You need a minimum of 4 feet and 8 feet is a lot better between the listener and any walls. After about 8 feet it really does not matter that much (diminishing returns).
If you cannot get at least 4 feet between you and the wall behind your head then you can reduce the problematic reflections by putting up some RPG skylines or heavy curtains.
Do not under estimate how bad teh wall behind your head can sound. It can ruin the bass and it will totally ruin imaging and soundstage - the sound will be claustrophobic and fatiguing. Those who cannot hear the deleterious effects of walls near the listening position should seriously consider whether it is even worth investing in high end gear.
If you cannot get at least 4 feet between you and the wall behind your head then you can reduce the problematic reflections by putting up some RPG skylines or heavy curtains.
Do not under estimate how bad teh wall behind your head can sound. It can ruin the bass and it will totally ruin imaging and soundstage - the sound will be claustrophobic and fatiguing. Those who cannot hear the deleterious effects of walls near the listening position should seriously consider whether it is even worth investing in high end gear.