I've got a strong bias on this subject: I'm a big proponent os hearing protection. Back in the Eighties, I started "H.E.A.R." (www.hearnet.com). And now that earplugs are legal in California, it's time to write this column.

Ears evolved to be sensitive to the faintest sounds. The mammal who heard the predator creeping up on him had an evolutionary advantage. Consequently, the ear evolved into an incrdibly sensitive organ. The outer ear, or pinna, gives directionality to sounds. It also helps "scoop up" sound waves and channels them down the ear canal. When we cup a hand behind our ears, we amplify this effect.

The ear canal amplifies sound by a factor of 10 or more before it gets to the end of the canal, hitting the eardrum. It's a flexible membrane, like a drumhead, and moves when sound waves hit it. When the eardrum moves, the tiny bone attached to its inside, called the hammer or "malleus," moves too. This moves anvil, or "incus," which in turn moves the stirrup or "stapes," that's connected to a tiny window in the hearing organ ("cochlea") that contains the hair cells that actually do the hearing. In the cochlea, the vibrations stimulate tiny hair cells, which vibrate at different frequencies. They then send signals to the auditory center of the brain, which interprets them.

The canal amplifies sound by a factor of 10. The eardrum is 15 to 30 times the size of the window in the cochlea, so it amplifies by a factor of 15 to 30. The bones triple the sound levels, due to leverage. Overall, the sounds getting to your inner ear have been mechanically amplified by a factor up to 900 -- almost 1000 times louder. The ear's an incredibly sensitive organ. Sometimes, it's too sensitive.

To temporarily reduce sensitivity, we have the stapedius muscle in the middle ear, attached to the stapes. Loud sounds make it contract, muffling the noise. It also contracts before speaking or chewing, protecting us against our own sounds.

But continuous loud sounds are unnatural. The auditory system evolved to pick up quiet sound, like the predator stalking its prey. There were no continuous loud sounds when ears evolved. Could it be that we hear better with less sound coming in?

It's been proven that earplugs improve the ability of riders to hear sirens, horns, etc. at highway speeds, probably due to lowering volumes to a level where our auditory systems are most sensitive. Not only do earplugs improve hearing at highway speeds, they prevent hearing damage. Riding without earplugs exposes our ears to about 110 decibels. Just fifteen minutes of this gives us a day's maximum permitted noise exposure. More than that can cause permanent changes in hearing.

A phenomenon called the "temporary threshold shift," or TTS, can result from noise exposure loud enough to permanently damage hearing. Here's how you can check yourself for TTS.

Before the sound exposure, turn a radio to an all-talk station while in a quiet room (or in your car, with the engine off and windows shut). Lower the volume until you can just barely understand the words. This is your "hearing threshold." Leave the volume where it is.

Immediately after noise exposure, see if you can still understand everything as well as you could before, at the same volume. If you can't, you've suffered a temporary threshold shift, which tells you the sound levels have been high enough to produce permanent hearing loss with time.

To prevent hearing loss in these situations, you can rest your ears several times an hour. This lets your hair cells "catch their breath," preventing them from dying and causing permanent loss.

It's easier to just wear earplugs. When inserted properly, good earplugs lower sound levels to a safe range. I've used both disposable foam plugs and custom-made plugs myself. The custom plugs can be used for years, and when made by someone who knows about

Foam plugs can be just as effective at cutting sound levels, but putting them in correctly takes some practice. First, roll the plug between your thumb and index finger to make a skinny cylinder. Then, pull the ear back while inserting the plug deeply into the ear canal. Hold them in as the plug expands, thus muffling sounds. I like foam earplugs with a cord attached, making them easier to remove and carry, and I reuse foam plugs for weeks. I've practiced enough that I can put in both plugs simultaneously -- I'd be happy to show folks how, in person. Just ask.

You can tell if you've inserted a foam plug correctly by looking at its shape right after you remove it. There should be a noticeable "S" curve. If you don't see it, you probably didn't put it in deeply enough.

Earplugs provide another specific advantage to motorcyclists: They help you relax while riding. When things are quiet and peaceful, you don't get as tired during a ride. It's much easier to enjoy a ride, and to ride more safely, if you're relaxed. The Iron Butt Association Archive of Wisdom says, "Eliminate all distractions and potential irritants," and earplugs help meet that goal. MCN's own David Hough writes, "It's very important to wear your earplugs," in his excellent book, Proficient Motorcycling.

Here's the bottom line --- wearing earplugs helps you:

• Hear warning sounds better
• Save your hearing
• Enjoy your ride
• Arrive more relaxed

But if you want to be unsafe, hearing impaired, uncomfortable and tense, don't wear earplugs. Unless, of course, you just want to look hip.

Because it's hip to hear.