In March 2019 we ran an article about an amazing new acoustic metamaterial which cancelled noise at specific frequencies without significantly impeding airflow. We were very interested to find reports of another new metamaterial developed at the University of Surrey in the UK and being developed by UK company Metasonics
This material creates a reconfigurable acoustic lens which is capable of shaping a wavefront and directing and focusing sound in a precise way. These are passive devices and they can be used to shape the sound at its source or at the listener.
Don’t Acoustic Lenses Already Exist?
To shape a beam of light we can use lenses, we’re all familiar with how these work and the control offered by simple lenses is amazing. You can do the same with sound but with far more limitations and that’s a pity.
This new metamaterial offers the ability to focus sound and unlike the current alternatives it is simple, inexpensive and reconfigurable.
Acoustic lenses exist but they are fixed. This isn’t the same as a horn or waveguide. They used to be popular with companies like JBL in the 70s and seem to have fallen out of favour since then. They usually look like a stack of angled, flat plates in front of an HF tweeter. If you’re not familiar with them or how they work here is an excellent article from 1962.
A much more modern approach to controlling the precise dispersion of sound is to use a phased array. These are used extensively in medical imaging and industrial testing and they are being actively explored as a way of creating very directional speaker systems. They rely on creating a soundfield through the use of multiple drivers working together with precisely timed offsets between the drivers to shape the wavefront. It is similar to the Spatial Soundwave Technology we reported on last month but with a very different wavefront being created. Large festival PA systems use a similar technique by using very precise delays between a line of subwoofers across the stage to shape and focus the sound of low frequencies. The drawback of these systems is that unlike fixed lenses that are dynamically controllable, they are complex and expensive to implement.
How Does It Work?
The grid is populated by small metamaterial bricks which contain a folded path of very specific lengths. These labyrinthine paths each introduce a specific phase shift and the different phase shifts introduced by each metamaterial brick combine to shape the wavefront in a similar way that a lens does to light.
What Can You Do With Metasonics Acoustic Lenses?
Applications range from the medical and engineering applications currently fulfilled by phased arrays through very directional transmission of sound for home entertainment and automotive applications to installed uses in live events and advertising.
How do you think these lenses could be used in a pro audio setting?