In the 19th century, the pendulum swung from the restraint of the Classical to the expressiveness of the Romantic. The aesthetic demanded an emphasis on the personal, on the dramatic, and on the passionate. Consequently, music in the Romantic period responded with modulation to remote keys and incorporation of greater dynamic contrast, changes that ultimately demanded an increased instrumental range and a more facile playing technique. Obviously, instruments had to be adjusted. Families of instruments again became important, and new tone colours were introduced.

The entire period has sometimes appropriately been called the age of mechanization. About the first quarter of the century, the period of Ludwig van Beethoven’s major orchestral works, more keys were added to existing woodwinds, and evidence from one passage in Beethoven’s Ninth Symphony (1824) implies that the instrument of the fourth horn player already had one valve. Almost immediately afterward, more drastic changes were necessary in order to fulfill the demands of the composers.

The central figure in the changes in woodwinds was a Munich flutist and instrument builder, Theobald Boehm. Profiting from the experiments of many others, Boehm devised the long axle to allow control of holes from some distance and then proceeded to redesign the flute on acoustic principles. Boehm made the holes in his flute as large as possible and changed all closed keys to open keys to allow full venting. He then placed all holes in an acoustically correct position, providing for comfort in fingering by using ring keys on the long axle. The ring keys allowed simultaneous closure of two or more keys that would normally be beyond the reach of the player’s finger span. In 1832 Boehm produced a flute with a conical bore that had multiple axles and ring keys. By 1847, however, Boehm had become convinced that only a cylindrical bore would solve certain problems in intonation, and by using covered finger holes, he could make them even larger. The Boehm experiments changed the character of the flute considerably, producing more volume and a more brilliant tone; with his improvements, along with the subsequent minor changes, the flute became one of the most versatile instruments of the orchestra, performing superbly in all keys.

Similar changes were made about the mid-century in other woodwinds. The Boehm system adaptations to the clarinet—implemented in 1939–43 by clarinetist Hyacinthe Eléonore Klosé and instrument maker Louis-Auguste Buffet, both French—finally conquered other key arrangements except in Germany. Charles Triébert and his son modified the oboe, finally adding some features from the Boehm flute to produce the “conservatory system.” Certain improvements were made in the bassoon in 1825 by Karl Almenräder, a chamber musician of Biebrich, Germany. Because the improvements were accompanied by deficiencies in tone, the French preferred to develop the classic bassoon. Although the Heckel family (Johann Adam Heckel and Wilhelm, his son and successor), also of Biebrich, eventually corrected the faults, the difference between the French and the German bassoon still remains, the former having a reedier, more individual tone and the latter, with its comparative richness, blending better. First the Americans and finally the British accepted the German instrument.

The Classical orchestra reached a certain perfection in balance between strings, woodwinds, and brass, which was distorted at the beginning of the 19th century by the addition of two horns and three trombones. From there on, the orchestra grew, and families of instruments again became important for additional colour and for balance. In his Principles of Orchestration (1913; written 1896–1908), the Russian composer Nikolay Rimsky-Korsakov developed the theory that the four basic woodwinds had a vast range of expression. At each end of the entire range were areas useful for their individual colour, and the instruments of smaller and larger sizes intensified those colour effects. This theory formed the basis of his orchestration (or instrumentation) and had profound effects on the art music of the early 20th century, even to the popular dance bands of the 1930s in the United States.

The piccolo was accepted early, carrying upward and intensifying the brilliance of the top octave of the flute. It remained for the 20th century to exploit the low tones of the piccolo. By the end of the 19th century, the alto flute, a weak instrument dynamically, had joined the orchestra, but it was exploited most effectively by the French composers of the early 20th century—for example, Claude Debussy. The oboe developed no satisfactory descant, but the English horn, first used notably in Hector Berlioz’s Roman Carnival Overture (1844), became increasingly useful for its peculiar dark and melancholy expression. A small clarinet in D (E♭ in wind bands) proved suitable for bright, strident effects, and the bass clarinet added a mysterious piquancy as an extension of the dark and colourful chalumeau register. The contrabassoon gained importance as the most effective wind double bass and the lowest instrument of the orchestra.

Little needs to be added about the trumpet and horn. By mid-century, valves had been established for horns and trumpets, but, even through the early works of the 20th-century German composer Richard Strauss, these were considered largely as a means for instant transposition of the instrument. At the same time, however, the full chromatic possibilities were exploited by such composers as César Franck and Pyotr Ilyich Tchaikovsky.

Since 1590, a wooden cup-mouthpieced instrument, the serpent, had been built to support voices in French choirs, but by the mid-18th century, it was serving as a double bass for the woodwind choir. The serpent and its derivatives, the Russian bassoon and the bass horn, were eventually replaced by the contrabassoon. The ophicleide, the bass of the keyed bugle, was prominent in the second quarter of the 19th century as a brass double bass.

The invention of the bass tuba by a German instrument builder named Johann Gottfried Moritz in 1835 provided a more reliable and more even brass bass. Tuned in F or E♭, it had a range that was, respectively, B♭′–e♭′ and C–f′. Later a BB♭ (double B-flat) contrabass became available. The tuba was distinguished by a wide conical bore and a deep cup mouthpiece, both of which favoured the fundamental and lower partial of the overtone series (see The production of sound). It was built in many sizes to provide a rich and mellow brass choir for the wind band, of which the cornet of similar proportions was the lead melodic instrument, in contrast to the more penetrating trumpet of the orchestra. The flügelhorn, slightly more conical than the cornet, is also an appropriate treble for the tuba family. The tubing of the various instruments could be and was bent into many different shapes. Some even had bells pointing backward in order to send the sound toward marching soldiers in a parade. When the bass instrument was bent into an over-the-shoulder model, it was called a helicon. Later, the American bandmaster John Philip Sousa established his own variation of the helicon, and it became known as the sousaphone.

