PC Fans and Noise "Q's".

Haggis123 · Aug 28, 2008

Got a couple of "Q's" about using PC fans and also how does "noise build up" hopefully someone will be in the know.

First up - Does anyone know how noise builds up ??

I am planning on making a micro stealth cab, but it needs to be completely silent.
I am considering using PC fans for intake and extraction because they are small and real quiet.
What I want to know is - say, I had 4 PC fans and the rated noise from these was 8db.....if I was using 4 of these would the noise coming from the fans be 4 x 8db.....or would the noise just stay the same at 8db regardless of how many 8db fans I was using ??

Second - Can you use a PC fan and carbon filter together ??

I have read a few posts about using PC fans in your cab and most always say that a PC fan cannot pull or push air through a carbon filter.......why ???
I know the most popular answer to this "q" is....."they ain't powerful enough", but surely the air that the fan is pulling or pushing regardless of the size of fan....has to go somewhere ??

Say you stacked a few PC fans on top of one another (sitting on top of one another, not spread out side by side), would the fans then have enough combined pull, to be paired up with a carbon filter ??

Surely a few of you guys have experience with using PC fans and will be able to give me the answers.

Thanks

Haggis.

samba · Aug 28, 2008

I'd say it's not 4*8dB, but I'd guess its a bit over 8dB.
For scrubbers you need static pressure, PC fans don't offer that.
Get something like this
http://pflanzburg.de/store/product_info.php?cPath=7_22&products_id=1623
18dB with scrubber and silencer, build a aquarium on top of your growbox, the noise from the air pumps in it will cover your growbox noise

Haggis123 · Aug 29, 2008

Samba, many thanks for the reply.
Still a bit too loud for what I need, I'm afraid.....but nice looking piece of kit.

Just to clarify what I am contemplating.
I am considering using a plastic garden storage box and equipping it with a couple of low power ceramic metal halides in a double cool tube, some T5HO fluro's along with a few PC fans for intake and extraction paired up with a home made carbon filter with a charcoal bed depth of 2.5cm and some sound proofing mat(to help silence any noise and act as insulation).

I plan on keeping this box in the garden as can't keep it any where else.
It will also have to be sited, right next to the garden fence between me and next door neighbours as this would be the most inconspicuous place to keep a box simillar to what I plan on using.....so hence the ultra stealth and complete silence.

Any one else got an opinion ??
Do any of you guys think that a few 92mm or 100mm PC fans would "cut the mustard" and be able to push through a 2.5cm bed of charcoal.
Ther was a guy on fleabay selling PC fans hooked up with carbon filters at looking at the pics he had put up.
Don't know if they were any good though.

CDM · Aug 29, 2008

Your going to need a squarel cage fan if your using a filter.. a simple computer fan will not create the pressure needed.

also, your not going to get Silent, just wont happen.
You can get pretty quiet, but never silent. Air moving makes noise, even if the fan did not

greenhead · Aug 29, 2008

If your computer fan is rated at 8db and you use two of them, you will get a total of 11db.

If you use four computer fans, and each one is 8b, then the total db will be 14.

:joint:

Bush Grower · Aug 30, 2008

greenhead said:
If your computer fan is rated at 8db and you use two of them, you will get a total of 11db.

If you use four computer fans, and each one is 8b, then the total db will be 14.

umm I'm not sure I get your math here...

8 x 2 = 16
8 x 4 = 32

eLiguL · Aug 30, 2008

Bush Grower said:
umm I'm not sure I get your math here...

8 x 2 = 16
8 x 4 = 32

I believe hes following an equation to calculate noise from multiple sources.

Bush Grower · Aug 30, 2008

Gotcha.. just googled it. I never knew there was such a thing.

Haggis123 · Aug 30, 2008

Wow, guy's thanks for the input.

Greenhead....that is genius. Thank you.

So I won't get complete silence, but very very quiet....that will probably do. Also by the looks of it...I won't be able to use a carbon filter with regular PC fans.
I had a look on fleabay last night for that guy's fan & filter combo I mentioned earlier. He's uing AC voltage PC fans, anyone know where you can source these and if they would be strong enough ?? I did do a brief search but ain't found anything.

wisco61 · Aug 30, 2008

http://www.google.com/search?q=ac+a...s=org.mozilla:en-US:official&client=firefox-a

Haggis123 · Aug 30, 2008

Wisco....many thanks.

ElGato · Aug 30, 2008

you fail to mention the size of your intended micro cab and the light you plan on using....that is crucial info bro

but....
you CAN use 12V DC comp fans and a scrubber...i've been doing it for yrs!!!

this cab uses two 85cfm 12v dc comp fans to ventilate

and you can see it uses a scrubber(canfilter 2600)

like said before , you will have some noise from the airflow>>no matter what

check here for high output 12v dc comp fans(check out the delta's)
http://www.sidewindercomputers.com/120mmfans.html

and here for AC axial fans
http://sofasco.com/acaxial.html

good luck

edit.... dont forget that once a fan is integrated into your system the Db rating will not be the same as when it was free running
>>most likely it will be more quiet, you can also insulate the fans to keep down the noise

mj

MrInterested · Aug 31, 2008

Warning: Science content

Noise is measured in watts/m^2 , or watts/sqft. , it then uses the decibel scale to interpret it's value.

calculate the w/m^2 with: 10^(noise_in_decibels/10-12)

then sum up all the power from your noise generators and calculate it in decibels again: 10*LOG(total_watts/10^(-12))

where 10^(-12) is the auditory threshold, this unit is the reference unit of the dBA scale, the lowest possible volume the human ear can sense.

