AV:Measuring Magnetic Emissions

Magnetic interference is a common issue that affects CRTs — particularly changing the image color or geometry. The most common source of magnetic interference is from unshielded speakers nearby. In general, modern speakers aren't shielded as a cost saving measure since CRTs are not prevalent any longer, thus you may encounter immediately apparent issues or ones that develop over time. This page aims to provide a way to gauge whether a speaker may cause issues over time.

Smartphone Apps
Any smartphone that has a compass or GPS built in has a magnetometer. This sensor can be used instead to loosely measure the strength of a magnetic field.


 * 1) Download a "Gauss meter" app from your phone's app store.
 * 2) Hold still and note the ambient magnetic field (e.g. 0.550 Gauss). Depending where you live, you may have a vastly different ambient value.
 * 3) Move your phone to the side of the speaker, the same distance away as you would have your CRT. Note the new value shown.
 * 4) Note the difference between your ambient value and the measured value.
 * 5) * If the difference is greater than 1 Gauss, it is likely an unshielded speaker.


 * For reference, a weak fridge magnet is approximately 20 Gauss.
 * Professional or broadcast monitors often have magnetic shielding built into their shells and will affect the magnetometer's reading if you are very close to it.