In John 5:34, Jesus says testimony is for the hearers' benefit, not his own—same selfless purpose as the voice here.

In John 11:15, Jesus is glad for their sake that he was absent so they would believe—same motive as the voice here.

In John 11:42, Jesus prays aloud so the crowd would believe he is sent by God—identical purpose to the voice here.

In Exodus 19:9, God speaks from a cloud so the people will believe Moses—same purpose as the voice here to authenticate Jesus.