Often the best way to improve the bass response is to shave back braces. The idea is to get the 'main back' tap tone to couple more strongly with the 'main top' mode, by getting them closer together in pitch. This lowers the pitch, and strengthens, the low 'main air' part of the bass reflex couple, which is the resonance that does the most to help reinforce the lowest notes. The nice thing about this is that it doesn't weaken the top, which is far more critical structurally. You can also check out the effect reversibly. Just get some poster adhesive and stick a wad onto the back over one of the braces. This will lower the tap tone pitch in the same way as shaving that brace would, so you can hear what effect that would have. If you don't like it you can try something else. I'd be even more inclined to do this if I were thinking of shaving top braces; at least you'd know going in whether removing material was likely to work for you.

I think Alan means poster adhesive like this: https://www.amazon.com/dp/B000BQMFEC/re ... 53622&sr=3

Keep in mind not to leave it on for too long (like days) because I've found it leaves an oil spot behind on walls and such.