velodyne spl-14 vs, DD- 15

I am answering because I see no one else has. I don't know the SPL-14 at all, but I own the DD-15. I think it's the adjustments on the TV monitor with the microphone that make it an exceptional subwoofer. You could also consider getting an SMS-1 to use with your existing sub. That way you would almost have a DD-15. Again it's the built in SMS-1 feature that I feel makes the DD-15 so great.

To my knowledge, there are 2 main differences:

The first was mentioned in the post above. As Koestner notes, this can be addressed with either the $400 SMS-1, or with Audyssey (or equivalent) if you have that in your pre-pro or receiver.

The second distinction is the "S" in SPL 14, which stands for small. The cabinet is smaller in the SPL series is smaller than equivalent sub in the DD series. The net effect is that the DDs go lower and louder (holding THD constant) than do the SPL subs. Might or might not be an issue for music program material.