Wherever one sits in a concert hall, the direct sound should be clearly heard before the energy in early reflections and reverberation have risen to the level that starts masking that sound. Freedom from masking of the direct sound is particularly important in the frequency region above 700
Hz. If the direct sound is not clearly heard, the music lacks impact and the listener may tend to go to sleep. This problem is particularly important in shoebox-shaped halls with small seating capacities because the sidewalls that reflect early sound are nearer to the listener, which means that the reflections start masking the direct
sound sooner. One possible design for a hall with limited seating is to make it fan shaped. This way, all listeners are nearer the stage, and the sidewalls do not reflect early sound toward the audience areas. In Boston Symphony Hall, which is shoebox-shaped, the statues and niches and edges of high-up windows reflect sound above 700
Hz back toward the stage, which decreases the energy that would otherwise reflect from the sidewalls and thus preserves audibility of the direct sound.