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.

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. If this value is greater than 2 Gauss, your environment may be highly magnetic.
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. 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.