Engineers 3D-Print a Sonic Black Hole That Swallows Sound

Echoes are a nuisance in recording studios. They are worse inside pipes. In ventilation ducts, air-conditioning channels, industrial exhausts and ordinary plumbing, sound waves bounce around until the rattle becomes hard to ignore. A team of engineers in Spain has built something to deal with it: a device that treats noise the way a black hole treats light, and swallows it.

The device is called a sonic black hole, and this version can be 3D-printed and inserted directly into an existing pipe. That plug-in design is a real step forward, according to reporting by ScienceAlert on October 12, 2026. Earlier versions had to be manufactured as part of the pipe itself, which made them difficult to retrofit into systems already in place.

The work comes from engineer Jie Deng and acoustics engineer Oriol Guasch at La Salle, Universitat Ramon Llull, in Spain, with the findings published in the journal Applied Acoustics. The physics is a little like Zeno's old paradox, in which a traveler covers half the remaining distance, then half again, and seemingly never arrives. A sound wave entering the device slows down progressively, its wavelength shrinking as it travels, so it takes longer and longer to reach the end.

Earlier sonic black holes were built the other way round. Conventional designs line the inside of the pipe itself with rings and cavities, manufactured together with the duct, which made them awkward to install in systems that already existed. Guasch and his colleagues wondered whether they could turn the whole thing inside out. They call the result a sonic Christmas tree rather than a funnel: the rings sit on a central rod instead of the pipe walls, so the device can be manufactured on its own and simply inserted into a duct, according to the team's paper.

The sound never comes back

The prototype is a 15-centimeter structure built from 29 rings mounted along a central rod, each ring a slightly different diameter. The gaps between the rings form cavities that interfere with how sound moves down the pipe, slowing the wave and concentrating its energy toward the far end.

Instead of bouncing back, most of that concentrated energy is dissipated as friction and heat exchange between the air and the device's surfaces. Guasch put it this way: in the ideal case, once a wave enters the sonic black hole, it does not come back out. An external observer sees something resembling what an astrophysical black hole does to light, with the wave appearing to take forever to reach its limit.

Guasch explained the effect with an example. Shout into a duct that is closed at the far end and an echo comes back after a short delay, he told ScienceAlert. Terminate that duct with a sonic black hole, he said, and you would hear almost no echo at all. Acoustically, it would feel as if the tube were infinitely long, with no end for the sound to bounce back from.

The researchers tested the printed prototype in an impedance tube, a laboratory apparatus for measuring how sound behaves when it meets a structure. A speaker sent waves of different frequencies through the tube, and microphones measured how much bounced back. The reflections broadly matched the team's computer simulations, though the device did not eliminate echoes completely.

A wider range than older designs

The simulations turned up an advantage the team had not set out to find. Older sonic black holes only worked across a limited range of frequencies, but the new plug-in geometry kept the black-hole effect going over a considerably wider band. It also reflected less sound than the conventional version across that range.

The reason is resonance. The cavities between the rings resonate at particular frequencies, changing how the device absorbs sound, and in the new design those resonances sit at higher frequencies. That keeps the effect working across more of the spectrum.

The near-term use is noise control, especially in ducts and silencers where reflected sound causes engineers trouble. The team is also looking at whether sonic black holes can be extended into two and three dimensions, with room acoustics as a possible target. Plenty of obstacles remain before any of this shows up in real buildings: dust and particles could clog the cavities, and temperature, pressure and flowing air all complicate the physics.

For Guasch, the draw is as much intellectual as practical. He told ScienceAlert that manipulating sound this way would have seemed like science fiction only a few years ago, and that the project brings together areas of knowledge that at first glance seem unrelated. Full details of the experiment are in the team's paper in Applied Acoustics, as reported by ScienceAlert.

IMAGE_SEARCH_QUERY: 3D printed ringed rod device inside clear laboratory pipe IMAGE_DESCRIPTION: A 3D-printed sonic black hole prototype made of metal rings mounted along a central rod sits beside a clear impedance tube in a laboratory, with the ring structure visible during acoustic testing.