View Full Version : Normal Modes of Vibration
rcampby
Oct-09-2016, 3:53pm
So as I understand it, there is a discrete set of frequencies that the top of a mandolin will vibrate at and similarly, there are certain frequencies that the air inside a mandolin can vibrate at (starting with the Helmholtz frequency).
Yet, if you play two different notes, they seem to be amplified by roughly the same amount. Wouldn't you expect frequencies that are at or near the normal modes of vibration to be amplified significantly more than other frequencies? What am I misunderstanding here?
DataNick
Oct-09-2016, 4:15pm
See Dr. Cohen's posts on this subject in the builder's section primarily
Helmholtz Resonance (http://www.mandolincafe.com/forum/showthread.php?12186-helmholtz-Resonance)
Yet, if you play two different notes, they seem to be amplified by roughly the same amount. Wouldn't you expect frequencies that are at or near the normal modes of vibration to be amplified significantly more than other frequencies? What am I misunderstanding here?
Regardless which note the instrument is tuned to, I don't think it is all that narrow a band pass. Not that it is irrelevant what note the build is tuned to.
David L
Oct-10-2016, 10:52am
The curves of the shape keep any one frequency from vibrating more than others as far as the internal shape goes. The same thing is bound to happen in the top also. The differing lengths across the top will emphasize different frequencies. There is an infinite number of different lengths of wood grains.
peter.coombe
Oct-10-2016, 4:57pm
The curves of the shape keep any one frequency from vibrating more than others as far as the internal shape goes. The same thing is bound to happen in the top also. The differing lengths across the top will emphasize different frequencies. There is an infinite number of different lengths of wood grains.
You really should read Dr Dave Cohen's posts before misleading people with this.