OB with Alpair 12P and Eminence Beta 15

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Nick
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#91 Re: OB with Alpair 12P and Eminence Beta 15

Post by Nick »

I would have thought the gap between panels was invisible at the frequencies you are dealing with.
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IslandPink
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#92 Re: OB with Alpair 12P and Eminence Beta 15

Post by IslandPink »

I haven't actually looked at the theory of OB's in much depth. I've always relied on James for this, as I know he had a level of sophistication in what he did to design the Quasar and the Quasar variants that isn't covered individually by any of the well-known commentators on this sort of thing.
With the dual pair of bass drivers the upper one will benefit less from the floor loading so it will have a slightly more rolled-off response than the lower driver ; however both drivers will see increasing amounts of wall loading ( 1-Pi ) and corner loading ( 0.5-Pi ) as you go down in frequency from 80Hz to ~35Hz and the wavelengths get quite long.
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simon
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#93 Re: OB with Alpair 12P and Eminence Beta 15

Post by simon »

Nick wrote: Wed Aug 23, 2017 12:17 am I would have thought the gap between panels was invisible at the frequencies you are dealing with.
James always said it was imperative the bottom of the baffle made good contact with the floor otherwise the benefits of it wouldn't be realised. So I presumed similar for the gap between the sub baffles. Though it seems such a small gap to me that it shouldn't make any difference either. An easy thing to check at least.
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#94 Re: OB with Alpair 12P and Eminence Beta 15

Post by IslandPink »

simon wrote: Tue Aug 22, 2017 10:15 pm If there is a gap between the sub baffles it might be worth putting some tape over it to see if it makes any difference? James' first baffle were cardboard so something simple should suffice to check.
I can't see this little gap being important at wavelengths of 3m or more, where the OB is really required to support bass. It's mainly the total area of the thing and the distance around any wings that makes thigns work ( or not ) . Iv've had OB trials on all sorts of lashed-up baffles with funny shapes and minor steps, it's not a big deal. Where the wavelengths become small enough for those things to matter, the radiation pattern is mainly coming forwards off the mid-driver anyway.
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chris661
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#95 Re: OB with Alpair 12P and Eminence Beta 15

Post by chris661 »

If the gap represents the new shortest distance from the front to the back of the cone, of course it makes a difference.

If not, it'll be fine.

Chris
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#96 Re: OB with Alpair 12P and Eminence Beta 15

Post by IslandPink »

And if the gap is 10µm wide ?
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Stanney2001
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#97 Re: OB with Alpair 12P and Eminence Beta 15

Post by Stanney2001 »

Hello,

I’m embarking on a similar build and wanted to ask how you were getting on.


Kind regards,

Andrew
chris661
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#98 Re: OB with Alpair 12P and Eminence Beta 15

Post by chris661 »

IslandPink wrote: Fri Aug 25, 2017 8:47 pm And if the gap is 10µm wide ?
Then there's likely to be a lot of friction, so probably a non-issue.
Something of the order of 1/2" would be likely to make a difference IMO.

Chris
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#99 Re: OB with Alpair 12P and Eminence Beta 15

Post by Max N »

Pure Audio Project have a new 10" coax driver option - I don't know whether this would be a suitable driver for any of the current OB experiments on the forum here. PAP used to be quite helpful for DIY, but I don't know if they would sell a pair of these new drivers separately. There is an upgrade option to retrofit these to an existing pair of PAP OBs, but that includes new central baffle sections and crossovers.
Anyway, details here in case it's of interest:
https://shop.pureaudioproject.com/produ ... e-speakers
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#100 Re: OB with Alpair 12P and Eminence Beta 15

Post by IslandPink »

There's not much data there, but the efficiency of 96dB for a 10" unit suggests it would reach down reasonably well , probably flattish to 150Hz and getting below 100Hz. That's useful as regards choice of bass unit and crossover.
Obviously that's only a limited part of what they would sound like.
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