Using The D1500 To Tune An Electronic Crossover; Using The 1500 To Set Crossover Delay Time - Samson D-150 Owner's Manual

Using the D1500 to Tune an Electronic Crossover

Using the D1500 to Tune an Electronic Crossover
A REAL TIME ANALYZER (RTA) is an especially useful
tool for setting up your crossover, as it will enable
you to set parameters like DELAY and LEVEL more
accurately. Some Audio Engineers can use their ears
to tune a loudspeaker system. Some will even use the
crossover to create the over-all system curve using
the crossover like an equalizer. For the rest of us, an
accurately set crossover with a flat response is the best
way to start, and using an RTA like the D1500 is the
best way to get there.

Using the 1500 to Set Crossover DELAY Time

In the real world, no single or multiple speaker system
is perfect. If there were such a perfect system, it would
more than likely be comprised of a single transducer
that alone could faithfully reproduce the entire fre-
quency spectrum. Because no such system exists,
we have to deal with the problems associated with
multiple transducers. The first problem that you will
encounter, whether you know it or not, is time travel.
That's when the delay circuit from a good electronic
crossover, like the Samson Audio S• 3-way, becomes
especially useful.
Ideally, the sound reproduced by each driver in the
loudspeaker system would be traveling through the
air ultimately reaching the listeners at the same time.
To accomplish this in a system using multiple drivers
or enclosures, the voice coils of all the drivers would
have to be lined up on the same vertical axis. This
is very difficult to achieve in many cases because of
the physical size of the different components, and
the position of the drivers in their enclosures. It is not
uncommon to have a physical distance of 2" to 24" or
more between the low and high frequency drivers.
For example, front loaded low frequency drivers and
compression drivers mounted on a large horn. With no
correction, the low frequency signal can be traveling
through the air 2" to 24" in front of the high frequen-
cies and thereby reaching the listeners at different
times because it is the spacial relationship between
the different drivers' voice coils that determine the
time it takes for the sound to reach the listener.
Although the delay time between the low and high
frequency signal may be relatively small, the negative
effects can be substantial. The problem is that both
drivers are reproducing frequencies at and around the
crossover point, which arrive at the listener at different
times. Typically, the resulting problem is comb filtering
or cancellations at the crossover frequencies.
A good crossover like the Samson S 3-way features a
DELAY control allowing you to dial up-to 2 millisec-
onds of delay. By using the D1500 and the S•3-way's
DELAY you can time align the drivers in your system
and minimize the possibilities of comb filtering. Now
follow these steps, separately, for both the left and
rights sides of your loudspeaker system:
Note: The following example is for a two-way loud-
speaker system in a small to medium size room.
• Set the crossover to the desired frequencies and
press all the Mute switches to the ON position, turn-
ing all of the S •3-ways outputs off. Position your
measurement microphone approximately 10-15 feet
from your loudspeaker array, halfway between the
low and high frequency drivers. Now turn all the
GAIN controls to the fully counter clockwise position.
• Use the D1500's Signal Generator to produce a
frequency tone tuned to the crossover frequency, or
use the Pink Noise generator and connect the test
tone to your loudspeaker system, either from your
mixer or directly in the crossover's input. Now turn
off the Low Frequency Mute switch and adjust the S•
3-way's INPUT GAIN to "0". Adjust the LOW GAIN con-
trol so that the signal is playing at a loud, but not too
painful level. Make sure you only hear sound from
the low frequency driver.
• Adjust the GAIN control of the crossover until the
D1500 reads 0dB at the crossover frequency. Now
press the LOW MUTE switch turning off the low fre-
quency output.
• Turn off the High Frequency MUTE switch and turn
up the High Frequency Level control until the D1500
reads 0dB at the crossover frequency.
• Now, press the LOW MUTE switch again turning
on the low frequency output. Notice the reading on
the RTA at the crossover frequency. If the reading is
+3dB, there is no need to adjust the delay time and
you can assume that the speakers are in phase. If the
D1500 reads less than +3dB you'll need to delay the
low frequency.
• While watching the D1500 RTA display, slowly turn
the DELAY control counter-clockwise until the dis-
play reads +3dB.
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