Double Ear Protection — Does 32 dB + 32 dB NRR Equal 64 dB?

[Ramki]

Dear members,

I just want to ask a question regarding double ear protection in extreme noise areas such as subway, gunfire, concerts. All of them are over 120 dB.

But if I wear earplugs (32 dB) and mufflers(32 dB) together would it decrease it by 64 dB?

Please help me to understand it. Thank you!!

 

[Julien87]

No, subways are definitely not over 120 dB. Even concerts, which are much louder than subway, usually never reach 120 dB..
Regarding your question, edited : actually I don't know, and what I thought is incorrect
But there is still noise going through the bones.

 

[Alue]

No, you would not be getting 64db attenuation. It is logarithmic so you cannot just add the two values. You would be seeing about 37db reduction.

 

[VRZ78]

Subway here in France is around 75 dB in the oldest train and 60 to 65 in the new ones. However when you're on the track and the train arrives it can reach 85.

I don't know where your are from but there is no way a subway is 120 db...
It might be good to wear some earplugs if you take it for long rides thought

 

[JurgenG]

http://www.hearingprotech.com/pdf/en/Pub_Double-hearing-protection.pdf

Can anyone btw shed a light on that formula?
33 × log((0.4 × B) + (0.1 × ST))

It makes sense only if you actually use earplugs, otherwise it's an unusable formula I guess?
For instance
If I use B (earplugs) of 9 dB and Muffs (st) of 30 dB I actually get a lower number of attenuation than using only the muffs..
= 27,044

 

[Bill Bauer]

http://www.hearingprotech.com/pdf/en/Pub_Double-hearing-protection.pdf

Can anyone btw shed a light on that formula?
33 × log((0.4 × B) + (0.1 × ST))

It makes sense only if you actually use earplugs, otherwise it's an unusable formula I guess?
For instance
If I use B (earplugs) of 9 dB and Muffs (st) of 30 dB I actually get a lower number of attenuation than using only the muffs..
= 27,044

All sites I had a chance to see seem to say that a good rule of thumb is just to add 5 dB to the NRR of the highest rated device (of the two hearing protection devices)
http://www.noisehelp.com/double-hearing-protection.html