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THX subwoofers
knob sets the upper rolloff point of the Subwoofer, eliminating mid-bass and midrange that are being
reproduced by your Satellite speakers. The control is a means of fine-tuning the transition between
your Subwoofer and Satellite speakers, and it provides a rolloff of 12 dB/octave up to 125 Hz, where
the filter shifts to 36 dB/octave. The frequency where the rolloff begins is labelled on the back panel.
In most systems, including M&K Satellites, about 80 Hz gives the best blend. If you don't want to
experiment, set the control at 80 Hz.
The goal is to get a balanced
acoustic
output in your room. This is not necessarily the same as
flat electrical output. Rooms typically reinforce bass frequencies around 100 Hz, so by leaving an
electrical gap, you may actually get a smooth acoustical response where it matters, in the room.
Think of this control as a mid-bass fine tuning adjustment that you set to achieve the best transition
between the Satellite speakers and the Subwoofer. When you hear a smooth sound overall, well
balanced between the deep bass and the rest of the audible spectrum, the control is set properly.
OPERATION OF THE "BASS EQ" SWITCH
This switch gives you two choices of subwoofer response in the deep bass region below about 30
Hz. For the flattest in-room frequency response, set the switch to the "THX" position. This position
also gives you the maximum output level, dynamic range, and headroom.
The "ANECHOIC" position produces flat
anechoic
response, which actually results in a
rising
output below about 30 Hz. Its in-room output will increase as you go lower in frequency, due to a
phenomenon known as room gain. Room gain means that the bass produced by a subwoofer in a
room actually increases in amplitude at frequencies below 30 Hz, at a rate of about 12 dB per octave.
Our own measurements in a very wide variety of actual rooms have clearly documented this fact.
In the majority of cases, we strongly recommend using the "THX" position. This will give you the
most accurate (flat) response, along with maximum output and dynamic range. The "EXTENDED"
position is provided for measurements and for those who might prefer that acoustic characteristic.
OPERATION OF THE "BASS LEVEL" SWITCH
When using the subwoofer with a non-THX processor, preamp, etc., this switch should be set to
the "VARIABLE" position. The subwoofer level can then be set independently to match your
speakers.
The "REFERENCE" level control mark is calibrated to the level set by the "THX" switch. If you set
the switch to "VARIABLE" and the level control to "REFERENCE," its output level is the same as when
you set the toggle switch to "THX." The +3 and +6 marks indicate the points where your subwoofer
is producing 3 dB and 6 dB more output, respectively, than the "REFERENCE" level.
WIRING WITH A NON-THX PROCESSOR OR PREAMP
The "FROM PREAMP" RCA terminals on the subwoofer allow you to connect the subwoofer to
preamp-level components other than THX controllers, such as preamplifiers, integrated amps and
receivers with preamp outputs, high-pass filters, crossovers, standard surround sound processors,
etc. All of the input connections and controls for the subwoofer are located on its large metal
backplate, which can be found on the back panel of the subwoofer cabinet.