[Double Naught Spy]

First, 22-Mag, how much hearing protection is afforded by different materials and barriers is not reflected in the testing of employees' hearing. You may be able to determine if the hearing protection afforded is working or not, but not how much hearing protection is provided by layers or materials. Why? Becuase hearing loss is a cumulative event that occurs over time, and can occur outside of the work environment.

Since you are up on the OSHA standards and facts, if you are operating a piece of equipment that is encased in a sound absorbing chamber that effectively reduces the noise level by 33 db but is still producing 140 db of sound that comes through that barrier to the operator's (your) position and you are wearing muffs that reduce noise by 31 db, how much sound is getting to the ear? By your information, the doubled protection would result in only another 5 db in reduction and the person wearning the muffs would be getting 135 db.

I love the math aspect. if you double the protection of a single barrier, you get a reduction of just 3 db because of the log scale whereby pressure doubles every 3 db. What you are claiming is that whether slightly more than doubling or slightly less than doubling the protection, you are geting 5 db more protection, not 3. That means that pressure is reduced by half with the first 3 db of reduction then another significant amount for the extra 2 db.

Please tell me how it is that the 31 db nrr muffs are not reducing the noise penetrating the muffs by 31 db and instead would only be 5 db.

Or is this a project of some mystical relationship between plugs and muffs? If so, please explain.

I have spoken with two audiologists who have both explained to me the apparent accepted normal that in wearing muffs and plugs, say they are both the same rating, reduces the sound to the ear by only another 3 db because sound level is cut in half by the double protection. Neither could knew or could explain if the NRR calculations and 3db pressure reduction was calculated using a single barrier or multiple barriers or how it is that sound passing through one barrier knows to only reduce by a small amount (either 3 or as you suggest, about 5 db) versus sound of the same exact level only passing through one barrier and being reduced the full 30 db amount.

Just how does 170 db sound reduced to 140 by a barrier know to reduce by only another 3 or 5 db when passing through the next 30 db barrier versus 140 db sound that hits only one 30 db barrier and knows to reduce to 110 db.

If you can come up with a source other than product packaging, please let me know. I am not an audiologist, but the facts and figures don't seem to work and the info you provided doesn't fit the info the others provided.