Well, I have had avery good experiences with the B&C products and some not so good ones with most others. You can count on their data sheets being correct. With most companies data sheets are targets, which are only sometimes hit with any accuracy. I also buy enough that I get a good deal on them and they are already a good deal.

But remember that I am using bandpass designs. The bandpass design is ideal for subs because the fs of the driver (in its rear box) is at the center of the passband - not at the lower edge. Thus the fs of the driver is not a big issue, but box size can be. Hence the big box for my 25 - 50 Hz. sub.

I can't figure out why so few subs are bandpass - it seems ideal to me and the ones that I have made work very well when compared to the ones that I purchased - which were not bandpass.

I think that you also asked about the lever.

Think of it as a passive radiator with gain. The gain is the ratio of radiating to driven areas. Two to one is typical, resulting in about 6 dB of increased output from a given driver.

Wish someone actually made levels as I'd certainly use those if they were available.