Understanding ISO 3745 in 5 Minutes: Essential for Acoustic Testing and Quiet Product Design
06/07/2025
As quiet design becomes increasingly important in product development, the international standard ISO 3745 is attracting growing attention. This standard defines methods for measuring sound power levels (PWL) using anechoic rooms and hemi-anechoic rooms.
This article explains the key points for engineers and acoustic testers, including:
- What is ISO 3745?
- How are measurements performed?
- What are the requirements for anechoic rooms?
—all in just five minutes.
What is ISO 3745?
ISO 3745:2012 is an international standard that provides high-precision methods to measure sound power levels of noise sources using anechoic and hemi-anechoic rooms.
Compliance with ISO 3745 ensures globally reliable evaluation of a product’s acoustic performance.
Core Formula for Measurement
ISO 3745 calculates sound power level with the following equation:
LW = (Lp − K1 − K2) + 10 log(S/S₀)
LW: Sound power level (dB)
Lp: Measured sound pressure level (dB)
K1: Background noise correction
K2: Environmental (sound field) correction
S: Measurement surface area (m²)
S₀: Reference area (1 m²)
Notably, K2 indicates how closely the test environment approximates a free sound field—a critical factor in accurate measurement.
3 Key Requirements for ISO 3745-Compliant Anechoic Rooms
To meet ISO 3745 standards, anechoic rooms must satisfy the following:
1. Inverse Square Law Validation
The sound pressure must decrease proportionally to the square of the distance from the source—demonstrating a free-field environment.
2. K2 ≤ 0.5 dB
The K2 correction must be small, confirming minimal influence from reflections or reverberation.
3. Optimized Acoustic Space
ISO 3745:2012 removed the strict “0.99 absorption coefficient” rule found in earlier versions. Now, meeting the inverse square law is sufficient, allowing more flexible design.
How Anechoic Room Design Has Evolved
Traditionally, anechoic rooms used glass wool wedges to achieve absorption coefficients above 0.99.
Recent trends feature:
- Thinner sound-absorbing materials
- New advanced materials
- Absorbers with damping capabilities beyond absorption
These developments have led to more comfortable anechoic rooms—without the uncomfortable “ear-popping” sensation.
How ISO 3745 Differs from ISO 3744
While ISO 3745 is intended for high-precision measurements, ISO 3744 provides practical methods for testing in semi-anechoic environments.
- ISO 3744 allows K2 values up to 4 dB, making equipment and room requirements more relaxed.
- Sonora’s MSAC and VSAC are examples of advanced semi-anechoic chambers that comply with ISO 3744.
In Conclusion: Toward Quieter Products
With the rise of EVs and consumer electronics, acoustic performance has become a key differentiator.
ISO 3745 is an indispensable tool for making noise “visible.”
For those looking to implement sound evaluation or introduce anechoic rooms, Sonora’s total solution offers ISO 3745-compliant environments—featuring proprietary technologies like Soramata Panels and BFW.