Generally accepted overall frequency response is +/-3db. In room bass response is tougher. If you can get from the bottom through the xover point and into the mains within +/-4 or 5, you're doing pretty well - much better than most people.
I agree with you. In my case, after installing the bass traps, the bass frequency response is a little bit better than without bass traps. However, the room sounds much better. The bass traps must do much more than just flattening basss frequency response as you said.
Note that Ethan mentioned that the ring times were greatly reduced.
I just built a couple of corber absorbers. I could definitely hear the improvement. When I ran ETF to verify, there wasn't a huge improvement in the FR, but in the waterfall plots, I could see that the decay time (ring time) was shortened. I think this was the improvement I was hearing. The reverberation times weren't as long, and so the sound is clearer.
You can see the test results over in the General Home Theater Forum, if you are interested. Though, I still need to run some more though.
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