6
Setting the Phase
Depending on the absolute phase of your main speakers and amplifier, and the distances of the subwoofer and the main speakers from
the listening position, the bass in the crossover region may be smoother if you reverse the phase of the subwoofer. Switch the phase switch
to 180 degrees to see if the bass sounds louder in the seating position. Play program materials with steady, consistent bass in the crossover
region (30 – 90 Hz). Filtered pink noise is best, but you may use music containing bass drums, double basses, bass guitar, etc.. The more
bass-heavy setting is where the output of the subwoofer and the main speakers are most in phase. If the 180 degree position is louder, you
will need to go back and adjust the volume level (Step 4). Otherwise, just switch the phase switch back to the original position.
Volume fine tuning
For this section, we assume that you have a controller with bass management and you have set the main speakers to small so bass is re-
directed to the subwoofer. Set the volume on the sub to 9 o'clock, crossover out, sub out level on the receiver to 0 dB.
For the most precise integration with your main speakers, go through test tones with a SPL meter. Setting the level using test tones by ear
may result in misconfiguration, so please use a meter. An analog Radio Shack SPL meter is inexpensive and works better for this application
than the digital Radio Shack SPL meter. It is available at RadioShack.com. Use the “C” weighting and “SLOW” settings and place the meter
at the listening position at ear level. Note that the Radio Shack analog meter is about 12 dB down at 16 Hz, 7 dB down at 20 Hz, 4 dB
down at 25 Hz, and 2 dB down at 31.5 Hz. Add these numbers to the readout on the SPL meter to compensate.
1) Using a test disk with one-third octave filtered pink noise or warble tones (such as the Hsu/BAS Test CD-1), play the 50 Hz test tone
and adjust the master volume level on the controller so that the SPL meter reads 80 dB at the listening position.
2) Play test tones from 20 Hz up to 200 Hz, and note the SPL reading on the meter at each frequency.
3) Take the average of four test tones below the crossover frequency (ie. 63/50/40/31.5 Hz when using 80 Hz crossover).
4) Take the average of four test tones above the crossover frequency (ie. 100/125/160/200 Hz when using 80 Hz crossover).
5) Adjust the subwoofer level so that the lower range average equals the upper range average (ie. if the lower range average is 5 dB more
than the upper range average, then adjust the subwoofer level down by 5 dB). If your controller allows you to adjust subwoofer channel
level, use this to adjust the subwoofer level. Otherwise simply adjust the subwoofer volume knob instead.
A less accurate method uses the receiver’s test tones, which are usually not in one-third octave increments. Measure from the listening
position and set the subwoofer volume level to match the other speakers.
Setting the Q Control
We have added an adjustable Q control on the subwoofer amplifier in order to give the user higher headroom, flatter in-room response,
and better ability to take advantage of room gain. Set Q = 0.3 for the highest mid-bass headroom in all room sizes, and for the flattest
deep bass response in small-to-medium room sizes. Set Q = 0.5 for the flattest deep bass response in medium-to-large room sizes. Set
Q = 0.7 for the flattest deep bass response in large room sizes. Note that the low bass is more rolled off in the lower Q settings. This
means that higher Q settings can result in less low bass headroom, ie. the subwoofer will run out of steam in the low bass earlier when
the Q setting is higher.
Removing buzzes and rattles from the room:
Annoying sounds can be fixed by using adhesives, tape, or felt pads in the area where objects are vibrating against each other.
Equalizing the subwoofer
If you have an equalizer, avoid raising dips in the frequency response. Instead, use the equalizer to remove peaks. This will prevent
potential speaker damage.
If you are using any auto EQ (such as Audyssey) to equalize your subwoofer, set the subwoofer to one port open, EQ1, Q = 0.7, as this
will help to counteract the auto EQ's tendency to over boost very low frequencies. After running the auto EQ, you can set the subwoofer
to any mode of your choice.
Enhancing performance in the future
The best way to enhance performance in the future is to add a second identical true subwoofer (and/or mid-bass module) to the system.
With a single true subwoofer in the system, it is very difficult to achieve optimal mid-bass and deep bass performance. The addition of
a second identical true subwoofer (and/or mid-bass module) results in much higher headroom, much lower distortion, and potentially much
flatter frequency response in-room due to better ability to optimize for strong mid-bass and deep bass output and response.
