PSpice

Spice is a free electronic circuit simulator which is owned by the public domain. This page looks at some applications of PSpice including Loudspeaker filter design.

But first you'll need a copy of PSpice. You can download version 6 from ftp.engr.unl.edu/pub/eeshop/ and download wnspi60a.zip, wnspi60b.zip and wnspi60c.zip.

I recommend this one because it is tried and tested, and I know it works. There are several newer versions you could try.

First Order 3kHz Crossover

The program to simulate a 3kHz first order crossover is shown below. (See also Loudspeaker Design.)

3kHz First Order Crossover
vin 1 0 ac 1
r1 1 0 8
c1 1 2 10u
r2 2 0 8
.ac dec 10 20 20k
.plot ac vdb(2) vp(2)
.probe
.op
.end

OK, Here's a brief description of what everything means:

vin 1 0 ac 1  means an AC signal of amplitude 1V connected between nodes 1 and 0.
r1 1 0 8  is a resistor of 8 ohms connected between nodes 1 and 0 to simulate the load of the bass driver.
c1 1 2 10u  is a capacitor of 10uF connected between nodes 1 and 2.
r2 2 0 8  is a resistor of 8 ohms connected between nodes 2 and 0 simulating the load of the tweeter.
.ac dec 10 20 20k  means do an AC analysis from 20Hz to 20kHz with a log scale.
.plot ac vdb(2) vp(2)  means plot a graph of voltage and phase at node 2 relative to the input signal.
.probe  means output a file for the probe graphing program.

The other bits are just required for correct program operation.

The graph below shows the output from Probe:

As you can see, the curve starts flattening out at about 3kHz.

Second Order 3kHz Crossover

Now for a second order crossover. Again, I haven't included the components for a low pass filter for the bass driver.

3kHz Second Order Crossover
vin 1 0 ac 1
c1 1 2 6.7u
r2 2 0 8
l1 2 0 0.42m
.ac dec 10 20 20k
.plot ac vdb(2) vp(2)
.probe
.op
.end

See my spreadsheet for an explanation of component values.

The graph below shows the result with a 2nd order filter. The scale is identical to that before. The curve is much steeper, but does peak above the original signal amplitude which is not so desirable.

The simulations could be made more accurate by also taking into account the inductance of the drivers and putting this into the circuit too. The data sheet for the loudspeaker should provide this information.