His flutes had five middle sections, each slightly different in length, so that the flute could be played at many different pitches. This new design set off a revolution in flute making and by the second half of the 17th century; all baroque flues had three sections to them and a much more conical bore. The extra key for the little finger of the right hand meant that the flute was now fully chromatic. The conical bore meant intonation was improved and volume was increased in the lower notes. Purely incidentally, the bore also meant that the finger holes could be placed slightly closer to the head joint meaning that it was easier to play.
The flute in its new form became popular first in France, where it was well suited for the refined gestures and elegant ornaments of the French baroque style.
However it was in the early 19th Century where the modern flute was born. In 1832, a German Flute Maker by the name of Theobald Boehm made an improved conical bore flute and in 1847 he patented his cylindrical-bore flute, which is the model in widest use in the 20th century. The cylindrical Boehm flute is made of metal or wood and has 13 or more tone holes controlled by a system of padded keys. It has a range of three octaves and a tone, upward from c' (middle C). Since World War 2 nearly all the world's flute manufacturers have built this type exclusively.
Boehm who was a great goldsmith, engineer and musician made great advancements in all of these fields combined.
The Boehm flute used today all over the world is in many ways the same instrument that was created in 1847 in Boehm's Munich workshop. The net effect of his work was the overthrow of the design principles of the old flute (conical bore, closed-standing keys, six open holes under the fingers) and the institution of new, rational and logical principles (cylindrical bore with large holes in acoustically correct positions, open-standing keys, and a sophisticated mechanism). This was not just 'evolution', but 'revolution'. The result was almost a new kind of instrument. In fact, it was argued by some that the character of the Boehm flute was different—that it was no longer had the charm or effect of the 'true flute'. There would be much resistance to it in some places and by some individuals.
This revolutionary design change did not happen all at once. There were numerous experiments by Boehm and others over many years. Boehm freely incorporated available mechanical and acoustic ideas. But only Boehm had the courage to throw out the entire old system and start over—while at the same time having the engineering know-how to produce something that actually worked.
One would not know from his published music that Boehm was anything but happy with the flutes of the time. But he, like others, was well aware of certain deficiencies of the simple system flute: the unevenness or inequality of tone, the occasional difficulty of intonation, and the lack of volume.
It may in fact be the lack of volume that bothered Boehm most about the old flute. He performed in London in 1831 and his sound was compared unfavourably to that of the English virtuoso Charles Nicholson (1795–1837), whose powerful tone was said to resemble that of the organ. In a letter (dated 1871) to J. S. Broadwood, Boehm writes "I did as well as any continental flutist could have done, in London, in 1831, but I could not match Nicholson in power of tone, wherefore I set to work to remodel my flute. Had I not heard him, probably the Boehm flute would never have been made." (Nicholson's seven or eight-key flutes had large holes, enabling a larger sound, but this type of flute requires a powerful embouchure to control the unevenness in tone and intonation.
The new flute had at first fourteen holes, twelve for the notes of the chromatic scale starting at d', a hole for the low c'# (the end of the flute served as the tone hole for the low c', of course), and a small hole for trills with upper note d'' or d'''. These holes were relatively large (except for the holes for c''# and d'') and located in their ideal places—not where the fingers just happened to be—the distance between the holes increasing slightly as they moved away from the embouchure. The correct positions and uniformity of size helped make the tone and intonation even; the larger size made the flute louder. These ideas were known before Boehm, but no one had incorporated all of them and made a practical instrument. A diagram of his 1832 flute is shown below.
A Model of this flute is shown below.
Boehm had to design a mechanism to allow the nine available fingers to govern the fourteen tone holes. This is where his engineering expertise was invaluable. His mechanism made use of ring keys mounted on rods or axles. (Keys mounted on sleeves rotating on post-mounted axles had already appeared on his earlier simple system flutes; see the illustration of the Boehm flute below.)
After a period of pursuing other interests, Boehm again turned his attention to improving the flute in 1846. He was not completely satisfied with his 1832 model. He had concerns about the intonation in the third octave, which tends to be sharp. He still had ideas about increasing the volume of tone in the low notes.
In 1846–1847, Boehm studied acoustics with a Herr Prof. Dr. Schafhäutl in Munich and claimed that his 1847 model flute was founded upon scientific principles. We should understand 'scientific principles' here to mean logic and systematic experimentation, rather than any elaborate theories and formulas. After numerous experiments, Boehm chose to use a cylindrical metal tube for the body.
The tone holes could be made larger on a cylinder (the tone holes on a conical body could not be larger than the bore), so large that they could not easily be covered by thin fingers. Boehm's very first model still used ring keys, but soon all holes were covered with solid key cups and pads (though ring keys occur sporadically for a few more decades).
The holes are still mostly uniform in size, and the space between them gradually increases as the holes move away from the top. The main exception is the C# hole at the extreme left, which is very small as it had to be put much higher than its 'scientifically correct position' for several reasons (e.g. it had to serve as a vent hole for the d'''). The resulting tone and sharpness of c''# remains one of the few defects on the Boehm flute. Otherwise, Boehm was pleased with the tone. It is flexible, but tends to be much richer, especially in the low notes, than the conical bore flute.
The octaves will not be perfectly in tune on a completely cylindrical flute. For an extreme example of this phenomenon, consider the renaissance flute. Because of its small diameter cylindrical bore and small tone holes, the octaves are very narrow. The a'' and b'' are so flat when one attempts to play them by over blowing the first octave that different fingerings must be used in the second. It is true that with larger holes and bore, as on many cylindrical ethnic flutes, and with proper cork placement and perhaps adjustments by the player, the first two octaves are pretty well in tune. But Boehm had to make a flute to play three octaves, because that is what the flute music of his time required.
Boehm's solution—to getting all three octaves in tune—was to put a taper in the head joint. This cannot be seen externally on a wooden head, but is evident on a metal head.
Boehm’s 1847 flute remains to this day the basis for all flute making techniques and design. This is unlikely to change anywhere in the near future.
