I've run 4-6-1/2" subs that people thought I had 12's.
A couple of song tests I run on a system to see how the sound quality is. AC/DC Thunderstruck, just the first 20 seconds or so. The bass drum should hit heavy and hard with a little overhang as the drum head stops oscillating. Then as the second drum hits there should be a very distinguishable double hit of the drum head. If it's muddy, or it just mushes out you are either clipping the amp or the enclosure is incorrectly sized.
The second one I seriously doubt any of you have heard is Enya, on the first album track 13 or 14 has a low 40Hz tone that plays for a long time then it drops to about 33Hz and there is a second of reverberation between the change in tone. If this isn't clear then your issue is the enclosure.
Jeff
