I would like to make an adjustable low pass filter for my subs. Ideally I would like to control the slope as well. Ideally I would like to allow the user adjust it between 40 to 80 cycles at a min...perfect case scenario allows 3and 4 octave slopes or more as well. Does this have to be done with opamps or is there some variable inductors and variable caps that would allow this? I image an opamp circuit would be the most transparent and allow adding a graphic screen as a display as well?
Any help is great.
Any help is great.
Operational transconductant amps? I actually just sold some studio grade filter banks and meant to check out the circuit but never got around to. I don't mind having multiple pots and I do not want to use DEP. I'm adding an extended low frequency circuit to it as well to Get deep infrasonic bass. I think 2 pots should be good, one for the cross over and one for the slope. Anything more may be confusing. Do you know of any topologies that I should look at or circuits to study?
Yes, those are the ones. For example NE5517.
Assuming you've only a mono sub then a dual gang pot to control the turnover frequency is reasonable. I can't quite see how to vary the slope with a pot though as different slopes need different topologies.
Decide what you want to achieve first then look up Sallen-Key filters. Or perhaps tone controls.
Well the xo point seems easy enough. If I have to settle w a 4 octave slope then I guess it is what it is. I have a Rane mixer where in the eq a toggle switch kills that whole frequency - I mean it's nonexistent with a kill switch and imagine it is steeper then 4 octaves. So even if a 4 octave slope is default with a kill switch toggle is used it would be almost perfect but I would like to implement a little more range of control if possible
I assume your subs are not in the same box as the other drivers but can be located to what tests-out as the most favourable location(s) in your room.
If the sub(s) are scattered, you need very sharp slopes or else you will be emitting notes (say, 180 Hz) with your sub that will distort the spatial image. A DSP will let you choose those sharp slopes and can be different in slope and freq for the sub and for the woofer/midrange, no kidding.
But silly to hard-wire ahead of time. You aren't seeing how your speakers are working in the room until they are set up in the room and you run REW. Then you can test different parameters and set things by mic. Then you can fine-tune by ear.
B.
If the sub(s) are scattered, you need very sharp slopes or else you will be emitting notes (say, 180 Hz) with your sub that will distort the spatial image. A DSP will let you choose those sharp slopes and can be different in slope and freq for the sub and for the woofer/midrange, no kidding.
But silly to hard-wire ahead of time. You aren't seeing how your speakers are working in the room until they are set up in the room and you run REW. Then you can test different parameters and set things by mic. Then you can fine-tune by ear.
B.
Don't know, if i got the point, but to chance the cut-off-frequency you need a 2way-pot like in the first pic. chancing the slope with the same ops? the second and third pic shows a 12db and a 24db 1000hz-filter...you have to use more switches and difficulties than useful. it's easier to built 2 crossovers with one switch...
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Switches are an option. I know I will need a steep slope - ideally greater then a 4th order. 3 way toggle between 4, 5 and 6 octaves would probably be pretty good or 4, 5 and kill is an option. Something like a q isolator for pro audio applications. I want to stay all analog. I figure most people would run the rca out from the low frequency out on a receiver for home theater applications which would have DSP anyway that would control the crossover. I also never really got to AB DSP crossing vs analog crossing in the same rig either so perhaps my preference for analog is not warranted. If I am not mistaken, people have done filters and xos w the raspberry pis? I have some good DSP chips here but I haven't had time to even consider touching them or learning to program them yet.
why so steep? "normal" is a 2nd grade filter at 80hz...high grade analogue filters struggle with complexity, noise and bad group-delays. dsp are in a better position to handle this...
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