Watt do I do?

I have a pair of ancient British-made speakers with 15 ohm Vitavox drivers, a horn and a woofer in each, and I want to avoid the loud
when I turn them on.  Any easy fix ideas here?  This initiating intrusion into the speakers by the nefarious watts can't be good for them.  They are old but in great shape.....cosmetically.  Everything sounds wonderful and smooth except for the very deepest bass which causes them to ping.