![]() Thefollowing issues must be considered: Sensitivity. The most important factor in choosing amicrophone is how it sounds in the required application. Condenser types require batteries or powerfrom the mixing console to operate, which is occasionally a hassle,and dynamics require shielding from stray magnetic fields, whichmakes them a bit heavy sometmes, but very fine microphones areavailable of both styles. ![]() There is no inherent advantage in fidelity of one type ofmicrophone over another. (Some popular dynamic microphones use plasticdiaphragms.) The major disadvantage of electrets is that they losetheir charge after a few years and cease to work. Most plastics conduct electricity when they are hotbut are insulators when they cool.) Plastic is a pretty good materialfor making diaphragms since it can be dependably produced to fairlyexact specifications. (Youoften get a piece of plastic with a permanent charge on it when youunwrap a record. Such a material is called an electret and is usually a kind of plastic. The amount of current is essentiallyproportioinal to the displacement of the diaphragm,and is so small that it must be electrically amplified before itleaves the microphone.Ī common varient of this design uses a material with a permanentlyimprinted charge for the diaphragm. Whenthe distance changes, current flows in the wire as the batterymaintains the correct charge. Thisdistance changes as the diaphragm moves in response to sound. The amountof charge is determined by the voltage of the battery, the area ofthe diaphragm and backplate, and the distance between the two. (The plate may or may not have holesin it.) A battery is connected to both pieces of metal, whichproduces an electrical potential, or charge, between them. In a condenser microphone, the diaphragm is mounted close to, butnot touching, a rigid backplate. This kind of microphone is known as velocitysensitive. It isimportant to remember that current is produced by the motion of thediaphragm, and that the amount of current is determined by the speedof that motion. The principles are the same as those that produce electricityat the utility company, realized in a pocket-sized scale. A magnet produces a magnetic field which surrounds thecoil, and motion of the coil within this field causes current toflow. In the magneto-dynamic, commonly called dynamic, microphone, soundwaves cause movement of a thin metallic diaphragm and an attachedcoil of wire. The two most commonly encountered in recording studiosare the magneto-dynamic and the variable condenser designs. The recording engineer isinterested in the accuracy of this transformation, a concept hethinks of as fidelity.Ī variety of mechanical techniques can be used in buildingmicrophones. Sound information exists aspatterns of air pressure the microphone changes this informationinto patterns of electric current. How They Work.Ī microphone is an example of a transducer, a device that changesinformation from one form to another.
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