[Alupis]

These seem to be more along the lines of what is issued:

http://archive.armytimes.com/article/20090908/NEWS/909080313...

> Soldiers can adjust the rocker with a quick "click" depending on the amount of protection they need. When it's in the open or "weapons fire" position, sound can travel through the sound channel filter into the ear.

> For noisy environments that don't require an acute listening capability, such as around helicopters, troop carriers or generators, the rocker can be switched to the closed or "constant protection" position.

There's also larger over-ear kinds that are integrated with comms:

http://www.bosssafety.com/p-10356-peltor-comtac-iii-a-c-h-he...

This style has both active and passive configurations.

[logfromblammo]

For those hitting the paywall on the the first link, the in-ear protection resembles 3M Ultrafit earplugs, with a hole bored through the center. The rocker switch may be lengthening or diverting the pass-through channel, like the rotary valves on a tuba or French horn. A longer or narrower channel would provide more attenuation of all sounds. It may also simply be closing and opening the channel.

They don't seem to have variable attenuation based on the acoustic energy, though. If the soldiers find them to be acceptable everyday gear at all, there would certainly be funding available to engineer improved internals.

The over-ear comms-integrated rig is priced at double my estimate for what an in-ear version might sell for, which tells me that I was probably underestimating.