AIEL
Purchase Guide
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MIRROR |
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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 ©
The first two have individually-cut glass mirrors. These give the best and brightest image, but being glass, they are prone to damage, as opposed to the plastic types. They are also heavier.
The substrate is important. The hard-shell types are more dent resistant and tend to hold the mirrors better over a longer period. The foam type, are lighter and cheaper, but the foam can disintegrate over time and is prone to breaking off. The mirrors don't stick as well and can drop off if the ball is handled roughly, as with repeated set up and take-down operations or with repeated cleanings. This tendency increases as the ball ages.
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 the 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 quickly, giving poor performance. This type of ball travels well, although scratches 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.
Some words on size. Mirror balls range from about 50mm up to 600mm, and 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 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:
MOTORS
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 wear faster on smaller, lighter-duty gears, thus reducing the motor's life.
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 revolve. Too fast and they blur, spoiling the effect, as well as making some susceptible people prone to dizzyness.
LIGHTLight sources for a mirror ball *must* supply concentrated, focused beams. The most common 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.
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. Less, and some of the effect is wasted, although the images will be brighter. More, 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 walls. You may have to go to a PAR 46 (or larger), or an ellipsoidal source, if budget permits.
Here are some suggestions for light sources based on the ball sizes as were given farther back:
(*) A crystal ball is a one of solid, clear glass, not a mirrored surface. Also, although "disco ball" is not erroneous, it is not favoured because the balls were used long before, and many years since, the 1970s disco era.
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