4 ms·

No, because decibles are logarithmic. 30db + 30db = 33db https://www.noisemeters.com/apps/db-calculator/ https://www.noisemeters.com/apps/db-calculator/ With

by TylerE 3y ago

No, because decibles are logarithmic. 30db + 30db = 33db https://www.noisemeters.com/apps/db-calculator/ https://www.noisemeters.com/apps/db-calculator/ With hearing protection the ratings are in isolation. They are not circuit components that work serially. Sound transmits through the skull physically.

kazinator 3y ago
I'm afraid are seriously misunderstanding what that calculator is for. In this calculator, whenever you add any equal decibel values X, you get X + X = X + 3: three more decibels. There is a familiar meaning behind that: it means that if we have two independent noise sources of about equal intensity, and add them together, the result is 3dB more intense. E.g. if we have a loudspeaker playing white noise, and add an identical loudspeaker playing the same kind of of white noise at the same level, we get 3dB more white noise. It has nothing to do with cascaded boosts or attenuations. If we add together two sources that contain the same signal, in phase, then the rule is 6 dB. Like two identical loudspeakers in a cabinet instead of one, playing exactly the same signal. The reason we can add decibels for cascaded attenuations and boosts is exactly the same reason why we can add displacements on a slide rule to do multiplication. Attenuations (such as a voltage divider) multiply the signal. E.g. multiplying by 1/2 is -6db. In the logarithmic space, multiplication turns to addition. This is typically covered in high school. > They are not circuit components that work serially. That's true, but I addressed in it my comment (with several redundant remarks) in such a way that the above remark doesn't add more clarity. I have a sneaking suspicion you might not have read it in detail.
- javajosh 3y ago
  Perhaps it would be helpful to consider the path of a phonon going through a barrier. The odds of that phonon making it through is 1 chance in N. If there are two barriers, the odds of a phonon making it through both in series is 1 chance in N^2. That is, the odds multiply, and you are absolutely correct that dB's add (since they are basically log(N) in this case and log(N^2) = 2log(N)).
  - kazinator 3y ago
    This probability model doesn't seem to add anything to just straightforward reasoning about how each barrier attenuates the intensity of the sound (or other signal) by a certain fraction. E.g. 50% is -3 dB, then 25% is another -6 dB for at total of -9 dB. 1> (log10 .5) -0.301029995663981 2> (* 10 (log10 .5)) -3.01029995663981 3> (* 10 (log10 .25)) -6.02059991327962 4> (* 10 (log10 (* .5 .25))) -9.03089986991944 Just logs turning multiplication into addition, like your grandpa's slide rule. In electronics we use a factor of 20 for voltage cuts/boosts. Half the voltage is -6 dB, because power/intensity (Watts) is voltage squared: half the Volts is a quarter the Watts (P = V^2/R).
- rrrrrrrrrrrryan 3y ago
  > ... is exactly the same reason why we can add displacements on a slide rule ... I know this analogy was intended to help understanding, but I'm curious - are most people actually familiar with slide rules work? Just for reference: I'm an engineer in my mid thirties, and I know what a slide rule is, and might even be able to correctly identify the object if it were placed in front of me, but I've never actually seen one (let alone used one), so the analogy you've made is meaningless to me. My girlfriend who's a few years younger than me and also works in tech is vaguely familiar with the concept of the device but had never heard of the term "slide rule". My father is also an engineer and only used one for one class when he was in high school.
  - deleted 3y ago
    [deleted]
sp332 3y ago
But physically, if you put a 30 db noise reducer behind another 30 db noise reducer, you will get 60 db noise reduction overall.
- TylerE 3y ago
  But you can’t! Sound waves have many paths to the eardrum and related tiny bones.
  - Retric 3y ago
    That applies when sound has a secondary path through the body. But not all noise reduction just cover the ears. Someone standing in a box with earmuffs could see 30 + 30 = 60db drop for some frequencies. As would someone standing far enough from a sound to see 30db drop off who then uses non distance related ear protection.
- kazinator 3y ago
  I predict that TylerE will not believe you.
  - TylerE 3y ago
    Neither does osha. They spec that when earring muffs and plugs the effective rating is the higher rated product +5db.
    - kazinator 3y ago
      Note that this estimate disagrees with the wholly inappropriate calculator you cited, which will never produce a value exceeding the higher value by more than 3 dB. OSHA almost certainly had to empirically determine the estimate, either with a real human head, a fake one, or some numerical model or something.
      - TylerE 3y ago
        It disagrees with me (2db) a lot less than it disagrees with you. (25db).
marcosdumay 3y ago
Attenuation is multiplicative.
- TylerE 3y ago
  If you are attnuating 100% of the signal, yes. That is very much not the case with earplugs.
  - thghtihadanacct 3y ago
    negative, shock waves from sound will travel through your person and reach your cute little ear plugs from the back side. Remember youre made out of slightly more than jello ... depending on fitness level

