Schu Posted March 10, 2015 Share Posted March 10, 2015 Why violin-makers adopted the f-shaped hole Why did violins slowly develop f-shaped sound-holes? Because it makes them more acoustically powerful than their ancestors, which had holes shaped liked a circle -- as a team of MIT scientists recently concluded. Back in the the 10th century, the makers of European stringed-instruments were building "fitheles" -- the ancestor of the modern violin -- but they used round holes. By the 12th century, they'd started using half-moon shapes, and a century later they'd refined it to a sort of C-shaped hole. Then in the 15th century they pioneered little circles at the ends of the holes, which, by the 17th century, had become the modern f-shaped hole. A team of MIT scientists recently wondered why the shape had evolved that way. After crunching the math and doing some experiments, figured it out: The f-shape turns out to have physics that push a lot more air than a circular hole, making the violin's output dramatically more powerful. From the Economist: "The answer, arrived at after several pages of advanced mathematics, and confirmed by experiment, is that holes’ sound-amplification properties depend not on their areas but on the lengths of their peripheries. They showed how the shape of the hole varied over the centuries, and how that affected its power output. The final Cremonese design had twice the sonic power of the circular holes of the fithele." The entire paper by the MIT team is online here and is pretty interesting too. That image above shows the gist of what's going on: You can see how the f-shape drives much more air-flow than the round one, with high air-flow marked as yellow and red. Below, an image from the paper showing the increase in power as the shape changes over time. 1 Quote Link to comment Share on other sites More sharing options...
CECAA850 Posted March 10, 2015 Share Posted March 10, 2015 Note to self. F shaped holes for sub ports on my next build. 3 Quote Link to comment Share on other sites More sharing options...
Mallette Posted March 10, 2015 Share Posted March 10, 2015 That is SO bleeding COOL! And an interesting thought, Carl. Dave Quote Link to comment Share on other sites More sharing options...
CECAA850 Posted March 10, 2015 Share Posted March 10, 2015 And an interesting thought, Carl. I don't have an original thought in my head. I read where Klipsch used a Tractrix flare for their ports and it made me think of this. Quote Link to comment Share on other sites More sharing options...
Mallette Posted March 10, 2015 Share Posted March 10, 2015 Not true at all...it's lateral thinking at its best. Dave Quote Link to comment Share on other sites More sharing options...
Thaddeus Smith Posted March 10, 2015 Share Posted March 10, 2015 Must.. resist.. juvenile.. comments. Quote Link to comment Share on other sites More sharing options...
CECAA850 Posted March 10, 2015 Share Posted March 10, 2015 Must.. resist.. juvenile.. comments. Why start now? Quote Link to comment Share on other sites More sharing options...
CECAA850 Posted March 10, 2015 Share Posted March 10, 2015 Oops, I guess I should have put a in there. Quote Link to comment Share on other sites More sharing options...
Mallette Posted March 10, 2015 Share Posted March 10, 2015 Sheesh. Took Michael all of 38 minutes to home in on that thread title. Must have been in the shower... Dave Quote Link to comment Share on other sites More sharing options...
DrWho Posted March 10, 2015 Share Posted March 10, 2015 Increasing flow velocity is bad for a subwoofer port... Quote Link to comment Share on other sites More sharing options...
CECAA850 Posted March 11, 2015 Share Posted March 11, 2015 Increasing flow velocity is bad for a subwoofer port... Then I'll make it really big Quote Link to comment Share on other sites More sharing options...
mustang guy Posted March 11, 2015 Share Posted March 11, 2015 (edited) The tuning of the f shaped port was to the Helmholtz resonance of the enclosure, which was based on the lowest frequency of the instrument, the volume of the enclosure, and the rigidity of the materials used in different parts of the instrument. What they found was that although the port area does indeed tune to the low frequencies, the increased perimeter length amplifies those low notes. Port volume increases this amplification, but not as much as the perimeter length. I may have that all wrong, but that is what I made of the original article here. For subwoofer enclosures this may mean more port perimeter area would benefit a sub; however, at a certain point, port air velocity can be heard (Chuffing). I have seen many modern enclosures which use thin oval ports. Could there be something to that which relates to this article? Edited March 11, 2015 by mustang guy Quote Link to comment Share on other sites More sharing options...
Mallette Posted March 11, 2015 Share Posted March 11, 2015 Jack Frazier used slots, which he referred to as modified Helmholtz radiators. Made his designs nearly as efficient as folded horns. The Eleven was about 25% physically larger than a K'horn and achieved 107db. I always thought that extra db was a jab at his friend and admirer PWK. Dave Quote Link to comment Share on other sites More sharing options...
Schu Posted March 11, 2015 Author Share Posted March 11, 2015 I may have that all wrong, but that is what I made of the original article here. the original article link is in the OP... Quote Link to comment Share on other sites More sharing options...
mustang guy Posted March 12, 2015 Share Posted March 12, 2015 (edited) I may have that all wrong, but that is what I made of the original article here. the original article link is in the OP... Thanks Captain obvious. That's how I found it. Jack Frazier used slots, which he referred to as modified Helmholtz radiators. Made his designs nearly as efficient as folded horns. The Eleven was about 25% physically larger than a K'horn and achieved 107db. I always thought that extra db was a jab at his friend and admirer PWK. Dave No kidding? With a slot port, the area of the port and tuning frequency determine port length. It seems to me like the proper order of this in WinISD would be: 1: Design ported enclosure to driver at frequency you need 2. Calculate the Hemholtz frequency of the enclosure's volume 3. Make the port shape rectangle and take an algebra class 4. Dimension the port slot so that it's acoustic conductance equals the Hemholtz frequency found above 5. Let WinISD calculate the slot length. The fraziers I have are slotted in the back. The slot tuned to the Hemholt's frequency and the fs of the driver and the enclosure would couple with the walls behind the Monte Carlo to again amplify those lows. I think that's cool, since JF was one of the people in the industry who PWK respected. Now we know why. He was ahead of this time. Edited March 12, 2015 by mustang guy Quote Link to comment Share on other sites More sharing options...
Mallette Posted March 12, 2015 Share Posted March 12, 2015 I have always wondered why other speaker manufacturers haven't used Frazier's designs. It was PWK himself who told me "Jack Frazier is the only other speaker builder I respect." That was all I needed to know. Heresy was the cheapest Klipsch at that time and well out of my range. Would up with Monte Carlos...which I still believe to be the finest cost/performance bookshelf speaker ever. Couple with my SCA-35 I had the same sound I have today, just not as much of it or the octave and a half of bass I get from my Klipschorns and Cinema F-20. However, on a string quartet at realistic levels I'd say the MCs would stack up just fine. Dave Quote Link to comment Share on other sites More sharing options...
Paducah Home Theater Posted March 12, 2015 Share Posted March 12, 2015 (edited) So why don't they make all acoustic guitars with F holes instead of round ones if it is that superior, generally speaking? Edited March 12, 2015 by MetropolisLakeOutfitters Quote Link to comment Share on other sites More sharing options...
Don Richard Posted March 12, 2015 Share Posted March 12, 2015 Bigger instrument, less need for augmentation. Quote Link to comment Share on other sites More sharing options...
Paducah Home Theater Posted March 12, 2015 Share Posted March 12, 2015 Bigger instrument, less need for augmentation. Then why does a double bass have F holes? Quote Link to comment Share on other sites More sharing options...
Mallette Posted March 12, 2015 Share Posted March 12, 2015 'cuz they need to be f'ing loud. Dave 1 Quote Link to comment Share on other sites More sharing options...
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