The limiter circuit occupies the typical gain setting position - an output to input feedback loop - on an amp. so the woofer loop/gain is dynamic. eventually, the more you turn it up, the louder it wont get. if you have a meter and slowly turn up a low tone you can watch the voltage increase at the woofer leads flatten off. input & tone control options probably made a limiter based on power delivery much simpler. have a tech rig a bypass switch and alt this dynamic circuit with a static circuit if it starts to itch.