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Old 02-07-2018, 01:11 PM   #1
SPL_Krayzie112

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Tuning Passive Radiators

How do you tune passive radiators? I'm pretty sure they all differ in diaphragm and suspension traits and ports and slots have their own equations...what is the formula for passive radiators?
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Old 02-07-2018, 02:55 PM   #2
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Some passives come with a chart that shows you how much weight you need to hit a given tuning frequency in X size enclosure.

You can tune by ear. You can also tune using your eyes. When the driver goes to ~zero movement, that is the tuning frequency (works for ports too). You can put talcum power on the woofer cone to help you detect movement. Don't play test tones below tuning or the driver will unload.
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Old 02-08-2018, 02:07 AM   #3
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What do you mean by "~zero movement"?
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Old 02-08-2018, 02:53 PM   #4
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Quote:
Originally Posted by SPL_Krayzie112 View Post
What do you mean by "~zero movement"?
I mean the subwoofer practically stops moving.

At FB in a ported enclosure the output is from the port not the sub. Same goes for passive radiators.
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Old 02-10-2018, 10:49 AM   #5
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Mmm. Never came across this before. What do you mean zero movement from the subwoofer? Zero excursion? How's the sound gonna happen then? You might have to elaborate a little, never came across this information before.
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Old 02-10-2018, 12:42 PM   #6
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Quote:
Originally Posted by SPL_Krayzie112 View Post
Mmm. Never came across this before. What do you mean zero movement from the subwoofer? Zero excursion? How's the sound gonna happen then? You might have to elaborate a little, never came across this information before.
By ~zero movement, I mean ~ zero movement, no excursion, cone movement comes to a near stop. Sound comes from the port, not the cone, that's how sound happens. The littlest "excitement" from the sub will cause massive output at the port. You can look up Helmholtz resonators for more info.
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Old 02-11-2018, 12:41 AM   #7
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How will the sound come out of the port if you're using a passive radiator?
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Old 02-11-2018, 02:27 PM   #8
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Quote:
Originally Posted by SPL_Krayzie112 View Post
How will the sound come out of the port if you're using a passive radiator?
A passive radiator and port operate the same way. In the case of a port the column of air inside the port moves back and forth like a piston. In the case of a passive radiator, the PR moves back and forth.
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Old 02-12-2018, 02:36 AM   #9
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So I suppose Cone XSus = Vent Mach?
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Old 02-12-2018, 11:00 AM   #10
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Quote:
Originally Posted by SPL_Krayzie112 View Post
So I suppose Cone XSus = Vent Mach?
No. PRs don't really have an equivalent to Vent Mach because a PR should eliminate the problems associated with Vent Mach. As a general rule of thumb the PR should be able to displace 2-3x the air you sub can displace.
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Old 02-14-2018, 12:59 AM   #11
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Quote:
Originally Posted by Jimi77 View Post
As a general rule of thumb the PR should be able to displace 2-3x the air you sub can displace.
That's the answer I'm looking for. Thanks!

Any basic formula for this?

Last edited by SPL_Krayzie112; 02-14-2018 at 01:13 AM.
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Old 02-14-2018, 10:27 AM   #12
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http://www.diysubwoofers.org/prd/
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