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Old 23rd October 2012, 10:56 AM   #571
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Yeah well to give you an idea (monopole sub vs dipolar ) he said that :

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Assume nearly 1m2 (10000cm2) (Acoustat-M3, perhaps M4 or 2+2, easily) ESL panel, with (for argument sake) max. excursion of +/- 1mm (2mm total movement) (practically, this is "elevator music level" volume on ESLs),
Assume a large (12") sub (cone area ~700cm2 - 14 times smaller area than ESL)
=> For the same volume of air to be displaced, the sub cone has to move +/- 14mm (28mm total movement)

Now, assume +/- 2.5mm average ESL membrane displacement, for a very low listening volume; Total Sub cone movement of 70mm!!! (coil in the magnet gap). In order for coil/magnet flux field to maintain the required motor strength (ability to pull back the coil) the length of the pole piece would have to be ... at least 100mm?
Seems like a completely erroneous comparison given that once you place the woofer in a box, you won't need anywhere close to that 70mm p-p figure. That's just crazy.
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Old 23rd October 2012, 02:30 PM   #572
gedlee is offline gedlee  United States
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Quote:
Originally Posted by Rudolf View Post
And Earl Geddes says that there is no pressure gain for monopoles also.

Rudolf
Why would you say that? because I never said what you claim. If the room is completely sealed then there is pressurization. But show me a completly sealed room! Now if it is not completely sealed then how can it contain a static pressure change?

Last edited by gedlee; 23rd October 2012 at 02:38 PM.
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Old 23rd October 2012, 02:37 PM   #573
gedlee is offline gedlee  United States
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Originally Posted by Rudolf View Post
Above Fs the dipole roll-off is steeper. Below Fs it could be shallower, if the monopole sub is of the BR or bandpass type.
And this is not correct either (having a bad day?) A bandpass is shallower below Fs (it is a monopole hence 2nd order), and a BR is the same because it too is a dipole below Fs (hence 4th order).
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Old 23rd October 2012, 06:09 PM   #574
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Quote:
Originally Posted by gedlee View Post
Why would you say that? because I never said what you claim. If the room is completely sealed then there is pressurization. But show me a completly sealed room! Now if it is not completely sealed then how can it contain a static pressure change?
Same way you can fill a bucket with a hole in it.
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Old 23rd October 2012, 07:53 PM   #575
Rudolf is offline Rudolf  Germany
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Quote:
Originally Posted by gedlee View Post
Why would you say that? because I never said what you claim.
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Originally Posted by gedlee View Post
And this is not correct either (having a bad day?)
Bad day indeed . I apologize.
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Old 12th November 2012, 06:53 PM   #576
OllBoll is offline OllBoll  Sweden
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One thing I've wondered when you optimize with say 3 subs a la geddes method, is it only the listening area that gets a good response or is the response good all over the room?
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Old 12th November 2012, 06:57 PM   #577
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You'd need to employ a DBA to get smooth response throughout the whole room.
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Old 18th November 2012, 03:41 PM   #578
gedlee is offline gedlee  United States
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Originally Posted by OllBoll View Post
One thing I've wondered when you optimize with say 3 subs a la geddes method, is it only the listening area that gets a good response or is the response good all over the room?
The response will get better everywhere, but maybe not as good as it will get at the location where it is optimized for. I don't have Marcus unfaltering faith in DBA.
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Old 18th November 2012, 10:07 PM   #579
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I don't have Marcus unfaltering faith in DBA.
No reason to doubt active absorption wouldn't work.
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Old 19th November 2012, 03:15 PM   #580
gedlee is offline gedlee  United States
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No reason to doubt active absorption wouldn't work.
Thats not the point, I don't deny that it works. I deny "You'd need to employ a DBA to get smooth response throughout the whole room." I don't see any one technique as being clearly superior to another. It may end up that one is more advantageous (but the jury is still out on that), but it would be a relatively small difference not a major one.
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