Question: Sub with Fs 54, but response remains above 95dB down to 27: How can I best build

@hsbrock , the modeled response that I described up-thead checks out.  It assumes 3 dB from boundary reinforcement at 40 Hz, and 6 dB from boundary reinforcement at 20 Hz, and a lowpass filter frequency no higher than 80 Hz.  It also assumes the T/S parameters are correct, of course. 

I suggest two 4" diameter Precision Ports, each 14" long including the flares.  And if you don't have an amplifier in mind, I use the Dayton Audio SA-1000 in my commercial subwoofer system.  

Best of luck with your project.

Duke

Thank you Duke @audiokinesis This is really encouraging. I've got the space to do 7 cu.ft., corner-horns, and to be able to get those results with an Fs 54 gives me hope. I was afraid my speakers would be a bust. Is there a modeling software you'd recommend for me? Again, thanks for taking the time to help me with this. I'm discovering the guys on here are great. 

@hsbrock , I used Bassbox Pro by Harris Technologies.  I have a couple of other progams but they are no longer available. 

Thanks, Duke @audiokinesis  I'll check it out.