Actually, yes, the human voice is able to break glass. But it’s extremely difficult. It requires an extremely loud and powerful voice and the ability to sing at a frequency that matches the resonant frequency of the glass. Trained opera singers are able to sing 100 db (120 db would make your ears hurt badly). And if their pitch range is large enough to hit that super high frequency, they may break nearby glass. But if the conditions aren’t exactly right the glass will just reflect the energy back into the room.