|The noise a fan produces can come from various sources such as bearing friction or the vortex flow. The loudest of these noises is stated on the fans specification sheet in decibel units. A higher “A-weighted sound level” or dBA number means a noisier fan. However, this rating is just the starting point and should only be used as a reference. There are many components which can cause the fan to become louder over time. The primary factors of a fans noise level is the fans speed, bearing system, mounting direction, and its structural design.|
| Sound Level Change
|2 to 3 dBA||Barely Perceptible|
|5 dBA||Readily Noticeable|
|10 dBA||Doubling or Halving of Noise|
|20 dBA||Dramatic Change|
A faster spinning impeller delivers more air but causes a higher friction to be produced between the bearing and shaft. As a result, there is a positive correlation between airflow and noise. Keeping size and bearing constant, higher airflow fans tend to be noisier. The fans speed is determined by its RPM rating or rotations per minute number. A goal of many engineers is to reduce the fan’s RPM as much as possible without compromising its heat dissipation performance.
The noise a fan produces is also dependent on the bearing system it uses. Initially, the noise level from bearings is overshadowed by the fans rotor blade turbulences. As the fan ages, the bearings get louder and may become the primary source of noise. Sleeve bearing fans start off quieter but become louder at a faster rate due to its lubricant design. On the other hand, dual ball bearings start off slightly louder but will remain more consistent throughout its life. More Information.
Improper Mounting and Oil Loss
The sleeve bearing system consists of a sealed cylinder of lubricant. This oil based lubricant will eventually evaporate as the fan ages even if it wasn’t used. A lack of lubrication will increase the amount of friction between the bearing and shaft. As a result, the fan will become noisier if not refilled with oil. Improper mounting of sleeve fans will also accelerate the oils evaporation. For this reason, sleeve bearing fans are noisier if not mounted or stored horizontally.
Frame and Impeller Design
The design of the fan is largely responsible for how much air it delivers and the level of noise it will produce. However, a loud fan does not necessarily mean an inferior design. Many fans are used in applications that have strict high airflow or high static pressure requirements. Others are used in environments that are already very noisy. In these scenarios, the noise level of the fan can be ignored in order to maximizing heat dissipation.
| Sound Rating
|0 dBA||Threshold of Hearing|
|20 dBA||Rustling Leaves|
|40 dBA||Quiet Library|
|60 dBA||Air Conditioner|