Qs on exhaust CPU Duct

[DonP]

After consulting (theory and practise) on making friend's and family's computers quieter for ages I finally got down to silencing the monster on my desktop.

By some miracle I managed to find an Alpha 8942t in the UK and the plan is to suck air off the Alpha (sitting atop a P4 2.26B) out the back of my case (Lian-Li PC60) through a duct.

Now, questions..

1) is it a better idea to have the fan on the Alpha then duct out a hole in the back? or have the fan on the back and duct to the top of the Alpha?
I prefer the latter because there is no motor "black hole" right up against the Alpha.. but then the fan at the back is nearly "outside" and therefore louder.

2) regarding the actual duct.. I was hoping to get a Sunbeam Overclockers Kit, but unfortunately I can't find it from any (trusted) UK resellers. The duct is 81mm in diameter.
I did however find a "tunnel kit" from Maplin. It looks like this Tiger Coolymax Tunnel Kit.. but the pipe is only 63mm in diameter
So.. is this going to be a problem? I'm not sure how this works.. but AFAIK the drop in airflow from a 63mm restriction would be dependant on the static pressure exerted by the fan - is this correct? And how bad woulc it make things? Would the restriction influence the answer to question one above? i.e. would it now be better to suck through the HS and duct or suck off the HS then blow into the duct?

btw.. I plan to use a NoiseBlocker S3 fan.. I chose it because it has a repsectable airflow at full speed, low noise, a speed sensor.. and includes a pot.

Any experiences, conjecture or imaginative thinking welcome.

Thanks in advance for the help guys and gals,
DonP.

PS Just to make things absolutely clear - I will _always_ be sucking air off the HS to exahust out of the back - the questions never consider blowing from the outside in.

[Bluefront]

This Alpha duct can be used either sucking or blowing. A drier vent part from BestBuy....fits the Alpha perfectly.

I used it with the fan on the case end.....ended up with a 92mm fan there. You could put the fan on the alpha end, but this particular setup would not have fit the case like that....

[TheWesson]

Yes, you lose a lot of airflow and get some noise ("whooshing") from the corrugated collapsible ducts like the Sunbeam - to the point where some reviewers reported a temp rise with the Sunbeam duct.

A 62mm duct would be even worse than an 80mm duct.

Go with Bluefront's suggestion. Or a curved section of 3" or 4" PVC pipe if you like.

Just not any small twisty thing with ridges on the inside.

Be sure to balance intake and exhaust fannage as well.

You might do as well or better with a Thermalright SLKxxx or SP-xx as with the Alpha, judging by their respective ratings, even with an estimated 20% penalty inflicted on the TR heatsinks by reversing the fan.

Of course Bluefront has it all wired for the dryer part to work with the Alpha and he seems to know what he is talking about.

Anyhow do-it-yourself in the ducting world should work better than the kits with a modicum of effort.

I think if you are in "suck" mode the hub "dead spot" is not nearly as dead, if you know what I mean, so I would just put the fan right on the Alpha.

By various means (spacers and shrouds) you could also raise the fan off the Alpha if it were a concern to you. But check out the construction of the Alpha - I think the fan is already raised off the sink a bit.

the wesson

[silvervarg]

Putting the fan on the CPU should in theory give you less noise, but with the minor drawback of the deadspot for the fan.
Putting the fan on the case might give you an option to put a bigger fan than you could put on your CPU heatsink, and you will put less stress on your CPU heatsink. The major advantage of putting the fan on the case is that it is much easier to make good decoupling of the fan there.

Beware that you might end up with vibrations that are enhanced be the duct. Doucoupling or use of semi-soft materials (e.g. soft plastic) will reduce this effect.

[SpyderCat]

My advise: Fan on the back of the case.
I think you will find amazingly low airflow coming out of your duct, still it will cool sufficiently.
I don't expect any major disadvantages from using a 63mm duct, as volume transported isn't that large, and the duct is short. A 63mm duct might also be more flexible resulting in an easier fit.

Not sure about your fan of choice. I have some NoiseBlockers here, and I wouldn't use them on my own rig. Neither would I use the Papst fans.

Tell us how about your adventures to come, Have fun.

