Acoustic Meta materials for the Reduction of Noise Emissions from HVAC Systems

Acoustic metamaterials are specially structured materials that can block or absorb sound in certain frequency ranges in a very targeted manner and can therefore also be interesting for the sound insulation of heat pumps and refrigeration systems.

What are acoustic meta-materials?

Meta materials are not new substances, but conventional materials (e.g. plastics, metals, glass) that acquire new acoustic properties through a micro or macro structure.
In acoustics, many small resonators (diaphragms, mass-spring systems, cavities) are often arranged periodically; this creates so-called stop bands, i.e. frequency ranges in which sound hardly propagates. A principle on which Helmholtz resonators are already based. Such structures can, for example, reduce sound in the range between 500 and 1K Hz by up to 20 dB through a baffle without the wall becoming thick or heavy.
Classic sound insulation usually works with mass (heavy walls) and porous absorbers; Meta materials, on the other hand, use targeted resonances and interference effects to strongly attenuate certain frequencies.
In Vibro acoustic metamaterials, mechanical resonators are integrated on or into a support structure; they absorb energy from the vibration in the exact frequency range for which they are tuned, thus reducing structural and airborne sound. There are passive variants (structure only) and active variants with sensors and actuators, in which the stop bands can even be moved during operation to adapt to changing noise spectrum's.

Relevant frequencies for heat pumps

Air-to-water heat pumps mainly generate noise from the fan, compressor and flow noise (air/refrigerant), often in the range of 32 to 8KHz. In my opinion, meta-materials are promising here to suppress exactly the dominant sound and tape noises (e.g. fan fundamental frequency and compressor frequencies) more efficiently without making baffles or sound enclosures very heavy or thick.

Possible applications for sound enclosures for heat pumps and refrigeration systems

Sound barriers are conceivable in which the wall panels are equipped with resonator arrays made of plastic or metal on the inside, similar to vibro-acoustically optimized foundations.
As with noise barriers, existing enclosures or walls could also be upgraded to "meta-walls" by glued or screwed on resonator modules without changing the base material. For example, walls around facilities or other obstacles could also be equipped with meta-materials to prevent the reflection of sound.

State of the art and practical relevance

Vibro Acoustic meta materials have already been prototype in noise protection (e.g. Fraunhofer ISE and IBP) and show significantly better reductions in the laboratory than simply doubling the wall thickness.

For heat pumps, classic soundproofing hoods and baffles with porous absorbers and air deflections through Louvre or Labyrinth systems are currently commercially available and achieve a reduction of 15–22 dB(A) over the frequency spectrum. The frequency range of < 63 Hz is not addressed by most products today, in-situ measurements show that in the range of 32 Hz with sound obstructions, a higher sound emission can also result.
Meta material-based solutions for heat pumps are currently still in the development stage, but should become interesting in the medium term when lighter, specifically frequency-tuned hoods with better damping are required, that these requirements will come is already foreseeable today due to the spread of heat pumps and air conditioning systems, who can then specifically reduce the insulation in certain sound emissions critical frequencies will be able to secure a leading market position.

Romolo Vicari 09.02.2026