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dBA and Bels
John H wrote in message news I need a physics lesson. Assuming sea level, how do you convert between sound power (bels) and sound pressure (dBA)? I think you'd have to assume that the acoustic power is being emitted equally in all directions (which may not be true for HDs). The other problem is that some noises hard drives make can be MUCH more irritating than others, even when they are identical as far as the measurement is concerned. WD tells you only the pressure (34 dBA for the 250 GB Caviar SE) while most other manufacturers tell you only the power (2.5 bel for the DiamondMax Plus 9 and Barracuda V). And that last is an illustration of the problem. Most find that the Barra is significantly quieter than that Maxtor drive. And the Samsung P80 is much quieter than the Maxtor, even tho its listed at 2.7 bel. How do you compare apples and oranges? Obviously you cant. Which is better to know, bels or dBA? The only thing you can really say is that bels are most commonly cited but clearly have a problem. I'm thinking that (for HDs anyway) 2.5 bels is less than 25dBA SPL, which makes the WD very noisy by comparison. And in practice thats bull****, particularly when compared with the Maxtor. (I have a cooling fan that's 3.5 bels and 12dBA) http://www.silentmaxx.net/know_how/a...ccoustics.html http://www.atra.mod.uk/atra/rsabst/p...5-Decibels.pdf |
#2
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Previously John H. wrote:
I need a physics lesson. Assuming sea level, how do you convert between sound power (bels) and sound pressure (dBA)? I think you'd have to assume that the acoustic power is being emitted equally in all directions (which may not be true for HDs). WD tells you only the pressure (34 dBA for the 250 GB Caviar SE) while most other manufacturers tell you only the power (2.5 bel for the DiamondMax Plus 9 and Barracuda V). How do you compare apples and oranges? Which is better to know, bels or dBA? dBA is actually deci Bel (A). So disregarding the (A) for the moment, 10 dB = 1 Bel. The (A) is a weighting curve that reflects the human ear's sensitivity, so dB(A) is more honest than dB or Bel. The problem is that the human ear's sensitivity is only loosely conectet to the human mind's resulting anoument. For that you need a measurement in "Sone". The german computer magazine c't regularly lists dB(A) and Sone in its HDD tests and there are drives that have good dB(A) ratings but only not so good Sone ratings. E.g. a high-pitched whine will cause that. I'm thinking that (for HDs anyway) 2.5 bels is less than 25dBA SPL, which makes the WD very noisy by comparison. (I have a cooling fan that's 3.5 bels and 12dBA) Depends. As I said above dB(A) is not a measurement for anoyment, just for how lound you can hear it. dB is just pure sound energy. Arno -- For email address: lastname AT tik DOT ee DOT ethz DOT ch GnuPG: ID:1E25338F FP:0C30 5782 9D93 F785 E79C 0296 797F 6B50 1E25 338F "The more corrupt the state, the more numerous the laws" - Tacitus |
#3
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John H wrote in message ... Rod Speed wrote John H wrote I need a physics lesson. Assuming sea level, how do you convert between sound power (bels) and sound pressure (dBA)? I think you'd have to assume that the acoustic power is being emitted equally in all directions (which may not be true for HDs). The other problem is that some noises hard drives make can be MUCH more irritating than others, even when they are identical as far as the measurement is concerned. That's usually ball bearing noise Nope, because that at least is constant. which should soon be history once WD switches over. Sure. Doesnt explain the significant differences in the irritation levels seen with fluid bearing drives tho. And the other variable is whether AAM has been enabled, and whether fools like Seagate have disabled that completely. WD tells you only the pressure (34 dBA for the 250 GB Caviar SE) while most other manufacturers tell you only the power (2.5 bel for the DiamondMax Plus 9 and Barracuda V). And that last is an illustration of the problem. Most find that the Barra is significantly quieter than that Maxtor drive. And the Samsung P80 is much quieter than the Maxtor, even tho its listed at 2.7 bel. Then somebody's lying in their specs. Nope, the problem is that the sound pressure levels have **** all to do with the percieved noisiness of a drive. Essentially because some noises are MUCH more irritating than others at the same sound pressure level. You wouldn't think that that could last long. Yep, so it cant be the problem. If say Samsung is put at a competitive disadvantage by telling the truth, they should complain to the FTC. The FTC has no say whatever on the problem of quantifying how irritating a noise level is. How do you compare apples and oranges? Obviously you cant. Then all manufacturers should give both ratings, dBA AND bels. The problem is that even when both are quoted, and the dBa which purports to make some allowance for the difference between the percieved noise level and the sound pressure level, it was developed WAY before the problem with the irritation some hard drive noises have. Adding a dBA rating (one reading) is easy compared to taking many readings to calculate bels. Maybe that's why WD provides dBA only - it's quick and easy. Or they recognise bels are useless and dont bother with them. A spec sheet I have for an old Quantum HD shows the noise rating as being 3.6 bels and 32 dBA. So how about saying dBA equals ~10*bel-0.4 for a HD. Would that be close? That would make a Maxtor only 21 dBA compared to WD's 34. And most consider the Maxtor to be a noiser drive. Which is better to know, bels or dBA? The only thing you can