Edit:

Come to think of it: 63mm is about the same size where a vacuum-cleaner with a 1400 Watts motor, and a 3 meter hose sucks it air through.
You are using a 2 Watts motor, over 12 cm. It'll be just fine.

[greenhorn]

..this would easily get you to dead silent at 2.26, particularly if you happen to have a motherboard where the cpu socket will allow it to be oriented with the airflow horizontal, eg the Abit IC7 series. There are alot of reviews out there proclaiming it the best aircooling available.

http://www.xcase.co.uk/acatalog/Coolerm ... C_V81.html

it just hit the market in the states and I'll be ordering it tomorrow to cool a 3.0e SL7E4 which I hope to eventually OC to at least 3.8 while retaining relative silence.

Your friend's right about the pressure, and this effect will be greatly exacerbated by a slow spinning fan, so try keep the restriction as minimal as possible. This will also reduce the turbulence noise. You may want to consider replacing the mylar duct in the kit with 10cm telescoping aluminum dryer duct like what this nutter's using http://www.electrophile.8m.com/terminal.htm

Also, if you're going for utter silence with the Alpha definately duct the heat out to keep your PSU fan from spinning up. Or swap the PSU fan for an undervolted fan.

[Bluefront]

check out another Alpha duct setup. The blue duct is off a Zalman 5700. Oriented like you see it, most of the heat is sucked out by the rear 120mm case fan. This setup is probably as quiet (maybe quieter) than a two-fan setup because of really reduced fan speeds.

[Tigr]

In my case, I get better results with placing the fan on the CPU. I use a Thermalright SLK900 with a Papst 80 mm fan on it ducted to the case exhaust hole with one of those collapsible ducts. The noise is definitely muffled by the case when the fan is deep inside compared to when the fan is attached to the case.

[TheWesson]

..this would easily get you to dead silent at 2.26, particularly if you happen to have a motherboard where the cpu socket will allow it to be oriented with the airflow horizontal, eg the Abit IC7 series. There are alot of reviews out there proclaiming it the best aircooling available.

http://www.xcase.co.uk/acatalog/Coolerm ... C_V81.html

it just hit the market in the states and I'll be ordering it tomorrow to cool a 3.0e SL7E4 which I hope to eventually OC to at least 3.8 while retaining relative silence.

I am quite skeptical about these tower heatsinks - I do not believe a ducted 'tower' HS will come close to a ducted 'low' heatsink like SLK-xxx or SP-xx.

I think 'low' heatsinks can have a "rebreathing" penalty when they are allowed to suck in their own exhaust - which the air-through plan of the tower will tend to prevent.

My experience with the Aerocool HT-101 - sometimes reviewed as a real competitor to the SP-xx - was that, when ducted, it was just about as good as a Vantec Aeroflow, or maybe a little worse. IOW, a decent heatsink but nowhere near the king.

I am seeing the same pattern with the Hyper 6 - some sites think it is fantastic, other sites are not too thrilled. I believe this depends on how it is tested vs the SP-xx - if you make sure the SP-xx doesn't "rebreathe", by having great case ventilation perhaps, then the SP-xx will be way ahead of the HT-101 and I'm guessing most any other tower.

Anyhow I'll be very interested to hear of your experiences with the Hyper 6.

the wesson

[DonP]

This Alpha duct can be used either sucking or blowing. A drier vent part from BestBuy....fits the Alpha perfectly.
I used it with the fan on the case end.....ended up with a 92mm fan there. You could put the fan on the alpha end, but this particular setup would not have fit the case like that....

I've seen this before - great setup bluefront! I've been looking around DIY stores in the UK for similar household ducting bits (water pipes, vents etc..) but what I can get in general DIY shops are actually quite limited - today I found a specialist ducting company on the web with a shop near my workplace.. and wouldn;t ya know it - they went bust and the shop was boarded over
Anyway - after reading all the replies this is probably the way I'll end up heading..
I'll stick with an 80mm fan since the PC60 has enough space below the rear 80mm fan for a second 80mm fan - I might need that since the current rear fan will be used for the duct.
<individual replies to other posts to follow>

[DonP]

Yes, you lose a lot of airflow and get some noise ("whooshing") from the corrugated collapsible ducts like the Sunbeam - to the point where some reviewers reported a temp rise with the Sunbeam duct.

