Is there a "correct" or "intended" surround speaker-type for the modern surround mixes? I plan on spending what is to me quite a lot of money on 6 or 7 new speakers, I would like to know the theory while I'm looking. I ask because I remember for pro-logic (4.0 matrixed) the "surround" channel was intended to be enveloping, not directional, and I think this was the origin of the bipole and dipole. I think THX may have had somethign to say about a choice between the two, I know I have read about it on these forums. This carried through, I believe, into 5.1. But today I somehow feel modern (typified by HD) 5.1 and 7.1 mixes make use of all speaker locations, seeking a much less "diffuse" effect. This is what I want to get the best out of. I am also debating an appropriate balance of expenditure which I think is roughly on the same topic, because typically buying 4 good bookshelfs as surrounds could cost 45% of the total, whereas I would think listeningwise it is better as say 25% centre 50% mains 25% surrounds? I ignore sub as I'm SVS'd up so no upgrading required. I hope this is an interesting thread or at least informative, I am always grateful for the advice readily forthcoming from the contributing forum members, thank you.