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Old 02-03-2015, 09:05 AM
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Default Passive radiator(s) for 2-12

Hey guys. Ok so I recently copied Jacobs idea for an sa-8 box (12.5" cube with a 10" psi passive radiator) and my friend got a chance to hear it last night. Needless to say he loved it in terms of output and sound quality. He then started talking to me about building a passive radiator setup for him for his two 12's (memphis mojos, the nicer 40+ lbs ones). However since I just kinda copied Jacobs design, I don't know a whole lot about these types of boxes so my question is would he need 2-15" pr's? Or would 1-18" pr suffice?
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Old 02-03-2015, 09:53 AM
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He will have to do some math. Rule of thumb is double the Vd, volume displaced, which is surface area (Sd) times Xmax, in your PRs as you have in your powered drivers. He can explore the configurations he wants to, two 15's may actually not work that well. I know I had two powered 15's, two 18" PRs, and with about 1.4x the Vd it had issues with bottoming out under full power around tuning.
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Old 02-03-2015, 11:22 AM
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2 15's or ideally 3-4 12's. Generally you don't do passives just to do passives. If he doesn't have an install contraint that requires them, ported is much cheaper and gives similar results.
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Old 02-03-2015, 11:40 AM
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I did passives just to do passives, and I'm glad I did. I loved the sound of them. Just wish I designed the system better.
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Old 02-03-2015, 12:12 PM
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Quote:
Originally Posted by gckless View Post
He will have to do some math. Rule of thumb is double the Vd, volume displaced, which is surface area (Sd) times Xmax, in your PRs as you have in your powered drivers. He can explore the configurations he wants to, two 15's may actually not work that well. I know I had two powered 15's, two 18" PRs, and with about 1.4x the Vd it had issues with bottoming out under full power around tuning.
Ha you mean I will have to do some math. He don't know a whole lot about this stuff. And I'd love to figure the Vd...issue with that is that he bought them pretty cheap off the sale table at the local car audio store used without original boxes/manuals and got some reason, it's extremely difficult to find specs on the mojo m3. I can find specs all day long on the original mojo and the later mojo (m5) but can't for the life of me find anything on the m3.

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Old 02-03-2015, 12:40 PM
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Quote:
Originally Posted by yzwrestler160 View Post
Ha you mean I will have to do some math. He don't know a whole lot about this stuff. And I'd love to figure the Vd...issue with that is that he bought them pretty cheap off the sale table at the local car audio store used without original boxes/manuals and got some reason, it's extremely difficult to find specs on the mojo m3. I can find specs all day long on the original mojo and the later mojo (m5) but can't for the life of me find anything on the m3.
I think it would be safe to just assume an excursion measurement around the two. Heir on the larger side to be safe.
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