Wondrous item, rare
While the gable door stands open, no creature within 15 feet of the casket can be deprived of its voice. Such a creature can speak, call out, testify, and cast spells with verbal components even while frightened, and it has advantage on saving throws against any effect that would silence it or take its speech away. Magic that creates silence does not hold in that space, for anyone in it.
Nothing said in that space is quiet. A whisper is heard at the edge of the 15 feet at the strength it was spoken, through cloth, through a hand held up, and through the noise of a crowded room. The sisters of St. Bavo kept the door open at evidence and shut at prayer.
Shutting the door is an action and ends all of the above at once.
Source: Provenance — The Quist Sale