by TylerE 3y ago

kazinator 3y ago

I'm afraid are seriously misunderstanding what that calculator is for. In this calculator, whenever you add any equal decibel values X, you get X + X = X + 3: three more decibels. There is a familiar meaning behind that: it means that if we have two independent noise sources of about equal intensity, and add them together, the result is 3dB more intense. E.g. if we have a loudspeaker playing white noise, and add an identical loudspeaker playing the same kind of of white noise at the same level, we get 3dB more white noise. It has nothing to do with cascaded boosts or attenuations. If we add together two sources that contain the same signal, in phase, then the rule is 6 dB. Like two identical loudspeakers in a cabinet instead of one, playing exactly the same signal. The reason we can add decibels for cascaded attenuations and boosts is exactly the same reason why we can add displacements on a slide rule to do multiplication. Attenuations (such as a voltage divider) multiply the signal. E.g. multiplying by 1/2 is -6db. In the logarithmic space, multiplication turns to addition. This is typically covered in high school. > They are not circuit components that work serially. That's true, but I addressed in it my comment (with several redundant remarks) in such a way that the above remark doesn't add more clarity. I have a sneaking suspicion you might not have read it in detail.

javajosh 3y ago
Perhaps it would be helpful to consider the path of a phonon going through a barrier. The odds of that phonon making it through is 1 chance in N. If there are two barriers, the odds of a phonon making it through both in series is 1 chance in N^2. That is, the odds multiply, and you are absolutely correct that dB's add (since they are basically log(N) in this case and log(N^2) = 2log(N)).
- kazinator 3y ago
  This probability model doesn't seem to add anything to just straightforward reasoning about how each barrier attenuates the intensity of the sound (or other signal) by a certain fraction. E.g. 50% is -3 dB, then 25% is another -6 dB for at total of -9 dB. 1> (log10 .5) -0.301029995663981 2> (* 10 (log10 .5)) -3.01029995663981 3> (* 10 (log10 .25)) -6.02059991327962 4> (* 10 (log10 (* .5 .25))) -9.03089986991944 Just logs turning multiplication into addition, like your grandpa's slide rule. In electronics we use a factor of 20 for voltage cuts/boosts. Half the voltage is -6 dB, because power/intensity (Watts) is voltage squared: half the Volts is a quarter the Watts (P = V^2/R).
rrrrrrrrrrrryan 3y ago
> ... is exactly the same reason why we can add displacements on a slide rule ... I know this analogy was intended to help understanding, but I'm curious - are most people actually familiar with slide rules work? Just for reference: I'm an engineer in my mid thirties, and I know what a slide rule is, and might even be able to correctly identify the object if it were placed in front of me, but I've never actually seen one (let alone used one), so the analogy you've made is meaningless to me. My girlfriend who's a few years younger than me and also works in tech is vaguely familiar with the concept of the device but had never heard of the term "slide rule". My father is also an engineer and only used one for one class when he was in high school.
- deleted 3y ago
  [deleted]

sp332 3y ago

But physically, if you put a 30 db noise reducer behind another 30 db noise reducer, you will get 60 db noise reduction overall.

TylerE 3y ago
But you can’t! Sound waves have many paths to the eardrum and related tiny bones.
- Retric 3y ago
  That applies when sound has a secondary path through the body. But not all noise reduction just cover the ears. Someone standing in a box with earmuffs could see 30 + 30 = 60db drop for some frequencies. As would someone standing far enough from a sound to see 30db drop off who then uses non distance related ear protection.
kazinator 3y ago
I predict that TylerE will not believe you.
- TylerE 3y ago
  Neither does osha. They spec that when earring muffs and plugs the effective rating is the higher rated product +5db.
  - kazinator 3y ago
    Note that this estimate disagrees with the wholly inappropriate calculator you cited, which will never produce a value exceeding the higher value by more than 3 dB. OSHA almost certainly had to empirically determine the estimate, either with a real human head, a fake one, or some numerical model or something.
    - TylerE 3y ago
      It disagrees with me (2db) a lot less than it disagrees with you. (25db).

marcosdumay 3y ago

Attenuation is multiplicative.

TylerE 3y ago
If you are attnuating 100% of the signal, yes. That is very much not the case with earplugs.
- thghtihadanacct 3y ago
  negative, shock waves from sound will travel through your person and reach your cute little ear plugs from the back side. Remember youre made out of slightly more than jello ... depending on fitness level