JBL Sub 140P – JBL sub 230 – Circuit Diagram

The performance of a subwoofer is directly related to its placement in the listening room and its physical position relative to the other speakers in the system.   While it is true that in general our ears do not hear directional sounds at the low frequencies where subwoofers operate, when installing a subwoofer within the limited confines of a room, the reflections, standing waves and absorptions generated within the room will strongly influence the performance of any subwoofer system. As a result, the specific location of the subwoofer in the room does become important to the amount and quality of bass that is produced.  For example, placing the subwoofer next to a wall generally will increase the amount of bass in the room; placing it in a corner generally will maximize amount of bass in the room. However, corner placement can also increase the destructive effect of standing waves on bass performance. This effect can vary depending on the listening position – some listening positions may yield very good results while others may have far too much (or too little) bass at certain frequencies.  In many rooms, placing the subwoofer along the same plane as the left and right speakers can produce the best integration between the sound of the subwoofer and that of the left and right speakers. In some rooms, the best performance could even result from placing the subwoofer behind the listening position .   Experiment with placement before choosing a final location for your subwoofer. One way you can determine the best location for the subwoofer is by temporarily placing it in the listening position and playing music with strong bass content. Move around to various locations in the room while the system is playing (putting your ears where the subwoofer would be placed), and listen until you find the location where the bass performance is best. Place the subwoofer in that location.

Rear-Panel controls

On/Standby LED: When the Power-On Mode switch is in the “Auto” position, this LED indicates whether the subwoofer is in the On or Standby state:

• When the LED glows green, the subwoofer is turned on.
• When the LED glows red, the subwoofer is in the Standby mode.
When the Power switch is set to “Off,” the LED will not light up, no matter what setting the Power-On Mode switch is in.
Crossover Control: This control determines the highest frequency at which the subwoofer reproduces sounds. 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 speakers. 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.
NOTE: The Crossover control functions only when you are using the Line Level In L/R connectors. The Line-Level In LFE connector bypasses the subwoofer’s built-in crossover and Crossover control.
Phase Switch: This 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 sound 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.
Power-On Mode Switch: When this switch is set in the “Auto” position and the Power switch is set to “On,” the subwoofer will automatically turn itself on when it receives an audio signal and will enter the Standby mode when it has gone without receiving an audio signal for 20 minutes.  When this switch is set in the “On” position, the subwoofer will remain on whether or not it is receiving an audio signal.
Subwoofer Level Control: Use this control to adjust the subwoofer’s volume. Turn the knob clockwise to increase the volume; turn the knob counterclockwise to decrease the volume.
Line-Level In LFE Connector: This input bypasses the subwoofer’s internal crossover circuitry, so use it only with a receiver or processor subwoofer output that has been low-pass filtered. If your receiver or processor does not have a dedicated subwoofer output that is low-pass filtered, use the subwoofer’s Line-Level In L/R Connectors (see below) instead.  Use the supplied mono RCA cable (purple connectors) to connect the Line-Level in LFE connector to the dedicated subwoofer output of a receiver or preamp/processor.
Line-Level In L/R Connectors: These inputs pass through the subwoofer’s built-in crossover. Use them if your receiver or preamp/processor does not have a dedicated subwoofer output that is low-pass filtered.
Power Switch: Set this switch in the “On” position to turn the subwoofer on. The subwoofer will then be in On or Standby mode, depending on the setting of the Power-On Mode switch.
Power Cord: After you have made and verified all subwoofer and speaker connections described in this manual, plug the power cord into an active, unswitched electrical outlet for proper operation of the subwoofer.
DO NOT plug this cord into the accessory outlets found on some audio components.

Exploded view

Circuit Diagram

Phase adjustment

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.

The Crossover control adjusts the subwoofer’s built-in 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 speakers.  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 control setting. If the bass seems too weak at certain frequencies, try a higher Crossover control setting.

• Sometimes the ideal subwoofer volume setting for music is too loud 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.

• If your subwoofer always seems too loud or too quiet, you may want 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.