I dont think so.. all speakers and subs are magnetically shielded these days so if wont spoil ur CDs/DVDs.. sub placement will only affect the sound... like placing too close to a corner would result in boomy bass.. so choose ur placement where u r satisfied with the sound..
also, unlike CD/DVD which u might plan to place inside a rack/cabinet, do not place a sub inside any cabinet, it can be too boomy....i had posted a question on sub placement i got this info...thot of sharing it......