| Parallel Notch Filter Question [message #15023] |
Tue, 31 May 2005 09:15  |
FredT
Messages: 704
Registered: May 2009
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Illuminati (1st Degree) |
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I was looking at one of the many parallel notch filter designer sites on the internet and I have a question. These sites require you to enter a center frequency (F), a lower frequency where the peak is up 3dB (F1), and the higher frequency where the peak is up 3dB (F2). You enter these numbers and the program computes the required C, R, and L values for a notch filter to tame the peak. For example, a 5khz peak with a 2.5khz F1 value and an 8khz F2 value causes the program to recommend a 6uF cap, a 4.8 ohm resistor, and a 0.15mH inductor. Now for the question: Is this computation done with the assumption that the speaker load is eight ohms or is a notch filter uneffected by the speaker impedance. Would the above notch filter work with a four of sixteen ohm speaker, or would those impedances require different C, R, and L values?
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| Re: Parallel Notch Filter Question [message #15029 is a reply to message #15023] |
Mon, 06 June 2005 12:24  |
Earl Geddes
Messages: 220
Registered: May 2009
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Master |
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All simple filter applications like this assume a very low input impedance and a very high output impedance when compared to the impedances of the circuit,. This is true no matter what type of filter it is. When the input and output do not abide by these rules - which is almost all of the time - then the loads become part of the filter and it must be analyzed in a more complex manner.
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