I have a Sound Dynamics THS-12 that has served me well for over ten years. It is a powered, down-firing 12". It is connected to the sub output of a Pioneer AVR.

For the past couple of months, I have noticed that it isn't always powering on (red LED in the back) when I turn on the AVR. Also, when it does come on, it will randomly turn off. Some time later, it will come back on. I actually swapped AVRs last night to see if the sub out was faulty. The sub behaves the same.

Today, I turned it around backwards to see if I could time the off/on cycles. It has shut off twice, and come back on twice. One "on" cycle was about one hour, followed by a 1/2 off. It is on now, and has been for about an hour and a half.

If it is off, I can get it to buzz and come on by pulling one of the RCA inputs.

Any thoughts for me? I really want this thing to work 100% of the time. Once you have the bass, you can never go back;)

Does it have an auto on/off switch that senses the incoming signal, if so you might want to disable that so it is always on. Also, where do you have the volume (gain) set on the sub and receiver. Sometimes if people crank up the subs volume, it requires you to have the sub level on the receiver very low to keep it calibrated with the other speakers, that is if you have everything calibrated to 75dB. Try something closer to 'zero' on the receiver, and readjust the sub volume down a bit, its all the same as long as the end result is that it matches the other speakers.

Or, you may have something technically wrong with the sub. On some subs, the LFE input/output are just pass-through, so try hooking it to the output jack.

I think I have fixed it. I turned up the crossover on the sub, and it doesn't go off anymore. It must have been too low, and therefore not receiving input often enough. It hasn't shut off since I turned it up.

Update: it is still turning off, but it is definitely a signal issue. I was running DVE, and the sub cut out while the narration was on. So, I cued up the sub test tone, and as soon as the 30Hz signal started, the sub turned back on.

How can I keep it on?

Just leave the power switch in the On position instead of Auto.

There is no power switch. It is auto only.

Sounds to me like it is going into thermal shut down. When it shuts down, feel the plate amp. Is it hot?

I was going to recommend you put a Y on the cable and plug into both inputs, but it sounds like you are already doing that. Try turning the gain on the sub lower and raise the sub output on the AVR.