Is there any difference between a panel advertised as a bass trap vs. simply stacking two or more absorption panels on one another?

Is there any difference between a panel advertised as a bass trap vs. simply stacking two or more absorption panels on one another?

Probably not for most bass trap panels, if they're basically resistive ones like fiberglass or mineral wool. However, keep in mind that some bass traps can be panels but of a different design, like membrane/diaphragm absorbers or perforated absorbers. One commercial example of the former is the RPG Modex Plate.

What he said.

Excellent non-commercial source for info about building your own bass traps:

http://forum.studiotips.com/viewforum.php?f=8

Regards,
Terry