BFD to pull double duty as crossover???

[O_ROD]

Hey guys, I just replaced my subwoofer plate amp for a QSC MX-700 pro audio amplifier. My Shiva will now see over 700 watts! But, unfortunately this amp does not have a low pass xover and my receivers low pass is a joke (does it even work?) I'm going to try using my BFD pro as a low pass. Has anyone else done this, is there any ill effects? I'd like to basically kill all frequencies above 90Hz going to my sub. If you guys have any tips or tricks on this please share. My amp is in the mail and im trying to get this fixed up for it's arrival!

Thanks a bunch!

[Otto]

Hi O_ROD,

Unfortunately, the BFD doesn't have an simple HPF or LPF built in, but I think you may still be able to approximate one. This will require that you have at least a few filters left to play with.

I would probably start with a cutoff slope of 24 dB per octave. That means that if your cutoff frequency is 90 Hz, that at 180 Hz, your signal is cut by 24 dB. Make a house curve that fits that description. Creation of house curves is discussed in various places around this Home Theater Shack.

Load the house curve into REW and let it do its thing. If the results are not satisfactory (i.e., your cutoff doesn't get deep enough), you may have to do some tweaking by hand. If you are out of filters, you may be able to play with some of the ones that REW has assigned > 90 Hz. If you have extra filters, engage them in that >90 Hz area. I would probably start by placing your cut at 180 Hz with a medium bandwidth. Then, expand the bandwidth as needed to start to affect the lower frequencies.

That's where I'd start. Perhaps someone else has actually implemented it like this, and they may be able to give more insight.

[Wayne A. Pflughaupt]

Your best bet would be to get a cheap pro audio crossover, like the Behringer CX2310. You can mail order it for less than $100. Better yet, eBay one. I’ll bet you can find them for about $50-60.

Regards,
Wayne