Originally Posted by DonH50
+1 to all above.
In free space each additional point source would add 3 dB if the distances equal and all sources were independent and in phase at the measurement (listening) position. All those conditions are almost never satisfied in the real world.
Assuming the following-1: All cabinets are the same and driven at the same level with the same signal.
2: All cabinets are within 1/4 wavelength at the highest freq of interest.
3: This is outside with no reflections that would cause cancellations and additions.
Will produce the following.
When you go from 1 cabinet to 2 you will get a 6dB addition.
To get another 6dB you need to go to 4 cabinets and another 6dB would require 8 cabinets .
You have to DOUBLE the number of cabinets to get the 6dB. It is real easy early on-but as the numbers get larger-they get REAL larger.
That is why you see so many subs at concerts-it takes more and more to get small gains.
So having a third cabinet would yield around a 3dB gain over 2 cabinets so 3 cabinets would be about 9dB louder than 1.
Yes the room can be a dominating factor (room modes).