Low-pass LC butterworth filter cutoff frequency question

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A 5-pole low-pass Butterworth filter is being designed with a target cutoff frequency of approximately 50 Hz, using a "T" configuration due to a source impedance of ~1 Ohm and a load impedance of ~50 Ohm. The designer initially calculated component values from "The Art of Electronics" but opted for more readily available components, resulting in slight deviations from the original values. The new component values are L1=250 mH, C2=100 uF, L3=220 mH, C4=56 uF, and L5=50 mH. The designer seeks to determine the actual cutoff frequency with these new values and is advised to use LTSPICE for simulation before physical construction. Accurate simulation is emphasized as a crucial step in the design process.
mehrlin
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I am designing a 5-pole low-pass butterworth filter to have a cutoff frequency of ~50 Hz. It has a source impedance of ~1 Ohm, and a load impedance of ~50 Ohm (The load impedance can be changed around if that will help later). Because of these, I am using the "T" configuration. I used the table in the back of The Art of Electronics by Horowitz and Hill, to determine the following values:

L1=245.9 mH
C2= 107.9 uF
L3 = 220 mH
C4 = 56.9 uF
L5 = 49.18 mH

The problem, however, is that I am unable/unwilling to order custom parts with these exact values. Thus, I have chosen parts with the following values:

L1=250 mH
C2 = 100 uF
L3 = 220 mH
C4 = 56 uF
L5 = 50 mH

My question is now what will be the actual cutoff frequency for these values? I have thus far been unable to track down an equation that will help me find this.
 
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Download LTSPICE from Linear Technolgy (linear.com) and simulate it. You should always simulate something before you build it, anyway.
 

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