LT Spice crossover filter simulation problems

I'm trying to create a simulation of a speaker system with woofer, tweeter, and midrange speakers.

The total Vout (output voltage of woofer+output voltage of tweeter+output voltage of midrange) should be 0dB in the passband and -6dB at the crossover frequencies (100Hz and 2500Hz).

Why is my total output graph showing it dip down to -40db at the cross over frequencies?

• Think about phase. If you just want to know the power delivered, you should probably measure abs(V(n002))^2 + abs(V(n004))^2 + abs(V(n005))^2rather than the phasor sum of three unconnected voltages. – The Photon Apr 29 '17 at 19:24
• Also, if you label your nodes with useful names, it will be easier to understand what your graph is graphing. – The Photon Apr 29 '17 at 19:28
• Note that in the majority of cases, loudspeakers do not act just like resistors. – PlasmaHH Apr 29 '17 at 20:38

Plot the phases for the three voltages and you'll find that they're out of phase at the crossover points:

The problem here probably is the phase of the midrange driver. Focus on that. You should also take into account the actual phase of each of the three drivers (which are just 8 Ohm resistive loads in your simulation).

Here is the result assuming a simple phase reversal (180-deg) in the midrange driver:

And here you have the total power delivered to the 3 loads, as suggested by The Photon, where you can see the approx -6dB power down at the crossover frequencies:

Also note that you may be looking after two things that are quite different from each other:

1. If you want to predict the frequency response that you would measure with a microphone, you need to factor in the response of the drivers (you just can't add them together), their physical positioning, etc.

2. If you want to predict the frequency response of the overall load seen by the amplifier's output, then you need to replace the 8 Ohm loads by the equivalent impedance of each driver.

1 and 2 can be very different things to simulate and measure, and will be highly dependent on the characteristics of each driver.

• The values that I used for this circuit are correct so I'm not sure how I would fix their phases without changing their values – python_ Apr 29 '17 at 20:06
• Where did you get those values from? – Enric Blanco Apr 29 '17 at 20:11
• Phase can probably safely be ignored, considering this is just a crossover filter. – Hearth Apr 29 '17 at 20:28
• Phase can only be ignored if there are means to compensate it in the drivers. At the end of the day, you want the frequency response of the 3-way system to be as flat as possible. It looks like the example from the OP already accounts for a phase reversal in the midrange driver. – Enric Blanco Apr 29 '17 at 20:44