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  #11 (permalink)  
Old January 17, 2008, 10:50 AM
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I think it's a way for a review site to warn people that they're ignorant enough to divide a linear measurement by a logarithmic measurement, and treat the answer linearly. That way, you don't go assuming anything else about the review was done properly either.
Sigh...LOL...I was wondering how long it would take before someone complained about that.

Honestly, I know the difference and don't take umbrage to your remark. The reason I included it was not as flame bait but because I write my reviews for the First Time Do It Yourself'er, who "gets" DBA and CFM...but static pressure may be a little bit over their heads. They can look at X and Y fans and see that one is "better" than another. Is this always correct...NO but it will get them into the right ballpark.

The industry right now does use DBA vs CFM as its benchmark. Thats why you see it mentioned in 99% of ALL fan titles in online stores. People want to know "how loud" and "how fast", and if its isn't there the first post you will see is "whats its cfm and dba ratings".

I will make it more clear in my next review that it isn't a great benchmark but to not assume that I ignorantly included it. I considered not including it, but honestly my ego is not wrapped up in my reviews and if for every 10 people that think I'm a schmo their is just one that it helped...well than so be it. In the end the Great Flying Spaghetti Monster will know his own
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Old January 17, 2008, 11:19 AM
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yeah, i can agree with using dB and CFM, but for the love of God please do NOT use a CFM-per-dB ratio as it is incorrect, misleading, and totally useless. if people start using the ratio and think "it must be right and valid since i saw it in a review", then at least half the time they'll make the wrong decision based on those numbers. i'm talking about the RATIO specifically - i came across a thread where one poor sap did the math for 8 or 9 different fans and was comparing the ratios and picking one with the highest number. if only he knew that the numbers are 100% meaningless and cannot ever be compared to any other number. it's like comparing a Toshiba DVD player against a Samsung DVD player by comparing their serial numbers.

if you're the guy who writes the reviews, then please stop using the ratios, and maybe even include statements that the ratios are useless, meaningless, and misleading. maybe eventually people will catch on... (hope springs eternal)
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Old January 17, 2008, 01:14 PM
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I'm not positive, but I'm fairly certain that the effective static pressure applies to both sides of the fan. The behaviour of the air affected by that pressure will differ, especially at very close range to the blades, which is why performance can still vary depending on whether a push or pull config is used. In general, I believe 'pull' configurations will tend to pull air from a wider field, whereas the 'push' effect is initially more focussed.
Your correct, ask any crazy watercooler(such as myself) and you'll get this answer, this is why most expreanced watercoolers have there fans in a pull configration on rads as it performace is slightly better.

Theres also the fact that its also genrally queiter as theres not a mass of air hitting a (perforated mind you but) wall which it then has to navigate around.
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Old January 17, 2008, 01:16 PM
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And this is why I'll be switching out my Tuniq for a TRUE or Noctua as I'm starting to believe its way of cooling isn't near as efficient in the same way as the TRUE is!
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Old January 17, 2008, 01:23 PM
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Quote:
Originally Posted by AkG
Honestly, I know the difference and don't take umbrage to your remark. The reason I included it was not as flame bait but because I write my reviews for the First Time Do It Yourself'er, who "gets" DBA and CFM...but static pressure may be a little bit over their heads. They can look at X and Y fans and see that one is "better" than another. Is this always correct...NO but it will get them into the right ballpark.
I'll admit I could have phrased that a lot more diplomatically, and even if I didn't cause offense, I still apologize. As it happens, I posted that shortly after seeing that being done in another fan discussion elsewhere, and there were some seriously brutal conclusions made.

As I posted, I quite liked your review, but going to the trouble of making graphs for the db/airflow ratio really works to legitimize what simply isn't a good method of comparison. Far better, I think, to simply highlight the differences. Explain to the reader that on the decibel scale, if two fans differ by say, 3 db, one fan is potentially twice as quiet as the other. Even if it's just a little, it never hurts to try gently steering people down the right road.
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Old January 17, 2008, 01:34 PM
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actually, acoustics is weird in that 10dB is twice as loud (or half as loud if it's -10dB). but at the same time, putting two identical sound sources beside each other (like a pair of 40cfm @ 21dB fans) increases the overall volume by only 3dB (so you'd get 80cfm @ 24dB), which makes the two fans NOT sound twice as loud as one fan of the exact same type.

i hope i'm remembering that right. it's been a bit over 10 years since i worked in that acoustics lab.
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Old January 17, 2008, 02:11 PM
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I believe a 10 decibel increase represents 10 times the sound energy (and 20 db = 100 times, etc.), which why a 3 decibel increase represents twice the sound energy. But yeah, acoustics is fweird.
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Old January 17, 2008, 02:39 PM
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LOL, no problem MPG and your are right, it may help them but it may hurt them more. I had planned on adding a big "please note" to it just like I did w/ MTBF's to explain its lack of usefulness but didn't want people getting in an uproar over too many things all at once. Was planning on including it in my next fan review...{looks at smoking gun}...{looks at hole in foot}.....Live and learn I guess. LOL
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