They are called FMODS and have a theoretical 12db/octave roll off. They are about $25 for a pair and are as simple to install as plugging in a RCA.
Igitur qui desiderat pacem, praeparet bellum -- Vegetius
"I told her about my conversation three years ago with the political leader of Islamic Jihad in Gaza. "What's the difference between suicide, which the Koran condemns, and martyrdom?" I asked. "Suicide," he replied, "is done out of despair. But remember: most of our martyrs today were very successful in their earthly lives." In short, there was a future to live for--and they detonated it anyway."