-- science content ends --

2x8dB = 11.01dB
3x8dB = 12.77dB
4x8dB = 14.29dB

But if you ask me, an 8dB fan ain't gonna move shit! a fan that's 8dB is most likely some low-speed ultra-quiet fan, great for PCs, horrible for pushing air through a carbon filter. For that job, you want AT LEAST 60CFM, but preferably something like 100CFM, those are some real fans :laughing:

You can find models from Thermaltake, scythe and other companies that move air in that range, but still keep the noise under 40dB. go to newegg.com, find some good models, if you're in the U.S. buy from there, or look up the models on eBay.

but surely the air that the fan is pulling or pushing regardless of the size of fan....has to go somewhere ??

Put your hand over the fan to block the airflow, the fan is still pushing, but does the air go through your hand...?
This "back pressure" is hard to explain really, but simply put: you have to establish some minimum pressure to be able to blow air though restriction. If you don't, the fan spins, thrusts the air, but it pushes back out, against the flow of the fan.

I have read a few posts about using PC fans in your cab and most always say that a PC fan cannot pull or push air through a carbon filter.......why ???

Because people are using shit fans they salvage from old computers. Not all fans are built equally. Some higher end models actually push up to six times the amount of air that a normal small, cheap 80mm fan does (which is about 20CFM). Get a POWERFUL fan, 120mm, 100CFM+ and it's gonna push through the carbon

If you decide to buy those 8dB fans, just remember, *when* you realize they're not doing their job... I told you so :rasta:

Haggis123 · Aug 31, 2008

ElGato said:
you fail to mention the size of your intended micro cab and the light you plan on using....that is crucial info bro

but....
you CAN use 12V DC comp fans and a scrubber...i've been doing it for yrs!!!

this cab uses two 85cfm 12v dc comp fans to ventilate

and you can see it uses a scrubber(canfilter 2600)

like said before , you will have some noise from the airflow>>no matter what

check here for high output 12v dc comp fans(check out the delta's)
http://www.sidewindercomputers.com/120mmfans.html

and here for AC axial fans
http://sofasco.com/acaxial.html

good luck

edit.... dont forget that once a fan is integrated into your system the Db rating will not be the same as when it was free running
>>most likely it will be more quiet, you can also insulate the fans to keep down the noise

mj

Great looking cab mate.
Have search for those CAN 2600 filters here in the U.K no-one seems to sell them here as those would do fine.

The cab I'm considering is 1.2m wide X 0.7m tall X 0.6m deep.
Considering using 2 x 100w Ceramic Metal Halides in cool tubes and a few 24w T5HO fluro's. What do you think.....do able.

Mr Interested, many thanks for the heads up on the noise equation and advice on the fans......sheer genius.

jdog12 · Sep 1, 2008

samba said:
I'd say it's not 4*8dB, but I'd guess its a bit over 8dB.
For scrubbers you need static pressure, PC fans don't offer that.
Get something like this
http://pflanzburg.de/store/product_info.php?cPath=7_22&products_id=1623
18dB with scrubber and silencer, build a aquarium on top of your growbox, the noise from the air pumps in it will cover your growbox noise

What exactly do you mean by static pressure? I thought CFM was CFm and it didn't really matter. Like MrInterested said, just get a more powerful computer fan.

NanoScroger · Sep 2, 2008

eLiguL said:
I believe hes following an equation to calculate noise from multiple sources.

math. umn.edu/~ macklin/ prog.htm

sound.exe is what you want. its a db calculator. wouldnt let me post a link for whatever reason

floppyfundanglr · Sep 5, 2008

How much sound is reduced when you have the airflow pushing through a carbon filter? Does it muffle the sound a bit? I purchased a 120v pc style cooling fan from Radio Shack. It runs at 2100 rpms and pushes 65cfm but it produces 38dB which isnt terribly loud but i can hear it. My old box i had similar but smaller fan than current and had it pull through the filter and blow out and that still made a loud rush. The sound of the air is all i hear not the fan. So basically i want to know if pushing through carbon will be quieter than pulling though it. Hopefully this makes sense. Thanks.

peace

NanoScroger · Sep 5, 2008

check the static pressure rating of the fan. it will quiet down substantially but airflow will be lessened as well.

floppyfundanglr · Sep 5, 2008

i dont know what the pressure is on it but it did mention about special design to keep high pressure.

NanoScroger · Sep 6, 2008

yeah you will prob want to push through the filter, that will quiet the fan alot. pulling through doesnt help with noise, and the fan will push better than it pulls anyways. make sure you are sucking air out the cab, not pushing air in. or the smell will leak out.

so basically cab should be negative pressure, fan exhausting into the carbon filter.

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