really say is that bels are most commonly cited but clearly have a problem. I'm thinking that (for HDs anyway) 2.5 bels is less than 25dBA SPL, which makes the WD very noisy by comparison. And in practice thats bull****, particularly when compared with the Maxtor. (I have a cooling fan that's 3.5 bels and 12dBA) http://www.silentmaxx.net/know_how/a...ccoustics.html http://www.atra.mod.uk/atra/rsabst/p...5-Decibels.pdf Some more links: http://www.phys.unsw.edu.au/~jw/dB.html http://ccrma-www.stanford.edu/courses/150/SPL.html http://www.silentpcreview.com/module...tid=121&page=1 None of which do a damned thing about the fundamental problem, that some hard drive noises are MUCH more irritating that others, at the same sound pressure level. Very occasional head exercising movements designed to ensure that the heads dont stay over the same tracks for too long when the drive is inactive are completely immeasurable in terms of sound pressure level and are damned irritating to the user. Some of the older drives produced a sound very close to the sound of a cricket trapped in a small cardboard box when moving the heads energetically. Bugger all sound pressure level but very irritating. If any of them answer my original question, how to convert bels to dBA, I missed it. There cant be a simple factor. Read the pdf, it spells out why. Your first link says "[it is] not possible to convert between sound power level and sound pressure level." Precisely. I think that would be true only if the sound source isn't emitting power equally in all directions. You're wrong. There is MUCH more involved than just that. If it is, I bet 10dBA/bel at 1 meter will be close. You've just lost your bet. I'm just guessing though. And havent managed to understand the basics. |
#4
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John H wrote in message ... Rod Speed wrote John H wrote If any of them answer my original question, how to convert bels to dBA, I missed it. There cant be a simple factor. Read the pdf, it spells out why. I read it and still don't know why. What did I miss this time? Basically dBAs allow for the ear's perception of sound, so there can never be a simple factor between bels and dBA. Your first link says "[it is] not possible to convert between sound power level and sound pressure level." Precisely. I think that would be true only if the sound source isn't emitting power equally in all directions. You're wrong. There is MUCH more involved than just that. Wrong how? Because dBA allows for the ear's perception of sound. Sound pressure readings are used to calculate sound power, are they not? Thats only PART of whats involved. If it's known that the sound source is emitting power equally in all directions, Which no real world device like a hard drive ever does. only ONE reading from any direction is needed because readings from all other directions would be the same. And they aint with real world devices like a hard drive. If one pressure reading at distance x is enough to calculate power, it follows that knowing the power is enough to calculate pressure at any distance. Only with a theoretical device that behaves different to real world devices like hard drives. Of course you need to know the air pressure (assume sea level) and not have any reflections (acoustic test chamber). All irrelevant with a real world device like a hard drive that doesnt even radiate the sound equally in all directions. You must have noticed the acoustic damping on the Barra drives. So what is the "MUCH more" you mention? The A in dbA indicates that it ALSO allows for the ear's perception of sound, AND thats an entirely separate issue to the MIND'S perception of noises which may well not even be measurable in terms of sound pressure levels, particularly with very intermittent sounds, but which are what the user objects to with a particular drive. Kindly give me the DETAILS if you know them. Already did. You just ignored them. Just like you did with what is spelt out in that pdf too. If it is, I bet 10dBA/bel at 1 meter will be close. You've just lost your bet. The Quantum I mentioned was close to 10dBA per bel, 3.6 bels and 32 dBA. And those ratios are entirely a result of the PARTICULAR noises that particular drive happens to emit and arent useful for a different drive which is different on that detail. That should be obvious from the different ratio you get with that fan you cited. Why would another drive be much different? Because the noises produced vary quite significantly. In spades when comparing say a hard drive and a fan. I'd guess that the SPL "gain" (any deviation from what equal power in all directions would be) for a drive mounted 1 meter in front of a SPL meter would be similar for all drives. Guess again. And thats an entirely separate issue to the A part of dBA. In other words if one drive has x dBA/bel, they probably all have about the same. Fraid not. Most obvious when comparing that hard drive with that fan. I'm just guessing though. And havent managed to understand the basics. Some noises are much more irritating than others at the same sound pressure level. I understand that. You claim you do, but when you still want a simple ratio between bels and dBAs, you clearly havent managed to grasp the problem. But what I was asking about is how to figure out what that sound pressure _IS_ when only the sound power is given. Not even possible, as should be obvious from the very different ratios you get with that hard drive and that fan. And that still leaves the entirely separate problem that stuff like occasional deliberate head moves wont even be measurable in SPL terms, but are what the user considers makes a particular drive particularly noisy. |
#5
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This web site...
