Why can 12V DC fans be so noisy ?

[HOORRELL]

Two new 12V DC fans (100mm and 75mm inline/duct) are extremely noisy. Powered from household 240V mains with the usual DC transformer/ power supply - correctly rated for DC supply to these DC 12V fans). Why is this happening ?

 

[Lucien Nunes]

Quiet fans cost more to make, as they need better bearings, better-balanced motors and impellers, more substantial housings etc. Small duct fans are in a very competitive market so they will not generally be as quiet as is technically possible.

 

[Vortigern]

I have a friend who wanted a silent cooker hood extractor. It was achieved by paying a grand for the cooker hood but silent even on high speed. You get what you pay for.

 

[Moley]

The fan died on my NAS (Network Attached Storage) and as it's in the bedroom the replacement had to be very quiet. Took me ages to find a suiable fan and it cost a fortune. Would almost have been cheaper to by a new NAS unit and move my drives over.

 

[telectrix]

The fan died on my NAS (Network Attached Storage) and as it's in the bedroom the replacement had to be very quiet. Took me ages to find a suiable fan and it cost a fortune. Would almost have been cheaper to by a new NAS unit and move my drives over.

or buy a set of headphones & put on a Pink Floyd album. no hear fan and good musik. 2 birds with 1 stone.

 

[pc1966]

As well as the technical details of quality of the fan, the faster they move air the noisier they get. Some info here:

Fans - Noise Power Generation

The sound generated by a fan depends on the motor power, the volume capacity, the static pressure increase and the discharged volume.

www.engineeringtoolbox.com

 

[telectrix]

the only place for noisy fans is at the Kop End on a Saturday afternoon.

 

[Marvo]

You didn't say if the fans are centrifugal or axial type and you didn't expand on what type of noise but here's a few pointers....

Before you pay a fortune for quieter fans just check the installation first. Make sure the fan and the ducts either side are properly supported, if the weight of the fan and ducting is hanging without supports it can distort the fan housing making it noisy.

Also check there's no ducting bends or harsh size transitions within a foot (350mm) of the fan, they run quieter if the airflow into and out of them is smooth and straight.

Check the static pressure isn't too high or too low, running a fan in a stall condition (too much restriction or long duct lengths) or in an almost 'free air' condition can increase the noise.

Finally check the power supply is up to the job, do a voltage test at the fan whilst it's running, if the voltage is low due to undersized transformer it can cause motor noise which is more like a rumbling sound.