MAT. Metamaterial Absorption Technology. Metamaterials are already being deployed by engineers working in optics and electromagnetism. Soon they will enter the hi-fi world. A two-year collaboration between GP Acoustics and Hong Kong neighbour Acoustic Metamaterials Group (AMG) will soon see KEF specify a metamaterial as a sound absorber in a (forthcoming model’s) loudspeaker cabinet.
From KEF’s press release: “Harnessing MAT, KEF has created a synthetic material that has the super capacity to absorb all unwanted sound radiating from the rear of the driver, reducing distortion and enabling the prevention of audio distraction.”
What’s going on here?
As listeners, we want to hear the sound waves fired forward by a loudspeaker driver but not the back-wave creating by its rearward motion. The majority of loudspeakers are built into cabinets to control this back-wave. Absorption materials like foams and fibres are often added to reduce the negative impact of internal standing waves that can build up inside the cabinet.
As the ‘meta’ in its name suggests, a metamaterial is not a material but one built using naturally occurring materials to create a synthetic structure that offers properties not found in those same naturally occurring materials. For loudspeaker manufacturers like KEF, that means a structure that can more accurately target a range of frequencies for absorption and with greater efficiency.
To wit, AMG has reportedly built an anechoic chamber prototype whose walls are lined only with 3-4 inch thick metamaterials.
Back to the press release: “MAT is a highly complex maze-like structure, where each of the intricate channels efficiently absorbs a range of specific frequencies. When combined, the channels act as an acoustic black hole, absorbing 99% of the unwanted sound. Other traditional approaches have only allowed around 60% absorption, so the resulting acoustic quality is incomparable. The difference is audible.”
KEF has yet to announce into which loudspeaker they will first drop their new MAT, only that it will be “contemporary”. Ours is now a waiting game…
In the interim, Steve Cummer of Duke University takes us deeper into metamaterials via two eminently comprehensible YouTube videos:
Further information: KEF