SUB 550P - JBL Audio Service Manual (repair manual). Page 8

Set the subwoofer’s Power Switch to the “On” position. The subwoofer will 
automatically turn itself on when it receives an audio signal, and it will go 
into Standby mode after it has received no audio signal for approximately 
10 minutes. The subwoofer’s LED will glow green when the subwoofer is 
on and will glow red when the subwoofer is in Standby.

If you will not be using the subwoofer for an extended period – for 
instance, if you’re going on vacation – set the Power Switch to the “Off” 
position.

NOTE: The Crossover control functions only 
when the Input Mode switch is in the “Normal” 
position.

The Crossover control adjusts the subwoofer’s 
built-in low-pass filter crossover between 50Hz 
and 200Hz. The higher you set the Crossover 
control, the higher in frequency the subwoofer 
will operate and the more its bass will “overlap” that of the satellite speak-
ers. This adjustment helps achieve a smooth transition of bass frequencies 
between the subwoofer and the satellites for a variety of different rooms 
and subwoofer locations.

To set the Crossover control, listen for the smoothness of the bass. If the 
bass seems too strong at certain frequencies, try a lower Crossover con-
trol setting. If the bass seems too weak at certain frequencies, try a higher 
Crossover control setting.

Use the Level control to set the subwoofer’s 
volume. Turn the knob clockwise to increase the 
subwoofer’s volume; turn the knob counterclock-
wise to decrease the volume. Once you have 
balanced the subwoofer’s volume with that of 
the other speakers in your system, you shouldn’t 
have to change the Level control setting.

Notes on Setting Subwoofer Volume:

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for films, while the ideal setting for films is too quiet for music. When 
setting the subwoofer volume, listen to both music and films with 
strong bass content and find a “middle ground” volume level that 
works for both. 

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to place it in a different location. Placing the subwoofer in a corner will 
tend to increase its bass output, while placing it away from any walls 
or corners will tend to lessen its bass output.

The Phase switch determines whether the subwoofer 
driver’s piston-like action moves in and out in phase 
with the satellite speakers. If the subwoofer were to 
play out of phase with the satellite speakers, the sound 
waves from the satellites could partially cancel out the 
waves from the subwoofer, reducing bass performance 
and sonic impact. This phenomenon depends in part on the placement of 
all the speakers relative to each other in the room. 

Although in most cases you should leave the Phase switch in the “Normal” 
position, there is no absolutely correct setting for the Phase switch. When 
the subwoofer is properly in phase with the satellite speakers, the sound 
will be clearer and have maximum impact, and percussive sounds like 
drums, piano and plucked strings will sound more lifelike. The best way 
to set the Phase switch is to listen to music that you know well and to set 
the switch in the position that gives drums and other percussive sounds 
maximum impact.

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