Ouput Impedance Calculation and circuit adaptation for Class D Amplifier

[elefurtronik]

Hello,
I am trying to create a class D audio amplifier. I have an input audio signal between 174Hz-494Hz.
I found a schematic on the internet and I would like to adapt this circuit to my usage. I have an 8 . speaker.
I will put an LC filter to the output of the half-bridge rectifier. I found the website below to calculate LC values. However, I need the INPUT impedance.
How can I calculate the input impedance?

https://util01.industrial.panasonic.com/ww/utilities/ds/lc-sim/

[wasedadoc]

1.  There is no half bridge rectifer.

2.  The output impedance is close to zero.  Just use that value.

3.  The mean output voltage is half of the supply.  You will need a dc blocking capacitor between output and speaker.

[elefurtronik]

1.  There is no half-bridge rectifier.
How can I call this half bridge circuit?
2.  The output impedance is close to zero.  Just use that value.
Thanks.
3.  The mean output voltage is half of the supply.  You will need a dc blocking capacitor between the output and the speaker.
I was thinking to use LC Low-Pass Filter. Where should I put this DC-blocking capacitor? Between the ground a speaker?

Please find my answers in the quote.

[wasedadoc]

To me it is just a push-pull output.  I can understand how it looks like one half of a H-bridge.  It was your inclusion of "rectifier" that I disputed.

The capacitor need to be in series with the speaker.  Doesn't really matter which end of it.

[elefurtronik]

To me it is just a push-pull output.  I can understand how it looks like one half of a H-bridge.  It was your inclusion of "rectifier" that I disputed.

The capacitor need to be in series with the speaker.  Doesn't really matter which end of it.

How can I calculate this capacitor value in theory according to this schematic?

[wasedadoc]

Same as you would for any audio amplifier.  The C and speaker are a high pass filter which needs to be adequate for the lowest audio frequency you want.  (NOT the PWM frequency.)