Make sure that the soundpost /bridge are positioned correctly to each other.
The bridge should have its back edge half over the soundpost.
This next one works for me every time,,,,,,,,,,,,,get a small beach ball and put it through the soundhole on the bass side,
pump it up ,and it has the same effect as a second soundpost ie damping the bass bar.
Just be carefull with positioning as you pump it up or you may move the soundpost.
The hardest part of this is fending off comments from your band mates..