http://www.silentmaxx.net/know_how/a...ccoustics.html says... Quote: Values in bel should be reserved for when talking on sound power level, while values in decibels should be used for when talking on sound pressure level. Values in bels can also be written followed by a capital B, but should be written in all small letters when stated as bels. The abbreviation for decibel is dB (always spelled with a small d and a capital B). A decibel is a tenth of a bel: 1 B = 10 dB. While possible to convert between bel and decibel, is it not possible to convert between sound power level and sound pressure level. "John H." wrote in message news I need a physics lesson. Assuming sea level, how do you convert between sound power (bels) and sound pressure (dBA)? I think you'd have to assume that the acoustic power is being emitted equally in all directions (which may not be true for HDs). WD tells you only the pressure (34 dBA for the 250 GB Caviar SE) while most other manufacturers tell you only the power (2.5 bel for the DiamondMax Plus 9 and Barracuda V). How do you compare apples and oranges? Which is better to know, bels or dBA? I'm thinking that (for HDs anyway) 2.5 bels is less than 25dBA SPL, which makes the WD very noisy by comparison. (I have a cooling fan that's 3.5 bels and 12dBA) |
#6
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On Tue, 02 Dec 2003 16:58:39 GMT
John H. wrote: On Tue, 2 Dec 2003 15:58:25 +1100, "Rod Speed" wrote: If any of them answer my original question, how to convert bels to dBA, I missed it. There cant be a simple factor. Read the pdf, it spells out why. I read it and still don't know why. What did I miss this time? Basically dBAs allow for the ear's perception of sound, so there can never be a simple factor between bels and dBA. Oops, I guess I did overlook that little detail. :-) (Takes a while to sink in) Power values are NOT filtered as pressure values are using the A scale. So converting bels to pressure would give a dB value, not dBA. But I see no reason why power couldn't be measured using the same filter to give you a'belA' rating. Wonder why they don't do it that way? Going by what the A filter looks like in the link I gave (attenuated highs and lows), a 'belA' value would be a lower number and therefore look better to some people. This seems to make a dBA rating a better indicator of how loud a drive will appear than what a bel rating is, and yet most manufacturers don't give you the dBA rating. Doesn't make sense. OTOH, all the acoustic power generated by a drive has to be dissipated somewhere, much of it in the case frame and covers which can resonate and make things worst, so I guess knowing the unfiltered power rating is good too. What would really help with HD noise is switching to 2.5" drives, even 10,000 RPM models. Why would that help? What leads you to believe that a 2.5" drive with a given capacity and performance level will be quieter than a 3.5" drive with the same capacity and performance level? 3.5" drive storage capacity is actually getting too big for most home systems unless used for video. But many home systems _are_ used for video. And for that a 200 gig drive is not all that large--I'm debating whether to upgrade my server to a terabyte array or just wait for terabyte drives to drop out of the bottom of the market at 50 bucks a pop. I'm a little surprised that somebody isn't making a high performance 2.5" drive (better than any 3.5" drive) for desktops yet. Where would be the market for it? What do you believe it would gain and why? -- -- --John Reply to jclarke at ae tee tee global dot net (was jclarke at eye bee em dot net) |
#7
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On Wed, 03 Dec 2003 17:52:00 GMT
John H. wrote: On Tue, 2 Dec 2003 16:48:43 -0500, "J.Clarke" wrote: What would really help with HD noise is switching to 2.5" drives, even 10,000 RPM models. Why would that help? What leads you to believe that a 2.5" drive with a given capacity and performance level will be quieter than a 3.5" drive with the same capacity and performance level? Would you have said the same thing back when only 5.25" drives were available and someone mentioned 3.5" drives? Yes. But why do you feel that that is relevant? Lower mass should help a lot Why would this be? Why do you believe that reducing mass will reduce noise? and also allow higher performance. Why do you believe that reducing mass will allow higher performance? The only drawback compared to a 3.5" drive would be storage capacity. But at the rate capacity is increasing, that would not be a problem for long. 3.5" drive storage capacity is actually getting too big for most home systems unless used for video. But many home systems _are_ used for video. And for that a 200 gig drive is not all that large--I'm debating whether to upgrade my server to a terabyte array or just wait for terabyte drives to drop out of the bottom of the market at 50 bucks a pop. In that case the 2nd drive in your system could be 3.5" until 2.5" drives got