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What are the Dots on the Side of Vinyl Turntables, is it Decoration?
DJ Machines in Motion
TLDR: The dots have utility and are not just to look cool. DJs use it as a tool to see what the rotating speed is relative to the normal speed. A quick look at the dots will tell you if your Turntable needs a service or is faulty. The illusion of the layers of Dots staying still depending on the tempo change is due to the “stroboscopic” effect.
Utility - Using the Dots as a Tool
Observing the motion of the dots, you can visually see the relative speed of the platter depending on what lines appear to be static. A row will appear frozen and stationary while the rest of the dots move.
The stroboscopic dots have explicitly been engineered as an indicator to show the change in the speed of the record relative to the standard rate. In simple terms, it’s a way to quickly see how much faster or slower the record is.
Observing the dots can be a helpful tool when keeping the music consistent and staying within the intended speed of the record, making it simple to see that the rotational speed of the platter is constant.
Troubleshooting Issues with Turntable Motor
Issues can occur if the dots' speed seems drastically inconsistent, jumping back and forth or drifting when the line should appear static. There could be an issue with your motor, or your pitch/speed slider may be faulty.
If the lines of dots do not line up, you must service the Turntable and have the pitch slider looked at.
The physics behind this magic concerns a concept called the stroboscopic effect. The light beam acts as a strobe, oscillating at specific frequencies depending on if you have a 50Hz or 60Hz turntable.
Pro Tip: Most new turntables can run on 50 or 60Hz power (It will say on the back of the device)
Buying a Turntable from a Different Country?
If you buy a turntable from a different country, ensure you get the correct power rating for your country.
The fluorescent light will operate at 50 or 60Hz, depending on your local power rating. 120V 60Hz is for America, Japan etc and 230V 50Hz is for Europe, Australia etc. For more information on outlet power, you can find all the power ratings here
Reference - Turntable RPM Speed Check