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"The image is oriented in the same way we see the group, not reversed left to right as is a usual virtual image in flat mirror. It is not quite clear to me how this effect is produced."
Pepsi-Pavilion's dome room with spherical mirror and "real" reflections

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Pepsi-Pavilion <1970>

Upstairs the main space of the Pavilion was a 90-foot diameter 210-degree spherical mirror made of aluminized mylar. The artists conceived of this space as performance area that could be used by many visiting artists during Expo '70.

The mirror fulfilled all our expectations. Our architect John Pearce devised an ingenious way the mylar mirror could be fitted inside an air tight cage structure. A slight vacuum of less than 1/1000 of an atmosphere, which could be handled by a couple of good sized fans, would be sufficient to hold up the mirror. By having a negative pressure air structure, there was no need for cumbersome air locks.

This optical effect in a spherical mirror of producing a real image resembles that of a hologram. The difference is that because of the size of our mirror, a spectator looking at an image could walk around the image and see it from all sides.

The space in the mirror was gentle and poetic, rich and always changing. It was complex in spite of its simplicity. We discovered new and complicated optical effects every day. The slide to the right is projected upside down. Once the visitors could see themselves as a real image in the mirror, the reaction was incredible. It created much more excitement than we ever could have expected.

David Tudor designed the sound system as an "instrument" with 32 inputs and 37 speakers arranged in a in a rhombic grid on the surface of the dome behind the mirror. Sound could be moved at varying speeds linearly across the dome and in circles around the dome. Sound could be shifted abruptly from any one speaker to any other speaker, creating point sources of sound. Or all speakers were capable of giving out the same sound. The lights and sound could either be pre-programed or controlled in real time by the artists from a console at one side of the dome.

The floor was divided into 10 areas made up of different materials, such as astroturf, rough wood, slate, tile, asphalt. Through handsets, like the one held by the boy in the left slide, visitors could hear specific sounds on each different floor material. On the tile floor: horses hooves and shattering glass; on the astroturf: ducks, frogs, cicadas and lions roaring. These sounds were transmitted from wire loops embedded in the floor.

Twenty 100-turn wire coils or loops 1 foot in diameter were embedded under each of the floor sections and were fed by tape recorders. The low frequency magnetic field they generated was picked up and amplified through handsets the visitors carried. The innovation in this system was the use of a large number of coils for each area to obtain an even distribution of the sound and not have sound spill over to another area.

– Billy Klüver