large enough for you. And what do you believe that I would gain by such a combination over two 3.5" drives? Even a terabyte is good for only about 100 hours of HDTV - way less if you need to store uncompressed data. True--perhaps I should wait for exabyte drives to become available. I'm a little surprised that somebody isn't making a high performance 2.5" drive (better than any 3.5" drive) for desktops yet. Where would be the market for it? What do you believe it would gain and why? If it's faster, quieter, and consumes less power than any 3.5" drive, the market would include just about everybody. Even if it cost $20,000 each? If it's faster, quieter, consumes less power, provides the same amount of storage, and costs the same, then it has a market. Until then it would be a low-volume niche product that wouldn't repay the development cost. But you have yet to provide a convincing argument that it would be faster, quieter, or consume less power. I know I'd buy one tomorrow if I could. -- -- --John Reply to jclarke at ae tee tee global dot net (was jclarke at eye bee em dot net) |
#8
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On Wed, 03 Dec 2003 17:52:12 GMT
John H. wrote: On Wed, 3 Dec 2003 05:00:32 +1100, "Rod Speed" wrote: But I see no reason why power couldn't be measured using the same filter to give you a 'belA' rating. That makes no sense. Its the distribution of sound with frequency and intensity thats relevant to the ear's perception of sound. So there cant be a simple factor that can be applied between the two. As should be obvious from the different ration you saw between bels and dBA with the hard drive and the fan. I agree that a drive with a lower 'belA' rating could still have higher sound pressure (dBA) in *some* directions (compared to the drive with the higher 'belA' rating) even though the average of *many* directions is lower. But the same is true for bel ratings. A drive with a lower bel rating *might* still produce a higher sound pressure at your ear. Sit at a different angle to the drives and just the opposite could be true. So maybe what you really mean is that 'belA' makes no more sense than bel. The 12dBA, 3.5 bel fan I mentioned (a Papst 8412NGL, http://www.papstplc.com/downloads/DC/8400n.pdf) would surely have very differently shaped isobars (is that the right word here?) than what a HD would, no doubt with a 'high gain' for the direction the fan is blowing in and much lower in back. A hard drive would have pressure variations too but I don't think anywhere near as much as a fan. If all fans were rated in bels (or belA) only, would the ratings be useful in comparing fans? I think so because the pattern for the isobars for one fan shouldn't vary by any significant amount from another fan. I suspect the same is true for hard drives of the same type. But you can't compare bels for a fan to the bels for a HD to determine which will appear louder (as my examples show very well). The difficulty with all of this is that there is no established standard for measuring the sound pressure or sound power levels of either drives or fans. Therefore any differences in the reported measurements may be the result of differences in the test procedures rather than in the devices themselves. Wonder why they don't do it that way? Because it aint even possible. I still think it's possible even if of no value. If the pressure readings made for computing sound power were all "A" filtered, the bel value would be "A" filtered too it seems to me. Going by what the A filter looks like in the link I gave (attenuated highs and lows), a 'belA' value would be a lower number and therefore look better to some people. And here you are massively mangling in the basic metric scale units into a MUCH more complicated concept. The difference between dB and B is just the metric scale unit. Like between M and kM. I don't know what you're talking about here. Bel is used for acoustic power, dB or dBA for acoustic pressure. I haven't used B anywhere. That statement makes no sense. "dB" is the abbreviation for "decibel", which is one tenth of a bel, just as "dm" is the abbreviation for "decimeter", one tenth of a meter. "Bel" is "B" and "B" is "Bel" when discussing acoustic measurements. B or Bel is used for acoustic pressure and acoustic power and many other things. dB is used for acoustic pressure and acoustic power and many other things. dB(A) is normally used for acoustic pressure because that's the only area in which weighting to provide a measurement comparable to the response curve of the human ear has real relevance. For some reason some disk manufacturers have been using B for acoustic power and dB for acoustic pressure but that is not anything that they are required to do by any standard or convention. This seems to make a dBA rating a better indicator of how loud a drive will appear than what a bel rating is, Yes. and yet most manufacturers don't give you the dBA rating. Doesn't make sense. Thats because even the dBA is pretty hopeless