Frequency Dependant voltage divider and all-pass filter

[Robin UK]

Hi,

Firstly, this is my first post, and i don't know if this is in the right section.

I'm having to design a frequency dependant voltage divider and all-pass filter for some speaker electronics im building (try to build an improved bessel array).

The voltage divider needs to half the gain going to a channel at about 2kHz (haven't got my design with me so can't remember exact frequency at the moment). I assume this will be a gradual change.

The all-pass filter needs to invert the phase of a different channel at the same frequency (again i assume this will be gradual).

Any information about where to look for designs/research this would be greatly appreciated (have done a fair bit of electronics building and repair before, but little-to-no design).

Thanks,

Robin

 

[MikeMl]

At what voltage/power level?

 

[Robin UK]

I guess line level, as the signal from this would be feeding a small 30Watt modular amp, and would be coming in from a mixing desk.

Hope that helps,

Robin

 

[Sceadwian]

The inverting all-pass filter you want can be realized with a simple opamp.
The variable frequency cut filter you want sounds like a simple 2khz lowpass filter, again this can easily be implemented with an opamp. It sounds like you're trying to produce a simple crossover to feed a bridge amplifier, simply look for low frequency crossover circut on Google, you should find hordes of information. Is any of this close to what you're asking for?

 

[Robin UK]

I'm not quite sure. Is it possible to tune the frequency at which the allpass filter will reach "-1" (and also the frequency at which it begins to change phase) using an op amp? Equally, i'd assumed that a crossover circuit would continually decrease in gain, rather than settling at 1/2 gain. If i'm wrong, this sounds great. Could you recommend any books or websites for researching this?

Sorry to seem slightly clueless.

Thanks,

Robin

(Also, to clarify, the two components would be feeding separate amplifiers going to separate speaker drivers)

 

[Sceadwian]

I didn't quiet understand that you wanted the phase to shift with frequency, thought you just wanted basic inversion. I'm sure you can do a 3db cutoff lowpass that doesn't continue to lose gain with higher frequencies but I'm not sure how to go about it or what it'd be called. I can make simple filters with opamps never had the need or desire to do anything more advanced. Have you searched on Google for Bessel filter? You may find more useful information. Give it another day or so, there are other users here that know more about opamp filter circuits and audio in general that will end up posting more than likely. It's the weekend though.

 

[Roff]

If I understand correctly, this should do what you want. If you want to use a single supply, the circuit can be modified.

 

[Robin UK]

Thank's Roff, that seems to be pretty much it. I've PM'd you with a couple of questions regarding them.

Thanks for the quick and informative response.

Robin

 

[Roff]

As per your PM request (-3dB shelf on filter), here is the .ASC file, along with modified schematic and Bode plot.