If I may add 2 cents...(for noobs like me)
When reading above, I was thinking that the harmonic distortion was a bad thing, I did some googling and found this
One woofer backwards. This design reduces harmonic distortion. The main cause of harmonic distortion in woofers is the difference between the out-stroke and the in-stroke of the woofer. This difference is caused by magnetic anomalies around the voice coil, manufacturing errors and suspensions that are stiffer moving in than out. When you mount one woofer backwards, but wire them up so that they both move in the same direction, the sound from the two woofers reinforce each other (in phase) while the distortions cancel each other out (out of phase). Clever, but the value is less than one might think. Not only are humans insensitive to harmonic distortion in the bass region, harmonic distortion by nature is, you guessed it, harmonious. So not that unpleasant.
So I guess it's ok then.