[Ilkka]

Chris Brunhaver wrote:

A few comments:

Hi Chris,

Hopefully you don't mind me mentioning that you used to work for Adire Audio, so that people know where we're coming from.

As you have probably noticed, I'm more of facts and objective data than marketing talk type of guy. I have no business interests towards any manufacturer making complete HT subwoofers or just drivers for them/car audio. Therefore I also do not campaign in any certain direction, other than towards good performance. Whether that road leads to TC Sounds, JL Audio, SVS, CSS, or any other company, doesn't really matter to me at all.

Obviously the LMS 4" diameter >3" long coil with an average of >4 layers will have higher self inductance (and issues with modulation distortion etc) than a 3" diameter ~1.5" long 4 layer coil like an SDX15 or Tumult. What you're seeing in the 5400 is a difference in implementation of shorting rings etc., not proof that there isn’t an issue with this with the LMS design.

I don't think anyone tried to even hint that it would have lower inductance than, say, an XBL^2 coil. But the way they have handled and tamed it is the impressive thing. For example the MK1 Tumult clearly shows that low self inductance doesn't really count unless also other improvements (shorting ring etc.) are being applied properly.

Measurements show extremely low THD and very flat upper-end frequency response for the LMS coil. In the end that is much more important than just saying that the other design must have lower inductance due to shorter VC.

The inductance graph shown by Dan is a simulation, not a measurement. However, you can see the effect of the shorting ring near the rest of the driver (i.e. between the top plates) and how it is effective more at higher frequency than lower. Of course, inductance increases inward into the motor because of the presence of more steel (making the coil essentially iron core instead of air core).

Thanks for the correction. I accidentally had the inward/forward stroke backwards.

The Klippel inductance result isn’t at all directly comparable. It is a lumped model which is somewhat skewed by the low frequency side of things (required to get the high displacement). In short, if you make this graph flat, you could be putting too much copper in the motor (making the curve very non-flat in the range where the copper is effective).

Ok. I was a bit hesitant to post it because I wasn't sure how comparable they would be. I edited my post to reflect this new info.