Clean F holes

[Stephen Perry]

My concern in cleaning up the edges of the ports is not in achieving a polished surface, but in eliminating the ragged junk hanging down from finishing. Suppose those edges move the 0.01 mm, a value that isn't unreasonable based on Dave's reference above. That's a fair number of nanometers and could reasonably be postulated to get into turbulence and so on. Regardless, something subtle happens with the smoothing of that break on the inside from the port to the interior. I started cleaning up the F holes on instruments because they didn't look good. The slight impact on sound wasn't really a surprise, but I hadn't thought about it. It's an interesting thing, but clearly not that well understood!

Now I'm wondering whether the smoothing does something to the vibration of the plate and has nothing to do with air movement. Or perhaps it has to do with waves in the air next to the plate, if indeed that type of model applies.

As to the old violins, the interior of the port is usually pretty well smoothed off by people poking things in!

[Tom Haywood]

Now I'm wondering whether the smoothing does something to the vibration of the plate and has nothing to do with air movement.

My opinion exactly. The famous guitar/candle demonstration helps me to visualize that there is not enough air movement going on to create the differences in sound that the ears hear. It takes a pretty decent tap to move that candle flame. The string movement won't do it. John, my good Martin guitars won't blow out the candle. The tops are too thick to move that much air. Still, they sound pretty good. It seems apparent to me that it is the characteristics of the wood, primarily the top and braces, that sets the characteristics of what the the ears hear. The air movement transmits the amplification of those sounds. Sanding the wood smooth and rounding sharp edges makes a difference in the vibration of the wood that can be heard. So does making slight changes in the thickness. The edges of the F holes vibrate a little more freely than the rest of the plate, because they are not glued down to sides or to braces. IMHO, the characteristics of the wood at those edges makes a difference that can be heard.

The air thing to me is kind of like whistling. Doesn't really matter how much or how little air is moving. What produces the characteristic sounds are the characteristics of the lips.

I do find the scientific discussion of air flow related to these instruments to be fascinating, so please carry on.

[Dave Cohen]

The edges of the F holes vibrate a little more freely than the rest of the plate, because they are not glued down to sides or to braces. IMHO, the characteristics of the wood at those edges makes a difference that can be heard.

The air thing to me is kind of like whistling. Doesn't really matter how much or how little air is moving. What produces the characteristic sounds are the characteristics of the lips.

Those things may be intuitive to you, but they are not real. I have literally hundreds of interferometry images, on numerous different instruments. All of them contradict what you said. Plates do not move less where there are braces and more away from the braces. The vibrational mode shapes occupy the entire plate. The shapes of the modes depend on the overall shape of the plate, and their frequencies depend on the overall properties of the plate. The mode shapes of plates extend through soundholes as if the holes were not there; there is neither more nor less amplitude at the edges of soundholes. Even if you don't trust me, the interferometric imaging of vibrational modes goes back to the late 1960s. All you have to do is look, and you will find numerous papers dating back to 1970 or so, corroborating what I just wrote here.

Regarding whistling: Even there, the whistling depends on the entire air cavity as well as the lips. It also depends on exceeding a necessary minimum air velocity, coming all the way from the lungs. The lips influence frequencies via influencing the opening size, but they are by no means all there is to whistling. In whistling, there is actually a continued turbulent airflow in one direction, which is entirely unlike the air movement in sound holes of string instruments.

Regarding Stephen's suggestion of turbulence at soundhole edges: Instead of just dropping the term, show me a reasonable physical mechanism that doesn't conflict with the conditions in a string instrument. Helmholtz did so 150 yrs ago, with no suggestion of turbulence. Similarly, Nia's theory did not invoke or even suggest any turbulent flow.

[haggardphunk]

sometimes when i clean my car i think it drives better. but in my head i know that can not be the case.

[Stephen Perry]

I have no problem with there not being turbulence. I'm not sure how I would detect it. Something is going on.

This is pretty fun, too: https://www.google.com/patents/US530...ed=0CDsQ6AEwBA

Edge diffraction? http://www.salksound.com/wp/?p=160

It's a real effect, primarily noticeable when the original edge was quite ragged.