Designing Anechoic Chambers for the Polish National Metrological Office

What happens when you step into perfect silence? Inside these chambers, the Sound Pressure Level (SPL) drops below the threshold of human perception. Your footsteps dissolve instantly, your breath feels amplified, and your heartbeat becomes uncomfortably loud. After a few minutes, most people begin to lose their balance. Some report hearing their own blood flow or the grinding of their joints.

Most people can tolerate only a few minutes before dizziness, nausea, or even mild panic sets in. This is not a thought experiment but a proven physiological reaction. Human orientation depends on subtle reflections of sound, and when those cues vanish in an anechoic chamber, the body begins to rebel. Studies published in the Journal of the Acoustical Society of America show that most people cannot remain in such an environment for long before discomfort sets in.

So, why deliberately build such a disorienting environment? Because silence, when controlled and engineered, becomes a tool of extraordinary precision. Silence allows scientists to measure the immeasurable, industries to refine the quietest technologies, and societies to better protect human well-being from harmful noise.

This is the story of how DECIBEL, together with partners in Poland, engineered one of the most advanced acoustic facilities in Europe: the anechoic chambers of the Polish National Metrological Office (GUM).

 

Silence as a Scientific Instrument Worldwide

Across the world, only a handful of chambers achieve cut-off frequencies as low as 50 Hz. The Microsoft Audio Labs in Redmond, the Orfield Labs chamber in Minneapolis, or the NTT Facility in Japan are often cited as the “quietest places on Earth.” Each is a cathedral of silence, used not for meditation, but for cutting-edge measurements: from testing smartphone microphones to refining medical hearing aids and calibrating aerospace instruments.

 

 

The new GUM facilities in Kielce, Poland, now join this exclusive group. With their 50 Hz and 100 Hz anechoic chambers, GUM has entered the international map of state-of-the-art metrological institutions. These chambers are not merely impressive structures; they are instruments in themselves, designed with surgical precision to guarantee Poland’s leadership in sound and vibration science.

 

As the CEO of DECIBEL, Eng. PhD. Tsvetan Nedkov explains, “Projects like this show why acoustics is not just about noise reduction but about progress. These chambers will allow Poland to lead in metrological science, and they demonstrate how silence, engineered with precision, becomes a global resource for innovation.”

 

The Client’s Requirements for Perfection

The Polish National Metrological Office demanded more than just impressive specifications; they required benchmarks that would position the country among global leaders.

• Two anechoic chambers: One large chamber of 1402 cubic meters operating at a 50 Hz cut-off, and a smaller chamber of 319 cubic meters at 100 Hz. Both spaces had to create true free-field conditions, where sound disappears as if in open air.
• Vibration protection: Active quarries only five kilometres away meant that vibration resilience had to be engineered to Class V0 standard - the strictest vibration isolation category, requiring ground motion in the chamber to remain below 4 micrometres per second across all relevant frequencies, ensuring near-complete immunity to external vibrations, ensuring that even the faintest external tremor would not distort measurements.
• Noise control: Internal noise had to stay below the NR5 curve (an ultra-low noise reference curve that corresponds to extremely quiet acoustic environments, much quieter than a recording studio, used here to define the maximum permissible background noise in the chambers), in compliance with ISO 8253-2 (an international standard for audiometric testing that defines how to measure and control sound fields to guarantee accurate hearing assessments and device calibration). This ensured that testing of medical devices, hearing technologies, and industrial noise emissions would be accurate and reliable.

 

The Engineering Approach to Silence

1. Box-in-Box Construction

To meet these standards, DECIBEL and its partners adopted a box-in-box principle, constructing each chamber as a reinforced concrete structure isolated from its surroundings. The result was two acoustic islands inside the laboratory complex.

 

 

2. Vibration Isolation Systems

Vibration control was the next frontier.

• 100 Hz chamber: Supported by 100 mm elastomer pads (f₀ ≈ 5 Hz - the natural resonance frequency of the vibration isolation system, meaning the system filters out vibrations above this frequency and prevents them from affecting the chamber).
• 50 Hz chamber: Built on 2.5 Hz steel springs with elastomer supports, designed with an option to upgrade to air springs with active damping if necessary.
  Finite Element Method (FEM) simulations (a computer-based engineering technique that divides complex structures into thousands of small elements to predict how they will respond to forces, such as vibrations from quarry blasts or heavy equipment), combined with real on-site vibration measurements during quarry detonations, validated that the system not only met but exceeded client requirements.

 

 

The project manager reflects on this phase: “Our communication with GUM was just as critical as the engineering itself. Every requirement had to be validated under real construction pressures. Working in an environment with active quarries meant vibration simulations and on-site testing had to be synchronised precisely. It was a logistical and technical challenge that required flawless coordination.”

 

3. Acoustic Absorption Wedges

Inside, the walls and ceilings were lined with polyether polyurethane wedges that gave the chambers’ iconic look:

• 170 cm long in the 50 Hz chamber
• 86 cm long in the 100 Hz chamber

These wedges prevent reflections, absorbing sound so completely that even footsteps vanish without a trace. For the installers, this was the most delicate task. “The polyurethane wedges were not just glued to walls,” recalls one member of the installation team. “Each wedge was precision cut on 3d CNC specialist equipment. The fitting and alignment were completed with millimetre precision by our skilled installers. Working in the confined void between the inner and outer structures to install the ventilation system was demanding. But when the last wedge was in place, we knew we had created something truly unique. Standing inside the chamber for the first time, we felt the silence; we had built it with our hands.”

 

 

4. Silent Ventilation

Ventilation was perhaps the most paradoxical challenge: how to move air in and out of a room without creating the faintest trace of sound. A 13 m-long HVAC duct with mineral wool lining and split silencers was designed to achieve attenuation across all critical frequencies.

• At high frequencies (4-8 kHz), staggered silencers blocked line-of-sight sound transmission.
• At low frequencies (63 Hz), additional silencing elements were introduced to reinforce damping.

The result was a breathable, comfortable environment that remained inaudible to both human ears and sensitive instruments.

 

 

Tangible Outcomes for Industry and Science

The impact of the GUM chambers is multifaceted. Now, they will:

• Provide ISO-standard testing environments for industry and research.
• Allow audiometric calibration, essential for medical devices and hearing technologies.
• Enable industrial noise testing, helping manufacturers build quieter, safer machines.
• Support fundamental research, positioning Poland as a European hub for acoustic science.

The Polish National Metrological Office now possesses one of Europe’s most advanced acoustic infrastructures. For DECIBEL, this project is both a technical triumph and a mission statement. It shows that silence can be engineered, that it has measurable value, and that it can shape healthier societies. As DECIBEL’s CEO concludes, “These chambers are not just about acoustics, they are about building the conditions for progress.”

 

 

Even the most complex environments can be mastered with precision, collaboration, and innovation.

Contact our team today for an individual consultation on your acoustic or soundproofing project, explore more of our case studies or learn how our products and solutions can turn your challenges into measurable success.