Very true - I didn't realise it was such a problem until I read this tidbit on ducting systems
Important quotes:
"..it is generally acknowledged that flexible ductwork offers approximately twice the resistance of a smooth bore duct, even when fully stretched."
"A sharp 90° bend in flexible duct has up to three times the resistance of a smooth bore duct."

A 62mm duct would be even worse than an 80mm duct.

Yes, the 63mm plan is a loser - the ridge problems aside, a 63mm diameter duct has only 62% the cross sectional area of an 80mm duct.

Be sure to balance intake and exhaust fannage as well.

You mean on the duct? I only plan to use one fan. Or do you mean in the case? That'd be hard - I currently have very negative case pressure - but hopefully less so when I use the duct and undervolt the fan (since the rear fan will no longer be a general case fan but the CPU duct fan and considerably slower).

You might do as well or better with a Thermalright SLKxxx or SP-xx as with the Alpha, judging by their respective ratings, even with an estimated 20% penalty inflicted on the TR heatsinks by reversing the fan.

Yeah.. hmm.. I already have the Alpha - I didn't go for the other chunky monkeys because I read about the performance hit due to sucking.

I think if you are in "suck" mode the hub "dead spot" is not nearly as dead, if you know what I mean, so I would just put the fan right on the Alpha.
By various means (spacers and shrouds) you could also raise the fan off the Alpha if it were a concern to you. But check out the construction of the Alpha - I think the fan is already raised off the sink a bit.

You are correct - in the Alpha there is a frame for the fan and it does raise the fan by a few millimeters so hopefully that'll be ok.

[DonP]

Beware that you might end up with vibrations that are enhanced be the duct. Doucoupling or use of semi-soft materials (e.g. soft plastic) will reduce this effect.

Very good point - one of my plans was to have the fan on the CPU and have a duct (maybe two joined ThermalTake DuctingMods?) pointing approximately at a rear case mounted fan.. then I realised this would be not unlike the old drum record players with the big horn amplifying the sound
The ridged flexible duct wouldn't resonate much.. but alas it causes resistance as mentioned in my previous post.
Assuming a rigid or semi-soft duct then I guess decoupling from the fan at one end and hard mounting at the other is probably the way to go.

[DonP]

My advise: Fan on the back of the case.
I think you will find amazingly low airflow coming out of your duct, still it will cool sufficiently.
I don't expect any major disadvantages from using a 63mm duct, as volume transported isn't that large, and the duct is short. A 63mm duct might also be more flexible resulting in an easier fit.

Hmm - true, the duct is short, but it's also bent at 90 degrees - like the link I posted earlier said, that's really going to increase resistance. The flexibility is a big bonus as the fan hole at the back is a bit below the CPU

Not sure about your fan of choice. I have some NoiseBlockers here, and I wouldn't use them on my own rig. Neither would I use the Papst fans.

Yeah.. this concerns me - I already have the fan.. I guess I'll give it a shot (haven't plugged it in yet). I chose the mid power one because sometimes I need power cooling - like today - a mini one-day heatwave hit London and I had to shutdown F@H . Another reason I chose the NB's over others was because I haven't seen many (in the UK) quiet fans with speed sensing. Papst or Panaflos (I have one or more of each) don;t have speed sensing so no dice.
I'm sorry to hear about your Papst unhapiness - I only have one, an 8412NGML and I'm pretty happy with it. I bought it some time ago but I've heard more people like you have had issues with the Papsts that followed.

Tell us how about your adventures to come, Have fun.

Of course.. with pics.

Edit:
Come to think of it: 63mm is about the same size where a vacuum-cleaner with a 1400 Watts motor, and a 3 meter hose sucks it air through.
You are using a 2 Watts motor, over 12 cm. It'll be just fine.

After what I've read I think the current best thinking is to put that little bit more effort into these shenanigans and source a smooth semi-rigid pipe or venting elbow or something.
You are probably right about the 63mm flexible pipe working but I'm going to try the harder and better solution.

