I have Golden Ear Triton One speakers that have a powered sub. In my case, there is an auto sensing mechanism that after determining no audio signal is present for about 20 minutes, the amp shuts down, albeit power is still supplied. At this point I power them down via a power conditioner switch.
I too wonder if switching them off while the auto sensor hasn't powered them down does any harm, because - as you state - there is a sizable thumping sound. That said, I do not believe the "thump" causes any real damage. I say this because there have been times when I've powered my T1s down "prematurely" (and intentionally) and there is no audible (or visual upon inspection) degradation the next time I use them. Also, many years ago I had a pair of JBLS412P. They too had a powered woofer and the same thump would occur if powered down prematurely. Doing so never damaged them.
I would recommend leaving your Sunfire's powered on in most circumstances. However, if your not using them for an extended period of time - like more than 48 hours - I would power them off completely. Just my .02.
I too wonder if switching them off while the auto sensor hasn't powered them down does any harm, because - as you state - there is a sizable thumping sound. That said, I do not believe the "thump" causes any real damage. I say this because there have been times when I've powered my T1s down "prematurely" (and intentionally) and there is no audible (or visual upon inspection) degradation the next time I use them. Also, many years ago I had a pair of JBLS412P. They too had a powered woofer and the same thump would occur if powered down prematurely. Doing so never damaged them.
I would recommend leaving your Sunfire's powered on in most circumstances. However, if your not using them for an extended period of time - like more than 48 hours - I would power them off completely. Just my .02.