Voice coil
In sound transducers, a voice coil is an electrical coil that serves as the drive system for the transducer. Applications include electrodynamic speakers or bass speakers . In the case of dynamic microphones , the alternative designation moving coil is common with the same functional principle .
construction
The voice coil consists of thin enamelled copper wire that is wound and glued onto what is known as the voice coil former. The thin coil thus formed is immersed in the air gap of the permanent magnet , in which there is a strong magnetic field . The coil former is connected to the speaker membrane. The alternating magnetic field created by the flow of current deflects the voice coil inwards and outwards. This moves the membrane attached to it and the attached air, which converts the electrical vibrations into airborne sound .
In the past, electromagnets were used instead of permanent magnets to build up the gap magnetic field, since sufficiently strong permanent magnets were not yet available or expensive. The electromagnets also served in the tube receivers as smoothing chokes for the anode voltage source.
Due to the electromagnetic induction , a movement of the diaphragm also induces a voltage in the voice coil. This fact is used with dynamic microphones like the moving coil microphone .
Loudspeakers are poorly suited as dynamic microphones, as the mass of the membrane can only poorly follow high frequencies and also because the source impedance and thus the voltage of the low frequency generated is very small.
There are also self-supporting designs of voice coils in which the coil wire has a rectangular cross section and is glued to one another over the entire surface within the turns. Aluminum wire is also used. Low mass benefits better impulse reproduction of the loudspeaker.
Responsiveness
Depending on the design, the transmittable frequency range extends from infrasound to far into the ultrasound range. It is limited at the top by the mass of the moving system (voice coil and membrane). So z. B. the heavy coils of large bass speakers only follow the frequency of the applied voltage down to the lower kilohertz range, the inertia is too great for higher frequencies. This is why high-quality loudspeaker boxes divide the frequency spectrum over several different speakers (multi-way boxes or separate boxes, subwoofers).
literature
- Vance Dickason: Loudspeaker construction. Proven recipes for the perfect sound. 4th edition, expanded and revised new edition. Elektor-Verlag, Aachen 2007, ISBN 978-3-89576-116-4 .
- Michael Dickreiter: Handbook of the recording studio technology. Volume 1: Room acoustics, sound sources, sound perception, sound transducers, sound technology, recording technology, sound design. 6th, improved edition. De Gruyter Saur, Berlin et al. 1997, ISBN 3-598-11321-8 , pp. 143-144.