Can I? Passive radiator
- Thread starter kfa888
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Dan ʕ•ᴥ•ʔ
Peanut Head
You can have fun experimenting! Remove the motor and play around with the cone mass to help tune it to the box. http://www.subwoofer-builder.com/passive.htm
bowtie427ss
Lunatic Member
My WAG here is that in some instances where the passive is now being moved by box pressure rather than the motor's kinetic force, the coil and former might not travel in the same linear path causing rubbing, just my WAG.
With a ferrite motor i might be tempted to try breaking the backplate and polepiece free of the ferrite, or if accessible/practical remove the magnet altogether.
Charivari
Fighting Naïve Realism
Making a guess here, you shouldn't have to remove the motor. So long as you don't jumper the leads, the coil in the magnetic field shouldn't affect the motion of the cone as a passive. However, unless you're really lucky and the Mms of the woofer cone is already the exact weight you've calculated your PR design requires, you'll need some easy way to add weight to the cone to tune the sub. Packing the voice coil former full of washers and clay is the typical way of doing that, but can't be done with the magnet in place. Something workable may be done to the front of the cone, underneath the dust cap akin to the plastic mass disks some sub driver manufacturers add to lower the driver Fs while leaving the magnet in place. The thing is, PRs designed for the job are readily available and can be fairly inexpensive; two factors that combined with their being easier to use might tilt the balance in favor of buying one rather than adapting a woofer to become one.
Oh, you should also realize that passive radiator designs behave similarly to a ported system with high group delay, though in a more compact size without the chuff. So, if you, like me, are not fond of tubby ported bass, you might not like the results.
- JP
kfa888
Addicted Member
Thanks for the info. Pretty much what I was thinking. I have some spare cabs and some matching blown 12" woofer and thought it would be fun to try and play with. I might just do that this weekend just for the fun of it.
the cheapest 12" passive I found at PE was $26 ea. After shipping for 2 it would be $60 some bucks. I was just looking to play with stuff this rainy weekend and thought this might be a quick and fun project.
brainsmasher
Mid-Fi Madman
Heck if you want them I have a pair of polk 10" passives you can have for shipping. Drop me a PM if they would be of use to you.
kfa888
Addicted Member
Throw AK a few centavos, eh?:yes:
gonzothegreat
Super Member
Pick up a copy of the loudspeaker design cookbook or spend some time at the various DIY audio sites on the net. Lots of good ideas for designs out there. GordonW has used dead pro-sound woofers as passive radiators for some of his anime convention speakers iirc.
Paul C
Super Member
Since there is no juice flowing through the coil, there is no magnetic interaction. The woofer, working as a passive radiator, will not know the magnet is still there.
On the other hand, removal of the magnet would allow you to access the voices coil and backside of the dustcap. That is where you would add mass (epoxy putty, a washer or two glued on with silicone, etc) to the cone in order to lower resonance.
And a big woofer magnet always has uses around the shop.
On the other hand, removal of the magnet would allow you to access the voices coil and backside of the dustcap. That is where you would add mass (epoxy putty, a washer or two glued on with silicone, etc) to the cone in order to lower resonance.
And a big woofer magnet always has uses around the shop.
Dan ʕ•ᴥ•ʔ
Peanut Head
It's why I said to remove the motor. More than likely you will have to play around with the mass to get it right. Upside of not removing the motors is that you'll still have functioning woofers if the experiment fails.
