The above sentiments are certainly useful. One more thing however, I highly recommend a laser distance measuring device. Using a tape measure, while often allowing a fairly close approximation, is, IME, not as precise as a laser device. And, it seems to me, a hell of a lot easier to work with. Distances of 100th's of an inch can be immediately determined. Not saying that 100's of an inch will be perceptible but, rather, the precision, with a high quality system, is to be preferred I think. Plus, they're not expensive. You can purchase one for about $20 and then loan it to your audiophile friends.