BU Engineers Send Loud and Annoying Sound Back to Where it Came

Getting an MRI can be an extremely nerve-wracking experience. In addition to the confining space, the noise can be highly annoying and anxiety provoking. Fortunately, acoustic engineers at Boston University have created a possible solution.

Relying on their mathematical prowess and 3D printing technology, Reza Ghaffarivardavagh and Xin Zhang developed an open, ring-like structure that attenuates sounds while maintaining airflow. Instead of a traditional sound barrier, the pair has created an open conduit that baffles sound.

The BU engineers calculated the dimensions and specifications that a PVC-like metamaterial that interferes with the transmitted sound waves but allows air to radiate through the open structure. The basic premise is that the metamaterial needs to be shaped in such a way that it sends incoming sounds back to where they originated.

During a trial run, they decided to create a structure that could silence sound from a loudspeaker. Based on their calculations, they modeled the physical dimensions that would most effectively silence noises. Bringing those models to life, they used 3D printing to materialize an open, noise-canceling structure made of plastic (as seen in the featured image above).

Next, while piloting the apparatus in the lab, the researchers sealed the loudspeaker into one end of a PVC pipe. On the other end, the tailor-made acoustic metamaterial was fastened into the opening. With the hit of the play button, the experimental loudspeaker set-up came oh-so-quietly to life in the lab.  

The metamaterial, ringing around the internal perimeter of the pipe’s mouth, worked like a mute button until the moment the ring was pulled out of the tube. The lab suddenly echoed with the screeching of the loudspeaker’s tune.

You can watch the noise attenuation in action here:

Ghaffarivardavagh and Zhang believe their “acoustic plug” has a variety of practical application where sound must be attenuated by airflow needs to be maintained. These applications include jet engine noise on an airport tarmac, automobile engines and even those anxiety-provoking MRI machines.

Source: BU