haha, true. however, i'd say that you're the optimist here since you're agreeing that30dB rated muffs and 30dB rated ear plugs worn together give you a combined protection of 60 dB.
That's not what I meant in my post. I meant that if the muffs and plugs themselves really, literally attenuated by 30 dB each, then their combined attenuation would be 60 dB. It's like turning down the volume on a preamplifier by 30 dB, and then by 30 dB again--the result is 60 dB less than before, not 33 dB less. The latter wouldn't make any physical or mathematical sense.
Then I said that NRR ratings are NOT merely how much these devices attenuate on their own, as we might assume at first, but are based instead on the relative level of the sound measured at the ear to that of the outside, which is a very different thing because the human body also transmits outside sounds to the ear, thereby limiting how much reduction is possible. Therefore it never makes sense to add the NRR ratings of different devices together because they include things that are separate and independent of the devices themselves.
Frankly, I'm not sure what to make of this.
Physically, the 30 dB NRR of each device takes into account the sound that leaks in through the body, which means that the actual attenuation of the device must be greater. Together the muffs and plugs add up to a pretty massive amount of innate attenuation (more than just 60 dB), which then gets mostly "wasted" because you always have to add in the same amount of leakage through the body, resulting in only a slight (but useful) improvement when doubling up (usually a few dB).
The post you've referenced offers no realistic physical explanation of this complex issue, and focuses instead on simple mathematics, which I've demonstrated to be inadequate. Furthermore, the math does not match the physical reality because it makes it seem as though each device subtracts some absolute amount of sound rather than attenuating them by a multiplicative factor, and that just ain't right. If I had to guess, I would say that the coincidence that 3 dB happens to be a good rule-of-thumb value for the improvement offered by doubling up on protection is causing confusion by making people mistakenly think that it's how sound attenuation works in a mathematical sense.
The underlying truth is far more complicated, but I think it should be sufficient to say that the human body itself is a major limiting factor in how effective devices such as muffs and earplugs can be, and it's probably fairly safe to say that doubling up coincidentally results in reducing the energy of the sound by half or 3 dB. Matters would be different and probably much simpler both physically and mathematically if one's entire body were encapsulated by such devices, but that's hardly practical, obviously.
Criminal to be honest
