I'd like to say the port goes back about 6-8" then there's a piece of grill cloth. after that, the openings for the port feed into the main enclosure for the cabinet.
Okay, Emperor did what I would have done with the Alpha 12A.
The Alpha 12A's characteristics (T/S parameters) make it well suited for a sealed box, but not so much a ported box, however we can put it in a very low-tuned ported box and get some increased in performance over a sealed box. They've tuned the box to about 31 Hz, the fundamental of low-B, which reduces its susceptibility to fartout relative to sealed box mode.
So as we look at woofers that have higher rated power handling, that's only moving the burnout threshold of the woofer. The fartout threshold is a function of the linear excursion (x-max) of these woofers, so I've indicated how much louder they'll go before fartout.
There aren't all that many woofers with as much top end as the Alpha 12, so our choices are limited if that's a priority. Top end extension is one of the things we often trade off when we increase the thermal power handling and/or excursion capability (how loud it will go before fartout). And of course the tone will change, maybe for better, maybe for worse, so be prepared to change your tone control settings.
The Beta 12A2 will work well in that box. It's rated at 250 watts, so not a huge increase in power handling, but an improvement nonetheless. The Beta 12A2 should go about 4 dB louder before fartout, but remember you'll be heating those voice coils up hotter to get there.
The Delta 12A has as much if not more top end energy, but no more excursion than the Alpha 12A. Of course it has much higher thermal power handling, so you're less likely to burn it up. But you'll have to crank in a fair amount of low-end EQ to get back to the warmth of the Alpha 12A. (Good call, Jimmy! I bet you didn't even have to crank up your modeling program!)
If you really want to up the thermal power handling, and be able to readily demonstrate the quality of your gear to anyone who dares question it, the Delta Pro 12A is a candidate. You're probably not going to burn up a quartet of those. Unfortunately you'll have to crank in a fair amount of EQ to get the low end warmth of the original Alphas. Once again, expect to go about 4 dB louder before fartout, and this time your voice coils can take the extra power.
I like the frequency response curve of the Beta 12A2 best. The Delta 12A will probably come the closest to replicating the performance you have now assuming you crank in some EQ. If you want louder before fartout along with higher power handling, go with the Delta Pro.
