Link to System #3
My wife's church has an organ with a very large subwoofer mounted in an alcove behind and above the choir. Having the subwoofer located in this position makes it impossible mic the choir. There is just too much organ bleed into the choir mics. The Pastor asked me what we could do about it. We discussed moving the existing subwoofer to an alcove located on the other side of the church. This turned out to not be practical as the existing subwoofer is an EV 30" driver mounted in a cabinet that weighs around 500lbs.
So, I set about designing a new subwoofer that had at least as much output as the 30" EV did. I had a hard time finding good data on the EV. I had some basic T/S data on it, but not detailed to do a good large signal analysis. I eventually contacted Don Keele, who was able to connect me with another exEV employee that had all of the data. The EV driver has a lot of midband sensitivity and decent Vd due to the very large cone area, but doesn't have a very deep native bass response. We ended up using eight of the npt-11-083-2 woofers in a 370l (13 cu ft) sealed enclosure. We built two enclosures for a total of 16 woofers. This ended up with about 3dB more sensitivity than the 30" EV plus it had an f3 of about 28Hz. It only needed 6dB of eq to make it flat down to 20Hz. Below 40Hz, it has a 10dB output advantage due to the much greater Xmax. I wanted to make absolutely sure that it had enough output at all frequencies.