This historic listening device features a circular permanent magnet placed close to an iron diaphragm. The design concentrated the magnetic field more effectively than straight bar magnets of the era, resulting in louder and clearer audio output. It was widely used in early telephone systems before being superseded by more compact bipolar receivers.
Heard on the job
The museum acquired a pristine Ader receiver, still showing the original ring magnet assembly under the earpiece.
Insider tip
Collectors often look for the distinct circular magnet housing which sets it apart from Bell's original bar-magnet designs.