If you are at an equal distance from both drivers, then there will be the same number of wavelengths of the sine wave to each driver and they add together at your ears, resulting in you hearing something twice as loud as the output of a single driver.
[15] "Loko makwenu a ku dyoherile, yana u ya n'wi komba ku hoxa ka yena, mi ri vambirhi ntsena; loko a ku yingisa, u ta va u vuyisile makwenu.[16] Kambe loko a nga ku yingisi, teka vanhu vambirhi, kumbe un'we, leswaku mhaka hinkwayo yi tiyisiwa hi milomo ya timbhoni tinharhu, kumbe timbirhi.[17] Loko a ala ku va yingisa, byela nhlengeletano; loko a ala ku yingisa na yona nhlengeletano, eka wena a a kotise muhedeni ni muluvisi.