Why Background Noise Levels Matter in Anechoic Chambers

Background Noise: The Invisible Enemy of Acoustic Testing

When you think of an anechoic or semi-anechoic chamber, you may picture a perfectly silent space lined with acoustic wedges.
But in reality, even the quietest test environments are not immune to a hidden adversary—background noise.

This “background noise” can stem from HVAC systems, equipment vibration, or sound leakage through cable ports.
Once it contaminates the measurement environment, it can compromise data accuracy and undermine confidence in the results.

The “-10 dB Rule” in Acoustic Standards

IInternational standards such as ISO 3744:2010 and ISO 3745:2012, which govern sound power level (PWL) measurements, define the following rule:

The background noise level should be at least 10 dB lower than the measured sound from the Device Under Test (DUT).

For example, if the DUT emits 40 dB at a given frequency, the background noise must be below 30 dB in that band.
This ensures the K₁ correction factor remains small and measurement reliability is maintained.

What Is the K₁ Correction Factor?

Let’s look at the typical formula used in sound power measurement:

If K₁ is too large or unstable, the calculated sound power level (Lw) becomes unreliable—especially critical for low-output devices such as sensors, motors, and cameras in the 30–40 dB range.

Controlling Background Noise Starts with Room Design

To reduce background noise, the following countermeasures should be considered:

• Low-noise ventilation design (e.g., silencers, reduced air velocity)
• Acoustic sealing of cable and duct penetrations
• Elimination of internal noise sources (vibration, transformers)
• Optimization of sound-absorbing materials—especially in the low-frequency range

At Sonora Technology, our solution is the proprietary BFW (Broadband Fractal Wedge) system.
This design enables chamber background noise levels below 25 dB(A), providing the ideal environment for high-precision measurements using HBK instrumentation.

A Reliable Testing Environment with Sonora × HBK

As the target sound levels of products continue to decrease, the testing environment must become quieter to keep pace.
HBK’s LAN-XI system and Type 4204 reference sound source are engineered to deliver peak performance only when background noise is sufficiently suppressed.

With Sonora’s anechoic chambers designed to meet the –10 dB requirement, we support stable K₁ correction and deliver measurement environments that ensure data integrity and promote low-noise product development.

Conclusion: Silence Is the Infrastructure of Accuracy

The quietness of an anechoic chamber is not a luxury—
It’s a critical infrastructure for precision acoustics, forming the foundation for valid design decisions.

–10 dB below the measurement sound level.
That’s the baseline for trust in your data.

He who controls background noise controls the accuracy of testing.

Experience the next generation of quiet development environments with the Sonora × HBK total solution.

Contact Us

For consultations on chamber design or acoustic measurement systems, please reach out to:

Moritani Corporation, Tokyo Headquarters – Machinery Division 2

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