Originally Posted by
Horn Fanatic
Hi RS -
First order of business. The K140 is a bass instrument speaker, and it makes for a marginal horn loader. The 2225 also, is not a decent horn loader. I highly recommend not using either. Even though JBL offered the rear loaded horns with the 2205, with an EBP of 136 it also wasn't the best choice. With an EBP of 190 you could do quite nicely with the E130, and the 2227 would work quite well also, if you can find them.
But what ever you chose to use, you must cross your woofers over. You can either use a compression driver with a phenolic diaphragm to cross over between 300 & 500Hz, or use a metal diaphragm crossed over at 500Hz. Since you're using the Bi-Radial horn you shouldn't need a tweeter with a large format metal diaphragm unless you like the sizzle, but you'll definitely need one with the phenolic. The next thing to check is the lowest recommended cross over point for the Bi-Radial horn you're using. I'm unfamiliar with it's parameters.
The driver that rightfully belongs in the 4520 & 4530, is the 2220A or B, depending on the load impedance you desire. The 130A or B will operate in identical manner, as it shares identical T/S parameters as the 2220. Put a 140 in a C34 or a C40, and see what you get. The ultimate choice of driver would be the 150-4C, but for most mortals the cost is out of reach. The 150 was the original driver that was loaded in the Westrex and Ampex theater horns, the Paragon, the Hartsfield, and offered in the C34. As we all know, the 150 & 375 were designed for Westrex.
One parameter I have yet to see addressed on this forum other than what I have posted, is the Efficiency Bandwidth Product, fs/Qes. Richard Small saw fit to write a paper on it. The EBP for the K140 is 136.3, for the 2225J it's 129. The EBP for the 2220J & 130B is 205.5. The lower the number, the larger the chamber that is required. The chambers for the 4520 & 4530 are too small for the 140, 2205, and 2225 to acoustically operate properly. The throat area and chamber volume are ideal for the 2220, but not so for the other drivers. The 2220 works quite well in a Klipschorn also. There are folks who like to use the E145 as a horn driver, but with an EBP of 134 I wouldn't recommend that one either. I also think the fs is far too low for use in the rear loaded horns. For those who think the Paragon sounds awesome with the LE15, have never heard one with the 150-4C. The difference is like night and day. In the day, the replacement driver for the Paragon should have been the 130B or 2220B.
I read a comment here about the 4520 wanting a higher fs, and I'm curious how the author of that comment arrived at his conclusion. But he is correct with his assertion that horns operate better with drivers with low Q's, rear and front loaded, makes little difference if the horn is designed properly. It's the throat area that determines the efficiency of the system. The throat area and chamber volume are interrelated. To change one, so change the other.
The choice between the 2441 and 2445 diaphragms is simple. Do you like the sound of aluminum diaphragms, or titanium? My preference is aluminum, because to me, titanium diaphragms sound like broken glass. Radian is offering Beryllium diaphragms now, but I'm unsure if they're in production of diaphragms for other brand drivers.
I hope I have been of help,
H.F.
BTW - My dream system would consist of a pair of reproduction C55's loaded with the 2220, a pair of 2395's with Radian Beryllium drivers, and a pair of 2405's, driven by an all tube front end.