SET-UP AND CALIBRATION
TESTING FOR PROPER SPEAKER POLARITY
Proper polarity throughout the system is required before level calibration can be estab-
lished. Wiring the loudspeakers in proper polarity is essential for precise localization of
images and bass response—both important goals of the Home THX Audio system.
Achieving proper polarity is made more complicated if amplifiers of different types are
used in the system. Some amplifier designs invert the polarity of their output relative to
the input signal. Speakers attached to these amplifiers must have their polarity invert-
ed again to get it back where it belongs.
The best way to ensure proper polarity in any home audio system is to compare each
speaker to a single speaker which is used as the reference for the system. We will use
the Left front speaker as the reference in our example. Check the wiring color code on
both the amplifier and speaker jacks to verify correct polarity.
L-R POLARITY:
Check Left-Right polarity by listening to both speakers in the stereo
bypass or center speaker off mode. Listen for a solid center image. If in doubt, reverse
the leads on the Right speaker only and compare the results. Speakers with mis-
matched polarity will have a poorly-defined image smeared all over their end of the
room. Some listeners will even feel strange pressure sensations in their ears! If you
have any doubt, try using the pink noise on Chapter 6 of
WOW!
—this should make the
difference extremely clear.
L-C POLARITY:
Check Left-Center polarity in the Home THX Cinema mode by feeding
mono program material (dialog, or Chapter 6 of
WOW!
) and setting the input balance
to the left so as to get equal sound pressure levels out of both the left and center
speakers. Again, listen for a solid image between the left and center speakers.
RELATIVE SUBWOOFER POLARITY:
If multiple subwoofers are used, it is important
to have their polarity with regard to each other correct. Reverse the polarity of one of
the two subwoofers while program material with deep bass is playing (being careful
not to momentarily short the two speaker leads to one another). The pink noise on
Chapter 6 of
WOW!
can be used as a constant source of bass energy by shutting off
all speakers except the subwoofers. You will immediately notice either a loss or an
increase in bass. The correct polarity is the one which exhibits the most bass.
ABSOLUTE SUBWOOFER POLARITY:
It is also important for both subwoofers to
have the correct polarity with regard to the rest of the system. Now that the LCR speak-
ers are all matched, play some program material (or Chapter 6 of
WOW!
) with signifi-
cant energy around 80 Hz. Reverse the polarity of all subwoofers in the system and
listen again. The polarity with the greatest bass output in this vital region is correct. (A
third-octave warble tone centered on 80 Hz is ideal for this test and is available on
some test compact discs.)
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