Ahem....
I don't recommend bringing up the client list. It is my understanding that the Harman work is not to be shared publicly. Could be wrong....hope I'm wrong.
Personally, I don't really like the split top plate approach for a variety of reasons. Aside from the increased reluctance, I think from a manufacturing standpoint you're leaving more room for error. With the older approach (ie. machining) your tolerances are as good as the machining is capable of, which is very tight tolerances indeed. This was actually a big advantage to their variable flux approach rather than the variable windings approach of split coil or LMS. Now with the split top plates, you're looking at the machining tolerances plus all assembly tolerances. In the case of a pressed top plate (the most affordable approach), you run the risk of poorly pressed top plates leading to larger gaps between the top plates and increasing reluctance.
I think in practice this newer approach has worked quite well for the XBL^2 designs (virtually all of which are doing so now); for most products, it seems to be a very good way to make quality products for less money more easily. Still, I prefer the older method.
And I'm still not completely convinced that copper in the rebate is the best approach. This is one thing no one has ever answered for me: a rebate in the middle of the pole piece would make inductance slightly lower at rest than at any other position (since there is less steel in the core). The only exception to this would be on the outstroke when windings start to pass the top of the pole. Adding a shorting ring in the region where inductance is already lower seems like you are opening yourself up to greater inductance variation (increased harmonic and intermodulation distortion). I propose this only as a theory, and not data, but would love to see Le(x) that shows otherwise.
The new Mag comes with an anodized copper shorting ring (can't remember how thick) on the pole. In my uneducated opinion, this is the best method of decreasing inductance as it does not increase variation. By comparison, single shorting rings decrease variation but don't do much for lowering inductance at all coil positions. The copper cap on the pole piece, for example, is one of the worst implementations of copper since you end up decreasing inductance at the position where it is already lowest (ie. fewest windings around the pole). However, the Mag also has the copper in the rebate.....I greatly look forward to seeing how this looks on the Klippel DA.
The Exodus Audio drivers use a slightly different approach that seems targeted at managing Le(x) and Le(i) variation (though they still use the split top plate). They call it AlCu...it's an aluminum shorting ring below the top plate on the ID of the magnets, and a copper shorting ring in the rebate. Still, I think it poses the same problem (in theory) that I mentioned above.
I really need to measure these drivers. //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif
I don't recommend bringing up the client list. It is my understanding that the Harman work is not to be shared publicly. Could be wrong....hope I'm wrong.
Personally, I don't really like the split top plate approach for a variety of reasons. Aside from the increased reluctance, I think from a manufacturing standpoint you're leaving more room for error. With the older approach (ie. machining) your tolerances are as good as the machining is capable of, which is very tight tolerances indeed. This was actually a big advantage to their variable flux approach rather than the variable windings approach of split coil or LMS. Now with the split top plates, you're looking at the machining tolerances plus all assembly tolerances. In the case of a pressed top plate (the most affordable approach), you run the risk of poorly pressed top plates leading to larger gaps between the top plates and increasing reluctance.
I think in practice this newer approach has worked quite well for the XBL^2 designs (virtually all of which are doing so now); for most products, it seems to be a very good way to make quality products for less money more easily. Still, I prefer the older method.
And I'm still not completely convinced that copper in the rebate is the best approach. This is one thing no one has ever answered for me: a rebate in the middle of the pole piece would make inductance slightly lower at rest than at any other position (since there is less steel in the core). The only exception to this would be on the outstroke when windings start to pass the top of the pole. Adding a shorting ring in the region where inductance is already lower seems like you are opening yourself up to greater inductance variation (increased harmonic and intermodulation distortion). I propose this only as a theory, and not data, but would love to see Le(x) that shows otherwise.
The new Mag comes with an anodized copper shorting ring (can't remember how thick) on the pole. In my uneducated opinion, this is the best method of decreasing inductance as it does not increase variation. By comparison, single shorting rings decrease variation but don't do much for lowering inductance at all coil positions. The copper cap on the pole piece, for example, is one of the worst implementations of copper since you end up decreasing inductance at the position where it is already lowest (ie. fewest windings around the pole). However, the Mag also has the copper in the rebate.....I greatly look forward to seeing how this looks on the Klippel DA.
The Exodus Audio drivers use a slightly different approach that seems targeted at managing Le(x) and Le(i) variation (though they still use the split top plate). They call it AlCu...it's an aluminum shorting ring below the top plate on the ID of the magnets, and a copper shorting ring in the rebate. Still, I think it poses the same problem (in theory) that I mentioned above.
I really need to measure these drivers. //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif
