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In Reply to: RE: He is right but is referring to low level detail posted by josh358 on September 21, 2012 at 07:40:47:
You are looking at the top limits on excursion. The low level issue is different because it is an onset of motion issue where the wires don't deform/strain and the stretch in the mylar is the limiting factor along with the air resistance. The wires are simply stiff and prevent stretching in the vertical dimension at low amplitude.
As you pointed out, air flow resistance increases with velocity, thus limiting the motion of the membrane when departing the onset of motion so that an output sine pattern would flatten relative to the sine signal supplied to the driver. flow resistance is at its highest while the membrane is traveling through the 0 displacement plane.
Resistance to onset of motion is in the mylar/miloxane CLD and the stiffness of the wires that are acting as hard solids since the stress levels applied are insufficient to deform them. At he onset of motion there are viscous effects in the mylar since it is an amorphous polymer rather than an elastomer like rubber. The energy applied is largely lost to plastic deformation at onset of motion and what is left is damped by the air flow resistance. again we have the highest rate of strain as we move through the 0 displacement plane and we have spring resistance as we move towards the peaks on the sine waves. So this also acts to flatten the output sine waveform at low amplitudes/signal. Velocity is near 0 at the peaks.
Once amplitude is sufficiently high, the main resistive force is the air resistance to piston action. The wires are still not deforming under these relatively low forces and the mylar is stretching in a spring like manner no different than the surround on a dynamic driver. The air flow resistance through the channels and holes is insignificant, and the plastic deformation forces are insignificant relative to spring behavior.
For a reference here is a random article that has a good summary on these issues for amorphous plastics vs elastomers. Note the presence of retardation and relaxation effects and the fit of Voigt Kelvin type viscoelastic models to the behaviors and that there is little permanence to the effects of short lived stress.
http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&ved=0CCYQFjAB&url=http%3A%2F%2Fwww.iupac.org%2Fpolyedu%2Fpage36%2Fpage19%2Fpage21%2Ffiles%2FDMTA_1_fixed_A_1.doc&ei=MDZeUMTsDqHl0gGUnYGIBw&usg=AFQjCNFVg0COLIbbodlsYCQgfaZ_H_Q6-A&sig2=CnmTf6ZTcIQZtO21N6rwgQ
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Follow Ups
- RE: He is right but is referring to low level detail - Satie 15:21:24 09/22/12 (7)
- RE: He is right but is referring to low level detail - josh358 09:06:59 09/30/12 (6)
- RE: He is right but is referring to low level detail - Satie 01:53:43 10/05/12 (5)
- RE: He is right but is referring to low level detail - josh358 05:35:30 10/05/12 (4)
- RE: He is right but is referring to low level detail - Satie 13:54:51 10/05/12 (3)
- RE: He is right but is referring to low level detail - josh358 12:04:42 10/07/12 (2)
- RE: He is right but is referring to low level detail - triamp 14:14:29 10/12/12 (1)
- RE: He is right but is referring to low level detail - josh358 08:00:53 10/14/12 (0)
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