I've been getting a lot of email on this. Let me try to respond here to cut-down on some of the redundant questions being asked and save my sanity:
#1 Where is this made?
My vendor is in Asia. They have several factories and I'm not sure which will be manufacturing this product. It is a superb vendor, with a great track record and they manufacture for a number of big-name companies. They were chosen for their track record, in-house engineering, and their willingness to work with me.
#2. Do you have distortion data?
No... I don't have a chamber in the USA and you really need a chamber to get reliable data. For us, the Klippel is more valuable because it tells us the mechanism, not the result. If you are engineering something knowing the cause is critical because that is what allows you to optimize/improve the design. A distortion plot tells us nothing except that there is a problem. It doesn't show us what we need to do to fix it.
Distortion plots are dependent upon how they are taken too. If you look at something like Zaphs site or other knowledgeable people taking distortion measurements, they will tell you that the data doesn't necessarily correlate to other distortion measurements. They are useful, if you are comparing two devices, measured at the same time under the same circumstances. They are less useful when taken alone without context.
#3. Why is there a asymmetric shape in the Klippel BL or the Kms? It doesn't look like you have a true 13mm X-max.
You have to take the Klippel for what it is. It is a measurement and all measurements have a range of variability and the device isn't perfect. If you get a slight 1mm offset, that is actually extremely good. Most people don't have the experience or the context to comment on good/bad measurements. Trust me.... these look very good even without the perfect marketing shapes.
In terms of the x-max, nobody has caught it but the shown Klippel was for a different prototype than the final one. There have been several revisions. If you look at the curve, the BL at rest is about 7.3-7.4. In the final design it is up around 9.8 so the coil has changed since that particular Klippel. It matters not... it is the same motor and I'll update the information once the production run is shipping. We would calculate x-max based upon a fairly simple formula. You take the resting BL, multiply by 0.7, and then trace the curve to see where it crosses. You will get slightly different numbers forward/back. The thing to keep in perspective, is that this is out at the edge of usability and we are often talking about 1-2mm differences. If you assemble a couple drivers you will quickly find it is pretty difficult to insure unit-unit a 1mm tolerance on placement of the coil. Measure different units off the production line and you might get slight differences in that asymmetry. It doesn't matter a whole lot because people don't run midwoofers at 26mm peak-peak. They run them significantly lower. Look at it this way, you are getting an extremely linear +/- 20mm P-P operation. The xmax is only a number that is reflecting what you are getting near the limits of operation and you shouldn't be operating anywhere near xmax with this type of device anyway.
#4. Why is it so cheap? What gives?
I'm giving them away near cost. That is why they are cheap. I'm doing it because I'm nuts.
#5. What did you sacrifice to get all that linear stroke?
Well.... you don't give up anything other than cost, size and weight. There is no tradeoff for xmax that sacrifices efficiency. The box size & bandwidth you target are what really determine the efficiency. Once you pick those things, the efficiency pops out the other side of the equation. We could easily make this 90db/1W/1M but it would no longer work in our target application without EQ and it would cost more because we would have needed a bigger motor.
High stroke drivers don't necessarily give up anything other than the fact that you have to design the suspension to deliver it. In the past, you also picked up more inductance with overhung VC designs but XBL^2 motors don't necessarily have that same tradeoff. The suspension can be troublesome for linear distortion issues (cone/surround resonances) but that has been successfully solved in this design. Don't ask me how, I'm not a soft parts guru but the engineer at the build-house clearly understands what he is doing. It is smooth, and easy to work with and there is no hidden ugliness. I have four samples and they measure great on all axis of measurement and they are fairly easy to work with.
#6: Why the rising inductance?
Inductance is a complicated topic. Suffice it to say, without the rising inductance we would have had a rising response. In general, you would want a flat inductance curve for a full-range driver or anything designed for upper midrange or HF response. That is not the design intent of the device. In terms of distortion, inductance is only an issue at higher frequencies unless you get flux modulation in the motor, DC offset/rectification and other voodoo motor stuff. As you can see from the Klippel distortion analysis, Le contributes the least amount to the THD of all the non-linear factors. BL & Cms non-linearities are the bigger sources of non-linear distortion. Improving Le wouldn't give us any meaningful improvement and I'm not interested in spending my time/money on something that doesn't make an audible difference in the final product.
That is it for now.