Projection Mapped Stage Deck for Utility and Production
Concept
The Voxel is a large blackbox theater with no permanent risers, chairs, or lighting. Some artists can have trouble envisioning how they could configure the space to suit their show. Our team wanted to transform the stage deck into a large projection surface where we could display full scale platforms and chairs, effectivley projectiong full-scale floor plans right on the deck.
Because of the improved video playback capability of Apple Silicon macs and QLab 5, large projection mapping installations have become much more affordable and practical to manage. Many smaller, affordable projectors can do the same job (at a higher resolution) as a single extremely bright projector.
Practical Requirements
- Low maintenance
- Keep video shadows of performers on stage as short as possible
- Projectors should be higher than the rigging grid so they are left alone
- Fixtures hung from the rigging grid should not cast shadows on the projection
- Reliable, high availability
- Simple interface
Feature List (order of desirability)
- Demonstrate different ways to arrange the room (alley, in the round, proscenium, etc)
- Simple NDI input for video designers to use the system
- Show PDF ground plans in scale
- Virtual spike system for Stage Managers
- Rigging guide (project the grid on the floor)
Design Considerations
The stage deck area at The Voxel is about 50' x 35'. Most projectors are 16:9 or 16:10 aspect ratio. We determined that a grid of (8) 16:10 projectors would align with our grid spacing and provide just enough overlap between projectors for good edge blending. With this many projectors, shadows of performers on the deck are kept quite short and are frequently nonexistant.
Projector Selection
We determined the best trim height for these projectors would be 25' over the stage deck. Using Vectorworks' projector tools, we found we needed a projector with a lens ratio around 1.06:1.
Additionally, we required:
- High brightness
- Remote control (power on/power off) via a built-in Ethernet port
- Ability to hang the projector with the lens facing straight down
- A relatively affordable price per projector
We found the Panasonic PT-VZ580U (now discontinued) met nearly all of our requirements- 5,000 lumens, Ethernet control, and only around $1600 at the time. However, the manual specifically requires the projector be installed facing horizontally. That problem can be solved with a 3D printed right angle mirror mount.
Rigging
We hung two 1.5" steel pipes horizontally from the roof steel at an elevation that would land the projectors at the required 25' trim. That height was also selected because it's well under the fire sprinklers- we're lucky that they're very tight to the roof in our building. Each pipe would carry (4) projectors plus their associated power and signal cabling.
The Voxel's roof can vibrate slightly when the HVAC is running full tilt, construction is nearby, or an especially big truck drives by. We used vibration dampeners in our load path to reduce vibrations.
We rigged the projectors to these new pipes using standard commodity projector hanging hardware.
Video Signal Flow
No Mac supports directly attaching (8) displays in a way that macOS can recognize. The Matrox QuadHead2Go units appear to the Mac as two simple 3840 x 2400 displays, but they internally slice that video into four separate 1920x1200 HDMI outputs. QLab understands video wall controllers like this and makes it easy to set up.
Copper HDMI cables are not reliable at distances over 15', so we used all-in-one fiber HDMI cables between the QuadHeads and the projectors. SDI cables and adapters were considered, but ruled out because SDI does not suport 16:10 resolutions.
In addition to the HDMI cable, each projector also had a Cat5 Ethernet cable run back to a switch housed next to the Mac Studio.
After hooking it all up and experimenting, we determined the optimal pixel resolution for the stage to be 3600 x 4586.
Reliability
This system has proven very reliable. Only the projectors themselves are ever turned off or restarted- the Mac and QuadHeads are online all the time. It requires very little maintenance and is integrated with other automations in the building.
Control
QLab cues can be triggered via OSC which initiate the following actions:
- Start/Stop a Camera Cue to display NDI content from another computer
- Power on/off all projectors via Network cues
- Display different seating layouts
- Display a centerline and rigging guides
- Run other effects, like a fake gobo wash or videos to demonstrate the system