A small structure with a “black hole” nickname can be made with a 3D printer and placed inside a pipe. Its job is to reduce the sound that bounces back out.
There is no miniature cosmic monster in the laboratory. The device is a sonic black hole: an engineered arrangement that changes how sound travels and is absorbed near the end of a duct.
ScienceAlert’s 12 October report includes an interview with acoustics engineer Oriol Guasch of La Salle, Universitat Ramon Llull, about research led by Jie Deng and colleagues. The underlying Applied Acoustics paper was published earlier; the new report brings the design and its possible uses to a wider audience.
The useful change is that it can be inserted
The university’s research summary describes a separate, independently manufactured insert. Conventional sonic-black-hole designs require changes to the duct wall itself, which makes the proposed alternative interesting for retrofitting.
That is a practical engineering distinction. Replacing or remaking a pipe is a different task from producing a component that fits into it.
The design is aimed at duct terminations. Its purpose is to absorb sound over a range of frequencies and reduce reflection, rather than make every sound everywhere disappear.
For an existing system, that raises questions about both acoustic behaviour and installation. A promising insert still needs to be suited to the environment where it would operate.
Sound travels as a disturbance through matter
To understand the idea, start with what is moving. NASA’s explanation of mechanical waves describes sound as energy carried through a medium, such as air, rather than a stream of air travelling all the way from source to listener.
Particles pass a disturbance along. A speaker produces changes in air pressure, and those changing pressures can propagate through the air in a duct.
A familiar comparison is a ripple moving across water while an object on the surface bobs locally. The wave carries energy onward even though the material does not simply travel with the wave to its destination.
That distinction is useful here because the insert does not need to collect and store a large volume of air to control sound. Its geometry changes how the pressure disturbance behaves within the available space.
Wavelength helps explain why geometry matters
A wave has a frequency and a wavelength. Frequency describes how often the oscillation repeats; wavelength describes the spacing between corresponding parts of successive waves.
NASA’s sound-wave teaching material relates these through the speed of propagation. At a given sound speed, a higher frequency corresponds to a shorter wavelength, while a lower frequency corresponds to a longer one.
Pitch is how we perceive an important part of that difference. A high musical note and a low note are therefore not just two loudness settings for the same disturbance.
For a device intended to control sound, testing more than one frequency matters. Success with one note does not establish the same behaviour across the range of sounds a real system might produce.
The dimensions and arrangement of an acoustic structure can interact differently with different wavelengths. That is why a carefully shaped component can be more useful than simply placing an arbitrary obstruction at the end of a pipe.
The prototype looks more like a stack than a hole
ScienceAlert describes a fifteen-centimetre prototype with twenty-nine rings mounted along a central rod. The rings and the spaces between them provide the structure that interacts with the sound.
In the reported explanation, sound entering the arrangement slows and its wavelength shortens. Energy becomes concentrated, with losses through friction and heat exchange reducing the energy available to return as an echo.
That description concerns the device’s acoustic behaviour. It does not mean air is being drawn into an event horizon or matter is vanishing from the experiment.
The physical component is finite, manufactured and testable. Its nickname is memorable, but the dimensions and measured behaviour are what make it an engineering result.
Measurements and models answer different questions
The university describes a sequence of modelling steps, moving from a continuous-waveguide approximation to a version with a finite number of rings, followed by experimental validation.
The reported prototype was tested in an impedance tube using a speaker and microphones. That gives a controlled way to examine the sound sent towards the structure and the sound reflected back.
ScienceAlert reports that the measurements broadly matched the simulations, while noting that echoes were reduced rather than completely eliminated. The idealised effect and the performance of a real printed object should be kept separate.
The primary research summary also reports lower reflection than a standard design when compared at the same free cross-sectional area. That comparison is more informative than judging one component in isolation, because it places the proposed geometry against an existing approach.
An astrophysical black hole is a different thing
NASA describes real black holes as enormous concentrations of matter within very small regions. Their defining feature is gravity strong enough that light cannot escape from within the event horizon.
The event horizon is a boundary, not a manufactured surface or an opening cut into a pipe. None of the duct experiment depends on creating that gravitational situation.
There is another important difference between sound and light. Sound needs matter through which to travel. Light is electromagnetic radiation and can move through a vacuum.
So the acoustic name should not lead to a claim that the researchers reproduced every property of a cosmic black hole. The work concerns the control of a mechanical wave in a designed structure.
A quieter duct still has to work outside the lab
The proposed attraction is a component that could be manufactured separately and used to reduce reflected sound in a duct. That is different from demonstrating a finished noise-control product ready for every ventilation system.
The controlled experiment establishes something useful about the concept. Conditions in an installation still need their own checks; a laboratory comparison does not automatically settle how a component should be used in every pipe.
What makes the idea worth following is the combination of a physical insert, an acoustic explanation and measurements that can be compared with the models. The “black hole” may get the first click. A small, independently made component that changes what comes back down a duct is the part that could prove useful.
Sources & further reading
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