with hard drive noises for the reasons I already pointed out. Still better than nothing. What I wish they'd do is provide an FFT of a drive's noise so you could see the amplitude of all frequencies. A sizable spike at some frequency (which would add practically nothing to the bel rating) would be a clear sign to avoid the drive. HD Reviewer's should do this. All they'd need is a PC with a sound board, a good microphone and the right software. Actually, that's not a bad idea. OTOH, all the acoustic power generated by a drive has to be dissipated somewhere, Yes, but thats not relevant to how noisy the drive itself is. much of it in the case frame and covers which can resonate and make things worst, And particularly the Barracudas can choose to add sound damping to the drive itself too. so I guess knowing the unfiltered power rating is good too. Trouble is that that brings up yet another problem. Some of the higher frequency sounds are rather easier to damp by how the drive is mounted, and that resonance effect can never be quantified with the drive itself, it depends on the case etc. So cant be stated by a drive manufacturer on a datasheet. They should provide everything, bels, dBA, sones, FFT plot and let potential buyers go by whatever they want. If you've got the FFT then you should be able to calculate the rest. What would really help with HD noise is switching to 2.5" drives, even 10,000 RPM models. Thats mad. It depends entirely on where the noise is coming from. If the drive rotation system is very quiet at 7200, and the bulk of the noise is from head activity, you wont get that effect necessarily. All else being equal, a smaller drive will be quieter. There's no doubt about it in my mind. 3.5" drive storage capacity is actually getting too big for most home systems unless used for video. Maybe. But 2.5" drives of what you consider to be a suitable size are much slower and much more expensive. That's because they're made for laptops. So far, the primary design goal for 2.5" drives has been low power consumption, not high performance. A 2.5" drive's performance should be able to exceed that of a 3.5" for the same reasons 3.5" exceeds 5.25": lower mass in every part. Do you think 3.5" is some kind of magic number for hard drives, that anything bigger or smaller must have poorer specs? Makes a lot more sense to say buy a very quiet 60GB single platter 3.5" drive like a Samsung P80 and revel in the tons on space and forget about analy comparing pretty useless dBA numbers and just revel in the quiet drive. That may be ok for now, but what would you want in 5 or 10 years? Wouldn't you prefer a 1TB+, 2.5" or less drive with much faster access times, lower power consumption AND lower noise? How about a one petabyte, .25" square solid state storage device with nanosecond access, milliwatts of power consumption, and zero noise? How long do you want to wait? How much do you want to pay? I'm a little surprised that somebody isn't making a high performance 2.5" drive (better than any 3.5" drive) for desktops yet. Because that is completely pointless when clearly its easy enough to make a very quiet 3.5" hard drive. You're probably one of those guys who said "64KB is enough memory for anybody." I'm not as anti-progress as you seem to be. Don't know if you've ever lived with Barracuda IVs. The ones I have are inaudible--the first time I powered one up I thought it was broken because I couldn't tell that it was doing anything. And when it started seeking I could feel it if I touched the drive but could not hear it. There is no real point in trying to make a drive quieter than that. The modern reality is that its only something that a couple of hard drive manufacturers care much about and one of those has blown both feet right off on that by disabling AAM which is an excellent way of making a drive quiet. I wonder how long Seagate will continue to do that if other manufacturers never follow suit and get away with it? If they're worried about a patent then they should just pay for it - probably wouldn't be over $0.25 or so per drive. IBM/Hitachi has been stupid enough to have the deliberate movement of the heads to avoid them staying on the same track for too long when idle, irritatingly noisy for no good reason at all. The fool responsible for that terminal insanity should be taken out the back and shot. How do other manufacturers avoid the problem of heat buildup? They don't move the heads too? BTW, how S.M.A.R.T. is your Samsung? Can it do temperature? How about the error rate attributes? For some reason reviewers never talk about S.M.A.R.T. capabilities or lack thereof. -- -- --John Reply to jclarke at ae tee tee global dot net (was jclarke at eye bee em dot net) |
#9
