Manual-7
Time Delay Adjustment Using a
Realtime Analyzer and 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 Rane RA 27
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 one-third or
two-thirds 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 mislead-
ing.
STEP BY STEP PROCEDURE
A 3-Way mode consisting of High, Mid and Low drivers
is used here as an example. For 2-Way systems, use the same
procedure by replacing LOW for MID and following steps 2
through 5. 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 microphone 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 INPUT of the cross-
over (or mixer or wherever is convenient). Turn up the
crossover MASTER LEVEL control and the MID LEVEL
control until noise is heard from only 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 frequency with any of the Rane analyzers set in
the ±1 dB mode.) For example, if your high crossover
frequency is 2 kHz, set the RA 27 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. 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 controls, turn up the HIGH LEVEL control
until the tone coming from only 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 necessary with full scale analyzers) and observe the
display reading at the crossover frequency:
i. If the display shows a +3 dB reading (red LED on with
Rane analyzers in the +3 dB mode), 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 (still in
green or in yellow on Rane analyzers), slowing turn up
Fine. So we put up with it. But to make matters worse,
when the two drivers are horizontally displaced – that is, one
is in the front of or behind the other, this “lobe” or dispersion
pattern gets tilted (usually upward) toward the driver that is
further behind (see Figure 1). This gets hard to put up with,
because the end result is that your speaker system will have
two, three, four or more tilted radiation patterns and only two
or three people in the house will have decent seats. And we’re
not talking trivial pursuits here—this rampant lobing error can
make a sound system a real headache, to listener and operator
alike.
The idea, then, is to be sure that all drivers are vertically
aligned and that all components are always in phase. Then all
the main lobes are on-axis, well behaved, and the system
enjoys the widest possible dispersion pattern so that everyone
gets good sound. The one catch is that in many cases it is
physically or otherwise impossible to get all the drivers
vertically lined up at the sound source. This is where time
delay comes in.
By electronically delaying the signal going to the driver
up front, enough time is allowed for the sound from the rear
driver to literally catch up to the forward driver’s voice coil,
so that signal from both drivers is emitted in phase (See Fig.
2). And it works! Time delay can make an appreciable
improvement in overall sound. The trick is finding the proper
amount of time delay: hence the rest of this section.
Unfortunately the amount of time delay is a function of
two factors (life ceased to be simple after age 9, right?): the
amount of horizontal displacement between driver voice coils,
and the actual crossover frequency involved. Setting Delay
controls by ear is supposedly possible, but very tricky and
unreliable. The following methods are a couple of (but by no
means all) means of setting time Delay.
