I bought these to use in my car as midranges from 300-2khz. As you can see, there is about a 5dB bump in response beginning at about 1.5khz, I assume caused by the dust cap. To that, the Scan Speak 15m exhibits the same bump a bit earlier in frequency. You can see their spec sheet here. Heck the Scan 15w looks nearly the same in this regard as shown here. While the FR isn't ruler flat, the bump in response in my measurements occurs where beaming begins, so this may alleviate that issue by low-passing the mid before this point.
The 8khz (likely modal) bump is about 10dB higher than the response at 2khz. At 4khz there is approximately a 10dB delta between 0 and 60 degrees response. The HD looks VERY good. Even at 102dB @ 1/2m equivalent the THD above 150hz is less than 0.30%. The separation between 2nd and 3rd order distortion at this output has about a 15dB delta above 300hz which is very nice.
Overall not quite stellar FR, but given the likely crossover point here around the 2khz region, the issues beyond this point aren't of huge concern. The THD is very nice. Overall, I think this is a really good midwoofer (even better used as a midrange).
Subjectively I can say that I've been using these in my car for the past couple weeks and have been VERY impressed with them. I actually prefer them over the Scan 12m, and the Scan 15m/15w ... but I'm basing these impressions on aural memory which isn't great, so take that for what it's worth.
As an aside... these things are just plain gorgeous!
here's a link to the test results:
Here's a picture:
PS: If you would like to help me keep up funds for testing, there's a little 'contribute' button that goes through Paypal all the way at the bottom of every page. Any little bit helps.. heck, $3 buys me painter's tape to help seal any small gaps in the baffle/blank interface.