What "sound" is - and how we "hear" it: Techno-geek alert!

My next few weekly blogs will concentrate on what speaker specs really mean to us guitar players in the real world.  I wanted to jump right in to a discussion of efficiency, frequency range, and so on - but I realized that I was getting a little ahead of myself.

When I teach introductory audio engineering classes, I always start with a day or so on what sound actually is and how the human ear hears it.  Since this is so basic to anything and everything audio, I decided it was prudent here as well.  I’d like to point out that the human ear is in fact an electro/acoustic transducer, just like a microphone or speakeris; I’ll get to that in a moment.  Let’s start with what "sound" is.  Warning: this is some seriously techno-geeky stuff!

Sound in a given space is actually air molecules in motion - it’s a very "physical" thing.  Think of one molecule crashing into the one next to it, now imagine that happening many thousands of times and you have an idea of what sound is.  Let’s say you hit a snare drum or a chord on an acoustic guitar, what you have just done is sent a bunch of air molecules flying!  They bash into the ones next to them that then bash into the next ones and so on and so forth - just like in a multi-car pile up on the freeway.  The point at which molecules crash into each other is called compression; then they bounce away from each other, that’s called refraction. As this goes on, each subsequent "collision" looses a bit of its energy (it’s partially dissipated as heat) until there isn’t enough energy left to put any molecules in motion.  In other words, it gets quieter as it moves away from the sound source.  This is an oversimplification to be sure - but what I want you to remember is what sound really is: air molecules that have been set in motion and subsequently set other molecules in motion.  This is important because that is precisely what a loudspeaker needs to accomplish to produce sound.  Just as one guitar may be able to do a much more accurate and articulate job of moving air molecules than another (leading to better sound), so can the same be said for one speaker over another.

Now on to the electro/acoustic transducer that our creator saw fit to endow each of us with two of: the ear.  Just like a microphone, the ear takes the acoustic energy (sound) I just described and converts it into electricity.  That electric signal is what our brain understands as "sound".  However, and this is what I want you to remember, the human ear is insanely sensitive - and like all sensitive instruments can be easily damaged.  In essence, the visible portion of the earcollects the moving air molecules and focuses them on our outer ear drum.  The outer drum is connected to an inner drum via three nearly microscopic bones (they’re shaped like a hammer, an anvil, and a stirrup).  These little bones serve to amplify the movements of the outer drum, so the inner drum’s response is exaggerated.  Then, sealed in the inner earbehind that second ear drum is the auditory nerve which is lined with thousands of microscopic hairs (called cilia) that actually "flap in the wind" and thereby create the electrical signals sent to the brain.  The hairs that hear the lowest frequencies are comparatively robust and toward the back of the inner-ear while the hairs that detect high frequencies are extremely fine and are right up next to the inner ear drum.  That’s why people generally loose the high frequency portion of their hearing first.  Those tiny little cilia are very easily damaged or destroyed! 

What does this mean to you?  First, be VERY careful with your ears, you just might want to use them when your old.  Second, be aware of the fact that everybody (especially men) experiences some amount of high-frequency hearing loss as they age. If you’re a man over 50 or so, it’s probably already started for you.  So, if that 20-something sound man tells you your guitar tone sounds shrill and thin, he’s probably right.  Trust me...

Next week, all about frequencies and decibels.

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