Advanced Venue Modeling & Geometric Prediction
The Philosophy of the Virtual Environment In high-level system engineering, the transition from a "technician" to an "engineer" is marked by the move from reactive adjustment to proactive prediction. Predictive analysis is the process of building a high-fidelity 3D model of an acoustic environment to simulate how sound pressure levels (SPL), frequency response, and phase relationships will behave before a single motor is flown. At the Clair Global level (Eighth Day/JPJ), we primarily utilize L-Acoustics Soundvision and d&b ArrayCalc.
A model is only as useful as its accuracy. The first principle of modeling is "Geometric Integrity." If the rakes of the seating or the height of the balcony are off by as little as 0.5 meters, the "Autosplay" or "ArrayProcessing" algorithms will calculate inter-box splay angles that create physical "shadows" or "hot spots" in the real world. We treat the venue as a series of Listener Planes. Each plane is assigned an acoustic property. A plush velvet seat has a different absorption coefficient than a concrete floor or a glass VIP box. In the theoretical realm, we must account for the Specular Reflection—where sound bounces off a hard surface like a billiard ball—and Diffusion, where sound is scattered.
2. Line Source Modeling: The Fresnel Zone and Ray Tracing As we discussed in Week 1, a line array is a "Line Source" that produces cylindrical waves. However, modeling software uses a combination of Ray Tracing and Wavefront Sculpture Technology (WST). For frequencies below 1 kHz, the software must account for the physical size of the array and the distance to the listener to determine if they are in the Near Field (3 dB drop per doubling) or the Far Field (6 dB drop).
The software calculates the Isocontour Mapping. This is a color-coded representation of SPL distribution. When looking at a "Mapping" view, an engineer isn't just looking for "enough volume"; they are looking for Spectral Consistency. If the 4 kHz map shows massive variations compared to the 250 Hz map, the system will sound inconsistent as the audience moves through the venue. We utilize Air Absorption Compensation. Since high-frequency energy is absorbed by oxygen and nitrogen molecules (especially in low humidity), the modeler must input the venue's expected temperature and humidity. The software then applies a "Pre-Emphasis" to the top boxes in the hang—which have the furthest "throw"—to ensure the back row receives the same high-frequency detail as the front row.
3. Boundary Conditions and Acoustic Shadowing One of the most complex elements of modeling is the Acoustic Shadow. This occurs when a structural element (a balcony overhang or a pillar) physically blocks the line of sight from the array to the listener. In a 3D model, we use "Hidden Surfaces" to determine where coverage terminates.
The Balcony Problem: Sound entering a deep balcony area often suffers from a loss of "Impact" and "Clarity." The modeler must determine if the Main PA can "reach" under the balcony or if a secondary "Delay" system is required.
Low-Frequency Diffraction: While high frequencies are shadowed by objects, low frequencies "bend" around them. A model must show the Low-Frequency Build-up in corners and under balconies, where long wavelengths ($>2$m) reflect and sum, creating "muddy" or "boomy" areas.
II. Practical Lab: The Arena Master-Model
Tool: Soundvision or ArrayCalc.
Tasks: * Construct a multi-tier arena: Floor (40m x 30m), Lower Bowl (15° rake), Upper Bowl (35° rake), and a Press Box.
Insert an array of 16 boxes (e.g., K2 or J-Series).
The "Manual vs. Auto" Test: Set all splay angles to 1° and map the SPL. Then, run the software’s optimization algorithm (Autosplay/ArrayProcessing) for "Best SPL Consistency."
Compare the inter-box angles. Identify why the software chose a $10^\circ$ splay for the bottom box and a $0.25^\circ$ splay for the top.
III. Daily Assessment (Monday)
Written: Explain the relationship between venue humidity and the splay angles of the top 4 boxes in a 16-box hang.
Prediction: You see a "hole" in the coverage at 2 kHz at the transition between the floor and the raked seating. What mechanical adjustment is the most likely fix?
Math: If the software predicts a 12 dB difference from front to back at 4 kHz, but only 4 dB at 250 Hz, what does this tell you about your vertical splay?