How to Fix Harman Kardon Subwoofers

Buzzing or humming with Harman/Kardon subwoofers is normally a result of a bad connection between the RCA cable leading to the sub and the "SUB" or "LINE" input jack. Loose jacks create bad signal ground, leading directly to this phenomenon. Hum may also be a result of ground potential differences between the receiver and subwoofer. Harman/Kardon subwoofers normally rely on a signal from the receiver to turn on, so until the jack is fixed users may experience continuous popping or clicking as the internal relay opens and closes.

Harman/Kardon subwoofers verified to be receiving proper signal that still refuse to turn on have prosaic and possibly larger issues requiring service. Many Harman subs have an On/Off switch independent of the signal relay. Ensure this is set to the "On" position. If the switch is on and the subwoofer is receiving signal, verify the green or blue power LED is lit. If the red or amber standby light stays on even when you think it's receiving a signal, check your RCA wiring or connection at the receiver. If everything is connected properly and the receiver is sending the LFE signal to the sub, you may need service. If there is no light at all, you may have a blown internal fuse or other nonuser-serviceable issue related to the amplifier. Some Harman/Kardon subwoofers have accessible fuses on the back panel, removable with a screwdriver. If yours doesn't, the unit must be sent to an authorized service center.

Harman/Kardon subwoofers relying on a wireless signal from a sound bar or other transmitting device must be powered on and set to the same wireless code. Additionally, H/K subs relying on these wireless feeds must be within 50 feet of the transmitter's line of sight. Obstructions like walls, water heaters and doors will reduce signal quality to varying degrees. Move the subwoofer closer to the sound bar or transmitter to resolve the issue.

Many Harman/Kardon subwoofers use speaker level inputs in addition to RCA jacks. Paying attention to wiring in this case is critical. Wiring positive receiver jacks to negative speaker wire terminals on H/K subwoofers places the speaker out of phase, resulting in low bass levels. When using speaker wires, ensure that they are all intact, devoid of nicks or cuts that may cause intermittent response from the sub. Here too you may find problems with the subwoofer activating, should the unit not be receiving sufficient signal to turn on.