Ear plugs & 90dB headphones sound 'blocking' combination

[shaunnutley]

I have noticed that when i insert a pair of ear plugs with an SNR of 30 and wear a pair of headphones over these which have a continous noise of 90dB the combined effect of the ear plugs and headphones (the sound level i can hear) seems to be less than when wearing the headphones separetely. I would have thought that the ear plugs would have increased considerably the lowest level of noise i could hear. I have found that i can hear the occassional word of a person talking in a room about 6ft in front of me (hence reaching me at about 50dB). This is also when the headphones are at 90dB. I can do this without looking at their faces, so as to not figure out certain words by 'lip-reading'.
I thought a possible answer was that the active 'blocking' was reduced by the ear plugs and therefore 90dB was reduced to about 60dB, and then the ear plugs increased the figure again to about 90dB depeding on the pitch. Does anyone have a explanation why this combination did not decrease my hearing abilities beyond that of headphones worn separately?

[riskman]

why are you wearing headphones that produce constant noise at 90dB?
The plugs will provide attenuation of 30dB (so if exposed to 90dB you will be exposed to 60dB(A) at the ear (depends on the frequency of what you are listening to).
You refer to pitch (frequency) and this will effect the attenuation figure for your plugs.
A little more info and I might be able to say more...