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Nick Allen

F hole edge rounding.

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Hey folks,

So I've seen on some violins, the f holes a ever so slightly rounded, as in, just barely had their edge broken. 

I like this effect, and want to know how to reproduce it. 

I don't think that it is something done during varnishing, like polishing the edge down, as many of the examples that I have seen have full color all the way through the edge. 

Thanks for any advice in advance!

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53 minutes ago, Nick Allen said:

I like this effect, and want to know how to reproduce it. 

pg. 274 of your long lost cousins book Violin Making A Historical and Practical guide says "if you cannot copy by eye and hand, leave off fiddle making, for as a luthier you are a failure". ha, ha.

Seriously, the manual say leave those edges as sharp/clean as possible for the most part.  It could be a school trade secret us uneducated mere mortals will never get to really know what to do.  

Maybe build up coats of varnish and gently rub them down later for possible tone enhancement, if needed.

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5 hours ago, uncle duke said:

pg. 274 of your long lost cousins book Violin Making A Historical and Practical guide says "if you cannot copy by eye and hand, leave off fiddle making, for as a luthier you are a failure". ha, ha.

Seriously, the manual say leave those edges as sharp/clean as possible for the most part.  It could be a school trade secret us uneducated mere mortals will never get to really know what to do.  

Maybe build up coats of varnish and gently rub them down later for possible tone enhancement, if needed.

Perhaps I should stick with the basics until I'm good enough to do less conventional stuff. 

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Major advantage to the "broken" edge you see on many fine old instruments - the edge of the soundhole is not quite as vulnerable to damage as a razor crisp edge. Why not take a white imported fiddle and play with it, then do some varnish experiments on it for good measure. 

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There's an argument that the edges should be rounded to reduce air movement friction in order to increase sound output.  Bass speakers have well rounded ports.  Old violins often have worn and rounded edges. Crisp edges takes skill and looks nice but I'm not sure this is good.  

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12 hours ago, Marty Kasprzyk said:

There's an argument that the edges should be rounded to reduce air movement friction in order to increase sound output.  Bass speakers have well rounded ports.  Old violins often have worn and rounded edges. Crisp edges takes skill and looks nice but I'm not sure this is good.  

I vaguely remember reading something along those lines, except the article was referring to edges on the plate interior. 

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12 hours ago, Marty Kasprzyk said:

There's an argument that the edges should be rounded to reduce air movement friction in order to increase sound output.  Bass speakers have well rounded ports.  Old violins often have worn and rounded edges. Crisp edges takes skill and looks nice but I'm not sure this is good.  

Marty, Is this for real? how much difference in amplitude could this really make?

If one did want to do this for aesthetic reasons I would recommend  being very accurate about the rounding starting with a tiny chamfer then breaking the edges on that so the rounding is consistent all the way around. I don't think the effort is really worth it but whatever you do to personalize your work is OK as long as it looks like you meant it and not just an accident or random wear. Details like this tend to be less important than the over all look of the fiddle and if the rounding obscures or detracts from the larger shape of the FF then you are doing yourself no favors. I also think you would only want to do this on an instrument where the general theme is softness including all the chamfers, edges and scroll. On lightly antiqued fiddles just a quick wipe with 400 paper over all the sharp edges is enough add to the look of age.

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13 hours ago, Marty Kasprzyk said:

There's an argument that the edges should be rounded to reduce air movement friction in order to increase sound output.  Bass speakers have well rounded ports. .  

There's also the argument (mine) that the rounded edges might increase the efficiency of the air movement and therefore lead to a higher peak A0 amplitude... but decrease the off-peak amplitude.  Who wants a louder C# and quieter C and D?  In any case, I don't think it's a big deal or if you could even hear the difference.  Maybe Anders would know.

Some bass reflex ports are rounded, some are not...

https://en.wikipedia.org/wiki/Bass_reflex#/media/File:Bassreflexrohr.jpg

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About half the amount of a violin's sound (A0, B1-, B1+, A1 resonances) below 1000Hz comes out through the f holes.  The other half, and the sound output at the higher ranges comes off from the outer surfaces.  So one would expect only a small overall effect from the f hole changes.  If there was a noticeable change from rounding the f hole edges it would be a small boost only in the lower frequency range.

I made a viola with the f hole edges fully rounded on the inside and outside corners with a radius equal to half the plate thickness--there was no straight vertical portion.  It sounded good but unfortunately I didn't put it together before I rounded the edges so I don't know the effect of the edge rounding.

