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.
|Shielded speakers are not shielded on the cone side. Avoid pointing speakers directly at the CRT.|
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.
- Download a "Gauss meter" app from your phone's app store.
- 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. If this value is greater than 2 Gauss, your environment may be highly magnetic.
- Move your phone to the side of the speaker, the same distance away as you would have your CRT. Note the new value shown.
- If the measured value is greater than 2 Gauss, it will likely cause issues.
- 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.