Sorry, I've been in/out of the office much of the week.
I don't have a FR of the DPL-15. It was really designed as a first couple octave device in which the T/S parameters accurately describe it's behavior. Also... to do a real design using it higher, you need to take a measurement of the device in the acoustical environment (the baffle) to do design work anyway. A 2Pi frequency response is of little value because it is only applicable to the environment in which it was measured.
I don't know anything about the IB15 other than what John has published. I've never seen one nor measured one. The things that stick out from just looking at the drivers is that we use the split gap motor (XBL^2), dual shorting ring arrangement. The shorting rings really only show their performance in the Klippel measurements (and in use). You can see that the inductance doesn't change with power and stroke in the same way as a device without them. That theoretically leads to less flux modulation, and less distortion. Due to the shorting ring configuration (aluminum in the rebate, copper down near the back plate) this motor is about 10-15% more expensive to make. The XBL^2 motor material cost is about the same, there is a rebate that has to be machined and I pay a 10% royalty to the patent holder to use the intellectual property. Those are the things that account for the price differences.
