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How plat panel speakers work

How they work

Flat panel speakers have conventional voice coil/magnet 'motor' assemblies that change the amplifier's electrical signal into motion. Instead of being attached to a cone made of paper, plastic or metal, the motor assembly is attached to the back of a specially-fabricated diaphragm made of expanded polystyrene.

Flat Panel Speakers work by acting as transmission lines, radiating vibrations from their entire surface, so they can even radiate sound even when covered with paint or wallpaper - the coverings simply become part of the speaker's radiating surface. This allows Flat Panel Speakers to be invisibly installed in walls and ceilings. Plaster, paint, wallpaper or other coverings are applied right over the speaker, allowing it to completely disappear into the wall or ceiling surface.

The variable-thickness diaphragm is what sets this transducer technology apart from all other types of radiating sources. Special grooves and channels are formed on the rear surface to precisely control vibrations. Dampening weights are added to tune the motional response of the entire structure. The diaphragm is then stretched and bonded to its supporting frame with proper amounts of tension.

This is atype of dipole loudspeaker design that combines aspects of both dynamic and electrostatic designs. The planar speaker consists of a large plastic sheet with conducting wires imbedded in it. These wires function as the voice coil. Many small magnets in front of and behind the sheet set up a magnetic field so current in the wires causes a force that moves the unit, similar to an electrostatic speaker. Planar speakers suffer from the same directional problems as other dipole loudspeakers, but their impedance is more similar to dynamic designs.

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Some theory

Sound sources are usually based on a vibrating surface that radiates sound energy into the surrounding medium. The type of sound field produced by the source depends on the source geometry, i.e. the shape and dimensions of the source, as well as possible surrounding structures

Plane wave source

An ideal plane wave source consists of a pulsating rigid surface that is infinitesimally thin and has infinite length and width. The surface radiates sound energy equally to its front and back directions. A plane wave source produces a plane wave, which (in the ideal case) does not exhibit geometric attenuation with increasing distance from the source.

Point source

An ideal point source can be considered as a pulsating sphere that is infinitesimally small in size. The sphere is omni-directional, i.e. sound energy is emitted equally to all directions. Due to geometrical attenuation, the sound pressure level is reduced by 6 dB for each doubling of distance from the source.

Doublet source

A doublet source is a pair of simple sound sources, separated by a small distance apart and vibrating in opposite phase. At q = 90 and 270, the directivity pattern approaches zero, as the wave fronts transmitted by the sources are effectively cancelling out each other. When the distance from the doublet is large, the sound field of the doublet source attenuates in the same manner as a simple point source.

Line source

An ideal line source can be considered as a pulsating cylinder that is infinitesimally thin and has an infinite length. The cylinder emits sound energy equally to all radial directions. A line source produces a cylindrical sound field, where the sound pressure level attenuates by 3 dB for each doubling of distance from the source. A line source may be approximated by a line array of multiple point sources, such as dynamic loudspeaker elements.