I have bookshelf speakers with 6.5" woofers I want to use as my front and rear surround speakers. They have a rear hole(port) and I was wondering if I mount them flush against the drywall will that ruin the sound? Or would it be a minor thing? Where I want to mount them there is no stud, but I could use drywall anchors if I had to for speaker brackets. What does the hole(port) do, how would it affect sound? Thanks.