This happens because the sound of your voice hits the walls and bounces back to you. These sound echoes are called reverberations. As sound tries to spread out farther and farther, it runs into walls. The sound hits the walls and comes back to your position. The harder the wall, the stronger the reverberations. This is especially true in narrow spaces with hard walls like a shower room or tunnel. Sounds echo a lot and reach your ears one after another. The reflected sounds gradually weaken and fade away. But when a new sound echoes together with a fading sound, the combination is pleasing to our ears.