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page 8V-1250THX subwoofer
The +2 and +4 marks indicate the points where your subwoofer is producing 2 dB and 4 dB,
respectively, more output than the "CALIBRATED" level.
SETTING SUBWOOFER LEVEL (THX)
The proper method of setting the level of the subwoofer in THX mode is to use the low frequency
pink noise test signal generator built into the THX controller and a sound level meter (available from
Radio Shack). First set the master volume of the THX controller to the "0" or "REF" position. Then set
the Subwoofer Output control on the THX controller so that the output of the subwoofer causes the
sound level meter to read 75 dB (C scale, slow mode) when that test signal is playing. All channels
of the THX system should be calibrated to this 75 dB level when using the unit's internal test signal.
Special Note: When calibrating the subwoofer level (and only the subwoofer level), you will find that
the needle on your sound level meter will bounce plus or minus a couple of decibels when measuring
the test signal. To set subwoofer level, read the AVERAGE meter level, not the peak level. Move
around the room as you measure levels, so that your measurements account for the room reinforce-
ments and cancellations found at various room locations.
For details on setting levels with your THX controller, see the instructions provided with that unit.
USING TWO SUBWOOFERS (THX)
Using two subwoofers in your THX system will give you the ultimate in bass performance. It will give
you improved bass impact and definition, as well as greater output and dynamic range. If you locate
the subwoofers in different parts of the room, you will get a better overall frequency response, because
the room modes excited by one woofer are complemented by the presence of the other subwoofer.
Alternately, if you stack two subwoofers, one on top of the other, their outputs will couple and give you
an additional total of up to 6 dB of output.
Wiring with two subwoofers is simple. Instead of running two interconnect cables to one subwoofer,
run one interconnect to each subwoofer, using each LEFT/MONO input jack. See Figure 2 (page 6).
6. OPERATION WITH A NON-THX PROCESSOR
OPERATION OF THE "LOW PASS FILTER" SWITCH
With a non-THX controller, preamp, etc., this switch should be set to the "80 Hz 24 dB/OCTAVE"
position. Do not operate this switch unless the "BASS LEVEL" control is set to "MIN."
For non-THX systems, your subwoofer has been optimized for an 80 Hz crossover with a 24 dB/
octave slope. This low pass filter makes a rapid transition to 36 dB/octave above 125 Hz, which
provides the extremely sharp attenuation needed to make the subwoofer's sound non-directional.
For optimal performance, we strongly recommend that you use an M&K HP-80 High-Pass
Filter. Your subwoofer with this filter and M&K Satellites forms a 4th order Linkwitz-Riley crossover
between satellite and subwoofer. The linear phase of this crossover means uncompromised
performance with great flexibility in system setup without elaborate calibrations or adjustments.