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Old 12th October 2012, 12:48 PM   #341
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Amen.
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Old 12th October 2012, 01:23 PM   #342
Omholt is offline Omholt  Norway
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Originally Posted by gedlee View Post
The difference between a monopole and a dipole (at modal frequencies) can be stated quite simply: A dipole excites the modes velocity while the monopole excites the modes pressure.
What do you mean? Given sound velocity is fixed.
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Old 12th October 2012, 02:26 PM   #343
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Monopoles are pressure sources and dipoles are velocity sources.
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Old 12th October 2012, 02:32 PM   #344
Rudolf is offline Rudolf  Germany
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A monopole placed in a room corner excites all room modes maximally - thereby delivering maximal energy into the room.
A dipole placed in the same room corner excites all modes minimally delivering minimal energy into the room.

A monopole placed in the middle of the room excites the first degree room modes (half wavelength between walls) minimally.
A dipole in the same position excites them maximally except the modes perpendicular to the dipole axis.

Rotation of a monopole in the room doesn't change anything.
Rotation of a dipole in the room can excite or attenuate a room mode relative to room modes perpendicular to it.

This should explain why measurements of a dipole and a monopole at the same position in the room can't decide on the best aptitude for either M or D for the room. Even if one can find different optimal placements for M and D in the same room, they need not be the best placements in another room of different size and proportions.

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Old 12th October 2012, 03:11 PM   #345
gedlee is offline gedlee  United States
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Originally Posted by Omholt View Post
What do you mean? Given sound velocity is fixed.
"Velocity" here refers to the "particle velocity" or the velocity of motion of the particles in space. This velocity can be any value from zero and up. The velocity of sound is the speed at which the pressure disturbance moves and is not the same as the velocity at which the particles in space oscilate.

This is exactly like voltage and current in a circuit. The pressure is like voltage and the current is like the particle velocity. We know that the electrons in a wire don't move back and forth very fast, in fact the actual motion about the mean is actually pretty slow, but the electric field that drives the electrons moves at near the speed of light.

And thanks John - sensibility is finally creaping into this discussion. But it's all "theoretical" and has no relavence to "beliefs" based on "what I hear".

Last edited by gedlee; 12th October 2012 at 03:15 PM.
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Old 12th October 2012, 03:30 PM   #346
Elias is offline Elias  Finland
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Originally Posted by john k... View Post
The only thing that can be said categorically about dipoles comparedf to other sources is that they can not pressurize a room, and this is what I think drives listeners to prefer a dipole woofer.
What is the connection of the pressurisation ability and the modulation reproduction ability ?
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Old 12th October 2012, 04:32 PM   #347
Rudolf is offline Rudolf  Germany
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Originally Posted by Elias View Post
What is the connection of the pressurisation ability and the modulation reproduction ability ?
Sorry to say that, but the connection is:
We are still lacking a controlled, fair and equal comparison, that shows categorically a better modulation reproduction ability of the dipole. Either by theory or by measurement.

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Old 12th October 2012, 05:21 PM   #348
badman is offline badman  United States
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Perhaps part of the advantage of dipole subs is in the directional nature above the passband, effectively creating a steeper filter on the power response than the filter on the axial?

Just a brief thought.
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Old 12th October 2012, 05:45 PM   #349
_Wim_ is offline _Wim_  Belgium
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Originally Posted by gedlee View Post
When I do EQ for my clients I often find that turning on one of the subs actually reduces the mean sound level in the room. Thus, this sub is working as a sink at that frequency, i.e. an active absorber. In this example then it would be very possible that a multi sub implimentation was reducing the modal decay.
How do you setup this EQ. Do you start with one sub and EQ all major peaks (leaving the dips alone), then add a second sub and again EQ the peaks, add a third sub...

Or do you use something proprietary?
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Old 12th October 2012, 06:15 PM   #350
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Is it enough to measure PH difference between apple and orange juices to tell why they taste differently?
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