Any audiophiles from the last century (like me) may remember a company called Magnepan that invented the electrostatic loudspeaker. It was a floor standing "flat" loudspeaker that was praised for its clarity. Martin Logan, Quad, Bose, and even Sony have made electrostatic loudspeakers over the years. While the form factor is flat, the technology is completely different than a Distributed Mode Loudspeaker (DML.) 

The flat form factor of a DML is more a byproduct of the technology itself than a design goal. The DML is significantly different, in fact, its method of generating sound is completely different than any other loudspeaker - a DML is an "uncorrelated" sound source. Traditional loudspeakers - even electrostatic loudspeakers -are referred to as "point-source" loudspeakers - meaning the sound generated by the transducer (the "flat panel" in this case) generates phase coherent sound waves emanating from a singular point on the device. This "correlation" is what makes point-source loudspeakers not behave well in rooms with difficult acoustics. In point-source, sound is generated from the diaphragm (cone shaped, flat panel, etc) via a pumping "piston - like" motion.

A DML is a resonant device - generating sound by "exciting" a very rigid flat panel - which emanates frequencies from different places on this panel, creating the uncorrelated (not phase-coherent) nature. This uncorrelated nature of the sound is what brings the many benefits to DMLs, such as minimal negative room interaction, lower sound pressure level than perceived, increased clarity, and much more. A byproduct of the DML is that it also happens to be flat.

As you peruse the internet, you will find many who experiment with DML loudspeakers in home environments - using transducers and standard home building products such as drywall, acoustic ceiling tile, etc. These are what I would call "DML at certain frequencies" - it's a great demonstration of the technology for sure, and we're really glad to see so much interest in the technology in the audio enthusiast market.

The DML enthusiast community uses "exciters" to excite their flat material of choice - and these exciters are good for around 15 watts, perfect for a home environment. And given that the surface area of the homemade flat panel is significantly larger than a traditional loudspeaker, they get a fair amount of sound from that 15 watt exciter. In contrast, the FlatPanel DML500 is a true DML, exhibiting DML characteristics consistently across its frequency range. It's even manufactured under a very different patent - the patent covers technology specific to how to generate high SPL sound from a DML, for use in live sound applications. The DML500 is capable of 400 watts continuous, and even higher peaks. 

I often say - the DML500's design comes down to fractions of an ounce, and millimeters - the engineering goes deep into the panel material, exciter design and placement, and so much more.

Commercial companies are even making "invisible" speakers, that can be installed behind drywall in homes and commercial spaces, and use the drywall itself as the transducer, using an exciter similar to what FlatPanel uses. However we believe that most of these fall under the category of "DML at many frequencies" and in many cases are a combination of a pistonic motion and some DML characteristics. 

In the end, there are many form factors of loudspeakers that are flat - but as of this writing, FlatPanel holds the rights to the only patent on pure DML technology for use in high-power live sound applications.