I'm making a violin now and maybe I'll do the rounding again with some before and after tests.

Of course it will look odd but for my violins it will hardly be noticeable.

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Another aspect is that rounded means a less defined opening for the air cavity.  Less hard edge and sharply defined geometry in resonance tends toward broadening response.

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2 hours ago, David Beard said:

Another aspect is that rounded means a less defined opening for the air cavity.  Less hard edge and sharply defined geometry in resonance tends toward broadening response.

That sounds backwards to me, thinking about frictional resistance... or maybe I'm reading it backwards.  Do you have a reference for that?

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The frequency of a resonance depends on material properties and dimensions.

If the dimension aspect is less defined, then the system will resonate to a larger range of frquencies and cut away less dramatically.

This is part of the stuff first sorted out with resonance cavities, etc.

****

Also part of what's good about the standard f hole shape.   Are we looking long skin shape?  Are we looking at large ovals that are partially covered? Etc.  The shape is vague and support resonances that want to see it in different ways.

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so I taped up the f holes on a beater fiddle.  The effect was audible. Using audacity, the fundamental of an open D was diminished as expected.  But the fundamental of the open G went up, lol.

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12 hours ago, David Beard said:

The frequency of a resonance depends on material properties and dimensions.

If the dimension aspect is less defined, then the system will resonate to a larger range of frquencies and cut away less dramatically.

This is part of the stuff first sorted out with resonance cavities, etc.

This description does not match up with the RLC circuit model of A0, where the capacitance is the volume (and wall flex), inductance is the F-hole, and resistance is the losses in pumping air and flexing the body walls.  I can not see how  a "less defined aspect" of the dimensions somehow makes any of these factors into a variable value... but I CAN see that rounding the F-hole edges would decrease the resistance value.

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12 hours ago, Roger Frankland said:

so I taped up the f holes on a beater fiddle.  The effect was audible. Using audacity, the fundamental of an open D was diminished as expected.  But the fundamental of the open G went up, lol.

I've done it many times, including in lecture demonstrations. What people seem to notice most is loss of high frequency "presence" or "sparkle"to the sound, rather than a drastic change in low frequency output (which is obviously very clearly seen in the change in the signature mode spectrum). 

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13 hours ago, Roger Frankland said:

so I taped up the f holes on a beater fiddle.  The effect was audible. Using audacity, the fundamental of an open D was diminished as expected.  But the fundamental of the open G went up, lol.

Yes, the frequency of A0 will tend to rise as the area of the sound holes is reduced.

Next, you could try taping off one ff or the other, and then try taping off various sections of each. :)

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34 minutes ago, Marty Kasprzyk said:

I hate to start the New Year so disagreeable but the frequency of A0 will ted to decrease as the area of the sound holes is reduced.

You are right. I stated it backwards. Thanks for the correction, and for bringing it to my attention. :)

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On 12/31/2019 at 6:51 PM, Marty Kasprzyk said:

There's an argument that the edges should be rounded to reduce air movement friction in order to increase sound output.  Bass speakers have well rounded ports.  Old violins often have worn and rounded edges. Crisp edges takes skill and looks nice but I'm not sure this is good.  

Rounding the edges around the ports on a bass reflex speaker is for the purpose of reducing air turbulence; this would be the equivalent of R in the LRC example, which directly affects the Q of the tuned circuit.The more resistance introduced, the lower the resulting Q, but resonance is spread over a wider bandwidth, albeit at a lower amplitude.

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4 hours ago, David Burgess said:

Yes, the frequency of A0 will tend to rise as the area of the sound holes is reduced.

Next, you could try taping off one ff or the other, and then try taping off various sections of each. :)

thx. well that was fascinating!  Got all the colors of the rainbow!  I even was able to balance the harmonics  between the G and D strings to identical peak levels!  Seems like  that should be a good thing, ie make the violin more playable.  I mean everyone strives for a balanced sound, right?  But,  in my hands,  it did not seem to matter after I played tunes for a while. With all respect, so amateur I am, bowing  technique trumped  “port tuning” the ff holes.  I need to practice more, a lot more, then try again.....  The other day I was watching an expert fiddler roll her bow and create some really awesome soundscape.

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 I can't speak about what's going on with the frequency of AO....

but I noticed that rounded edges appear spontaneously as soon as you used knifes and gouges to cut the "f hole"...

 

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