Large Advents (1974) woofer pops with deep bass.

@vcheney The suspension of the woofer is probably done in. You can get it rebuilt at a speaker reconing service. I would google it to see if one is in your area. We have one here in Roseville Minnesota that is quite good and been around for over 60 years. If that one is bad the woofer in the other channel likely isn't far behind.

Turn the volume down you're overdriving the woofer voice coil.

Mike

Before surgery/replacement try rotating the faulty woofer 180 degrees.

The woofers also need to be sealed to the cabinet (it's a sealed system and any air leakage will increase the woofer's travel distance/excursion).

Once snug the bolts should be tightened systematically and gradually (like tightening up the oil pan on a car).

I don't know what would be good to seal them with (RTV silicone?) but others here should know.

DeKay

Here ya go!

 https://www.simplyspeakers.com/advent-replacement-woofer-p001-31858.html