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"Mark M" wrote in message John H. wrote: If any of them answer my original question, how to convert bels to dBA, I missed it. From http://tinyurl.com/xis6 ... ========START QUOTE Values in bel should be reserved for when talking on sound power level, while values in decibels should be used for when talking on sound pressure level. Values in bels can also be written followed by a capital B, but should be written in all small letters when stated as bels. The abbreviation for decibel is dB (always spelled with a small d and a capital B). A decibel is a tenth of a bel: 1 B = 10 dB. While possible to convert between bel and decibel, is it not possible to convert between sound power level and sound pressure level. ======= END QUOTE Aha, now I get it. You and CWatters are one and the same person, It just takes you a day to switch from one to the other. |
#10
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John H wrote in message ... Rod Speed wrote John H wrote in message Power values are NOT filtered as pressure values are using the A scale. Not clear what you think that sentance means. So converting bels to pressure would give a dB value, not dBA. Correct. But I see no reason why power couldn't be measured using the same filter to give you a 'belA' rating. That makes no sense. Its the distribution of sound with frequency and intensity thats relevant to the ear's perception of sound. So there cant be a simple factor that can be applied between the two. As should be obvious from the different ration you saw between bels and dBA with the hard drive and the fan. I agree that a drive with a lower 'belA' rating could still have higher sound pressure (dBA) in *some* directions (compared to the drive with the higher 'belA' rating) even though the average of *many* directions is lower. But the same is true for bel ratings. You're mangling the entire story utterly. The only difference between bels and decibels, B and dB is the usual metric scale factor. Just like between M and KM etc. The A signifys a quite different application of the A law to the sound being measured to allow for the ear's frequency response. Thats all an entirely separate issue to whether the sound is being radiated uniformly in all directions. Thats hardly ever the case with real world sound sources and certainly isnt whats seen with hard drives or fans. A drive with a lower bel rating *might* still produce a higher sound pressure at your ear. Sit at a different angle to the drives and just the opposite could be true. Correct. BUT thats an entirely separate issue to the A law compensation for the frequency response of the ear. So maybe what you really mean is that 'belA' makes no more sense than bel. Wrong. The frequency response of the ear is still a very important factor in the perception of how noisy a drive is. The problem is that its only part of the story and the other real problem with quantifying how noisy a drive is is the MINDS perception of noises. Some sounds produce very little sound pressure but are very irritating to the MIND. And the reason that isnt quantified is because its essentially unquantifiable. Unlike the frequency response of the ear. The 12dBA, 3.5 bel fan I mentioned (a Papst 8412NGL, http://www.papstplc.com/downloads/DC/8400n.pdf) would surely have very differently shaped isobars (is that the right word here?) Nope. Presumably you mean the spacial contours of equal SPL. than what a HD would, Yes, but the much more important factor is the different frequencys of the sounds produced, and the effect of the A law filter on those. THATS the main factor in the different ratio between the dBA and bel values with the two devices. no doubt with a 'high gain' There is no 'gain'. Certainly the sound isnt uniformly radiated in all directions with both types of device. for the direction the fan is blowing in and much lower in back. You dont get that effect either with quiet fans. A hard drive would have pressure variations too but I don't think anywhere near as much as a fan. Thats just plain wrong too, particularly with the drives that have acoustic damping designed in like the Barracudas. Clearly there wont be as much sound getting thru the thick rubber mat in some directions. Thats the whole point of it. If all fans were rated in bels (or belA) only, would the ratings be useful in comparing fans? To some extent, particularly because fans are much more uniform noise sources, particularly if they are constant speed fans. Uniform in the sense of the frequency distribution of the noise they make. So dBA is more useful when comparing fans than it is with hard drives which produce different noises depending on what they are doing etc. And its the dBA that matters because that allows for the frequency response of the ears. But you STILL cant have a simple ratio between dBA and bels even with just fans, because some fans produce a lot more high frequency noise than others, particularly high speed small fans produce a lot more air turbulence noise than much slower rotating large fans moving the same volume of air. I think so because the pattern for the isobars for one fan shouldn't vary by any significant amount from another fan. Thats just plain wrong too. The spacial distribution of the noise will