Eminence wrote to say that they have finished running magnetic FEA simulations and found that a flux stabilization ring can be added and electro-mechanical parameters be maintained as described in the thread above. But the way this was accomplished in their simulations was to add add steel to the core surrounding the cooling vent and reducing its ID. This was done in order to replace the steel that was removed to add the flux stabilization ring.

I have asked that they consider other methods of increasing flux. Possibly using a larger magnet or use another alloy, perhaps a layer of neodymium. Decreasing vent size is an option, and it may be worth testing to see what the end result would be. It is possible that this is a non-issue, we'll see. But my gut feel is that I would prefer to address this by adding magnet instead of by adding steel and reducing vent size.

On the other hand, Eminence makes several long-throw woofers with a smaller vent. It is possible that there isn't a problem with the smaller vent. Certainly it isn't an issue until power is high, so as a high-fidelity woofer, the flux-stabilized version would perform better at reduced power levels even if the vent were smaller. And, as hulkss has pointed out, the LABhorn has breathing issues anyway, due to the fact that the cooling vent is restricted.

Still, since the woofer is designed to be an all-out performance improvement, I tend to not want to cut any corners. I'd rather not decrease the vent size. There is another option that is being considered, and the only thing is that we'll have to wait a few more months. It's a no-compromise solution, so I think I'm leaning in that direction.

We don't know what vent size is too small, so maybe it's worth building a sample to find out. But then again, we are sure that keeping the vent size large will allow the speaker to breathe better than a smaller one would. A larger vent will also help reduce chuffing, which becomes audible when excursion is high. I have been discussing these and other issues at length with people at Eminence.

Jerry McNutt and John Sheerin have analyzed the problem and come to the conclusion that adding magnetic material wouldn't increase flux. The core is saturated, so the only way to increase flux is to add steel. So the existing motor configuration will need a smaller vent to include flux stabilization and meet required T/S specs.

That leaves us with two options. One is to decrease vent size and use the existing motor layout with the addition of flux stabilization.
The other option is to mount shorting rings in the plates, outside the voice coil. This option would allow the vent to be made larger, but is a major undertaking that would add a couple months development time.

So let's cut to the chase. A flux stabilized subwoofer with required T/S specs and a 0.75" ID cooling vent can be made immediately. We would have evaluation units in April and if they met our expectations, we could be taking delivery on production runs in May or early June. Or we could wait for Eminence to tool-up for a version that puts the flux stabilization ring in the plates, allowing the cooling vent to be made larger. This would push back the dates, with evaluation speakers ready around the end of summer. If everything goes well, we'd be looking at late 2nd quarter 2004 for evaluation units and early 3rd quarter 2004 for production units to ship. That puts us into August or September.

Since the woofer is designed to be an all-out performance improvement, I tend to not want to cut any corners. I'd rather not decrease the vent size. This subwoofer is intended as no-compromise solution, so I think I'm leaning in that direction. But I've told Jerry that I would let Eminence sit on this for a little while and think about it. I trust these guys, and I value their opinions. They've been successful at solving problems like these, and have the best engineering tools, magnetic FEA and measurement systems to pull it off. I'm confident they'll choose the best direction to go.

I also want to get input from Chris Rose and Rob Gault on this matter, because it's a pretty big undertaking. It's big both in technical scope and in production requirements. So I think it is prudent to let them think on this one a while before making any further comments. I'll report back in just a few days.

I still reckon that a smaller vent is not a good idea, just as you say. What is the point in improving one thing, and then making another aspect worse than used in the woofer which needed "improvement"? (hmmm thats a nice catch phrase, I think)

Just as an idea, if it will shorten production time, some manufactures vent underneath the cone instead. Here is a cutaway view of what Peerless does on their XLS woofers:

A. Aluminum Spacer: The aluminum spacer serves as heat sink for the coil to reduce power compression.

E. Vented Cone: To eliminate compression under the dust cap the cone is vented by 8 large holes. This way the coil is cooled and there is no need for a bore in the pole piece.

If you look where the letter "B" is written, theres a gap there and the voice coil is actually exposed for extra cooling.

It would mean you wouldn't have to redesign the whole motor layout, so you could get it out earlier. Maybe Eminence should do something like this?

In Australia it's already end of Summer, when is it end of Summer in the US?

Adrian

Eminence vents in front and back on the Kilomax Series, so I don't think they're opposed to that sort of thing. They also have radially spaced holes on them rather than a single large vent as other models do. But I think they're planning a central rear vent on the new motor. I don't know; They're still looking at it.

Summer is pretty much June, July and August for we Americans. I'd love to spend spring and summer here, and then "fall" and "winter" there!

Chuffing sound may be an issue in a dipole bass speaker or in an application where the speaker is mounted backside out. Does Eminence believe that a .75" magnet vent could ever be audible or cause distortion in a closed back front horn cabinet?