Yep....these days it's typically a function of the amp, and usually an optional knob/cord to plug into the jack on the amp.
In the old days one of my favorite equipment companies (a/d/s) put that capability in their equipment, though they did it via the crossover. Once the bass frequencies had already been split off, the knob was then use to control the amount of voltage travelling out on those RCAs.....It made it amplifier independent.
I suppose there are other companies that did it the same way, so if you wanted that feature bad enough, you could try to locate the a/d/s 642CSi (or 642ix)crossover and AC-501 bass control knob on eBay.... and wire them in????
This is the setup I have for "The System" that is now in boxes, but will someday be re-installed in the '72. It's the one in my photo gallery.
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