vary significantly between a high speed very small fan and a big slow rotating fan both moving the same volume of air. And then you have the other massive difference between the types of fans, radial bladed fans and turbines/blowers, cylindrical fans etc. At the extremes you get quite different effects when the tip speeds are approaching the speed of sound too. I suspect the same is true for hard drives of the same type. You're wrong. Most obviously because the design of the body of the drive has a big effect on the spacial distribution of sound. AND when the frequency of the sounds vary from drive to drive, there cant be a simple conversion between dBA and bels either, just because of the A law curve. But you can't compare bels for a fan to the bels for a HD to determine which will appear louder (as my examples show very well). You cant with hard drives either as I pointed out in your original list of particular drives. Wonder why they don't do it that way? Because it aint even possible. I still think it's possible You're wrong. It aint. While ever the frequency of the noise produced by drives vary from drive to drive, there cant ever be a simple ratio between dBA and bels. even if of no value. If the pressure readings made for computing sound power were all "A" filtered, the bel value would be "A" filtered too it seems to me. You're wrong again. The is NO filter applied the bel reading. Thats the whole point of the A letter in dBA, it signifys that THAT value has the A law filter applied. Going by what the A filter looks like in the link I gave (attenuated highs and lows), a 'belA' value would be a lower number and therefore look better to some people. And here you are massively mangling in the basic metric scale units into a MUCH more complicated concept. The difference between dB and B is just the metric scale unit. Like between M and kM. I don't know what you're talking about here. Bel is used for acoustic power, dB or dBA for acoustic pressure. I haven't used B anywhere. B is just Bel. dB is decibel. dB aint the same as dBA. This seems to make a dBA rating a better indicator of how loud a drive will appear than what a bel rating is, Yes. and yet most manufacturers don't give you the dBA rating. Doesn't make sense. Thats because even the dBA is pretty hopeless with hard drive noises for the reasons I already pointed out. Still better than nothing. Sure, and thats why its quoted. What I wish they'd do is provide an FFT of a drive's noise so you could see the amplitude of all frequencies. That would be useless as far as how irritating it is TO THE MIND. A sizable spike at some frequency (which would add practically nothing to the bel rating) would be a clear sign to avoid the drive. Nope. Some frequencys are barely audible. True in spades of TVs where the line frequency isnt even audible for most people. HD Reviewer's should do this. All they'd need is a PC with a sound board, a good microphone and the right software. And that would be completely useless when the main problem today is how irritating the sound is TO THE MIND. You dont even get general agreement on that. Some find that white noise is quite soothing and produce it deliberately. Some find that the residual whistle you end up with with very quiet systems not objectionable at all, others hate it. Some find soft sounds produced by a drive seeking quite acceptible and the sound like a cricket in a small cardboard box very irritating indeed in comparison. OTOH, all the acoustic power generated by a drive has to be dissipated somewhere, Yes, but thats not relevant to how noisy the drive itself is. much of it in the case frame and covers which can resonate and make things worst, And particularly the Barracudas can choose to add sound damping to the drive itself too. so I guess knowing the unfiltered power rating is good too. Trouble is that that brings up yet another problem. Some of the higher frequency sounds are rather easier to damp by how the drive is mounted, and that resonance effect can never be quantified with the drive itself, it depends on the case etc. So cant be stated by a drive manufacturer on a datasheet. They should provide everything, bels, dBA, sones, FFT plot and let potential buyers go by whatever they want. Might as well cut to the chase and include a wav file measured under standard conditions, say the drive running bare, outside any housing at all and captured at the maximum SPL direction. But even that would be pretty useless because some sounds would be muffled much better by the typical case than others. Non fluid bearing whine is particularly bad there. And that opens up a whole nother can of worms, the variation in bearing noise over time, and from copy to copy. Its a lot simpler to quote the dBA and accept that that is only useful for the most gross differences between drives. What would really help with HD noise is switching to 2.5" drives, even 10,000 RPM models. Thats mad. It depends entirely on where the noise is coming from. If the drive rotation system is very quiet at 7200, and the bulk of the noise is from head activity, you wont get that effect necessarily. All else being equal, a smaller drive will be quieter. Bull****. There's no doubt about it in my mind. Your problem. 