The ‘sub-thump’ question has come up several times in the Saloon, though the suspected source of trouble is not always related to a ceiling fan. Of the several possible causes, the interfering signal must either be arriving via the input (shielded interconnect or speaker cable, depending on how you get the intended signal to the sub), the power cord, a combination of the two, or even via a ‘broadcast’ by the fan, switch and associated wiring which is being picked up by one or more parts of your system.

You could go through quite a few diagnostic and remedy scenarios, but your main concern seems to be, “Can this damage my sub at all in the long term?”

I would say your chances of this damaging the sub are near zero. Why would I say that? When you play music or movies, aren’t you asking the sub to handle grossly larger signals on a regular basis, some of them quite ‘explosive?’ I would say that playing music and movies through your sub uses much more of whatever capacity your sub has than a slight thump when you turn on your ceiling fan.

My subs use an auto-detect circuit to monitor the incoming signal. When no signal is present for several minutes, the power amp section is turned off while the input is still monitored. When some small signal is detected, the input monitor turns on the rest of the circuitry. If your sub operates similarly, it could be that, even if the rest of your system is off, the small electrical change that occurs when you turn on your ceiling fan is enough to trick the monitoring circuit into going out of standby mode and powering up the sub’s internal amp, hence a little thump made in this process is heard because it is not masked by any incoming music or other intended signal.

As a crude diagnostic tool, tune an AM receiver on the same circuit as the sub to a place on the band where there is no station. Listen for any ‘pops’ in the AM hiss when you turn your ceiling fan on or off. Compare that to what you hear in the hiss when you turn a standard incandescent lamp on or off on the same circuit as the ceiling fan. If the ceiling fan ‘pop’ is much louder than what the lamp causes, it could be minimal arcing in the switch you use to turn the fan on and off.

If you are using speaker cables to a powered sub, try a well shielded interconnect instead. If you are using a shielded interconnect cable, is it at least as good as the ‘radio shack $15’ type, not the $5 type? Also, do what you can to make sure that the physical connections of both the interconnect cable and equipment at either end are good, clean and have a solid grip so that the electrical connections are the best they can be. If you suspect the interconnect cable, try swapping in another cable you know is good from another part of your system to compare results.

Plug the sub into power with the interconnect cable not connected to the sub. Does the sub still thump when you turn the ceiling fan on?

If you decide to put an un-interruptible power supply (UPS) before the sub, make sure it has the capacity to handle the power requirements of your sub.

I wish I could be more concise, but there are quite a few variables involved and quite a few possible solutions.

I hope you find what you need, and that it is one of the more inexpensive solutions!


[This message has been edited by bestbang4thebuck (edited August 10, 2004).]