Resonance

[Delwin D Fandrich]

----- Original Message -----
From: "Carl Meyer" <cmpiano@home.com>
To: <pianotech@ptg.org>
Sent: June 08, 2001 8:30 PM
Subject: Re: Resonance


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

As did I. I'd worked on pianos for about four years before my Uncle decided
he wanted me to fix various electronic devices for him in Alaska and, later
on, in Thailand. I didn't make the connection at the time but a couple of
years after leaving his employ I started applying some of the ideas of basic
electrical circuitry to mechanical soundboard system. Later, when I actually
started studying the stuff I discovered that the texts on mechanically
vibrating systems start with an electrical circuitry analogy to explain the
mechanical function.



> 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.

They are and they do and it is.

There are multiple resonances in a soundboard. These can be controlled, but
not eliminated, but the sizing, shaping and placement of the ribs. The
thicknessing and shaping of the soundboard. The stiffness and mass of the
mounting system including the rim, bellyrail and any soundboard shaping
devices. Etc.

I've been working on this concept for some time now. I've tried a variety of
aproaches ranging from shaping the soundboard in ways that seem more
appropriate to the actual tone production of the system to controlling the
impedance of the soundboard in non-traditional ways. My own impedance
matching device--yes, it's patented--for the vertical piano was one
development along this line. As is the fan-shaped rib dispersement pattern
I've been using for the past 15+ years. We keep working on refining our rib
crowning systems and rib shaping. We're not there yet, but we do keep
trying.



> 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.

Your literary skills are just fine. As is your memory. I know what you mean
about all that short term stuff, though.

Regards,

Del