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THX subwoofers
an additional total of 6 dB of output.
Wiring with two subwoofers is simple. Instead of running two interconnect cables to one subwoofer,
just run one interconnect to each subwoofer, using the "LEFT/MONO INPUT" jack on each subwoofer.
You don't need a Y-connector. See Figure 4 (page 9), or Figure 6 (page 10).
7. SATELLITE/SUBWOOFER PHASING TEST
(WITH BOTH THX AND NON-THX COMPONENTS)
Before you can sit down to enjoy your new subwoofer, you need to perform one simple Phasing
Test. This test insures optimum sound in the critical bass frequencies where your subwoofer and
Satellite or L/C/R speakers overlap. There are two methods of tessting, which are listed below.
When using the subwoofer with a THX controller and THX L/C/R speakers, or with M&K Satellite
speakers and an HP-80 High-Pass Filter, the crossover slopes are linear phase. When the subwoofer
is placed along the same axis as the front speakers, the system will tolerate a plus or minus 28 inch
offset before significant losses at the crossover point are seen.
SPECIAL NOTE IF YOU HAVE A THX 5.1 CHANNEL PROCESSOR
Your THX 5.1 channel processor or receiver has a feature that allows you to electronically "move"
the position of the main speakers so that the signal from each speaker arrives at your ear at the same
time. It does this by time delaying the signal that is fed to the speakers that are closer to your ears.
In order to properly set the phase of the subwoofer, you must set the time delay of the main and/or
surround speakers
first. Any time you change the amount of time delay to the other speakers, it can
affect the phase relationship between those speakers and the subwoofer.
PHASING TEST METHOD ONE
Set the switch labelled "PHASE" to the "+" position. Then, play a familiar CD, LP, laserdisc or tape
with steady, consistent bass content. Listen carefully to the "mid-bass" region of 70 - 125 Hz. This
is the part of the spectrum where electric or string basses and drums predominate.
Then, reverse the position of the "PHASE" switch. If it is set to the "+" position, set it to the "-"
position. If it was set to the "-" position, set it to the "+" position. The best way is to have a partner
work the switch while you sit in the main listening position and listen.
Now listen to the same music, concentrating on the mid-bass. If you hear less bass, set the
"PHASE" switch to the opposite position. If you hear more bass, leave the switch where it is; the new
position is correct.
PHASING TEST METHOD TWO
First, set the toggle switch labelled "PHASE" to the "+" position. Then, feed wideband pink noise
(found on test CDs, the THX "Wow" disc, or a pink noise generator) through your front channel
speakers and your subwoofer. You can do this test by listening, but it is best to use a spectrum
analyzer and look at its display in the "mid-bass" region of 70 - 125 Hz.
Then, reverse the position of the "PHASE" switch. If it is set to the "+" position, set it to the "-"
position. If it was set to the "-" position, set it to the "+" position. The best way is to have a partner
work the switch while you sit in the main listening position and listen.
Now, listen to the same wideband pink noise or look at the spectrum analyzer output in the mid-
bass region. If you hear/measure less bass, set the "PHASE" switch to the opposite position. If you
hear/measure more bass, leave the switch alone; the new position is correct.
This test is necessary because the different distances from each speaker to your ears mean that
it is possible that the Subwoofer's output may arrive at your ears out of phase with the Satellites'
