how loud 45-50 db fan ?

[nour]

I am not sure if this is the right place to write this topic, so if not please move

I want to buy ac fan like this one
http://www.tme.eu/en/details/uf13a23-h/ac230v-fans/fulltech/uf13a23bth/

I want it quiet as possible but also maintain a good level of air flow

I have compared it with this one
http://www.tme.eu/en/details/dp202a2123mbt/ac230v-fans/sunon/dp202a2123mbtgn/

but I don't know which one should I buy

I am going to build one like this
http://www.tme.eu/en/details/wel.wsa350eu/soldering-fume-extraction-systems/weller/wsa350eu/
this is fume extractor which cost around 83$  doesn't include shipping and I can build it under 20$ (including the filters and the enclosure)

I want to have a good air flow and quiet as possible
any advice ?

[Rerouter]

18db is the line i draw to be able to sleep near to, 50 is about what a video card sounds like on full tilt,

[nour]

18db is the line i draw to be able to sleep near to, 50 is about what a video card sounds like on full tilt,

video card, do you mean computer VGA card

if so that's actually very loud

[ataradov]

50 dBA is LOUD. 40 dBA is a normal office noise level. 50 dBA of constant noise will induce fatigue.

[nour]

I Think I will buy the higher one and add speed controller later if I found it not comfortable

[Paul Price]

You will be quick to notice that using more than one fan, each smaller but each running at slower speeds results in a much quieter, less-maddening experience. The faster the fan the bigger the noise.

[Skimask]

10db louder than a 35-40db fan?

[LaurentR]

50dBA is incredibly noisy for a fan.
I also like to keep my fans to below or near 20dBA if possible.

If you look at the Weller datasheet, it says the fan does ~75 m3/h
The incredibly noisy Fulltech fan you link to does 175 m3/h, which is quite a bit more, but even slowing it down to something equivalent will not net you anything bearable.

Now, looking at properly low-noise fans, the Noctua NF-A14 ULN can do 80 m3/h (about as much as the Weller) at 11.9dbA, which is basically inaudible.

Without going to the Noctua range, which is the golden standard in quiet fans, you can find PC fans of 120-140mm diameter that will push as much airflow as the Weller extractor at <20 dBA, where most of the noise will come from the filter air flow impedance, not the fan.

[nour]

You will be quick to notice that using more than one fan, each smaller but each running at slower speeds results in a much quieter, less-maddening experience. The faster the fan the bigger the noise.

that's actually very nice idea 
I will give it a try

[rich]

Can I ask a (possibly stupid) question about how to read fan noise specs?  Is the dbA figure quoted in the data sheet right by the fan, or is it a fixed standard distance away?

[Rerouter]

It appears from digikey of all places that a normal distance for the sound rating will be taken at 1m

[rich]

Thank you, that's good to know. I shall now take readings of my troublesome power supply at 1m distance as a baseline for replacement fan shopping.