jackgiff
Well-Known Member
The Hi efficiency crossover seems to be suitable for use with the B&C De250 driver mounted on a QSC HPR152F waveguide (horn) as is. I had a few dedicated hi efficiency versions designed for the JBL LE14A on hand, so used a pair of them for these tests. The LE14A likes a low pass of 900 Hz rather than the standard Xovers 1.2 KHz. The first set of FR's shows the unit with a 900 Hz low pass on the bottom. The upper is after the parts are changed to 1.5 mH and 12 microfarads to raise the low pass to standard. As Gordon predicted, the crossover becomes pretty seamless. Much nicer.
I tried increasing the HF compensation capacitor to 2.5 microfarads with no basic difference in FR between the 1.5 and 2.5 values. Trying less capacitance would not yield the desired effect (it would cut the correction), so I didn't try that.
The last picture shows the test of a B&C DE250/QSC waveguide mounted in the cabinet, along with a Selenium D220Ti mounted on the JBL 6 X 12 waveguide sitting directly above the QSC waveguide. The FR's generated were accomplished by connecting the desired combo to the same crossover with the same settings on the L-Pad. The microphone was aimed down the throat of the waveguide under test. The only difference during testing was the height of the JBL/Selenium combo was about ten inches above the B&C/QSC. The mic stand was not moved, only the angle of the microphone.
The second set of FR's shows both units at maximum setting of the L-Pad. The B&C is the top FR, and the Selenium is the bottom. The difference in output level looks to be about 1-2 dB at best. The HF compensation is virtually identical, except that the B&C falls off above 16 KHZ, while the Selenium falls off at a slower rate.
The third set of FR's is with the L-Pad set to a decent listening level. Again, the top FR is the B&C and the bottom is the Selenium. The Selenium looks to have a bit of drop in the mid range, but that could be instrumentation error or even my body positioning during the test. Both ends of the FR's are virtually identical except that the B&C has that drop off above 16 KHz.
I will etch another pair of crossover boards this afternoon to build a low efficiency set to test both combos against each other. That will be simpler than cutting most of the HF parts off the existing boards, since they are dedicated to a particular unit. RTV silicone is a great way to hold parts down, but it does make repair a nasty proposition.
I tried increasing the HF compensation capacitor to 2.5 microfarads with no basic difference in FR between the 1.5 and 2.5 values. Trying less capacitance would not yield the desired effect (it would cut the correction), so I didn't try that.
The last picture shows the test of a B&C DE250/QSC waveguide mounted in the cabinet, along with a Selenium D220Ti mounted on the JBL 6 X 12 waveguide sitting directly above the QSC waveguide. The FR's generated were accomplished by connecting the desired combo to the same crossover with the same settings on the L-Pad. The microphone was aimed down the throat of the waveguide under test. The only difference during testing was the height of the JBL/Selenium combo was about ten inches above the B&C/QSC. The mic stand was not moved, only the angle of the microphone.
The second set of FR's shows both units at maximum setting of the L-Pad. The B&C is the top FR, and the Selenium is the bottom. The difference in output level looks to be about 1-2 dB at best. The HF compensation is virtually identical, except that the B&C falls off above 16 KHZ, while the Selenium falls off at a slower rate.
The third set of FR's is with the L-Pad set to a decent listening level. Again, the top FR is the B&C and the bottom is the Selenium. The Selenium looks to have a bit of drop in the mid range, but that could be instrumentation error or even my body positioning during the test. Both ends of the FR's are virtually identical except that the B&C has that drop off above 16 KHz.
I will etch another pair of crossover boards this afternoon to build a low efficiency set to test both combos against each other. That will be simpler than cutting most of the HF parts off the existing boards, since they are dedicated to a particular unit. RTV silicone is a great way to hold parts down, but it does make repair a nasty proposition.
I was able to finish one speaker so I just hooked it up on one side with the stock CS-77A on the other side. I haven't measured anything yet, but it sounds like the mids are scooped. (Probably because I'm so used to the emphasized mids in the CS-77s.) Overall, I think it's got great potential. Can't wait to finish the other speaker tomorrow and give them a real workout!
