Direct Sound

In any acoustic environment, the sound arriving at a listener consists of three time-ordered components: direct sound, early reflections, and late reverberation. The direct sound arrives first because it travels the shortest path — a straight line from source to listener. Its arrival time establishes the time reference for all subsequent analysis (it defines t=0 in the impulse response). The direct sound follows the inverse square law: SPL decreases by 6 dB for each doubling of distance from a point source. At 1 meter from a loudspeaker, the direct sound level equals the speaker sensitivity. At 2 meters, it drops 6 dB; at 4 meters, 12 dB; at 8 meters, 18 dB. This predictable decay is used for coverage calculations and explains why front rows in a concert are louder than back rows. The ratio of direct sound to reflected/reverberant sound determines clarity and intelligibility. Within the critical distance (where direct and reverberant levels are equal), the direct sound dominates and the room has minimal influence on the perceived tonal balance. Beyond the critical distance, the reverberant field dominates and the room response colors the sound. Critical distance depends on room volume, absorption, and source directivity: dc = 0.057 × √(Q × V × α / RT60), where Q is the directivity factor. In the impulse response, the direct sound appears as the initial spike. Its amplitude relative to subsequent reflections determines the C50 and C80 clarity metrics. A strong, isolated direct sound followed by much weaker reflections produces high clarity — ideal for speech. A direct sound that is barely distinguishable from dense early reflections produces low clarity — potentially problematic for intelligibility but acceptable or even desirable for music. SonaVyx identifies the direct sound as the peak of the impulse response and uses it as the time reference for all subsequent analysis.