A method to combine an input device and a virtual device's signals into a single virtual input device using pipewire & pactl

sound-box

# Based on the response from user Pujianto over https://superuser.com/questions/1675877/how-to-create-a-new-pipewire-virtual-device-that-to-combines-an-real-input-and-o

# Create combined sink
pactl load-module module-null-sink media.class=Audio/Sink sink_name=my-combined-sink channel_map=stereo

# Link audio source (mic) to combined sink
## Get the mic device name with: `pw-link -o`
pw-link $NAME_OF_THE_INPUT_DEVICE  my-combined-sink:playback_FL
pw-link $NAME_OF_THE_INPUT_DEVICE  my-combined-sink:playback_FR


# Create sound-box virtual device
pactl load-module module-null-sink media.class=Audio/Sink sink_name=sound-box-sink channel_map=stereo

# Link audio sound-box virtual device to combined sink
pw-link $ID_OF_THE_SOUND_BOX_VIRTUAL_DEVICE my-combined-sink:playback_FR

# Create Virtual mic (The communication applications will use this one)
pactl load-module module-null-sink media.class=Audio/Source/Virtual sink_name=my-virtualmic channel_map=front-left,front-right

# Link sink and virtual mic
pw-link my-combined-sink:monitor_FL my-virtualmic:input_FL
pw-link my-combined-sink:monitor_FR my-virtualmic:input_FR

# Send sound to sound-box device

pw-play $PATH_TO_SOUND_FILE --volume 0.5 --target sound-box-sink