3.5" drive storage capacity is actually getting too big for most home systems unless used for video. Maybe. But 2.5" drives of what you consider to be a suitable size are much slower and much more expensive. That's because they're made for laptops. Nope, thats the inevitable result of having to be smaller. So far, the primary design goal for 2.5" drives has been low power consumption, not high performance. The primary goal for 2.5" drives is the physical form factor. A 2.5" drive's performance should be able to exceed that of a 3.5" Bull****. for the same reasons 3.5" exceeds 5.25": lower mass in every part. More bull****. And when the drive is essentially silent when its idle, just rotating, reducing the size of the platters cant make it any quieter than that. Do you think 3.5" is some kind of magic number for hard drives, that anything bigger or smaller must have poorer specs? Obviously not. But like I said, if the 3.5" drive is already essentially silent when its idle, just rotating, reducing the platter size wont have any effect on that noise, and you are just wasting your money on the higher cost of the smaller platters. Particularly when a single platter 3.5" drive has already got ample space for all except video with desktop systems. Makes a lot more sense to say buy a very quiet 60GB single platter 3.5" drive like a Samsung P80 and revel in the tons on space and forget about analy comparing pretty useless dBA numbers and just revel in the quiet drive. That may be ok for now, but what would you want in 5 or 10 years? Likely a much bigger drive to replace my current collection of video tapes. They're a pain in the arse physically, just excellent value per GB. And I only use those for time shifting, not for archival. Wouldn't you prefer a 1TB+, Yes. 2.5" or less drive I dont care about the physical size. with much faster access times, Nope, that has no effect on what I do now. lower power consumption Dont care about that either except that a little less would be easier as far as being able to stack drives adjacent and ignore the drive temp is concerned. AND lower noise? Already got that. Its already so low that I cant detect it being powered down or not. Already lower than ALL the laptop drives I use. Amd thats with the 3.5" drive in a case with never useing the case covers for convenience. I'm a little surprised that somebody isn't making a high performance 2.5" drive (better than any 3.5" drive) for desktops yet. Because that is completely pointless when clearly its easy enough to make a very quiet 3.5" hard drive. You're probably one of those guys who said "64KB is enough memory for anybody." Nope, never did. I'm not as anti-progress as you seem to be. I'm not anti progress at all. I've got the sense to have noticed that the drive is ALREADY completely silent in the sense that I cant detect when its been turned off and the sense to realise that it would be stupid to use a 2.5" drive that wont perform as well and which will cost significantly more in that situation. I would welcome that drive available in multi TB size at as low a cost as the video tapes per TB, but that wont be happening any time soon. When it does, I'll bin the video tapes as quickly as I have floppys. The modern reality is that its only something that a couple of hard drive manufacturers care much about and one of those has blown both feet right off on that by disabling AAM which is an excellent way of making a drive quiet. I wonder how long Seagate will continue to do that if other manufacturers never follow suit and get away with it? I doubt too many of the mug punters who buy the absolute vast bulk of hard drives would even know what AAM was if it bit them on their lard arses. If they're worried about a patent then they should just pay for it - probably wouldn't be over $0.25 or so per drive. Yep, thats what I meant. IBM/Hitachi has been stupid enough to have the deliberate movement of the heads to avoid them staying on the same track for too long when idle, irritatingly noisy for no good reason at all. The fool responsible for that terminal insanity should be taken out the back and shot. How do other manufacturers avoid the problem of heat buildup? Basically move the heads silently. They don't move the heads too? Yep. BTW, how S.M.A.R.T. is your Samsung? Can it do temperature? Yep. How about the error rate attributes? Its fine, as complete a set as with any. For some reason reviewers never talk about S.M.A.R.T. capabilities or lack thereof. Yeah, most of them wouldnt know what SMART was if it bit them on their lard arses. I dont recall any of them actually citing the SMART temperature rise seen in active use in their reviews. Tho admittedly I dont bother with reviews much. |
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