But I cannot hear it unless the room is silent.

Basically, this might be useful for listening to something in a silent room or a libary.

While they sound may get lost in an overly noisy room, it works great in places like offices and homes

Yes, if you were in a quiet room, you would be fine for this type of use.

We put about 12 lullaby songs on it, and for a quiet room playing soft music, it works great.

but I need a room completly silent and

device is simply great, meaning it's v-e-r-y easy to use and ideal for casual (non-audiophile quality) listening