http://www.mogami.com/e/cad/coil-01.html
http://www.emclab.umr.edu/new-induct/index.html
A spreadsheet approach to crossover design.
http://www.wssh.net/~wattsup/audio/formulas.zip
By Jeffrey D. Taft, PhD. Java applets for designing several types of FIR and IIR filters, including low-pass, bandpass, high-pass, notch, comb, Hilbert transform, and more. Includes interactive frequency and phase plots. Only problem is that it is difficu
http://www.nauticom.com/www/jdtaft/
Line Interference Analysis. EMI Suppression Filter Modelling. Feedthrough Filter Modelling.
http://www.westbay.ndirect.co.uk/westbay3.htm
allows the design of low-pass filters up to an 8th order filter with Chebyshev, Bessel or Butterworth responses from frequencies of 0.1 Hz to 10 MHz.
http://www.wssh.net/~wattsup/audio/flb1039.zip
Software solutions for passive, active, Tx line, IIR, and FIR filter design, synthesis, and analysis.
http://www.filter-solutions.com
Read this article on lowpass Butterworth filter design and change the values of the example to your own design specs. The example changes to show your design. By the time you finish reading the article, you have also designed your filter - complete with a
http://www.bessernet.com/articles/lowpfilt/bwfiltstep00.html