My visitors have problems to hear me and I to hear them,too. The voice is not loud enough.
Hey @Piet. The only volume that is externally outputted from the Doorbell 2 that can be changed will be the Doorbell Ringer Volume, which you can alter under the Device Settings > General Settings. Although, this is just for when it rings. I would make sure that when you are talking through the Live View, especially if it is on your phone, that you do not have any bluetooth devices connected to your phone.
A bluetooth device may be using the microphone from there, or that you can try talking into any other microphones that are on your phone. Sometimes there is one microphone picking up audio when you’re on the phone, with it up to your face, or another when it’s on speaker, which may be the microphone you need to talk into (normally at the top of the phone).