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You should be designing an active filter. Filterpro from TI can be used to design those. Passive higher order RC filters have very poor characteristics and are usually not used.
Don't quite understand your question about the corner frequency. The corner frequency is usually the -3dB point on the filter roll-off, independent of the filter order.
The disadvantage of a 3rd order filter is that it's more complex than a 1st order filter.
The circuit topology looks ok. You are running the opamps on + and - split power supplies, right?
If not, you will have to bias the inputs so that they are approx. half-way between the positive supply and ground
Sorry If This is a bit of topic,
My question is about dB:
I do know both voltage and power formulas explained by dB, But please tell me how to translate an attenuation of 15 or 20 dB for instance? an example would be very good to help me to understand this magically tool?!
Thanks
An LM386 is not an opamp. It is a power amplifier complete circuit. It has built-in biasing and built-in negative feedback so it will not work in your opamp filter circuit.
An OPA2132 is an opamp, not a power amp. It cannot drive a speaker.Ok, thanks i replaced them with a opa2132 will that work? because i'm still having a gain problem but the filter works if i give it lots of current but then my speaker distorts.
An OPA2132 is an opamp, not a power amp. It cannot drive a speaker.
Your opamps have no input bias voltage, no low impedance signal source and no power supply.
The filter circuit has a gain of 1 at very low frequencies.
If a voltage is said to be -15db, that means its ratio against the reference voltage is
-15db = 20 log(V2/V1)
-15/20 = log(V2/V1)
V2/V1 = 10^(-0.75) = 1/(10^0.75) = 1/5.6234132 = 0.1778279
So that means an attenuation of 0.177