Venting is the ratio of hole size to bore diameter at the same point. While we (will) have looked at these parameters separately above, the ratio gives us a more meaningful understanding of their combined impact. A few general points before we look at the flutes one-by-one...
Types of flutes
This is an open-ended question (there's always another type of flute to add!), but so far, we're considering:
and, to provide a modern context, we'll slip in a modern Boehm cylindrical flute.
With all that on board, let's look at some flutes. The horizontal axis shows the notes from the top of the flute tube to the bottom. The vertical axis is the degree of venting of each note. On the right, we see the average degree of venting for each of the flute types.
Richard Potter's German Flute
Patented in 1785, it's our earliest example. In yellow in the chart above, you can see he went for uniformity in the body - at around 40%, with a smooth transition in the foot notes up to the perfect termination of the bottom C note. The only big deviation from that plan is the G#, made smaller because it has to be squeezed in above the middle joint, and even that works fine as it gets venting support from the nearby G and F# holes. Uniformity of response was prized in those times, and Richard sold heaps of flutes. The average venting of Potter's flute is 48%.
The Improved era. Potter's was still called a German flute, and essentially was, but when Nicholson senior took to an Astor flute (similar to the Potter) and increased the size of the holes, he really kicked off the English flute tradition. And you can see from the chart above (in purple) that it was really only some of the holes that Nicholson enlarged - particularly B (L2), G (R1), F# (R2), F and Eb and D on the foot. He was constrained by finger stretch from doing much with A (L3) and E (R3), and probably not too worried about the closed key holes - they do alright even if small because of venting support from the next open hole down. Interesting in that light, he did increase the size of F, probably because it couldn't get much support from the small E hole.
The supersized Eb and D holes are amusing - well over the bore size at that point - and well past the point of diminishing return. Was this perhaps a desperate attempt to do something about flat foot syndrome? Why not just move the holes up a bit? Seemed that had to wait for Boehm to give us permission.
Needless to say, Nicholson's flutes are big and powerful, but not that uniform in response from note to note. E stands out as very weak - see how low it is compared to the F# and D. Nicholson's average venting was 64%.
Probably the most famous makers in the Improved Era were Rudall & Rose, and we see very similar dimensions and results in flutes made by them.
Boehm's 1832 Conical Ring Key flute
Boehm was stunned by Nicholson's flute and his playing, and decided he'd only be able to compete if he made an even better flute. In the new flute, he used relatively uniform hole sizes, which, as the brown trace shows, makes for a fairly smooth graduation of venting (the hole sizes are uniform but the bore gets narrower). He did let F#, F and E fall below the trend, probably limited by practical considerations. Although the average venting is 64%, the flute did not attract the English, who preferred the Nicholson style flute, which had the same average venting. So we can see, venting is not everything!
The flute we have used here is a French version, by Laube. The dimensions do not vary significantly from the original Boehm version.
Not much more happened until 1842, when Siccama started working on his flute, patented and released in 1847. He went back to the Improved flute as his starting point, but added keys for both third finger to let him put A and E where they should be. This enabled him to make them much bigger and overcome the venting problems Nicholson's flute had on these notes. Our chart reveals (aqua trace) that his is actually one of the best vented flutes around, at a very impressive average of 75%. No wonder those who hear it are impressed by its smooth tone and uniformity. Note that the graduation between holes is fairly uniform, but it starts at the C, rather than the c#. Siccama presumably recognised that the c# is a special case and shouldn't be allowed to dictate the size of the other holes.
Boehm's cylindrical flute came next (also in 1847). It started with very small, uniform holes, offering, in conjunction with the cylindrical bore, a uniform venting of about 60%, terminating in an abrupt leap at the end to 100%. I haven't shown that flute as that arrangement didn't last long. Instead I've shown a modern arrangement published by Trevor Wye on Larry Kranz's web page. A much fuller analysis of how one lead to the other can be found at Cylindrical flutes - a History of Holes.
The modern cylindrical flute is shown on the chart above in pink, and represents an average venting rate of 74%, virtually identical to Siccama's. Being an open-system flute it will actually achieve a higher value than that. Interesting also in that Boehm mentions in his book that a 75% venting is needed to get the best out of his flute.
What will perhaps surprise readers is that the modern Boehm does not exhibit substantially better venting than Siccama's. Sure the holes are much bigger. But so is the bore, and it is the ratio of these that determines venting.
Pratten reverted the Siccama back to an 8-key to create his Pratten's Perfected in 1852. You can see (navy trace) that many of the holes are the same size, but that he was forced to compromise heavily on the A and E, just like Nicholson had to. Indeed he's ended up with sizes for these notes not significantly different to Nicholson's, with an overall venting score of 68%. So once more, uniformity suffers.
Summary on Venting
We can see that in the first half of the 19th century, the venting of flutes increased from around 40% to around 75%, bringing a dramatic increase in power and brightness. Uniformity suffered in the Improved and Perfected period 8-key flutes, while Boehm and Siccama were able to devise flutes that had both good and uniform performance. Achieving this required adding more keys - just two more in Siccama's case, but lots more in Boehm's.
Thanks to Trevor Wye and Larry Krantz for the figures on the modern flute.