sound systems and concert halls. The goal is to make sure that all the instrumentssound realistic everywhere in the room.Suppose you have a sound system set up in your living room. You sit on the couchand listen to music. Imagine that, for the particular placement of speakers with respectto your ears, sounds propagate well at 1, 3, and 5 kHz, but poorly at 2, 4, and 6 kHz. Thiswill affect the way musical instruments sound. It will distort the sounds from some in-struments more than the sounds from others. Unless all sounds, at all frequencies,reach your ears in the same proportions that they come from the speakers, you will nothear the music the way it originally came from the instruments. For certain instrumentsand notes, the sound can be altered so much that it doesn’t resemble the original at all.Figure 31-1 shows a listener, a speaker, and three sound reflectors, also known asbaffles. It is almost certain that the waves traveling along paths X, Y, and Z will add upto something different, at the listener’s ears, than the waves that come directly from thespeaker. Path X might be most effective for the bass, path Y most effective for themidrange, and path Z most effective for the treble. This will distort the waveforms pro-duced by various musical instruments. It is just about impossible to design an acousti-cal room, such as a concert auditorium, to propagate sound perfectly at all frequenciesfor every listener. The best an engineer can do is optimize the situation and try to avoidthe existence of any “disaster zones.”Loudness and PhasePeople do not perceive the loudness (also called volume) of sound in direct pro-portion to the actual power contained in the waves. Instead, your ears and brainLoudness and Phase585SpeakerListenerXYZBafflesD31-1Sounds from reflected paths (such as X, Y, and Z)combine with direct-path sound (D) to producewhat a listener hears.