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Old 2nd July 2016, 06:53 AM   #21
planet10 is offline planet10  Canada
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MarkAudio 12P and 12PW question
Quote:
open baffle isobaric years ago
It isn't really an isobarik if it is an open baffle.

dave
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Old 2nd July 2016, 09:38 AM   #22
MITsound is offline MITsound  Canada
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MarkAudio 12P and 12PW question
Smile Isobaric, generic- not Isobarik

Not sure what else to call it.
The "front" of each driver is exposed to the room, one on the front, one on the back, of the baffle.
They share a sealed air chamber between them, as the drivers are mounted magnet to magnet, in a cylinder shaped shallow enclosure.
In this case, it was a small maple ply tom tom drum flush mounted at the front, embedded on on a baffle.
Iso (isolated) baric (pressure) , where the cylinder of air is a sealed away chamber from the room.
Not Linn's branded Isobaric box speaker implementation of a sealed chamber between 2 magnet to magnet arrayed drivers in a box.
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Old 2nd July 2016, 04:34 PM   #23
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MarkAudio 12P and 12PW question
One thing that that will do is cause a series of peaks & dips related to the distance from the front driver to the back driver. That might be tuned to kill a resonance but it comes with a lot of collateral damage.

dave
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Old 2nd July 2016, 05:03 PM   #24
MITsound is offline MITsound  Canada
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MarkAudio 12P and 12PW question
Even though the drivers are arrayed back to back, and wired out of phase?
Would the peaks and valleys be from the same reflections off the baskets, but summing due to two sets of baskets in a sealed area?

I was going to attempt this, as I just landed two 12PWs in great shape, used, but hadn't realized their efficiency is not the same as the 12P.

Looks like it'll be a biamped split between the two pairs.

Still trying to get used to less midrange slam than my homemade Onken style 3 ways.

High efficiency (98db/watt) 15"ers are hard to beat for fun; but there's no denying the ease and refinement of the Alpair 12P presentation, when paired with an open baffle sub.

Thanks for the insights.
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Old 2nd July 2016, 05:38 PM   #25
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MarkAudio 12P and 12PW question
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Originally Posted by MITsound View Post
Even though the drivers are arrayed back to back, and wired out of phase?
It has to do with the distance between the drivers, back-to-back makes for the worst case. There is a time delay between front & back drivers. At low frequencies this is not an issue, but as the distance starts approaching frequencies where the radiation of the back driver is out of phase with the front driver (at the front driver) you get dips…

Quote:
Would the peaks and valleys be from the same reflections off the baskets, but summing due to two sets of baskets in a sealed area?
Completely different cause.

Quote:
I was going to attempt this, as I just landed two 12PWs in great shape, used, but hadn't realized their efficiency is not the same as the 12P.
If you haven't got A12p i'd suggest some of the smaller drivers. Our 1st trials were with A7PeN in an MTM, then we swapped in A7.3eN (better yet). For maximum slam perhaps A10p.

Click the image to open in full size.

Hoffman's iron law says that to get lower bass, it has to be lower efficiency or need a bigger box, A12pw is both and it does dig low.

dave
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Old 2nd July 2016, 06:08 PM   #26
MITsound is offline MITsound  Canada
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MarkAudio 12P and 12PW question
Thanks, I do already have the A12P pair.
While I'm happy enough with them, I'll be splitting these to assess how the 12P does with the lower doppler distortion which comes from handing off some lower frequencies to the A12PW.
As I'm nearly satisfied with the treble when digitally highpassing them at 120 hertz, I'm hopeful things clear up a little more by having the A12P handle things from maybe 800 hertz and up.
It may be serendipitous anyways, against all advice of friends, I prefer my little push pull EL84 for the vocal range, and a 300B for everything above that.
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Old 2nd July 2016, 06:13 PM   #27
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MarkAudio 12P and 12PW question
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While I'm happy enough with them, I'll be splitting these to assess how the 12P does with the lower doppler distortion which comes from handing off some lower frequencies to the A12PW.
My experience is that they will get better (given that the split is done well).

With the A12pw and any of the MA FRs, there is a huge range of accepatable XOs. We XOes the above at 250 Hz to keep most of the midrange in the bandwidth of the midTweeter.

dave
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Old 4th July 2016, 10:51 PM   #28
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Not that it's likely still germane to the conversation re isobaric, but if I recall correctly, Linn's approach on both the original Isobarik PMS/DMS monitors and smaller Sara9 had the drivers stacked closely together, cone to magnet.

Among other things, that gave them the distinction of being an absolute pain in the butt to service the drivers.
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Old 4th July 2016, 11:13 PM   #29
MITsound is offline MITsound  Canada
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MarkAudio 12P and 12PW question
Default Totem Mani-2

Used the same arrangement.
Perhaps one of the 3 or 4 best sounding speakers I've ever heard, for sure the best stand mounted speaker I've heard.
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