The Mirror Ball, often erroneously referred to as a
`crystal ball'(*) is the staple of many clubs and
portable disc jockey setups. There are several
types available, each with advantages and
disadvantages. Here is a guide to help you
select one for your intended purpose.
THE FOLLOWING MAY NOT BE REPRODUCED
WITHOUT PERMISSION FROM THE AUTHOR ©
Other Mirrored Products
The substrate is important. The hard-shell types are more dent resistant and tend to hold the mirrors better over a longer period. The styrofoam type are lighter and cheaper, but the foam can disintegrate over time and is prone to breaking off in chunks, taking mirrors with it. The glass tiles don't stick as well and can drop off if the ball is handled roughly, as can happen during repeated set-up and take-down operations or with repeated cleanings. This tendency increases as the ball ages. Very large mirror balls with glass mirrors cannot have styrofoam cores because of the overall weight.
For home use, or for short life in a club, the foam-core balls will suffice. Being lighter, they require a less heavy-duty motor. Also, since glass reflecting surfaces are brighter, they work better in a large room where the mirrored inmages must travel farther to hit a wall or object. Those images will be much sharper at greater distances with glass mirrors.
The plastic balls are a hollow, shaped sphere with facets moulded into the outer surface. The ball is very hardy and resistant to damage, but is a poor reflector. Plastic mirror balls tend to give a dimmer, less distinct image and are really only good in a short-throw situation. If used in a club where dust and dirt are problems, the reflectivty degrades more quickly than glass, giving poor performance. This type of ball travels well, although scratches and scuffs are common, further reducing the image quality and brightness.
The plastic mirror ball is only recommended for the budget conscious and for those in small rooms using bright light sources to illuminate the ball.
(*) A crystal ball is one of solid, clear glass, not a
hollow sphere with a surface covered in mirrors. Also,
although "disco ball" is not erroneous, it is not a
favoured term because the balls were used decades
before, and decades since, the 1970s disco era.
Mirror balls range from about 50mm up to 600mm, but there are those which fall outside of that. The general rule is the bigger the room, the larger the ball should be. Also, the larger the ball, the larger the individual mirror sizes should be. Larger mirrors reflect a larger image, which is important at great distances because bigger dots appear to be brighter. Because of greater surface area, a larger ball will have more mirrors (even with a larger mirror size), thus the images on a distant wall will be more numerous and closer together. A small ball will project fewer dots, and at great distances, the dots will be sparse in number so they will be far apart. This diminishes the effect greatly.
Room versus ball size is somewhat subjective depending on what the user wants. Ceiling height should be taken into account, as well. Here are some suggestions:
In addition, there are half-spheres available. These are used in large rooms with low ceilings because the half-sphere hangs tightly to the ceiling due to it being suspended from within its concave surface. Such a setup allows for a large diameter despite the ceiling, so there are plenty of mirror squares to fill a large space.
There are several types available, with the main difference being in the weight-handling ability. Do not skimp on a motor. One which is too small for the ball weight will struggle upon startup causing overheating. During operation, the ball weight will cause faster wear on smaller, lighter-duty gears, thus reducing the motor's life. The best motors have ball bearings for smooth operation and higher weight handling abilities.
There are also battery-operated motors available, but should be limited to home use where an electrical cord across a celing is not wanted. They are not recommended for a ball larger than 200mm, unless an all-plastic ball is used. Then one may use up to a 300mm ball. Keep spare batteries on hand, and remove them if the motor is placed in storage. If you are storing the batteries with the motor, place them in a plastic bag to catch any leaks, should they occur.
Finally, a word on motor speed, which is rated in revolutions per minute (RPM). The general rule is that the larger the room, the slower the RPM. The reason is that the farther away the walls are, the faster the mirror images will travel along that wall. Too fast and they blur, spoiling the effect, as well as making some susceptible people prone to dizzyness. Typical speeds are 3 RPM for close walls and 1 RPM for walls that are far away.
A light source for a mirror ball must supply a concentrated, focused beam. Household floodlights, and even theatrical fresnels, are not suitable! The most common source is the pin spot, although in large installations, ellipsoidal theatre lights are used. Pin spots come in PAR 36, 46 and larger sizes. The larger the number, the bigger the light and brighter the output. The light will be determined by the distances involved and desired effect intensity. An LED version of the PAR pinspot is also available.
In a darkened room with a small ball and short distances, the PAR 36 is fine. These units are low voltage with built-in transformers. Typical voltages and wattages are 6 volts and 30 watt, although 12 volt and higher wattages are available. Check the lux (light) levels. A higher voltage/wattage does not always translate to higher light output.
The light should be placed at a distance which covers the entire face of the ball and no more. Shorter distances mean some of the effect will be wasted, although the images will be brighter. Longer throws, and some of the light will travel beyond the ball, diluting the effect and reducing light levels for the projected dots. Remember when choosing a light source to take into account that the light must travel from the source to the ball and from the ball to the wall. A bright light on the ball will not necesarily result in bright enough images at the wall. You may have to upscale to a PAR 46 (or larger), or an ellipsoidal source, if budget permits.
Here are some suggestions for light sources as
based on the ball sizes that were given farther back:
Spheres are not the only shape having mirrored surfaces that are used for entertainment purposes. Mirrored cylinders come in various sizes and lengths, and one may hang them statically or turn them with standard mirror ball motors, one for each cylinder. Cylinders are pleasing when three of the same diameter, but differing lengths, are arranged in groups.
There are also pyramids, cubes, pentagons, hexagons, etc. that have a solid mirror or mirror squares on each side. The solid ones are often used for laser setups, while the ones with mirror squares are used as alternatives to the mirror ball.
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