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Old 08-24-2011, 01:54 PM
njtt njtt is online now
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Fridge decibel ratings and subjective loudness

I am looking to buy a cheapish, smallish fridge-freezer. One consideration, however, is that there is no room for it in the kitchen, so it is almost certainly going to have to live in the room that serves as my living room, dining room, computer room, TV room and study, where I do my writing and my reading. Thus, quiet is important. (Most of the time, there is not an annoying amount of noise coming from outside, especially at night, which is often when I am most trying to concentrate.) I do not require absolute silence to work and concentrate, but I am still a bit concerned about how noisy the fridge is going to be.

At the moment there are two models I am considering (both from the same manufacturer). One is rated at 43dB noise level and the other is rated at 39dB. However, the first is a little bit cheaper, and has a little bit more room inside. What I want to know is, when there is little or no other background noise, am I going to notice a big difference between 43dB and 39dB? Also, do either or both of those ratings sound either unacceptably loud for a situation like mine, or low enough to be negligible?

As I understand it, decibels work on a logarithmic scale, so that, according to Wikipedia (if I am reading it right) 3 more decibels approximately doubles the “power ratio” of the sound (and here we are talking about 4 more decibels, so that sounds bad). However, I have no idea how “power ratio” relates to subjective loudness. I do know, however, that psychophysical relations between physical quantities and subjective impressions of their intensities are usually nothing like linear. I suspect that a 43dB noise level is not going to seem anything like more than twice as loud as a 39dB one, but I am by no means sure about that. Does anyone actually know?
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  #2  
Old 08-24-2011, 02:43 PM
constanze constanze is offline
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It depends. Noise is not only based on decibel, because humans are not machines. This also means it varies from person to person how some noise is perceived.

There are several lists giving examples of typical noise in dezibel amounts.
A whisper is 30 dB,
soft music 40 dB
normal noise in a flat 45 dB
rain or fridge 50 dB
loud (heavy) rain or normal conversation 55 dB

But loudness of noise is also relative. If surrounding noise is 50, a pen falling to the ground is barely heard; but in the dead of the night, a pen falling down can make you sit upright in bed because it's so sudden that it seems very loud.

In addition, the quality of sound plays a role - a fridge is pretty good in that regard because a low continous hum is easier for the mind to tune out than irregular, high-frequency shrieks. (That's why they sell CDs of ocean waves to relax or mask unpleasant noise). Still, one fridge can make, due to the way it's built, a special tone that grates on you personally regardless of actual decibel level or frequency.

Is there a chance to tape the noise of the running fridges and play the tape in your home before buying?

Last edited by constanze; 08-24-2011 at 02:43 PM..
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Old 08-25-2011, 03:23 PM
njtt njtt is online now
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Quote:
Originally Posted by constanze View Post
Is there a chance to tape the noise of the running fridges and play the tape in your home before buying?
Thanks, but no. I think that would be ridiculous overkill, even if practicable.

I was really just hoping for some guidance on whether the subjective difference between a 43dB and 39dB fridge hum is likely to be significant (at 9 or 10 feet away, and assuming an otherwise very quiet environment).

