Low Pass Speaker Crossover Filter Schematic
Lowpass Filter		 To determine the crossover frequency a certain amount of inductance will give you, use the formula:

RL/(6.283 x L) = F

Explanation of Terms
RL - is the impedance of the load (speaker) you will be using.
L - is the inductance value (in Henries) - to convert to Henries divide the value shown on the inductor in mH by one thousand.
F - is the crossover frequency you will get.

 

by frequency
Crossover Frequency (Hertz) inductance mH (milliHenry)
8 Ohms 4 Ohms 2 Ohms
80 15.92 7.96 3.98
100 12.73 6.37 3.18
120 10.61 5.31 2.65
150 8.49 4.24 2.12
200 6.37 3.18 1.59
280 4.55 2.24 1.14
400 3.18 1.59 0.8
600 2.12 1.06 0.53
800 1.59 0.8 0.4
1000 1.27 0.64 0.32
1200 1.06 0.53 0.27
2000 0.64 0.32 0.16
4000 0.32 0.16 0.08
5000 0.25 0.13 0.06
6000 0.21 0.11 0.05
8000 0.16 0.08 0.04
10000 0.13 0.06 0.03
12000 0.11 0.05 0.03

 

by inductor
inductance mH (milliHenry) Crossover Frequency (Hertz) approximate
8 Ohms 4 Ohms 2 Ohms
0.1 12733 6366 3183
0.2 6366 3183 1592
0.27 4716 2358 1179
0.3 4244 2122 1061
0.33 3858 1929 965
0.4 3183 1592 796
0.5 2547 1273 637
0.6 2122 1061 531
0.7 1819 909 455
0.8 1592 796 398
0.9 1415 707 354
1.0 1273 637 318
1.2 1061 531 265
1.8 707 354 177
2.0 637 318 159
2.2 579 289 145
2.7 472 236 118
3.0 424 212 106
3.3 386 193 96
4.0 318 159 80
4.7 271 135 68
5.0 255 127 64
6.0 212 106 53
7.0 182 91 45
8.0 159 80 40
9.0 141 71 35
10.0 127 64 32
12.0 106 53 27
15.0 85 42 21