Multidirectional Array Design & Sub Alignment
1. Horizontal Interaction and the "Power Alley" When two line arrays (Left and Right) reproduce the same low-frequency content, they create an interference pattern. In the exact center, the signals arrive in phase, creating a +6 dB summation known as the "Power Alley." As you move off-center, the time difference between the two arrays causes destructive interference (nulls).
2. Cardioid Subwoofer Theory: Gradient vs. End-Fire
Gradient (Back-to-Front): By placing one sub behind another and inverting the polarity/delaying the rear sub, we create a "null" behind the stack. This keeps the stage clean.
End-Fire: A line of subs where each is delayed to match the physical travel time of the sound. This creates massive forward impact but occupies significant physical space.
3. Geometric Crossovers The "Crossover" between a flown Main PA and a ground-stacked Sub is physical, not just electronic. The time-alignment between these two sources is only perfect at one specific distance. We align them for a "Priority Zone" (usually FOH).
II. Practical Lab: Cardioid Sub Modeling
Tool: Prediction Software (Soundvision/ArrayCalc).
Tasks: * Model 4 subwoofers in a standard stack. Observe the 360° dispersion.
Configure them as a Cardioid pair (1m physical offset). Calculate the required delay (use your Inverse Square/Wavelength calculator).
Observe the "Stage Rejection" in the 3D map.
III. Daily Assessment (Wednesday)
Q1: Calculate the delay for a sub 1.2 meters behind another (Speed of sound = 344m/s).
Q2: What is the primary disadvantage of an End-Fire sub array compared to a Gradient array?