With bandpass enclosures as well? I've never really used WINISD for bandpass before.. As another few posters mentioned though, the RE HC 12 really doesn't lend itself very well to a 4th order alignment. 4th order subs tend to be higher Q and lower fs as the rear of the driver is sealed, so unless your driver plays loud and low in a sealed box, it won't do much better in a 4th order. Anyway, PWK does very good bandpass designs if your looking for some semblance of SQ in your design.. IMO, he'd be the way to go for you even though the designs are somewhat expensive, he really does do a good job. If you tell him you want good air movement with a flat response he can build something to suit your needs. He is quick too as long as you do rush status, less than a week from start to finish IME.