| 摘要 |
A long and narrow loudspeaker on an entire wall gives off a cylindrical wave, which covers the entire room. Extra loudspeakers fixed at an angle against the wall will be heard in another direction, producing angle stereo independent of where one is in the room. Electro-dynamic loudspeakers are made of long plates of iron with air gapes between them where magnetic fields are produced. In the air gaps are strips, which conduct the sound currents. The strips influence directly one or more membranes. The magnetic field can be produced by permanent magnets, electromagnets or through concentration of geomagnetic fields. Long loudspeakers, which use other forces such as electrostatic forces, only need to be made for small sound pressure at the membrane.
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