"When you have more than one box covering the same area, you WILL have interference," this principle also applies to multiple drivers within the same box?
An example is what I have: the DB Technologies IG4T. 4 drivers deliver the low-mid frequencies. When they are stacked, they stack so that the horns are closest together.
So (overly simplistically), although there is some destructive interference, it is taken advantage of in a way that helps create a more controlled, cylindrical dispersion pattern? And that you can make it so the inverse-square law is tricked a bit by the vertical spread of the drivers?
*barring the use of a horn to combine multiple drivers
Interference from the same box is dependent on frequency, driver spacing, the listener's angle off axis and distance.
The simplistic line array "wedge of cheese" cylindrical dispersion pattern and 3dB drop per doubling of distance only applies to the destructive interference in the near field, which varies with frequency.
The DB Technologies IG4T uses a vertically asymmetric high frequency horn above 1100 Hz. The horn's coverage area is directed slightly downward.
When two IG4T are stacked horn to horn, their -6dB coverage pattern results in ~ 0dB on axis constructive interference above ~ 1100 Hz.
For a stacked pair of IGT4, (75.28 inches tall, just under 2 meters) you are out of the near field on-axis destructive interference zone at ~5.5 feet (1.68 meters) at 100 Hz, and ~60 feet (18.5 meters) at 1100 Hz, using 1130 feet (344.2 meters) per second as the speed of sound (at 72 degrees Fahrenheit, 21.7 Celsius).
If it's hotter, the near field is closer, colder is further.
From:
https://www.prosoundtraining.com/2010/03/17/line-array-limitations/The near field distance can be defined by the following relationship:
D=1.57 L squared/λ
where
D is the distance to the far field transition
L is the physical length of the line source
λ = the wavelength of the frequency in question (all lengths in identical units).
Beyond this distance the listener is in the far field and there is 6 dB drop in level per doubling of distance. The transition distance can be quite long at short wavelengths, that is, high frequencies, but it is shorter at low frequencies. For each octave lower in frequency, the transition distance is cut in half.
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