[Ktechlab-devel] filter problem.

[Zoltan Padrah]

 Hi,

in order to do analysis on this schematic, you need to define the
input and output impedance seen by the inputs and outputs of the
circuit. Considering that you have put there buffer-s, I assume that
the output of the buffer is practically zero, and the input is
infinity.

In order to calculate the circuit, you can take the Fourier transform
of the elements and solve those as a normal circuit. The results can
be also plotted. In this case, the circuit will look like:


        600ohm (ish)    1 / (j*w*C1)
BUFFER>--^^^^----+------||------+---------BUFFER>---O v_out_h
v_in            |              |
                |              3
                |              3 j*w*L1
                |              3
                |              |
                |              =
                |     j*w*L2
                +----nnnn------+---------BUFFER>---O v_out_low
                               |
                               |
                              ___
                              ---   1/ (j*w*C2)
                               |
                               =

where

j*j = -1 ; the imaginary number
w = 2*pi*f, the angular frequency; f is the frequency in Hz

Based on this schematic you can get the transfer functions

v_out_h / v_in
and
v_out_l / v_in

And when you have those, you can calculate the components.

Your circuit will have 40dB/decade attenuation, because it's a
second-order filter (RLC).

See more details on wikipedia:

http://en.wikipedia.org/wiki/Low-pass_filter

http://en.wikipedia.org/wiki/RLC_circuit

Hope this is useful,

  Zoltan


2012/2/21 Alan Grimes <agrimes at speakeasy.net>:
> I want a 2-output filter for an active/electronic crossover. I want the
> crossover frequency to be 2,250 ohms.
>
> I'm considering a passive filter network between three buffers.
> Inductors are to be preferred over resistors.
>
>
> The sketch I have is
>
>         600ohm (ish)    C1
> BUFFER>--^^^^----+------||------+---------BUFFER>---O
>                 |              |
>                 |              3
>                 |              3 L1
>                 |              3
>                 |              |
>                 |              =
>                 |     L2
>                 +----nnnn------+---------BUFFER>---O
>                                |
>                                |
>                               ___
>                               ---  C2
>                                |
>                                =
>
> I figure that the HPF and LPF will load down the resistor so that the
> total load will be fairly constant. I'm not sure what other interactions
> will take place though. =\ The filter sections might need some
> additional loading or how to analyze the circuit further. I usually do
> basic reactance computations but this requires a more thorough analysis.
>
> As an audiophile I'm always trying to minimize the parts count, without
> consideration of the price of individual parts.
>
> The other concern is whether the filter will roll off the tweeter
> steeply enough... It is very important that tweets aren't overloaded or
> passed too much LF, this is a fairly low crossover point (stock is about
> 2450...)
>
>
> --
> E T F
> N H E
> D E D
>
> Powers are not rights.
>
>
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