Resonance

[Carl Meyer]

I'm feeling quite resonant tonight.

This term resonance brought back many memories of the places I've worked
during my corporate days.

I first learned about resonance over 50 years ago in radio repair school.
If it weren't for resonance your radio wouldn't work.

Everything is resonant, more or less.  I guess the lowest resonant frequency
item would be the earth.  An earthquake produces a very low frequency of
several seconds per cycle at least.  I supose there are several different
resonant frequencies depending on the location and other factors and an
overall composite resonance including them all and each may have a different
level. I've never measured that, because I wouldn't know where to put my
feet.

That brings up a term I haven't heard much discusion  about.  That is the
"Q" factor, sometimes called quality factor.

"Q" is the resonant frequency divided by the bandwidth.
Bandwidth is defined as the frequency difference between the upper and lower
half power points.

Now if we look at A4, the resonant frequency is 440.  I have no idea what
the bandwidth is and I wouldn't know how to measure it.  Just imagine that
string putting out just a little 439 and a little 441.  Then if those
frequencies were putting out half as much power as 440, then the bandwidth
would be 2 cycles and the "Q" would be 220.
I believe it would be much higher than that.  If anyone knows, I'd like to
know too.  A piano string is a very high "Q" resonant device.

I would say that a soundboard is a very low "Q" device and would have
multiple resonances.  I am certainly not a soundboard designer, but I think
the goal would be to get those resonances to be as small and broad as
possible.
They could be moved around to enhance the boards response as necessary.

I worked for a company some years ago that made servo hydraulic vibration
testing equipment.  A typical simple application would be to mount the
spindles of a large truck on an actuator and shake it till something broke.
Due to RESONANCES any part that needed redesign would vibrate like mad and
so it would be changed in some way to eliminate the high "Q" resonance.

I later worked for a company that made lasers that were tunable.  A
fascinating application was to mount these on a truck and drive around the
country and analyze the polutants in smokestacks.  FROM THE GROUND!
Molecules are resonant, too.  By pulsing a laser beam into the smoke the
molecules in it would respond to certain frequencies of light and from that
response the type of molecule could be determined.  Every element on earth
has it's own resonant frequency.  That is basically how a spectrascope
detects chemicals in a solution with such awesome accuracy.

People have resonance, too.  Think about your best friend.  Ask yourself,
how fast and how hard would I have to rattle his cage to get a reaction?

I wrote this partly to see if my literary skills could handle this kind of
subject.  Hope I didn't bore anyone to distraction.  I'm not sure all my
comments were accurate.  Been a long time, but my long term memory is better
than my short term nowadays.  Feel free to correct or add to what I said.

Best to all.  Isn't resonance grand?

Carl Meyer    cmpiano@home.com