I can think of three causes: 1) Electrostatic induced hum. Probably not the problem due to low impedances of speaker circuits, but can easily be cured by shielding the cable.
2) Power line magnetically induced hum. can be cured by using a third wire next to the speaker wires that is grounded at both ends to the power grounding system. 3) Imbalance/Mismatch. Your source of the sound may not be producing a perfectly balanced output. There may be some slight reference to chassis ground, or it could be at the speaker end too. I would take some totally isolated source of audio, phone, battery radio etc and connect it at the far end and see if you get hum. If no hum, then it is your receiver output and you will probably need a high quality isolation transformer that is designed for low audio frequencies. If there is hum with the isolate audio source then it might be getting picked up in the cable. To check for that, move the isolated audio source to the speaker and make sure there is no hum. From: can...@believewireless.net Sent: Wednesday, November 7, 2018 5:40 AM To: AnimalFarm Microwave Users Group Subject: [AFMUG] OT: Powered Subwoofer Hum I ran regular cable between my receiver and amplified subwoofer. Approximately a 70ft run through the house. Avoided running in parallel with the power lines but it is about 6" away from an electrical outlet. No cable plugged into sub, no hum. Cable plugged into sub but not into receiver, loud hum. Plugged in a ground loop isolator device and hum dramatically reduced. However, so was the signal to the sub. To the point it might be blocking it completely. This was a very cheap ($9) device from Amazon. Swapped with shielded Cat5e cable from Shireen. Same results. Any idea how to fix this? Get better shielded cable? Better isolator? -------------------------------------------------------------------------------- -- AF mailing list AF@af.afmug.com http://af.afmug.com/mailman/listinfo/af_af.afmug.com
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