Simultaneous subwoofer outputs cannot be predicted from individually measured responses

Evidence

When measurements are done, it is common for some individuals to try equalizing each subwoofer separately and then to combine them. Again, disappointment is almost guaranteed because when the system is in “play” mode all subwoofers are operating simultaneously, and the result of the acoustical summation is unpredictable. The measurement that matters is the one done with all subwoofers operating simultaneously. For individually measured subwoofer outputs to sum in a predictable manner, the measurements must be of the transfer function—amplitude and phase—not the steady-state amplitude response. — Toole, Floyd E, Sound reproduction- the acoustics and…, 1663

Categorization

• DEFINE: Clarifies why transfer function (amplitude+phase) measurements are needed rather than steady-state amplitude responses for predictable acoustical summation.