I'm trying to turn down the noise in whatever environment I am using some earplugs I got from Amazon. It has the best rating compared to it's comfortability. Even as this is so, I can still hear noise from around me.

If I add another layer, like let's say, an ear protector(like the ones you see people wearing when they go out shooting), will that decrease the noise compared to what I am hearing right now with only the earplugs alone?

  • Hi Aurora Afable, Welcome to stack.exchange. – Stan Jul 10 '16 at 2:50
  • About what noise pressure level are you asking? Is it above 85 dBA? – ott-- Jul 10 '16 at 18:07

Yes, as you observed with shooters, layering your hearing protection is a common (and effective) way to increase your level of hearing protection.

The American National Standards Institute (ANSI) requires that all safety devices used for noise reduction be labeled with a noise reduction rating (NRR) to quantify their effectiveness. Even though NRR is expressed in decibels (dB), it is important to understand that hearing protectors DO NOT reduce the surrounding levels by that amount. You can do the math (see below(1)), but for the sake of this post, know that the higher the NRR number, the greater the capacity for noise reduction.

Layering Noise Reduction

If you are layering you hearing protection, it's also important to note that layering noise protection is not additive (i.e. 33 dB + 29 dB ≠ 62 dB reduction), nor is the noise reduced by a fixed percentage. The exact math is outside the scope of this post, but with your average safety device (with an NRR of about 20-33db), the math will work out to about 5 dB reduction with a second layer.

(1) For anyone interested in the measurements:

OSHA defines what noise levels warrant hearing protection to assure safe working conditions. Excessive noise is generally defined as exposure to 85 or more decibels of sound over an 8 hour period. But if the ambient noise exceeds those levels, the amount of time until damage can occur will decrease.

To calculate the noise reduction, you can get a pretty good approximation by taking the NRR rating, subtract 7, and then divide by 2. For example, if you have a piece of machinery operating at 110 dB with hearing protection rated at 33 NRR, the reduction would look like this:

110 dB - (33 - 7) / 2
110 dB - 13
= 97 dB

You can then use the chart above to determine if addition noise protection is necessary.

There's obviously little downside to being overly conservative when it comes to protecting your hearing. I tend to use it even if I don't absolutely need it; it's just a good habit.

If you are occasionally working with something particularly loud, you can double up the methods of protection… but if you do this often, it is best to just buy one, convenient piece of protection that will handle those levels.

If you are concerned about blocking out the "normal" noises as a matter of safety (communicating with people, hearing alarms, etc), then you might want to consider investing in some good electronic ear protection (search). Devices like these will provide an effective reduction of loud noises while allowing (or even amplifying) the normal sounds you might want to hear. That's pretty cool.

I use electronic hearing protection almost exclusively. When I am working with loud equipment (or things that go <boom>), I want to be able to hear the things going on around me. When the equipment goes off, I don't have to remove my hearing protection or remember to put it back on again. When it starts to get noisy, it's just there. And I like to assure that I can continue to communicate normally with the people or things around me.

  • Wasn't the question "if" additional layers were necessary "when" the noise was still audible with plugs alone rather than the numerical calculation of the various safety standards in force? I think that sometimes we get involved with minutae at the expense of an understanding. Am I wrong? – Stan Jul 11 '16 at 6:44
  • @stan That's why the topmost part of my post is stated very simply -- yes, two layers will reduce noise more. The detail that follows is simply expanding on that for the benefit of anyone who might comes after. I even annotated it as such. These question aren't only meant to help one person. Does that make sense? – Robert Cartaino Jul 11 '16 at 6:53
  • For sure. Yet, it is lifehacks. I thought that "I" was getting carried away. Anyways, I see that someone else agrees with you. Best. – Stan Jul 11 '16 at 6:56

Yes. You will get less noise by using both of them together in combination.

Sound, as you recall from high-school science, is the differences of air pressure produced by a moving mass.

An air-pressure wave pushes on our ear drum and produces the sensation we call sound. Big differences produce loud sounds and small differences, soft sounds. If we don't like the sound, we call it noise.

Ear plugs can partially block the air pressure that enters our ear canal. Nothing is perfect. The more effective the block, the better the ear plugs reduce the pressure difference. We experience a reduction in volume since the seal isn't perfect and the insulation of the plug isn't perfect either. Let's say the plugs reduce the sound by one half.

Ear protectors surround the ear with sound deadening insulation inside a cup that fits over each ear. Let's say the protectors also reduce the sound by one half.

Each device cuts the pressure by half. Together the two will reduce the sound pressure waves by half of a half. That's equal to one-quarter.

Sound insulation is additive. You can multiply the sound deadening numbers to find out the sound deadening capabilities of them in combination.

The kind people at explainthatstuff.com go into the details with more detail about the mathematical relationship when you combine materials.

  • 1
    Unfortunately, your statement about determining total noise reduction is not correct. Hearing protection does not reduce sounds by a fixed percentage nor can you simply add or multiply the reduction ratings with each additional layer. – Robert Cartaino Jul 11 '16 at 2:26
  • @RobertCartaino I was under the impression that adding logarithms was arithmetical multiplication. – Stan Jul 11 '16 at 6:35
  • @RobertCartaino Where was my error? I was trying to give an illustration rather than give exhaustive calculations. – Stan Jul 11 '16 at 6:46

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