Dr. Azah
12-21-2015, 01:11 AM
I was picking up some old items for a friend out of storage at another guy's house when I spotted something in a pile of stuff in his back yard. Surrounded by an old mower, some rusty lawn chairs and stack of soggy cardboard boxes was something that reminded me of an old set of Electro Voice corner speakers I used to have - only bigger. The wood was all warped and delaminated plywood veneers. Then I spotted it… the vintage JBL crossover mounted on the back. Then I looked at the other side and saw the tattered and faded grill cloth. I tried to peal it back a bit to see what was behind it and spotted the large aluminum cone. JACKPOT! whatever this was it had what looked like a D130!
I asked the guy if he was keeping it or was willing to sell it. He thought about it and said I could just have it. I took it home, looked a little closer and saw it also had a very oxidized bullet tweeter. I was sure the speaker was toast after sitting outside in the rain for probably more than a year. The wood was destroyed and smelled like mildew, the inside was full of cobwebs and layers of grime. I plugged it into an old Yamaha tuner and this speaker actually worked! It sounded pretty good too.
I did a little research and figured out it was a C34 (no potato masher) with the 030 option - D130 and 075 with the N2400. Some examples on eBay were going for 100s, if not 1000s, of dollars. Of course this one was a mess and it was only one, not a pair.
I love to tinker with building things and have lots of cabinet and woodworking tools. I'm really into music equipment, and I LOVE LOVE LOVE JBL gear. The first thing I did was open up the cross over. The date on it was 1962 and there were no resistors inside. From other postings about crossovers, it seems JBL added them later to better protect the tweeter.
Many people say that the caps should be replaced since they don't last forever. In following the basic crossover design tools, I found that JBL seems to have made up their own rules. The high side is first order (6dB slope), while the low side is 2nd order (12 dB slope). I would have expected the opposite since the 2500 cps crossover point is a little low for the 075. However, the 6 microfarad caps don't really add up to 2.5kHz. it's more like 3.3kHz on the tweeter and the same cap with a coil would be closer to 2.3kHz for the woofer. This seems like it would leave a big gap of frequencies between hi end and low end.
Is there anyone on the forum that can explain this better for me?
btw, the next project is to dissect the dilapidated cabinet and clone a new pair out of nice walnut veneer plywood.
thanks for reading.
I asked the guy if he was keeping it or was willing to sell it. He thought about it and said I could just have it. I took it home, looked a little closer and saw it also had a very oxidized bullet tweeter. I was sure the speaker was toast after sitting outside in the rain for probably more than a year. The wood was destroyed and smelled like mildew, the inside was full of cobwebs and layers of grime. I plugged it into an old Yamaha tuner and this speaker actually worked! It sounded pretty good too.
I did a little research and figured out it was a C34 (no potato masher) with the 030 option - D130 and 075 with the N2400. Some examples on eBay were going for 100s, if not 1000s, of dollars. Of course this one was a mess and it was only one, not a pair.
I love to tinker with building things and have lots of cabinet and woodworking tools. I'm really into music equipment, and I LOVE LOVE LOVE JBL gear. The first thing I did was open up the cross over. The date on it was 1962 and there were no resistors inside. From other postings about crossovers, it seems JBL added them later to better protect the tweeter.
Many people say that the caps should be replaced since they don't last forever. In following the basic crossover design tools, I found that JBL seems to have made up their own rules. The high side is first order (6dB slope), while the low side is 2nd order (12 dB slope). I would have expected the opposite since the 2500 cps crossover point is a little low for the 075. However, the 6 microfarad caps don't really add up to 2.5kHz. it's more like 3.3kHz on the tweeter and the same cap with a coil would be closer to 2.3kHz for the woofer. This seems like it would leave a big gap of frequencies between hi end and low end.
Is there anyone on the forum that can explain this better for me?
btw, the next project is to dissect the dilapidated cabinet and clone a new pair out of nice walnut veneer plywood.
thanks for reading.