BillFitzmaurice.info

Thought I'd share this.

Built a pair of Simplex 12 wedges loaded with Eminence Beta 12 CX + ASD 1001 drivers. Ran some response curve tests and holy cow, these two cabs came out effectively identical. Pretty flat to down to about 50hz. They sound really good too. Definitely going to make good vocal wedges. I can also see using these as full range mains in a coffee shop gig or something like that.

This is flat, no EQ. I did have to reverse polarity on the HF drivers to get the response smoothed out. I'm curious why. Is it due to some phase shift in the crossover or ??? It doesn't bother me as long as they sound good, just curious.

Dave

Correction: I used KL3012 CX-8 drivers, not Beta 12 CX.

A dip around the crossover frequency can be caused by the crossover, and it can be caused by the positions of the driver diaphragms, as phase shift is cause by both electrical and physical leading and lagging. The polarity testing procedure is in the plans because you can't predict the result with every crossover and high frequency driver combination.

Thanks Bill. That makes sense. With the HF driver mounted on the back of the LF driver that puts the HF diaphragm a few inches (or 1/2 wavelength) behind the LF diaphragm right around 2K. Right where the response was a bit wonky. That could have also been compounded by crossover phase shift if the two were aligned. I didn't notice any of this with the OT12s I built. Just the way they came out I guess. As you say, not really predictable and an easy thing to test. Sure nice how just reversing that smoothed out the response. There's a little rise at 2K now but nothing a bit of EQ won't deal with.

The crossover adds 90 degrees of shift for the woofer, 360 for the tweeter, for a total of 90 degrees, which in and of itself isn't a problem. But if the driver offset adds another 90 degrees or close to it you'll get a dip.