Specifications

An easy way to determine the best phase relationship is to listen to a low-
frequency source while standing in front of the system and have someone
change the setting of the Phase Reverse Switch from normal to reverse while
you listen. In one setting you should hear a distinct increase in mid-bass, and
in the other setting you should hear a distinct reduction in mid-bass. It’s
important to listen in front of the speaker system for accurate acoustic eval-
uation.
If you do not hear a change in the bass response, it’s because either:
(a) The full-range system that the subwoofer is being used with does not
reproduce enough bass output to cause either a cancellation or addition with
the subwoofer’s output, or
(b) The full-range and subwoofer systems are displaced by a distance of
around 1/4 wavelength of the frequency region where they both provide the
most output. In such a case, neither polarity position will result in addition or
cancellation, hence the lack of change in response.
The solution to situation ‘a’ is to leave the subwoofer in the normal position.
No harm will come if the full-range system simply cannot reproduce energy
low enough to compete (either positively or negatively) with the subwoofer’s
output.
The solution to situation ‘b’ is to either change the physical relationship of
the two speaker systems, or delay one of the two systems (whichever one is
positioned closer to the listeners) with a digital delay unit. A good quality
measurement system that can read and depict phase response and/or
impulse response would be very useful in such a situation. However, without
such a system, you can determine an effective delay time by trial and error.
Simply increment the delay time in small steps (1 ms) until the action of
changing the Phase Reverse Switch produces the maximum cancellation in
one setting, and maximum addition in the opposite setting. With the switch
set for maximum acoustic addition, the two systems should be in time and in
phase with one another.You will have preserved optimum impulse and phase
response and can now filter out any objectionable mid-bass overlap with an
equalizer.
(5) Absolute Phase
Quite a bit has been written about absolute phase, particularly in regard to
studio recording and hi-fi sound reproduction.The subject is, however, often
ignored in the field of sound reinforcement.
Essentially, absolute phase refers to configuring the system so that the elec-
tro-acoustic drivers move toward the listener and produce a positive wave-
front upon the first cycle of excitation by source material.This means that at
the instant of impact, when the head of the kick drum moves outward
towards the microphone, the speaker cones also move outward.
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