Why does my speaker rattle at 50-60Hz and not below that frequency or above it?

-Seems you have a bit of a resonating issue. I'm not too experienced with this, but one of the other answers seems to be.The 50 to 60 HZ is the sub woofer range frequency, most speakers can not handle the low frequency at all. Most full range speakers are designed for the 80HZ and above, those below that will be handle by the subwoofer. You need to get a sub woofer to handle the lower frequency of 80HZ and below. The low frequency are more demanding in power than those of the higher frequencies. Look at your owners manual for the frequency range it can handle. Hope this will help you out.
They shouldn't rattle at all in the audible frequency range, but every speaker has a resonant frequency, and for yours 50-60 Hz appears to be it. It sounds like poor design to me, or maybe something has damaged a speaker cone and that is the problem.
In most case, bbt91945 is correct. In this particularly instance, he is totally wrong.



Bookshelf speakers can easily go down to 60Hz and sometimes below that. A decent pair of floor-standers will go as low as 40HZ with ease, and many will go lower than that (my Jamo D870's are rated to 33Hz).



A good quality subwoofer won't even start working at anything above 50Hz.