
EL controls until the tone is heard through the mid driver.
Adjust the SPL meter control and/or the crossover LEVEL
controls until you obtain a 0 dB reading on the meter. Verify
that no sound is coming from any other speakers except the
mid driver.
4. Now press in the MID MUTE switch on the crossover so that
the tone is removed from the mid driver. Without re-adjusting
either the meter or the crossover MASTER or MID LEVEL con-
trols, turn up the HIGH LEVEL control until the tone com-
ing from only the high driver reads 0 dB on the SPL meter.