Transducer

A sound transducer is a transducer that converts acoustic signals as alternating sound pressures into electrical signals ( electrical voltage ) or, conversely, converts electrical voltage into acoustic signals and thus serves as a sound source . Examples of sound transducers are the microphone , the sensor and the pickup as a sound receiver and the loudspeaker .

Executions

The following principles can apply to electroacoustic converters:

• electromagnetic : attraction of iron parts due to inhomogeneous magnetic fields (old telephone receivers, simple headphones , historical loudspeakers , record pickups )
• electrodynamic : induction in the moving conductor, force on a current-carrying conductor in a magnetic field (dynamic microphone , ribbon microphone , electrodynamic loudspeaker, record pick-up)
• electrostatic : force on the membrane, change in voltage and capacitance of the membrane during movement ( condenser microphone , electrostatic loudspeaker)
  • Electret : permanent electric field through polarization of the material (electret microphone)
• Piezoelectric : change in length when the voltage changes and vice versa ( signal transmitter , record scanner, structure-borne sound receiver , ultrasonic transducer)

In the past, magnetostrictive transducers were used to generate ultrasound under water ( echo sounder ) .

Electrodynamic principle

See also : electrodynamic loudspeaker

Electrodynamic sound transducers, for example microphones and loudspeakers, basically consist of a fixed, permanent magnetic field and an electrical conductor arranged movably in it , which in practice is either wound into a voice coil or consists of a light metal foil. In turn, the conductor is mechanically coupled to a vibrating membrane .

The following linear relationship exists between the Lorentz force F exerted on the membrane by the electrical conductor of an electrodynamic loudspeaker or headphones and the excitation current i:

${\displaystyle F_{\omega }=B\cdot l\cdot i.}$

With

F _ω = force exerted on the membrane

B = magnetic induction or magnetic flux density

l = length of the electrical conductor

i = electric current in the conductor

If it is structurally ensured that the movable conductor remains in the homogeneous part of the permanent magnetic field even during the largest movements to be carried out , sound transducers with particularly low distortion can be built according to this transducer principle due to the mechanical vibration magnitude .

The signal voltage (open circuit voltage or original voltage) emitted by an electrodynamic sound sensor without a load is proportional to the magnetic flux density (induction), the conductor length and the speed  v of the conductor perpendicular to the magnetic field:

${\displaystyle u=B\cdot l\cdot v\,}$

With

u = signal voltage

B = induction

l = length of the electrical conductor

v = speed

The best-known practical versions of electrodynamic sound sensors are the moving coil microphone and the ribbon microphone.

literature

• Thomas Görne: Sound engineering. 1st edition, Carl Hanser Verlag, Leipzig, 2006, ISBN 3-446-40198-9
• Heinz Sahm: HIFI loudspeakers. 2nd edition, Franzis Verlag GmbH, Munich, 1982, ISBN 3-7723-6522-1
• Michael Dickreiter, Volker Dittel, Wolfgang Hoeg, Martin Wöhr (eds.), "Handbuch der Tonstudiotechnik", 8th, revised and expanded edition, 2 volumes, publisher: Walter de Gruyter, Berlin / Boston, 2014, ISBN 978-3- 11-028978-7 or e- ISBN 978-3-11-031650-6 .