Car audio technology sure is coming at us fast. In only the last couple of years we've seen big changes in amplifier technologies, specifically digital amps that really are switching power supply amps or class D. DVD has hit car audio not only for video but soon there will be DVD-Audio. In fact, Panasonic's newest mobile DVD players already have the software in them to play both an audio DVD and a video DVD.
RequiredWith amplifiers changing and getting better, and with so many new choices for a head unit, seems as though speakers have been left out in the cold. In a way they have because we haven't see anything truly new or unique for decades. The speaker with a cone attached to a voice coil that's driven by a magnet-based motor is really old, nearly 70 years.
There have been significant improvements to the design and today's subwoofers are a testament to just how solid of a design a cone speaker is. But it's another type of speaker that may soon redefine the speaker. It's called DML or Distributed Mode Loudspeaker. Visually it's a flat speaker, but a flat speaker is really nothing too new, there have been flat or even electrostatic speakers for a significant amount of time.
What makes DML really different is that it's not a piston-type speaker. Basically, today's speakers move back and forth to make sound, just like a piston in an engine. But a DML speaker vibrates or resonates to make sound.
A good example of how a DML speaker works is to take a large piece of thin metal. If you pick it up and shake it violently it will make sounds like a wobbly, wavy noise. Certainly not music, but sound. As well, you can see the waves in the metal as you shake it. This is fundamentally how DML speakers work.
First discovered in 1991 by Dr. Ken Heron of Britain's Defense Evaluation & Research Agency (DERA), the discovery of DML was almost an accident. Dr. Heron was working on advanced lightweight composites in military planes. His team had installed some ultra stiff panels into a cockpit to try and reduce jet noise. Instead of reducing noise, it had just the opposite effect. The panel resonated with incredible efficiency. Looking a little further into things, he discovered that they could actually get panels to reproduce specific frequencies, not just its resonant frequency.
DERA recognized that this had some true potential and started work on making it into a speaker technology but, they were not successful. The technology was then sold to the Verity group, who own English speaker and hi-fi companies Quad and Mission. They got their own group of scientists (under the banner of NXT) to develop the panel into a speaker and in just two years, and DML (Distributed Mode Loudspeaker) was born.
Turns out, the whole thing is rather simple once you do some really complex math. All you need is a lightweight, stiff panel and what's called an exciter. Some things like the size, thickness, stiffness, torsional and bending resistance of the panel have to be found out, but these aren't hard to find. Then you simply plug those numbers into a computer program NXT sells its licensees, and it does the rest.
Going a bit deeper than that, DML works by attaching the exciter to the back of the panel. The exciter works much like a cone speaker because it only moves back and forth. When it does this, it causes vibrations in the panel. The panel then creates complex waveforms all over its entire surface. It's not moving in and out like a cone speaker at all. Instead it could be pulling back in the left corner, pushing out in the right corner and sideways somewhere towards the center.
It's all these waves moving around, like when you drop a bunch of rocks into a smooth body of water, that creates the sound you hear. You could also think of it like all the waves in the ocean being reduced to a small panel and that makes sound. Out in the middle of the ocean the waves are going all directions, same with DML