Re: [Harp-L] Carbon Fiber Reeds, 3D printing, plastic metal adhesion technology...?

[Vern <jevern@xxxxxxx>]

I think that Ingram had in mind the question:

Q. Would carbon fiber be superior to the commonly-used metals for harmonica reeds?
It seems that the answer is "no" for a number of reasons.

However, much of the discussion has addressed a different question:

Q.  Would it be possible to make a reed of carbon fiber?
...to which the answer seems to be "maybe".

There is a previously undiscussed property that would affect the performance of any material as a mechanical resonator.  That is damping or the Q (quality) factor.  It depends on the ratio of the amount of energy lost in a cycle to the amount of energy stored. A material with no damping would, when tweaked, vibrate forever.  The greater the damping, the more quickly the vibration decays.  

See: http://en.wikipedia.org/wiki/Q_factor

When you bend a reed, the stored energy is the integral of the bending force times the displacement.  When the reed un-bends, it returns less energy than was required to bend it.  This loss appears as damping.  Air viscosity also absorbs energy but we can assume that to be the same for any material vibrating at the same pitch and amplitude. 

Plastics are generally more highly damped than are spring metals.  My assumption is that damping is desirable in most applications  and undesirable in a reed. In a reed, the energy absorbed by the material must be made up by pumping of the air stream. Maybe there is enough energy available in the air stream to make this loss negligible.  Without quantitative data, I don't know.

Q. Does anyone have comparisons of Q for carbon fiber composites vs spring metals?

Vern