Hans Christian Oersted (August 14, 1777 - March 9, 1851) was a renowned Danish physicist and chemist who discovered that electric currents create magnetic fields, a discovery that had a dramatic impact and influence on scientific and technological development of the 19th century.
In 1820, during one of his lectures, H.C. Oersted noticed a compass needle deflected from magnetic north when an electric current from a battery was switched on and off, showing a relationship between electricity and magnetism. His initial interpretation was that magnetic effects radiate from all sides of a wire carrying an electric current, as do light and heat. He began more intensive investigations and published his findings, showing that an electric current produces a circular magnetic field as it flows through a wire. Oersted, the unit of magnetic induction (Oe), is named for H.C. Oersted’s contributions to the field of electromagnetism.
The science behind cartridge manufacturing
Transforming mechanical energy into electrical signals
When material capable of conducting electricity (a silver or copper coil) is set into motion perpendicular to a magnetic field, or when a magnet is moved near such conductive material, electrical current is generated in the circuit. The direction and speed of the movement determine the amplitude and frequency of the current.
Thus, the generating system of a cartridge converts the movement of the stylus and cantilever into voltage, that we call the output signal. The magnet and coil are two main components that allow us to transform mechanical energy into electrical signal. Other electrical transducers, such as e.g., microphones, convert sound waves into electrical signals for the amplifier to amplify, and a loudspeaker converts these electrical signals back into sound waves.
Technological and Industrial applications of Electromagnetism
Electric motors, microphones, loudspeakers, and transformers are only a few of the inventions that are based on this discovery, impacting our daily lives in a way that makes it hard to imagine life without. Ortofon specializes in development and manufacturing of phono cartridges, bone conductors (see the picture), and pulse simulators, all of which are electrical transducers. An electrical transducer is a device which converts one type of energy into another, such as electrical energy into mechanical or acoustical and vice versa.The fundamental principle of the transducer operation is based on the discovery of electromagnetism.
Oersted’s experiment showed that electricity and magnetism are linked
The H. C. Oersted discovery showed that by connecting a battery to a wire, the wire generates an independent magnetic field. Now, imagine the same battery connected to the wire, which is placed close to a magnetic material. Considering that the magnet mass is significantly larger than the wire’s, the wire will be attracted or repulsed, depending on the direction of the current. Different aspects of this discovery were further investigated and developed by other well-known physicists, whose research and efforts gave us valuable insight regarding electromagnetism and its applications.
The MC cartridges principle of operation
Compared to the Moving Magnet cartridge, the reverse principle is applied in the Moving Coil cartridge. Here a powerful fixed magnet is used, and the coils are mounted on the cantilever itself. When the coils move in the field of the magnet, they cut the flux lines of the magnet, and voltages are generated in the coils.Pic.: the MC principle, where the coils on the cantilever move in a magnetic field, and voltages are generated by induction.
The function of the cartridge is to transform the undulations in the record groove to electrical oscillations that are then amplified in an amplifier to finally drive the loudspeakers in the HiFi system. Common to all cartridges is a diamond stylus that mechanically follows the record groove, transmitting its modulations via a cantilever to a miniature generator, which in turn transforms the mechanical movements into electrical currents/signals.
As mentioned, Ortofon products rely greatly on the principle of electromagnetism. Ortofon phono cartridges, both for DJ and HiFi customers, constitute a significant part of our manufacturing capacity.
There are a few different principles of operation of phono cartridges - Ortofon dedicates its production between Moving Magnet (MM) and Moving Coil (MC) types.
In a MM cartridge, the magnet is mounted on the cantilever and placed between the set of coils. The cantilever moves by following the tracks of the record, and hence the magnet moves with it. As the magnet gets closer to one of the coils, the magnet’s magnetic field induces a current in the coil, or in other words it generates electrical energy in the coil. Pic.: the MM principle where the movements of the magnet produce current in the coils by induction.