How do you calculate the noise reduction rate when using earplugs and earmuffs at the same time?

[Lesky]

How do you calculate the noise reduction rate when using earplugs and earmuffs at the same time?

If you have earplugs with a NRR of 33 dB and ear muffs with a NRR of 30 dB.

What would the correct total NRR be?

Please also explain your calculation

I tried googling this, but did not find any clear answer.

Thanks in advance!
/L

 

[Markku]

See my post here: https://www.tinnitustalk.com/thread...ir-cells-safe-—-discuss.745/page-2#post-17753

("However, the attenuation of the combination is not equal to the sum of the individual attenuation values (Berger, 1983), as illustrated in Figure 1. Note for example; at 1000 Hz the combination of a 26-dB plug and a 34-dB muff does not yield 60-dB overall, but rather about 41 dB. The principal reason is the bone-conduction (BC) limits to attenuation, which are also illustrated in Figure 1.")

 

[Lesky]

http://www.audiologyonline.com/articles/extra-protection-wearing-earmuffs-and-1218

"No empirical or theoretically derived equations are available that can predict the attenuation of an earplug and earmuff combination with sufficient accuracy to be useful"

What the hell?

 

[CDNThailand]

http://www.audiologyonline.com/articles/extra-protection-wearing-earmuffs-and-1218

"No empirical or theoretically derived equations are available that can predict the attenuation of an earplug and earmuff combination with sufficient accuracy to be useful"

What the hell?

Markku is right, that website is wrong