M-Audio BX Guide D'utilisation page 10

Placing the BX Subwoofer
The "location, location, location" cliché applies to more than just the real estate market. It is
equally (if not more) applicable to loudspeakers and room acoustics. Where you place the BX
Subwoofer in your room can have a huge impact on how it will sound. In fact, any well-
designed, powerful subwoofer can sound like a complete dud in your monitoring setup if you
have placed it poorly. (This applies for any loudspeaker, but it is especially true for low-
frequency reproducers like subwoofers.)
There are many opinions on the best method to determine the optimal location for your
subwoofer (if you ask three different studio engineers, they will probably give you six different
answers), but we cannot emphasize enough how important this issue is.
Things to Remember
Always place the subwoofer on the floor when you are using it, never on a table or speaker
stand.
Take time to consider your subwoofer's placement, keeping in mind that the shape of your
room, its dimensions (including ceiling height), the wall construction, any acoustic treatment,
and other obstacles like furniture can affect the subwoofer's apparent performance.
Remember that the frequency of any given signal is inversely proportional to its wavelength
(e.g,. at 40 Hz, one wavelength is approximately 28 feet [8.5 meters]; at 80 Hz, one
wavelength is a little over 14 feet [four meters]).
Different Methods
One theory suggests that the best position for a subwoofer in a two-channel system is on the
floor halfway between your left and right direct-field monitors, with its front facing forward and
in the same plane as the direct-field speakers. From there, you can adjust the subwoofer's
position until it is most "correct."
Another theory dictates that you should start with the subwoofer in a corner of the room's
floor, where the adjacent walls can help the subwoofer maximize the amount of sound it
radiates; and then you can adjust the position to suit your specific monitoring setup.
Another method that many mix engineers have employed with great success uses the law of
bilateral symmetry. Place the subwoofer in the chair in your listening position (presumably, this
is at the apex of an isosceles triangle between your left and right direct-field monitors). Play
some music with substantial bass frequencies (pink noise works well, too) into the subwoofer
at a comfortable listening level. Get down on the floor of the room and listen for a place where
the sound is "fullest" but also "tight"-sounding, and place your subwoofer there. To be more
precise, use a 1/12th-octave real-time spectrum analyzer instead of your ears and perform the
same exercise using pink noise as the test signal and observing where the spectral response
is smoothest and has the greatest low-frequency extension.
Further Adjustments
Because low-frequency signals radiate omnidirectionally, you may find that the best location
sonically for the subwoofer is inconvenient (like in an area of your studio with a lot of foot
traffic). If this is the case, try flipping the Phase Selector on the rear panel and repeat the
exercise to see if you can find a more convenient place.
Finally, once you have placed the subwoofer where you believe it will sound best, play some
material along with direct-field monitors, listening from your standard mix position. Make sure
the subwoofer's Volume Control, Phase Selector, and Variable Crossover are set
appropriately. If something sounds "wrong" to you, experiment with other locations and
different directions for facing the driver. You may inadvertently find a better placement, even if
you think its current location already sounds good.
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