A monopole radiator is - by definition - a spherically symmetric source that radiates equally in all directions. You could make an acoustic monopole radiator by, for example, making a little sphere with a radius that moves in and out with time. It moves out and pushes air away from itself, then moves in and sucks it towards itself, etc. Woofers in sealed boxes are pretty close to that, since the entire box vibrates in and out, but directional sources like tweeter are nowhere close to it. The acoustic radiation of a tweeter in a box is *not* monopolar.
An acoustic dipole radiator is two monopoles sitting close together and oscillating out of phase. A speaker driver in free space or an open baffle is a pretty good approximation to that. For tweeters the magnet assembly on the back is big enough that it absorbs quite a bit of the back-directed radiation, making it less like a dipole. That's why the Orions have a back-directed tweeeter. There is no ambiguity about these term (and by the way that wikipedia article doesn't disagree - it's just not very detailed). They are a useful way of characterizing sound because any sound field can be decomposed into a sum over multipoles, each having certain unique characteristics, and because acoustics is close to linear. As for the room, you have to normalize to something. We're only talking about bass here (room modes get averaged out for treble), where the radiation of a box speaker is pretty much monopolar (so it radiates in ALL directions). The point is you have to normalize either the SPL at some point or the power going into the speaker. Then you want to ask what the amplitude of the room modes is. If you normalize to the SPL on axis, a dipole radiator radiates 1/2 as much power as the monopole (basically because it's not radiating to the sides). -- opaqueice ------------------------------------------------------------------------ opaqueice's Profile: http://forums.slimdevices.com/member.php?userid=4234 View this thread: http://forums.slimdevices.com/showthread.php?t=38593 _______________________________________________ audiophiles mailing list [email protected] http://lists.slimdevices.com/lists/listinfo/audiophiles