Last edited by njtt; 08-25-2011 at 03:25 PM..
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Old 08-25-2011, 03:35 PM
jz78817 jz78817 is offline
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in general, if two sounds measure the same dB, the one with more higher frequency content will be more annoying. A lot of sound quality testing now uses loudness measurements such as sones to try to quantify this.
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Old 08-25-2011, 03:59 PM
njtt njtt is online now
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Quote:
Originally Posted by jz78817 View Post
in general, if two sounds measure the same dB, the one with more higher frequency content will be more annoying. A lot of sound quality testing now uses loudness measurements such as sones to try to quantify this.
OK, but all I have to go on here are decibel ratings. Presumably two fridges from the same manufacturer will not differ much in noise frequency anyway. At any rate, I think I have to assume that, until fridge retailers start rating their machines in sones, anyway.
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Old 08-25-2011, 04:24 PM
jz78817 jz78817 is offline
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well in all honesty if this is a cheap little fridge, it probably doesn't matter what they say it puts out anyway. The rating (if it's legit) was probably taken on a reference sample in a quiet room. Manufacturing variations (not to mention loose parts) will mean that the one you buy might be markedly different. It's a hassle, but you might end up having to buy one and see how it is. if it's too loud return it.
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Old 08-25-2011, 06:34 PM
njtt njtt is online now
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That is my question really. Given that noise is a consideration, should I be taking these dB ratings and the difference between them seriously, or should I ignore them and just just go for the (slightly) cheaper and (slightly) bigger model. I guess you are saying I should ignore them.
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Old 08-25-2011, 06:52 PM
Gorsnak Gorsnak is offline
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First, remember that decibels are a logarithmic scale.

A 3db difference is a doubling of the amount of sound energy. It's also about "one notch" on a volume control. 6-10dB is generally said to be a subjective doubling of volume, though just what "twice as loud" means is rather subjectively vague to begin with.

I'm not sure how they measure fridges to get noise ratings, but the usual practice is to stick the object in an anechoic chamber and measure the sound with a mic 1m away. If it's dBA, then it's measuring with an "A" weighting, which is a frequency profile that's supposed to match human hearing - this is standard practice. In this context, 39 and 43dB are both going to fall into the category of definitely audible in the context of a quietish room. What you're concerned with, however, is how annoying the sound is going to be to you. This will be determined to a great extent by things other than sound pressure level. Higher frequencies are more annoying than lower, pure tones (single frequencies) are more annoying than broadband sounds (like a wooshing fan). Abruptly or frequently changing sound is more annoying than steady sounds.

I think you're right to be concerned about the noise the fridges make, but the dB ratings aren't going to give you conclusive information. If the fridges are from the same manufacturer, then the dB rating should be at least consistent, so the 39dB rating should sound like it's a notch or two lower in volume (assuming the tested samples were representative), but that doesn't guarantee it will be more pleasant to listen to.
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Old 08-26-2011, 02:51 AM
constanze constanze is offline
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Quote:
Originally Posted by njtt View Post
That is my question really. Given that noise is a consideration, should I be taking these dB ratings and the difference between them seriously, or should I ignore them and just just go for the (slightly) cheaper and (slightly) bigger model. I guess you are saying I should ignore them.
No, what we're really saying is that dB alone doesn't tell enough to say. You could be more annoyed by the model with less dBA because the sound frequency is different (even from the same manufacturer). You could find even the lower dB to be too loud when you're working in the middle of the night and the house is very very quiet, or you could find that even the louder model's hum gets drowned out in the everyday background noise. You could even find the louder model better because it hits just the right way to mask other noise and simulate trees in a breeze or ocean waves.

We also can't guess how much a certain noise bothers you personally, because that varies from person to person. If you are very sensitive to noise in general, you could go with the less loud model, but that's not any guarantee. You might feel like wasting a lot of money if that's the more expensive model, and that the other model would work just as fine. Or you might be angry with yourself if the cheaper, louder model bothers you for not going the expensive route.

Can you go to a store and listen to them running, or are you going to buy online?
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Old 08-26-2011, 07:27 AM
njtt njtt is online now
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I have been to the store, but none of the fridges there were running, and I doubt whether any (or most) of them were near enough to an electrical outlet to be plugged in. In any case there was much too much background noise in the store to make a reasonable judgment about how they would sound in a quiet apartment.

Thanks for trying to help.
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  #11  
Old 08-26-2011, 09:28 AM
constanze constanze is offline
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Note: I guess you know this already, but for fullness sake:

Never turn on a fridge that's been delivered right away. You need to let it sit for at least 24 hrs., if it's big or has been jostled a lot, 2 or more days. If you turn it on while the cooling fluid is still churned up from the transport, you can ruin it. (I recently replaced my fridge and was warned about this).
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