I am building a class D amplifier and need to design passive low-pass filters for H-bridge with cut off frequencies at about 400 Hz. However, I am unsure about few things, this is the simplified equivalent circuit:
Speaker values were measured using an RLC meter set to 100 Hz.
Lets say that the signal is coming into the L1 coil. Should I calculate the cut-off frequency only for L1, C1 pair? If L2 is grounded, do L2 and C2 have a noticeable effect on L1, C1 filter? How can I calculate it then?
I often see a capacitor in parallel with speaker what exactly is its purpose? I am thinking it is to lower reactive power of the speaker, right? To what \$cos\phi\$ should I lower it, and should I use middle range values for voltage and current?