What's Noise?
Noise is unwanted sound judged to be unpleasant, loud or disruptive to hearing.
There are two important characteristics of sound or noise - frequency and loudness.
The higher the frequency, the more high-pitched a sound is perceived.
Loudness of sound is commonly expressed in decibel (dB), the more intense the sound, the higher the db count. Long exposure at 85 dB is dangerous; at 120 dB, even short exposure can do damage.
Here's how some sounds score:
| Sample | dB count |
| Nearby Whispering | 30 dB |
| Refrigerator Humming | 40 dB |
| Air Conditioner | 60 dB |
| Lawn Mower | 80 dB to 85 dB |
| Approaching Train | 100 dB |
| Ambulance Siren | 120 dB |
Causes of Fan Noise
Noise emanating from ventilation fan is a function of many variables and causes, for example:
1.Vortex Shedding
This is a broad band noise source generated by air separation from the blade surface and trailing edge. It can be controlled somewhat by good blade profile design, proper pitch angle and notched or serrated trailing blade edges.
2.Turbulence
Turbulence is created in the airflow stream itself. It contributes to broad band noise. Inlet and Outlet disturbances, sharp edges and bends will cause increased turbulence and noise.
3.Speed
Speed is a major contributor to fan noise. For instance, if the speed of a fan is reduced by 20%, the dB level will be reduced by 5 dB.
4.Fan Load
Noise varies as the system load varies. This variation is unpredictable and fan dependent. However, fan are generally quieter when operated near their peak efficiency.
5.Structure Vibration
This can be caused by the components and mechanism within the fan, such as residual unbalance, bearings, rotor to stator eccentricity and motor mounting. Motor mounting noise is difficult to define.
How to reduce inline fan noise?
There offer some simple methods of reducing noise from fan.
1. Isolate The Fan with an enclosure
An excellent way to stop the vibration and noise made by the fan is to use acoustic boxes. What is the best thing about acoustic boxes is the fact they can be homemade, as long as you have some basic woodwork skills and can obtain the acoustic foam padding needed for the inside.
2. Use insulated ducting.
Noise reducing ducting also works wonderfully well in in reducing noise in the ducting. The result is a far more silent way to deliver air, without losing any throughput, vastly reduces the noise created by air movements.
3. Add a silencer to the exhaust duct
A Silencer is basically designed to attach between the exhaust fan and the carbon filter.
Similar to acoustic ducting, silencers will absorb the sound that would have been produced by the passing air. Silencers come in various sizes depending on which diameter ducting you are working with, and are easy enough to install and hang.
4. Fan Speed Controllers
Most models of fan are fixed at one rate of speed (RPM) and depending on the power output and speed of the fan, will dictate how much of a loud noise there will be. An excellent way to reduce the amount of noise is to use a fan speed controller.
5. Duct Clamps
The joint between the inline fan and the adjacent filter or duct silencer. The vibration of the fan amplifies even more at this kind of joints.
To overcome the issue, Use a Clamp as a joint media in between the fan and filter/silencers. If done properly, that will definitely lower the fan noise by a few decibels.
There are various sizes of them are available such as 4 , 5 , 6 inches and so on.
7. Using vibration isolation pads under fan installations
Placing fan on the ceiling or wall, usually amplifies the vibrations and transmits the noise. Suggests placing highdensity rubber foam between them reduces this transmission drastically.
8. Using quieter fan
Instead of trying to add material to reduce the noise generated by fan, choosing a low noise fan at purchase time. As a guide, look for a slower fan with more blades. This will move as much air as a faster fan with fewer blades, but more quietly.
9. Soundproof the room
10. Proper installation of fan
Conclusion
Although noise is unavoidable when fan are used, this can be reduced largely by following simple rules. And using more efficient fan may be more welcome.