crossovers

[caz]

whats it mean when a crossover is 2nd order or 4th order or whatever. i saw recomenations fo some crossovers on speakers i was looking at. it said 2nd order 2500herts highpass. do i need something special or can i just use the crossover on my linear power dspq50. i can reach a 5k highpass with it, and it says its a 12db ocatve slope.

what the hell does 12db octave even mean lol

[sreten]

6dB/octave = 1st order, for a tweeter a series capacitor
12dB/octave = 2nd order, for a T series cap + parallel inductor
18dB/octave = 3rd order, s cap, p inductor, s cap.
24db/octave = 4th order, s cap, p L, s cap, p L.

sreten.

[BobEllis]

And an octave change is a doubling or halving of frequency - eg. 100 Hz is an ocatve below 200 Hz and an octave above 50 Hz.

So a 24 db/octave 1000 Hz filter will pass 24 db less signal at 2,000 Hz than it does in the flat region below 1,000 Hz. at 4,000 Hz the signal passed is 24 db lower still.

This is just an approximation because real filters start to roll of gradually a little before their designated cutoff frequency and take a little while to reach the final slope. the "corner" of the filter is not sharp, but approximating it this way should let you get a basic understanding of the concept.

Of course, the devil is in the details and crossover behavior in the overlap region as affected by driver response is why standard crossover filters rarely work well.

The overlap between drivers is much more than you'd think even with steep slopes. I turned off the mid-bass amp of my actively crossed over system first when shutting down, so just the sub and tweeeter were playing. Crossovers are nominally 4th order at 60 and 2400 Hz. I was surprised how much music was still there. Male voices were still intelligible through the tweeter.

Bob