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DIY 12" Subwoofer Driver

3

31Orcas

Member
If you're thinking that this thread will be about a 12" subwoofer driver made from scratch, then you're right!

It started about a year ago, when I was bored. I was thinking of ideas of projects that I could work on in my free time. And then, it came to me. I know enough about speaker drivers, to build one from scratch! And my pencil started drawing a cross-section of a traditional speaker driver.

But what do I make it out of? I tried cardboard, but I used too much tape and it still was falling apart (due to lack of duct tape, my only option was scotch tape). I tried chopped up latex gloves for the surrounds, and it worked out surprisingly well, but the noise of the scotch tape drew me back again.

I came across videos about speakers on YouTube that could hardly compare with dome tweeters, and then this one person seemed to know what he was doing. Apparently, he used foam board that you buy at Michael's to make the subwoofer. He used duct tape for the surrounds, at rubber bands for the suspension. Simply put, he's a genius for making such a beautiful driver.

The driver's excursion was breaking 2 inches, still producing clean, undistorted bass as you can see in his videos.

So, it really is possible to make a very nice driver out of scratch from materials that not only can you find at Home Depot, be even more likely to find at art supply stores!

This inspired me, and I'll take it a little step further by making my own. I'll be using them in my emtpy subwoofer box for 2 12" subwoofers, that my neighbor gladly gave to me for free (they had it in their driveway, and I asked them for it and they said take it).

So, I have the plans and designs for it, and all I need is the funding for materials. I'd like as much feedback as possible, and critisism of my designs to improve them!

Here is a link one of the videos of his subwoofer (he made an 8" and a 12"; this vid is of his 8") http://www.youtube.com/watch?v=oXmVzn5wI1I&feature=channel
You can check out his other vids if you want to know more.

And here's a 3D rendering I made of my subwoofer. This is what it should look like when it's done : )
Subwoofer0001lowres.jpg

And I had a 2-D cross section, but the image was too big. I'll upload the high-res version of both images when I get a Flickr tomorrow (hopefully).

And BTW, please excuse typos. It's very late at night ATM. :banana:
 
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Looks like fun. You don't really need that much magnet if you can figure out a way to complete the magnetic circuit. Or by completing the circuit you could pump up the efficiency quite a bit. Something like a steel can with a big washer on top would work if you could get a washer sized right. Otherwise you'd need to do some metal fab. It'll add to the complexity but will also add a lot to the output.

Also, if you're not going to be using a monster amp to drive it, you might want to go down a bit in wire gauge. Using standard values for 22ga wire and his estimate of 80' he's looking at about 1.5ohms or thereabouts.

Ray
 
The magnetic circuit will have a core piece (in this case the neo magnet) and will need a return path. The can will take the magnet's strength from the bottom around the sides. A large washer on top where the OD fits the can and the ID is big enough to allow the coil to pass through will complete the circuit. The smaller the gap between the outside of the gap and the inside, the stronger the magnetic field in the gap.

In a normal ferrite magnet type speaker this would be the top plate.
 
@londonstraus: I tried to go for a TC Sounds type design, but both drivers are very loud and have very good SQ, 8 D.

@RayW: So, I put a large metal circle (a washer) and set it around the voice coil in it's idle position? And try to get the gap between the coil and the washer as small as possible? Does the thickness of the washer play a role?
 
@Jailtime: Haha, I was still typing when you posted : /. It's going to be made of foam board (if only I could make it out of metal). And thanks, I've based the design off of other subwoofers known for being loud and hardcore, so I think I've done very well with my design : ).

I don't know for sure, but instead of the small center magnet that looks like a center pole, I could get a (much more expensive) ring magnet, so that ventalation for the coil will be easier, and it would be 2 or 3 times stronger, and allow me to design a much bolder looking sub too.
 
Ok, I've started constuction on the sub about 4 days ago. I'm waiting until we can purchase the magnet and wire to continue.

And I have an important question, how does the top plate (AKA faraday ring) effect the linear excursion? Can someone please tell me if the height of the ring increases linear excurision, or is it the width of the ring? Will it be worth it to implement one if I have the magnet inside the voice coil (replacing the pole piece)?
 
Sorry, I missed this a few weeks ago.

First, a top plate and Faraday ring are 2 different things. A top plate is magnetically conductive and is used as part of the magnetic circuit. A Faraday ring is a non-ferrous metal (usually copper but sometimes aluminum) that is used to "short" the magnetic circuit at a certain spot and keep the magnetic field more uniform on both sides of the top plate.

The thickness of a top plate will dictate the overall strength of the field in the gap. The steel will saturate at some field strength and it won't matter how much magnet you have, you won't get more strength in the gap. As of the time I left Eminence, we were using 3/8" as the thickest. We used ceramic magnets up to ~160oz (stacked 80oz). I left before they started doing neodymium motors so I don't know what the top plates look like for those.

Using it to complete the circuit will increase the magnetic field in the gap, since there will be a gap. Using just a neo slug with no circuit means that there is no real gap to be had. Using a thicker top plate will increase excursion but if your magnet is not strong enough to magnetically saturate the plate then you will have less strength in the gap, however it should still be more than just the magnet by itself.
 
I'm a bit confused about the terminology. What exaclty is the magnetic gap? The distance between the magnet and the coil? Can you find a diagram that explains what you are saying? Thanks in advance!
 
Wow, I need to visit AudioKarma more often. So, the magnetic gap is the distance between the top plate and the voice coil?
 
Gap usually denotes the space between the magnet and the pole piece. The voicecoil is situated in this space or gap. The closer the tolerances in this area, the more linear and stronger, the force of the flux. Did I get it right, Ray?
 
Almost. The gap is the space between the top plate and the core. In your case the core would be the magnet slug.
 
Core = center pole peice? So, simply put, the closer the coil to the magnet, the better the X-Max and the speaker produces more force? And does a subwoofer really produce about one horsepower per kilowatt?
 
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