It has been shown that stray magnetic fields as low as 10 Oe AC or 50 Oe DC can cause permanent damage to recorded magnetic tape. Including a safety factor of 2, it is recommended to keep tapes away from fields exceeding 5 Oe AC or 25 Oe DC.

In practice, special care must be taken with carrying cases housing tape recorder, recorded tapes, dynamic microphones and dynamic headphones adjacent to each other. On the other hand, loudspeakers (except those in miniature enclosures) are not nearly as dangerous as has been thought up to now. Also, the AC and DC stray fields found in the tape path of tape recorders can be considered harmless. They could, however, easily be avoided completely by proper design of the machine.

This paper was presented at the IASA Technical Committee Session in Salzburg and some very interesting suggestions were made in the discussion period. These focused on magnetic hazards to tape during transport. These problems will be dealt with in a subsequent report which we hope will also include data on metal detectors, magnetic gates (in airports, etc.), electric trolleys, fork lift trucks, electric railways, air freight, etc.


Dipl.Ing. Franz Lechleitner (Phonogrammarchiv der Österreichischen Akademie der Wissenschaften) for invaluable help with measurements;

Dr. Werner A. Deutsch (Kommission für Schallforschung der Osterr. Akademie der Wissenschaften) for doing the spectral analyses;

Institute für Allgemeine Elektrotechnik der Technischen Universität Wien, for assistance in instrumentation.


G.A. Knight: “Factors Relating to Long Term Storage of Magnetic Tape,” Phonographic Bulletin, no. 18, (July 1977), pp. 15-35.