Kulkornsmikrofon
En kulkornsmikrofon er en af de tidligste typer af mikrofoner: Den var meget brugt i telefonens barndom, men dens store skavank er dens sårbarhed: Får en kulkornsmikrofon et hårdt slag, vil den derefter levere et meget støjfyldt og "knasende" signal.
Kulkornsmikrofonen er en beholder fyldt med kulstøv, hvor "bunden" og "låget" er elektrisk ledende, men elektrisk isoleret fra hinanden så en elektrisk strøm kun kan passere gennem kulstøvet. "Låget" er udformet som en tynd membran, som kan svinge når den rammes af lydbølger: Når det sker, forplanter svingningerne sig til kulstøvet inde i beholderen, og når de enkelte kulpartikler bevæger sig i forhold til hinanden, ændres den elektriske ledningsevne gennem kulstøvet, og med den den strøm der passerer.
En kulkornsmikrofon er derfor forspændt med en jævnspænding gennem en formodstand, hvorover mikrofonsignalet kan udtages potentialefrit gennem en kondensator. Kulkassen, som kælenavnet også er, producere(de)s til forskellige forspændinger, f.eks. 6, 10 og 100 volt.
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Western Electric Model 357 double button carbon microphone in 1B housing, used at WFBM, the first radio station in Indianapolis, Indiana, USA, from its founding in 1924. The double button microphone was developed around 1921 by Western Electric and was extremely widely used as a broadcast and recording microphone through the 1920s because it had significantly lower noise and harmonic distortion. It is often called the "ring and spring" micrphone, as it is often seen in period photos with its cover removed. as a small microphone cylinder suspended in the center of a metal ring by springs. Carbon microphones consist of a cell containing carbon granules between two electrodes in contact with a diaphragm, but they have high harmonic distortion because the change in resistance of the carbon is nonlinear, different under compression than under tension. The double button design used two carbon cells in contact with the diaphragm on either side. They were connected to a battery and center-tapped audio transformer in a "push-pull" circuit, which canceled even-order harmonic distortion. The stiff duralumin diaphragm had a small excursion which further reduced distortion and high resonant frequency and air damping which gave it a flatter frequency response. However the cost of this higher fidelity was that it had very low output.
Forfatter/Opretter: Google, Licens: Apache License 2.0
A colored Emoji from Noto project, released under Apache license
Unicode name: Speaker with one sound wave
Annotations: Low, Sound, Speaker, Volume, Wave