Covert Ops... said:
You're somewhat correct. Since the cardboard in the cupholders is a basic pressed cardboard and it is extremely thin, it is not going to absorb to much, and the frequencies that it will absorb will probably be over 20k. Also, Low frequencies will pass right through it because the have enough energy too.
It might be able to do a little diffusion, but not enough to be effective because of its thickness and mass.
The only reflection you will get out of it again is the hig frequencies.
You really should think of acoustics as another piece of gear that can dramatically improve results. There is a reason that Pro Studios drop over half their budget on acoustics. It has a drastic affect on how you hear thing, even more so than your monitors, therefore you shouldn't cheap out on acoustics, if you really are serious about your music. Altho i guess if you REALLY are serious about your music, you should be going to a pro studio in the first place.