dB laws, etc.

dB SPL laws
rule gain
double amplifier wattage +3 dB
double number of speakers +3 dB
double distance from sound source -6 dB
halve distance from sound source +6 dB
double driver excursion +6 dB (note: equiv to doubling wattage and # of speakers)
drop down an octave -12 dB (due to increased excursion requirements)
put speaker on the floor +3 dB half loading
put speaker floor, against a wall +6 dB quarter loading
put speaker floor, wall, in corner +9 dB eighth loading

Miscellaneous facts
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