Acoustic “black hole” for pipes printed on a 3D printer

Researchers from La Salle University (Ramon Llull University, Spain) have developed an acoustic device that damps echo in pipes, ducts and mufflers. Such structures are called sonic black holes: the wave slows down so much that it almost does not return. The 2026 work was published in the journal Applied Acoustics; engineer Jie Deng is listed as the first author of the article, and acoustician Oriol Guasch is among the co-authors.

How it works

A classic sonic black hole is built as a set of rings and cavities embedded directly in the pipe walls. The new variant is assembled differently: the rings are mounted on a central rod, and their diameters gradually change along the length. The spaces between the rings form cavities that change the course of the sound wave. On entering the structure, sound slows down, its wavelength shortens, and the energy gathers ever more densely at the far end. There it dissipates through friction and heat exchange between the air and the surfaces of the device, so far less energy is reflected back. Guasch compares this to the behavior of a wave at a real black hole: to an outside observer it appears to spend an infinite amount of time getting to the limit point.

Prototype testing

The prototype was printed on a 3D printer. It is a 15-centimeter structure of 29 rings on a central rod, inserted into an impedance tube, which shows how sound behaves when it meets a material or a structure. A speaker sent waves of different frequencies into the tube, and microphones recorded how much sound came back. The results generally matched the computer calculation, but it was not possible to get rid of the echo completely.

The simulation also compared the new geometry with the conventional one. The insert reflected less sound over a wide range of frequencies. The reason lies in the resonances of the cavities between the rings: in the new scheme they fall at higher frequencies, so the black hole effect is maintained over a wider frequency range.

The device is manufactured separately from the duct and simply inserted into an existing system. The nearest application is combating noise in ducts and mufflers, where reflected sound interferes. The authors are already studying whether such structures can be made two-dimensional and three-dimensional, up to room acoustics. Before real deployment, problems have to be sorted out: the cavities can clog with particles, and temperature, pressure and air flow have an effect.

Image: Dejan Krsmanovic CC BY 2.0 · License

Translation editor: Ловушкин А.