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 Post subject: How to build muffler?
PostPosted: Thu Jan 16, 2003 1:04 am 
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Joined: Wed Aug 21, 2002 10:11 am
Posts: 14
Here's an idea for an article: a guide to effective mufflers or something like that. Based on actual knowledge and not urban myths :)

Here's what I know about this.
- Airflow needs nice pathways, no extremely sharp turns, etc. or it may cause too much airflow resistance.
- No straight paths from sound source to outside world. Make the sound bounce around.
- Add sound absorbing material inside the muffler. Each time the sound bounces of a wall that's covered with sound absorbing material some of it is absorbed.
- Need different sized chambers in sequence to widen the frequency band(muffler silences wider range of sound frequencies). This is where some real knowledge and knowhow would come helpful. What sizes and shapes the chambers should be? What kind of entry and exit holes work best and their positioning?

Sami


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 Post subject: architects guide to building a quiet enclosure
PostPosted: Tue Jan 21, 2003 12:46 am 
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Joined: Thu Jan 09, 2003 5:04 pm
Posts: 2
Location: Sebastopol, CA
I found this article on the web by some German architects on how to build a sound insulation enclosure for a noisy computer:

http://www.carsten-buschmann.de/noise-p ... /index.htm


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 Post subject: book
PostPosted: Sun Feb 09, 2003 12:51 pm 
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Joined: Sun Aug 11, 2002 3:26 pm
Posts: 191
There's quite a lot of information about absorbing unwanted sound in Scientific Design of Intake & Exhaust Systems (Smith, Morrison) - although they were dealing with internal combustion noise
http://www.amazon.com/exec/obidos/tg/detail/-/0837603099/qid=1044821425/sr=1-1/ref=sr_1_1/102-8545854-6292948?v=glance&s=books
IMHO, the easiest way to design/build a muffler would be using an "absorbtive" system - i.e. a tube lined with sound-absorbtive material (like that "acousti-stuff" that often gets stuffed into speaker cabinets).
If you know the frequency range(s) you are trying to reduce, convert the frequency(ies) into wavelength (wavelength in feet = 1130 / frequency) - see Master Handbook of Acoustics (Everest) http://www.amazon.com/exec/obidos/tg/detail/-/0071360972/qid=1044822099/sr=1-1/ref=sr_1_1/102-8545854-6292948?v=glance&s=books and make sure the lining is thicker than half the wavelength (if a sound wave bounces at the bottom, then pressure will be at max at the bottom and velocity will be at max a half wavelength away - and max velocity is where you can most easily convert energy to heat through friction). See the handbook for details on how this works (or just trust me on it... :-).
Oh - you could use 3/4" acoustical tile and get attenuation on 250Hz (and higher freak's). Cheap to buy and it might be relatively easy to assemble (just use the tiles for structure).
Is this making sense? Too much "urban legend"? I haven't bothered to build any of this because my watercooled system is quieter than the ambient noise level in my office so there's little point...
Bob


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 Post subject: Re: book
PostPosted: Sun Feb 09, 2003 4:26 pm 
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Joined: Sun Jan 19, 2003 4:47 am
Posts: 218
bobkoure wrote:
IMHO, the easiest way to design/build a muffler would be using an "absorbtive" system - i.e. a tube lined with sound-absorbtive material (like that "acousti-stuff" that often gets stuffed into speaker cabinets).


Hmm... IYO would a bass duct lined in "acousti-stuff" significently muffle a case fan compared to mounting straight on the case?

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 Post subject: fan noise
PostPosted: Sun Feb 09, 2003 6:09 pm 
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Joined: Sun Aug 11, 2002 3:26 pm
Posts: 191
Yes, assuming the noise you were attempting to attenuate had a wavelength less than twice the thickness of the "stuff".
I think to try it, I'd get a piece of lightweight PVC or sheet metal tubing (the sheet'd be easier to work with tin snips, but would also be sharp). I'd then make an "inner tube" of something like chicken wire, wrap the stuff around the wire, and shove the wire tube with stuff around it into the outer tubing.
The thicker the layer of stuff, the lower the frequency (longer the wavelength) that'd get attenuated.
There'd be a trade-off in how heavily you stuffed the "stuff" (how dense) - you want the sound waves to penetrate, reflect on the surface furthest from the airflow and convert to heat on the way out. Stuff the "stuff" too densely and it'd just reflect off the top surface.
If you already have your PC under a desk, I'd try the cheap and easy - acoustic ceiling tiles on the underside of the desk and the back wall (the wall the fans face). The experiment might cost you all of $5 - and be easier to build...
Oh - wait - are you talking about putting a tube on the PC and mounting the fan on the outside end of that? I don't think that'd do much for you at all.


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 Post subject: SilentPC Pro
PostPosted: Wed Feb 12, 2003 10:39 am 
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Joined: Wed Feb 05, 2003 10:29 am
Posts: 33
What do you guys think of the SilentPC Pro Series case by Fujitsu-Siemens? I would, at the least, remove the Q-Tech power supply from it. I also found an interesting website, http://www.muffledcomputing.com/ that sells fan mufflers and foam kits offering from 5-15dBA reductions in sound.


Last edited by Hebrews126 on Thu Feb 13, 2003 8:56 am, edited 1 time in total.

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 Post subject:
PostPosted: Wed Feb 12, 2003 2:46 pm 
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Joined: Sun Jan 19, 2003 4:47 am
Posts: 218
link was down so I checked the google cache. Their mufflers seem on the right tract to me, but for $30 I'll steal their designs and make my own :lol:

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 Post subject: Re: SilentPC Pro
PostPosted: Wed Feb 12, 2003 3:45 pm 
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Joined: Wed Aug 28, 2002 4:48 pm
Posts: 460
Location: My Secret Laboratory
Hebrews126 wrote:
What do you guys think of the SilentPC Pro Series case by Fujitsu-Siemens? I would, at the least, remove the Q-Tech power supply from it. I also found an interesting website, http://www.muffledcomputing.com, that sells fan mufflers and foam kits offering from 5-15dBA reductions in sound.


LOL "Western Digital 80GB 8MB buffer 7200RPM. This hard drive is one of the quietist 7200RPM drives around, but its 8MB buffer puts it in a league of its own."

I have both the WD1200JB and WD800JB, and they are the loudest drives I have. Seek noise is really quiet, but the idle noise is loud! I'm waiting to get a nice SATA Cuda V. Or maybe I'll wait longer for their next gen of Cudas.

-Ed

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 Post subject:
PostPosted: Thu Feb 13, 2003 12:48 am 
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Joined: Fri Oct 04, 2002 9:52 pm
Posts: 2057
Location: United States, Mobile, AL
you know whats strange though. My moms dell has a WD 800JB and you can hear it click when its acessing data, really its just a soft thumping noise, but other than that its silent, maybe dell decouples them somehow, I might open the case up when shes not home and see. :D


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