Hippopotamus that sounds like a trumpet key to acoustic tagging

A method that controls sound waves to give objects a unique acoustic signature has been presented at Siggraph 2016. Columbia Engineering researchers worked with Disney Research and MIT to develop the approach that allows the design of acoustic filters that can fit within any 3D shape and achieve specific sound filtering properties.

The team, led by Computer Science Professor Changxi Zheng, designed acoustic voxels, small, hollow, cube-shaped chambers through which sound enters and exits, as a modular system. The group likens the voxels, which can be connected to from adjustable, complex structures, to lego. Internal chambers in the voxels allow changes to the acoustic filtering property of the structure. 

In a statement on the Columbia University website, Zheng said: “In the past, people have explored computational design of specific products, like a certain type of muffler or a particular shape of trumpet. The general approach to manipulating sound waves has been to computationally design chamber shapes. Our algorithm enables new designs of noise mufflers, hearing aids, wind instruments, and more – we can now make them in any shape we want, even a 3D-printed toy hippopotamus that sounds like a trumpet.

He added, “We also have proposed a very intriguing new way to use acoustic filters: we can use our acoustic voxels as acoustic tags, unique to each piece we 3D print, and encode information in them. This is similar to QR codes or RFIDs, and opens the door to encoding product and copyright information in 3D printing.”

The team believes the approach could have an impact on the development of a number of products including vehicle mufflers and instruments.

“With 3D printers today, geometric complexity is no longer a barrier. Even complex shapes can be fabricated with very little effort,” Zheng said. “So the question is: can we use complex shapes to improve acoustic properties of products?”

The team has also explored acoustic tagging to uniquely identify a 3D-printed object and acoustic encoding to implant information (like a copyright) into an object’s form. Two objects may have the exact same exterior appearance, but if their hollow interiors contain different voxel assemblies, each object, when filtering a sound wave, produces a sound unique to that object. The researchers recorded the sound made by objects with different voxel assemblies and used an iPhone app they created to accurately identify each object.

The work, presented in a paper titles ‘Acoustic Voxels: Computational Optimization of Modular Acoustic Filters’ was funded in part by the National Science Foundation and Adobe.