ACUA wrote: i was under the understanding that many sound guys used wattage to calculate how much equipment was needed for venues, i have heard it said 3watts per person, or so many watts per square foot of space etc, are these things not talked about like this?
Not by anyone who understands what is going on. The difference between 50,000 watts and 100,000 watts on the same rig is only 3 dB's, 3 dB's is a barely perceptible increase in volume. The problem is that different rigs have different sensitivities (amount of output compared to the amount of input). 100 w into a home speaker might
get you 109 dB's of output at 1 meter, 100 w into 4 DR250's would get you closer to 131 dB's of output at 1 meter. 131 dB's is a whole lot more sound than 109 dB's.
To cover a space, you have to know the SPL level required at what distance. Then work that level back to 1 meter, for every doubling of distance sound drops (outdoors) 6 dB's. Then you need to know the output your cabs are capable of and know that for every doubling of cabs, you get 6 dB's.
Example: if I need 110 dB's of bass at 32 meters from stack of subs (about 100 ft), then 32 meters is 5 doublings of 1 m (2,4,8,16,32), so 5 x 6 dB's per doubling is 30 dB's. 30 dB's + 110 initial dB's = 140 dB's at 1 meter.
1 dual T60 can do about 128 dB's at 1m at full power, so 140 dB's - 128 dB's = 12 dB's more than 1 dual T60
That means we have to double the cab count twice, which gives us 4 dual T60's at full power to get 110 dB's at 100 feet out. More cabs would put less stress on the system but 4 dual T60 cabs would be the minimum.