Also noteworthy are the Wagner tubas, specially built for Richard Wagner’s four-opera cycle, Der Ring des Nibelungen. Narrower in bore than the baritone horn, they are supplied with a funnel-shaped mouthpiece in order to form a tone intermediate between the orchestral horn and the tuba. Built in tenor and bass ranges, the instruments fulfill their purpose admirably.

The 19th century gave rise to families of reed instruments. The Belgian instrument maker Adolphe Sax patented the saxophone in 1846, combining a wide conical bore with a large single reed and producing an instrument that overblows at the octave and covers a written range of b♭ to f‴. Sax’s patent covered instruments in 14 different sizes, and others were added later. Intended for the military band, the saxophone has found only occasional use in the orchestra. It has been used most familiarly in the United States in jazz ensembles since the 1930s.

The Chinese sheng, which had reached Europe in the late 18th century, inspired the invention of three distinct musical instruments in the West: the harmonica, the accordion, and the reed organ. The sheng is a mouth organ consisting of free-reed pipes vibrating under wind pressure from a globular wind chamber into which the player blows. The pitch is determined by the reed itself, which activates vibrations in the surrounding air.

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The harmonica, invented about 1825, is a mouth organ that possesses a series of paired reeds. Each reed of a given pair produces the same pitch and either vibrates or rests depending on the direction of the air flow—as controlled by the player’s inhaling and exhaling. The slotted edge that is placed in the player’s mouth directs air to and from the reeds. Tones are isolated by covering the slots, so a skillful player can produce a single tone at a time. The instrument is normally completely diatonic, although there are chromatic models. Some highly skilled players have developed chromatic techniques for diatonic instruments, however. The harmonica is largely confined to folk and popular music, but since the late 20th century, a number of prominent composers have written for the instrument.

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The accordion was invented in 1822 by Friedrich Buschmann of Germany (or by Cyrill Demian of Vienna in 1829) and operates on the same principle as the harmonica except that a bellows substitutes for the breath and buttons or keys open channels to free reeds. Melody is controlled by the right hand and the bass and accompanying chords by the left. Although originally a diatonic instrument, by mid-century it had become chromatic. Piano accordions, with keyboard for the right hand, have also become popular. By the early 21st century, the range and versatility of the instrument had expanded considerably. While acoustic models retained their popularity, MIDI-equipped accordions also became commonplace. The instrument’s repertoire similarly expanded to include a broad spectrum of folk, urban popular, and classical music styles.

The reed organ dates from about 1810. It was a free-reed instrument with a foot-operated bellows providing wind pressure to vibrate reeds whose access was controlled by a keyboard. The instrument was provided with an assortment of Greek-derived trade names, of which the harmonium appears to be most prominent for those organs operating on the principle of pressure bellows. An instrument operating on sucker bellows was later developed and became especially popular in the United States; in fact, all such suction instruments are commonly known as American organs. In the 19th century, the reed organ, mellow in tone and inexpensive, became an important instrument in homes and small churches. (The harmonium became standard accompaniment for many South Asian vocal recitals.)

The 20th and 21st centuries

The 20th century began with few radically new ideas in instruments. Many people were still debating the merits of Wagner and Johannes Brahms, while Richard Strauss, the Impressionists, and the Russian nationalists were continuing the exploitations of the tone colour and technical capacities of the expanded orchestra. Challenged by these works, instrument makers continued to make minor alterations to solve fingering problems or to produce even tone. For a time, the standards of increased size and greater technical capacity were most important, but eventually such works as Arnold Schoenberg’s Pierrot Lunaire (1912) and Anton von Webern’s Five Pieces for Orchestra (1911–13) disturbed the overripe late Romanticism, and the emphasis on bigness evaporated. The entire aesthetic became disunified. In general, after the first quarter of the century, ensembles became smaller, and an anti-Romantic, if not a purely Classical, trend was discernible. In instruments, two diverse directions became apparent: (1) a return to the historically accurate sounds for the music of the repertoire and (2) the application of electrical power to do everything from duplicating known tone colours with artificial amplification to the creation of entirely new instruments.

With the revival of early music came the reproduction of early brasses and woodwinds. In roughly 1925, an English musician and instrument builder named Arnold Dolmetsch began making Baroque recorders, which had been in eclipse for more than 100 years and which again became one of the most widely played wind instruments. Later in the century, reproductions of other historical instruments became available, including crumhorns, shawms, Renaissance flutes and recorders, Baroque transverse flutes, Baroque oboes, and Baroque trombones. The Baroque trumpet was again made, although few trumpeters returned to the valveless long D trumpet of the period; with a discreet use of narrow bores, shallow mouthpieces, and valves, they obtained trumpets that give the range and character of the clarino trumpet.

Since the 1970s, there has been considerable interest in adapting electronic technology to wind instruments. Synthesizer control devices that treat the sound of the wind instrument as input to be manipulated electronically have been used successfully, as have synthesizers with breath-operated control. Other electronic instruments use digital technology to generate, sample, and manipulate wind instrument acoustics.