[DonP]

http://www.xcase.co.uk/acatalog/Coolerm ... C_V81.html
it just hit the market in the states and I'll be ordering it tomorrow to cool a 3.0e SL7E4 which I hope to eventually OC to at least 3.8 while retaining relative silence.

I like it.. but 1) I already have the Alpha and 2) I'd like it to be at least a little portable - hanging a beast like that on my CPU would make the case hard to shift. I will however use a similar cooler in a forthcoming HTPC undervolted mobile Barton project I was planning - something not dissimilar to what silvervarg did recently with his overture.
Mounting robustness is also the reason I chose the Alpha over the Scythe Kamakaze.

Also, if you're going for utter silence with the Alpha definately duct the heat out to keep your PSU fan from spinning up. Or swap the PSU fan for an undervolted fan.

That's the hope - ever since I read about ducting I really like the idea of getting the hot CPU exhaust air out of the case ASAP.

[DonP]

First of all a big thank you to everyone who answered, your help is very much appreciated.

So.. the current thinking is to ditch the flexible duct idea - I thought it would be a quick fix but after reading reviews of the (in)effectiveness and the comment from Vent-Axia I'll try and go out of my way to find a smooth semi-rigid angled pipe or drier vent or something and mount the fan on the CPU. I might attempt the joining of two thermaltake mods, but they are expensive for what it is and won;t make a perfect fit with the rear fan hole.

Thanks guys, I'll report back as to how it goes.

EDIT: btw.. found an interesting overview of noise and sound and airflow here on the Vent-Axia website. There's also an interesting section on "System Design" and what are good and bad desgins. Fan Laws here

[josephclemente]

Here is my classic duct I performed in 2002 with a Lian Li case:



It was made with aluminum sheet. The hole on the side of the duct is a mini plexiglass window, so I could see the fan spinning. With that configuration, I tried the fan as intake and exhaust, and found that intake was superior and made less noise. I guess it shouldn't be a surprise, since the heatsink was designed for blowing.

I returned to ducting with my current system, only this time the duct is straight, leading directly to the CPU (now 3.0GHz) from the side of the case. That thread is floating around here in this forum. All of my temperatures have greatly improved, and my fans are spinning as slow as my Zalman Fanmates will allow.

I know the intake strategy sounds bad - pulling hot CPU air into the case. But that air is always fresh and passes through the CPU only once. It is still cool as it passes through the heatsink fins and it even cools my other devices as well.

However, since you are using an Alpha which is designed for "suck mode", I think you are correct in using it for exhaust. Good luck - you will love ducting once it is complete!

[yermolovd]

Could you please post more pics of your duct? I'm just gathering ideas on what to do, and any pictures would be greatly appreciated.

[jojo4u]

I've a very cheap mod bought in the do-it-yourself store. It's a Palomino 1700+ and Alpha 8045 with the fan mounted on the Alpha. I'm very satisfied.

[Bluefront]

Well I may as well post a link to the stealth duct I'm currently using with an Alpha 8942, on a Prescott 2.8. When the foam panel with the air deflection duct is assembled, it forms a negative pressure area of the case, which effectively exhausts all the heat off the CPU. The case fan and the PSU fan run at minimum speeds, and the 80mm fan on the Alpha maxes at about 2300rpms. This setup keeps the Prescott below 53C....and the rest of the case super cool. A duct without a duct.

Six Photos

[josephclemente]

Here is another picture of my duct from two years ago:



I put the LEDs in the fan myself.

Here is a link to my current system's duct with fan running at 1065 RPM:
http://forums.silentpcreview.com/viewtopic.php?t=12617

[yermolovd]

I'm more inclined to you current duct, as it would be a straight duct, no bends, looks great too. Hmm..

Thanks for pictures .

[josephclemente]

I'm more inclined to you current duct, as it would be a straight duct, no bends, looks great too. Hmm..

Thanks for pictures .

Thanks! Yes, the straight duct works very well. Ducts that change direction (like my old one pictured above) seem to require more fan power in my experience.

[yermolovd]

Ok, having my mind made up, I have this question, sorry im not into doing things like that myself; but how would u measure precisely the position of the hole on the side panel of the case so it fits nicely with the position of the heatsink? Surely, I can ask my dad, but I don't want to bother him .