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Old 26th October 2013, 02:44 PM   #1751
gedlee is offline gedlee  United States
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Originally Posted by weltersys View Post
Earl,

Are you saying that there is no difference in room modal excitation whether the radiator is a dipole or a monopole?
Of course there is a difference, but you cannot view it as a directivity response problem. In a room that has discrete modes the wave is restricted to move in only one direction per mode (well actually two orthogonal directions). The idea of directivity requires the response of a source along a variable direction, but the sound cannot travel away from the source in an arbitrary direction if there are discreet modes. As Markus says it is best to view LF sources of all types as sums of discrete sources separated in space and phase. This is always safe, but looking at it from a directivity standpoint is dangerous.

It is this kind of thinking that leads to false concepts like "Dipoles excite fewer modes." which is false. You can see this if you view a dipole as two sources out of phase and separated by a distance. The dipole will actually tend to excite more modes, which of course is desirable, not the other way around.
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Old 26th October 2013, 06:06 PM   #1752
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Originally Posted by gedlee View Post
The idea of directivity requires the response of a source along a variable direction, but the sound cannot travel away from the source in an arbitrary direction if there are discreet modes. As Markus says it is best to view LF sources of all types as sums of discrete sources separated in space and phase.
Agreed.

As Markus also said:
"The direct sound is swamped by the room response. So the radiation pattern isn't exactly meaningless but just one parameter in getting smooth response in frequency and time."

After further review of the tests posted in #1730, appears that time alignment has less to do with smooth response at my listening position, and "luck" at choosing the right place to put my couch in relation to the room modes more .

One interesting finding was that opening the rear room doors increased LF +8 at 33 Hz at the listening position.
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Old 26th October 2013, 06:31 PM   #1753
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Originally Posted by gedlee View Post
As Markus says it is best to view LF sources of all types as sums of discrete sources separated in space and phase. This is always safe, but looking at it from a directivity standpoint is dangerous.
My traces in #1713 illustrate nicely the complex interaction of enduring modes arising from room shape and the influence of seat location. The room modes are clearly enduring, but the two traces are distinctly different as well. (If you wanted to name the major artifacts, you'd name the room modes.)

Without even whispering a word about human hearing that might give a major twist to this discussion, it is easy to fall in fallacious thinking by confusing the simplifying assumptions and inspirational diagrams used to propel analysis with the sound of music introduced into a room. We all simplify to analyze, I'm just saying (pending better and better 3-D waterfall charts) there's a big step between that and the final audition.

Although thinking about the complex sound of dipoles might give the more analystic among unipole fans the heaves, it sure seems to fill-the-bill for dipole fans. Ditto for the topic of this thread: multiple subs.

Ben
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Last edited by bentoronto; 26th October 2013 at 06:36 PM.
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Old 26th October 2013, 08:24 PM   #1754
gedlee is offline gedlee  United States
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Originally Posted by bentoronto View Post
Without even whispering a word about human hearing that might give a major twist to this discussion, it is easy to fall in fallacious thinking by confusing the simplifying assumptions and inspirational diagrams used to propel analysis with the sound of music introduced into a room.
Huh!?
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