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Fan Noise Testing and Acoustic Quality Evaluation

Fan Acoustic Measurement Methods and Standards

Advanced acoustic testing to ensure low-noise performance and long-term reliability

Following the CNS 8753 test method, we perform fan noise measurements inside a professional semi-anechoic chamber. As shown in the illustration, the fan is placed one meter away from the sound level microphone, and the acoustic signal is recorded from the intake side. All measurement data is processed through our acoustic analysis software, which generates multiple frequency-domain charts, including:

FFT Analysis – Converts time-domain data into the frequency domain to identify how the acoustic energy is distributed.
Octave Band Analysis – Breaks the sound into standardized frequency bands to visualize overall sound pressure patterns.
Loudness Evaluation – Estimates how the human ear perceives the sound level.
Modulation Analysis – Detects tonal peaks, abnormal harmonics, or periodic vibration that may indicate unwanted noise.

These advanced analyses allow us to clearly understand each fan’s acoustic signature, identify potential noise sources, and further improve structural design and rotor balance—resulting in quieter operation and enhanced product stability.

Purpose and Importance of an Anechoic Chamber

To ensure that fan noise measurements are accurate and repeatable, testing must be performed in a controlled acoustic environment.

1. Block external noise, preventing interference from the surrounding environment.

2. Eliminate internal sound reflections, ensuring that no echoes distort the measurement results.

Types of Anechoic Chambers

Anechoic chambers are generally categorized based on whether the floor absorbs sound:
◼️ Full Anechoic Chamber – All surfaces, including the floor, ceiling, and walls, are covered with sound-absorbing materials.
◼️ Semi-Anechoic Chamber – The walls and ceiling are treated with acoustic wedges, while the floor remains reflective.

At ADDA, all fan acoustic tests are performed in a semi-anechoic chamber with a background noise level as low as 10 dB(A). This setup provides a stable and interference-free environment suitable for evaluating:

◼️  Ultra-low-noise fans Automotive-grade
◼️  cooling components Thermal modules for IT
◼️  and communication equipment

It ensures consistent and reliable acoustic measurements across all product categories.

Ways to Describe Sound Levels

Sound energy can be expressed in several different forms, such as:
◼️ Sound Pressure
◼️ Sound Power
◼️ Sound Intensity

In most engineering applications and acoustic tests, the primary metric used is the Sound Pressure Level (SPL).

Relationship Between Sound Pressure and Sound Pressure Level
Sound pressure is measured in Pascals (Pa).
The quietest sound the human ear can detect is roughly 20 μPa (20 × 10⁻⁶ Pa), and this value is used as the reference sound pressure in acoustics.To make comparisons easier across different sound levels, sound pressure is converted into a logarithmic scale, expressed in decibels (dB):

SPL = the sound pressure level referenced to 20 μPa, expressed in dB

This means:
◼️ When the sound pressure is higher than 20 μPa → the SPL value becomes positive.
◼️ When the sound pressure is lower than 20 μPa → the SPL value becomes negative.

Difference Between dB and dB(A)

The human ear does not respond equally to all frequencies.

Even when two sounds have the same measured sound pressure level, our ears perceive low-frequency and mid-to-high-frequency sounds very differently.

For example, when a sound measures 30 dB:

At 100 Hz, the ear perceives it as only about 10.9 dB
At 500 Hz, it is perceived as almost 26.8 dB

Because of this difference in human hearing sensitivity, noise measurements often apply a correction curve that reflects how our ears actually perceive loudness. This is known as A-weighting.

The corrected value is expressed as dB(A), which represents the sound level as perceived by the human ear, rather than the raw physical measurement.

Selecting the Right Microphone and Its Measurement Range

The accuracy of a fan noise test depends greatly on the type of microphone used. At ADDA , we utilize two categories of test microphones:

◼️ Standard ½-inch Microphone Measurement range: 15 dB(A) – 148 dB Suitable for most general-purpose fan noise measurements.
◼️ Low-Noise Microphone

Measurement range: 6.5 dB(A) – 113 dB Designed for ultra-quiet products.

When selecting this microphone, it is important to consider its very low self-noise to avoid measurement distortion.

Every microphone has a minimum measurable noise level.

For example: A standard microphone can only measure down to 15 dB(A). If a fan is actually quieter than 15 dB(A), the reading will still show 15 dB(A) — resulting in a measurement that appears louder than the real sound.

In contrast:

A low-noise microphone can measure down to 6.5 dB(A), allowing it to accurately capture the acoustic performance of extremely quiet products.

For low-noise, silent, or precision applications, using a low-noise microphone is essential to avoid overestimated or distorted data.

Sound Quality Analysis Parameters

Sound quality analysis focuses on understanding the acoustic characteristics generated during fan operation. Rather than looking only at the overall dB level, the evaluation considers multiple acoustic parameters to determine whether the sound is smooth, stable, and free of abnormal noise.

Common parameters used in sound quality analysis include:

◼️ SPL (Sound Pressure Level) – Evaluates overall loudness.

◼️ Loudness – Reflects how the human ear subjectively perceives the sound.

◼️ Modulation – Identifies impact noise, rubbing noise, or periodic tonal fluctuations.

◼️ Peak Ratio (P.R.) – Detects sudden spikes or abnormal noise events.

ADDA utilizes professional equipment from HEAD Acoustics (Germany) together with the Artemis acoustic analysis software. This system allows detailed sound-quality diagnostics during both development and product validation, including:

◼️ Whether the fan produces smooth and steady operating noise.

◼️ Detection of abnormal sounds such as rubbing, ticking, or motor-related modulation.
◼️ Whether sound characteristics degrade over time or under different load conditions.

◼️ Consistency of acoustic performance across production batches.

In other words, we do more than measure “how loud it is”—we ensure the sound is pleasant, stable, and free of defects.

Vibration Measurement and Noise Improvement

Fan noise is often caused by vibration from the motor, impeller, or structural components. Vibration measurement is therefore essential for identifying the true source of noise and developing effective noise-reduction solutions.

For example:

A fan may sound normal when tested alone, yet produce abnormal noise once installed inside a system. This is typically due to vibration transmission or resonance within the system structure. In such cases, vibration measurement is required to locate the issue and determine the corrective actions.

During vibration testing, ADDA uses both single-axis and tri-axial accelerometers, allowing us to measure:

◼️ Acceleration (g / m/s²) – Identifies vibration strength and potential abnormal sources

◼️ Velocity (m/s) – Helps detect resonance or amplification of vibration

◼️ Displacement (μm / mm) – Used to evaluate the structural stability of bearings, impellers, and shafts

Using these measurements, we can accurately determine:

◼️ Which component or location is generating the vibration.

◼️ Whether the issue is caused by imbalance, bearing wear, or system-level resonance.

◼️ Whether noise-reduction improvements are truly effective after corrective actions.

Need support in creating a test plan or customized validation?

Contact the ADDA technical team —

we can recommend the most suitable testing approach based on your application.