How does the sound pressure level fluctuate when the rotational speed of the cooling fan becomes unstable?

2025-04-21

I）， What is Unstable Fan Speed?
1.1 Manifestations of Unstable Rotational Speed
The unstable rotational speed of a Cooling Fan typically manifests as fluctuations in speed, where the fan's rotational speed varies within a certain range instead of maintaining a constant value. This phenomenon may result from various factors, including fluctuations in power supply voltage, issues with the drive circuit, motor failure, or changes in the external environment.

1.2 Causes of Unstable Rotational Speed
• Unstable Power Supply: Voltage fluctuations or frequent interruptions in current can lead to instability in the fan motor's rotational speed.
• Motor Failure: Wear, aging, or other mechanical defects in the motor itself can cause variations in rotational speed.
• Load Changes: Sudden increases or decreases in system load may compromise the stability of the fan's rotational speed.
• Environmental Factors: External conditions such as temperature and humidity fluctuations may also impact the fan's operational performance.

2），How does the sound pressure level fluctuate when the rotational speed is unstable?
2.1 Relationship between Rotational Speed and Sound Pressure Level
In general, the sound pressure level of a fan exhibits a certain degree of positive correlation with its rotational speed. Higher rotational speeds result in faster airflow velocities, which typically generate greater noise levels. However, when the rotational speed becomes unstable, the relationship between sound pressure level and rotational speed deviates from a simple linear pattern. Fluctuations in rotational speed can induce periodic variations in noise, with the specific fluctuations depending on the amplitude and frequency of the rotational speed changes.

2.2 Noise Characteristics under Unstable Rotational Speeds
- Low-frequency noise fluctuations: When rotational speed fluctuations occur at a relatively slow pace, low-frequency noise fluctuations are often perceived. These fluctuations may arise due to variations in motor load and are typically characterized by a lower-pitched sound.
- High-frequency noise fluctuations: Rapid fluctuations in rotational speed can produce sharp high-frequency noise. This occurs because the manner in which fan blades interact with the air changes at different rotational speeds, leading to frequent air disturbances.
- Irregular noise fluctuations: When rotational speed fluctuations are highly irregular, irregular noises, including buzzing sounds, may be heard. Such phenomena could stem from issues within the motor or control system, resulting in unstable airflow during fan operation.

2.3 The Amplitude of Sound Pressure Level Fluctuations
The instability in rotational speed typically results in a significant fluctuation range of sound pressure levels, particularly when the fan operates at lower rotational speeds. This occurs because, at reduced rotational speeds, fan noise exhibits greater sensitivity to variations in rotational speed. Conversely, at higher rotational speeds, fluctuations in rotational speed exert a relatively stable influence on noise generation.

3）. How to Mitigate Noise Fluctuations Caused by Unstable Fan Speed?
3.1 Employ a Stable Power Supply
To ensure the stability of the fan's rotational speed, it is essential to maintain a stable power supply. Utilizing high-quality power adapters or voltage regulators can minimize the impact of voltage fluctuations on fan speed, thereby preventing noise fluctuations caused by power inconsistencies.

3.2 Conduct Regular Inspections of the Motor and Drive System
Periodic evaluation of the fan motor's operational condition and the drive circuit can effectively prevent speed instability issues arising from equipment aging or malfunction. Timely replacement of worn components ensures smooth fan operation and reduces noise fluctuations.

3.3 Enhance Load Management
For applications experiencing significant load variations, implementing an advanced load management system can ensure stable fan operation under varying load conditions, thus avoiding speed fluctuations induced by load changes.

3.4 Utilize a High-Performance Speed Controller
A high-performance fan speed controller enables precise regulation of fan speed, mitigating instability caused by load variations or voltage fluctuations. By dynamically adjusting the fan speed, it is possible to optimize heat dissipation while minimizing noise fluctuations as much as feasible.

4）. Summary
When the rotational speed of the cooling fan is unstable, the sound pressure level frequently exhibits fluctuations. Noise characteristics may present as variations in low or high frequencies, or even irregular noise patterns. To mitigate these fluctuations, several measures can be implemented, such as utilizing a stable power supply, conducting regular inspections of the motor and drive system, and enhancing load management. By adopting these strategies, noise fluctuations can be effectively controlled, thereby improving the overall stability and acoustic comfort of the system.

In practical applications, the performance of fans and noise control are inherently interconnected. Rational design and precise control mechanisms are essential for ensuring the reliable operation of equipment while minimizing noise pollution. It is anticipated that this article will provide valuable insights into understanding the relationship between the rotational speed of the cooling fan and the sound pressure level.