Originally Posted by
Don C
I haven't told the full story about the drivers and diaphragms here, it involves me screwing up. When I saw the horns at Speaker Exchange, I also saw the drivers, 2452H, and brand new at better than half off, looking like a bargain. I suspected that I really wanted 2451s, but looking around, none were for sale, at least not at prices that I wanted to pay. So I got the 2452s. Right after the 2452s were delivered some used 2451s showed up on ebay, prety cheap. (2451SL-16) I debated with myself for a while and then ended up buying those too.
When I got the adapter plates I knew that they would need to be modified to take both styles of driver. After imposing upon a friend who spent 45 minutes setting up a fixture to mill out the slots, this was done. We set a bit to just kiss the inside diameter of the original holes, then moved it out from center .375, making the slots long enough for a four inch circle. I was sure this was correct. I was wrong. The 2451s need a 4.5 circle, and I'm a bonehead.
So more work is needed but it has to wait.
What I did do, was this. After I listened to the uncoated 8 ohm ti diaphragms for a few hours, I removed them and borrowed the -SL diaphragms from the 51s. They fit right into the 2452s. You just have to move the terminal posts from the old diaphragms to the new ones. These are a big improvement, immediately it was obvious that something had changed for the better. I thought that I would be adjusting the levels up by 3db, to compensate for the impedance change, instead I ended up with 5db more, and they are less harsh even at that level. I'm still fooling with the settings too much though. I set the horn comp down to to 3Khz and have played with the levels endlessly. It's probably a sign that the horn levels are correct and my music selection is the problem. I also have some Truextent diaphragms that 4313B sold me. But I'm not going to install those until I get the resistor network straightened out. And those slots elongated more. And then I'll probably put them into the 2451s.