Crossover would serve its usual purpose. One amp drives the subwoofer. Other amps drive the rest of the speakers. Its just like the old passive crossovers, except this is active, and comes before the amp.
This is how its generally been done with subwoofers for a long time now.
I just want to hear ideas about active filter topologies.
The typical sub plate amp will have a 12db/octave variable active low pass filter. Usually this works well enough. I've seen a few that employ 24db/octave slopes but they're a little hard to find. There seems to be a lot of attention paid to FIR crossovers lately. Mostly, I think, because there's now software available for PCs to emulate a FIR crossover. There's also a very expensive external component being sold using this technology claiming the ability to rolloff at 100db/octave. The problem I have with it is you're taking an analog signal, digitizing it, processing it and converting it back to analog again. Excellent for pro sound however. In the realm of active crossovers, I tend to prefer 4th order LR filters.
Timn8ter, thank you and please go on. A FIR filter is obviously a digital filter. Please tell us more. In my mind I was envisioning and analog active filter.
I'm interested to know people's ideas. I'm also interested to know how most of the stuff sold on the market actually works.
Most active filter use Sallen-Key circuits. So you get two orders per op-amp.
This still means you have to have one for the low pass part, and one for the high pass part.
I'm wondering if anyone is doing it with just one type of filter, and then some subtraction?
This would give you flat summation, regardless of component tollerances.
I'm not an EE but what I know is Finite Impulse Response filtering is digital signal processing. There are self-contained components you hook up just like any other audio component and there is computer software you can run on your PC. PC based FIR filters allow the user to create multiple filter solutions. The art to doing this properly is knowing which window function to apply. The choice of window selection will depend on how steep you want your rolloff to be. The steeper the rolloff the more processing that is required. You want to use the least amount of processing to achieve your desired response. Essentially, you input your signal, perform A/D conversion, manipulate the signal in the FIR program, perform D/A conversion then send it to your amp. Yes, Sallen-Key is the standard. I'm not aware of anyone using subtraction although I know it's been talked about. It's as you say, one op amp will produce a 2nd order rolloff, two will produce a 4th order rolloff.
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Some say that some workmen at the house decided to mess around with him some, and started holding him under the water. He drowned, and these workers fled and denyed any knowledge of it.
Brian, I go to DIY, and find it quite good, although the sign in seems to be a bit of an issue. Lots of posters here are also on DIY, and regularly talk about things that are regularly above my head. Learn, learn,learn...