DIY Rotary Woofer

**icnivad** · **10-20-08, 05:16 PM**

After doing a little research of rotary woofers, they seem pretty cool, but the $+15k price tag seems a little exorbitant. Has anyone tried a DIY version of one of these?

It seems like mounting a stepper motor (or one for each blade) onto a fan or motor and controlling it with a computer should do the trick.

Any thoughts?

**thxgoon** · **10-20-08, 06:37 PM**

I'm sure you could build something but I imagine most of the research goes into the aerodynamics of the rotor. A dc motor being fed the ac signal or a servo would do the trick I'd think.

**Mike P.** · **10-20-08, 06:57 PM**

There was a start of a diy rotary sub on the diyaudio.com forum a while back. I don't know if it was ever completed.

**TheEAR** · **10-21-08, 09:16 AM**

Doing a DIY version (COPY) of the rotary sub is a grand waste of money and time. You have to have connections with people who can custom manufacture a few parts and understand fully all the inns and outs of the design(I am sure many think they do but have little idea).

Waste of time and doomed to fail,unless you are ready to invest serious time and money.

**Mike P.** · **10-21-08, 03:06 PM**

Here's a link to one type that was not finished.

http://www.betteraudio.com/geolemon/servoproject/

**icnivad** · **10-24-08, 01:36 PM**

ok, it looks like they use a voice coil mounted in between the motor and the rotor to control the blade pitch. I think I could make the linkage, fans, and hook up the motor but I don't know about the voice coil as I've never taken one apart. My questions(and possible deal breakers) are:

1. Would a voice coil taken from a large speaker be able to exert the force required to move the blades? This will exert more back pressure on the coil than just a cone and I wouldn't want to design and build everything it just to find that I would need a high powered custom voice coil that would be inhibitavely expensive.

2. In order to mount the voice coil directly in between the motor and the rotor, you would need to run the shaft directly through the center of the coil. Has anyone ever tried to drill a hole through a speaker magnet?

Another option that might be a little easier would be to mount the voice coil on the rotor itself. You'd need a slightly bigger motor since you now have more mass to rotate, an it would probably take longer to turn on, but since the rotor spins at a constant speed, this shouldn't really cause a problem. In fact, it might help even out the rotational speed of the rotor as it would have more mass.

**Mike P.** · **10-24-08, 01:51 PM**

I can't help you with any of your questions. If you're interested in this, then you definitely have some research to do.

**thxgoon** · **10-25-08, 01:38 PM**

For one thing you are going to need to figure out how to pass the electrical connection from the amp to the spinning voice coil assembly as you obviously can't just use wires. As for the motive force to turn the fan blades I imagine you will have to research and test this though a powerfull enough motor should do the trick and you can always design the linkage assemblies to amplifiy the tourque. As far as drilling through the magnet.. I dont see the need. Why not just connect everything on the 'top' of the motor? You'll also want to make sure that the forces exerted on the linkage assembly is in line with the motion of the motor so you don't cause it to rub and damage itselft. In all this sounds like a pretty complicated project!

**buggers** · **10-27-08, 01:23 PM**

It is a very complicated project. http://www.hawthorneaudio.com/forums...1454&start=615

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