Manual-12
less amount of correction capability. If the drivers are
built into a single cabinet and/or it is impossible to
change relative positions, then you will have to obtain
additional external delay to achieve proper phase
alignment. The Rane AD 22B would be suitable.
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 situa-
tion. 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 disper-
sion 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 accommo-
date the majority of common speaker configurations;
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 omnidirectional, 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-15.
Time Delay Adjustment Using
SPL Meter & 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 straightforward SPL meter (obtainable at
most local electronics stores, the best is the Rane RA 30) and
some kind of variable tone generator.
In order to exclude the effect of room acoustics and
imperfect 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 backward until the SPL meter
reads +3 dB; then the two drivers are electronically aligned
and the on-axis cancellation is eliminated. This procedure is
then repeated for the next lower crossover point(s).
