Distributed Mode Speaker

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A flat panel speaker which produces sound when vibration is applied to part of the panel.
 
Sound is created by fluctuations in air pressure, which are then perceived by us when they hit our eardrums. As sound is a time variation of air pressure, its amplitude can be determined by measuring air pressure change over time. As a high frequency sound is heard best in the facing direction of the conventional speaker, it has a narrow directivity.
 
A distributed mode loudspeaker (DML) has wider directivity because the vibration or bending motion covers the entire surface of the panel, so it can be heard from many directions, at a consistent sound quality. The Flat Panel Speaker is a new technology from Fujitsu Components,based on the technology patented by New Transducers Limited (NXT) and developed by Authentic Ltd, who develops the required application technical design with the customer. The system employs SoundVu TR (Two Region) by NXT, which enables the location of two different frequency generators on a single vibration panel, resulting in a significant reduction of low frequency movement in the viewing area. The simplicity of this technology brings about space saving, eliminates the need for an amplifier or 3D filter, and ensures impressive design flexibility, because of the ‘invisible speaker’ involved – making it absolutely ideal for digital signage audio purposes.
 

Also known as a distributed mode loudspeaker (DML), the flat panel speaker produces sound by the use of a bending wave of a panel, as vibration applied to part of the panel generates a bending motion. This motion travels on the panel surface towards the panel edge, where it is reflected. It then moves back to the panel centre so that the bending waves cover the entire surface of the panel, making sound by activating the surrounding air. Mode is a motion pattern in which the vibration panel bends; each mode corresponds to a specific resonance frequency. Smooth frequency response is achieved through the generation of many modes which interweave.
 
The driving device behind the speaker is the actuator, which is necessary to achieve panel bending waves. DML uses either electro-magnetic (EMA) or piezo-electric (DMA, standing for distributed mode actuator) actuator types, depending on the application. EMA produces a force by using amagnet and coil, as the electric current in the coil controls the force. DMA consists of piezo layers attached to both sides of a metallic centre plate, and suits small devices particularly well. Application of voltage develops an electric field across the piezo layer, which causes curvature; an AC signal causes a swing. A plastic part in one end attached to the panel supports it and transfers this movement to the panel, so the panel bends and produces sound.
 
SurfaceSound, the panel speaker which utilizes the NXT DML mechanism, can be made of a variety of materials. The material of the panel can be chosen from paper honeycomb, aluminium honeycomb, or a tri-layer material made of aluminium skin and foam core, opaque or transparent plastic; both light and rigid material is suitable for the vibration panel.
 
SoundVu is another technology which unifies sound and visual information by using transparent material. A vibration panel is set in front of the display, at whose edge actuators are attached so that the sound and image are produced in the same panel.Glass can be used, but it producesless sound than plastic because of its different mass.