Why Line Arrays Dominate Modern Concert Sound
A conventional point-source speaker radiates sound in an expanding sphere, losing 6 dB of sound pressure level (SPL) for every doubling of distance. In a large arena, if the front row is blasted at 110 dB, the back row 60 meters away hears only 74 dB.
A tall line array forces sound waves to couple constructively in the vertical plane, producing an expanding cylindrical ribbon wavefront that drops by only 3 dB per doubling of distance! This delivers vastly more uniform sound coverage from front row to bleachers.
The Near-Field Transition Distance ((d_c))
A line array does not propagate cylindrical waves forever. At a critical distance (d_c), the wavefront transitions into standard spherical radiation:
Where (L) is the physical vertical array height, (f) is frequency, and (c) is the speed of sound (343 m/s). Taller arrays extend cylindrical wave projection much deeper into the venue!
The Half-Wavelength Driver Coupling Limit ((f_{ ext{max}}))
For discrete drivers to couple constructively into a coherent wavefront without destructive lobing and comb-filtering notches, the center-to-center distance between adjacent drivers ((d)) must be less than half an acoustic wavelength ((d le lambda / 2)):