Hi all, excuse my ignorance but I'd appriciate your help. I'm looking to built a sub using a 15" driver I have, but I also have a pair of 8" PR's sitting around. The question is... given that the surface area of the driver is almost the same as 2x 8" PR's could I built the cabinet to make use of the PR's?
As a general rule, the passive radiator(s) should have at least double the displacement of air (Vd) as the active woofer(s) in the system.
Vd= Xmax times Sd (cone area). Passive radiators may be rated in Xmech rather than Xmax. When a passive radiator reaches it's limits, it will usually make some sort of a bad, loud noise ("whup, whup") unlike ports, which make less audible "chuffing" wind noise.
As you can see in the example below, 2x8" would have about 5 dB less output at 36 Hz than a single 15" with the same excursion.
Vd= Xmax times Sd (cone area). Passive radiators may be rated in Xmech rather than Xmax. When a passive radiator reaches it's limits, it will usually make some sort of a bad, loud noise ("whup, whup") unlike ports, which make less audible "chuffing" wind noise.
As you can see in the example below, 2x8" would have about 5 dB less output at 36 Hz than a single 15" with the same excursion.
Attachments
Or one 15" PR with the displacement of two 15":
Dayton Audio's RSS390-PR 15" passive radiator has 60 mm peak to peak displacement, depending on the 15" Kernowdragon has, that may be plenty.
I had a Mackie HRS120 that used a 12" passive radiator with far less excursion potential than the RSS390-PR 15", and it was enough to make the drywall flap between 15-20 Hz ;^).
Dayton Audio's RSS390-PR 15" passive radiator has 60 mm peak to peak displacement, depending on the 15" Kernowdragon has, that may be plenty.
I had a Mackie HRS120 that used a 12" passive radiator with far less excursion potential than the RSS390-PR 15", and it was enough to make the drywall flap between 15-20 Hz ;^).
All things equal, double the woofer will lead you to no harm.
Well, you specifically want double the displacement.
I'd generally aim to use an even number of PRs, though, and arrange them for force cancellation. The moving mass can be very large, so there's a very real risk of the cabinet going for a walk when large signals are applied.
Chris
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