NOTE: all the clarinet sound samples were performed by Gaetano Nenna on 04/12/2007. Sound engineer: Valerio Carboni.

Structure of the instrument

Clarinet	Component parts

The clarinet consists of a cylindrical tube, usually made of ebony, ending in a conical bell. The instrument is not built in one piece, but is divided into five sections that fit together.

1. The mouthpiece is an ebonite support to which a single reed is tied, that is, a thin blade set into oscillation by the player's breath.
2. A short joint shaped like a small barrel.
3. Two central sections, in which 24 tone holes are drilled, and which carry on the outside a complex system of keys to control the holes.
4. The last section is the conical bell, whose main function is to make the lowest notes more uniform. The bell corrects the effective length of the resonating pipe, but most of the sound energy is not radiated through it, but from the tone holes.

Upper joint	Lower joint	Bell

How the sound is produced

• The reed is the mechanical generator of the oscillations in the instrument. It is a thin blade of cane or flexible plastic. Its stiffness varies, and is usually indicated by a number from 1 (soft) to 5 (hard) on a non-standard scale.
• The reed turns the steady air flow coming from the player's lungs into an oscillating flow suitable for coupling with the cylinder of air contained in the resonating body of the instrument.
• The pressure the player must keep inside the mouth to keep the reed oscillating is rather high: about 3 kPa above atmospheric pressure, that is, three times higher than for the flute.

The source of the oscillations

Mouthpiece	Reed and ligature	Vibrating reed

Bernoulli's theorem (that is, the principle of conservation of mechanical energy in the motion of fluids) governs how the reed works. As with the oboe, we can identify the typical phases of the motion of the reed as follows:

1. The air flow enters the mouthpiece passing between the (flexible) reed and the (rigid) mouthpiece. The air flow speeds up as it passes through the narrow gap and, by Bernoulli's theorem, the pressure of the fluid inside the mouthpiece decreases.
2. As a result, the reed tends to bend towards the inside of the mouthpiece, until it closes the air inlet slit.
3. Once the flow is interrupted, the air speed in the mouthpiece drops to zero and atmospheric pressure is restored. The reed can return towards its equilibrium position but, because of its elasticity, it overshoots it.
4. Now the slit is wider than in the initial condition, but the air flow resumes, lowering the pressure in the mouthpiece again and bringing the system back to the initial condition. From then on the motion repeats cyclically.

This description explains why the reed can oscillate on its own. In the instrument, however, the rhythm of the oscillation is set by the bore: the pressure wave returning from the far end of the tube makes the pressure in the mouthpiece vary, and it is these variations that open and close the reed in step with a resonance of the air column (see the formation of timbre below).

Tuning and resonances

• As far as acoustics is concerned, the bore of the clarinet must be considered closed at one end. This becomes clear when the range of the clarinet is compared with that of the flute. The two instruments have roughly the same length, but the range of the clarinet extends an octave below that of the flute.
• This shows that the wavelength of the lowest notes on the clarinet is twice that of the flute. In the flute half a wavelength fits inside the instrument, while the clarinet contains only a quarter.
• The lowest note that can be played on a B♭ clarinet is D₃. Indeed, knowing that the bore is about 60 cm long and can contain at most a quarter wavelength, we find that the frequency corresponding to this wave is about 146 Hz. The speed of sound used, about 350 m s^-1, of course refers to the warm, humid air inside the instrument.

The formation of timbre

• Once mounted on the instrument, the reed oscillates at the frequency imposed by the resonances of the tube: its natural frequency of oscillation (see natural frequencies of the bar) is much higher than the notes played (see the sound of the reed below).
• However, the reed is not a simple oscillator, so its motion actually produces a non-sinusoidal waveform. The reed can be made to oscillate in several regimes, by changing the pressure of the lips on the mouthpiece and the air pressure inside the mouth. This changes the waveform it produces, which in standard conditions has roughly a "sawtooth" shape. The generated wave therefore contains all the higher harmonics of the fundamental (even and odd). This can easily be heard by listening to the sound of the reed when the mouthpiece of the clarinet is detached from the resonating tube.
• When the reed is coupled to the cylindrical body of the clarinet, the body enhances the frequencies in the sawtooth wave that correspond to the resonance frequencies of the tube and attenuates the others.

clarinet	flute
CL_SIb.mp3 B♭4 on the clarinet	FL_Sib.mp3 B♭4 on the flute

Acoustic characteristics

• As already noted, the clarinet is acoustically equivalent to a pipe stopped at one end and open at the other. The acoustic impedance is extremely high at the reed end, and the instrument operates in resonance at the frequencies where the impedance has a maximum.
• A sound wave reflected at the reed end keeps a pressure antinode near the reed, while a wave reaching the open end is reflected keeping a pressure node at the edge (equal to the pressure of the outside air).
• The timbre of the instrument is determined by the effect of the closure at one end, and is less bright than that of the flute or the oboe, since all the even harmonics are strongly attenuated (or completely suppressed).
• For the same reason, when the register key is opened the note does not rise by an octave, as in the flute and the oboe, but by a twelfth (an octave plus a fifth): the instrument switches to the next resonance of the bore, which is the third harmonic (see Conical bore).

The holes can be used not only to play different notes, but also as register holes, in the same way as on the flute.

• Most of the radiation of the clarinet comes from the tone holes, which are much smaller than the characteristic wavelengths emitted in the band between 1000 and 4000 Hz. Consequently, at these frequencies the clarinet behaves like a practically point-like source, without any marked directionality.
• The conical bell at the end of the instrument transmits high frequencies quite well, but not low ones. Its function is therefore to make the spectrum more uniform in situations where the high frequencies are attenuated by the high-pass effect of the row of open holes (see the discussion for the flute).
• As already noted, the reed has its own natural frequency, much higher than the notes played, and in the instrument it oscillates at the frequency imposed by the resonances of the air column in the body of the instrument. The effect of the reed can, however, become dominant when playing particular effects, such as the glissando made famous by the opening bars of G. Gershwin's Rhapsody in Blue.

waveform	sonogram	Audio
		CL_SampleDRY.mp3 CL_SampleDRY
		CL_Sample.mp3 CL_Sample

The sound of the reed

As we did for the oboe, first of all we detached the mouthpiece from the instrument and recorded the following sound samples, in which the sound of the reed mounted on the mouthpiece is not filtered by the resonances of the bore.

The sound corresponds to a periodic, non-sinusoidal wave containing all the harmonics (even and odd, as the sonogram shows), with a natural frequency of 1105 Hz. The player can lower the frequency to about 930 Hz by changing the air pressure in the mouth, and by changing the spring constant of the vibrating part of the reed, moving the lips forwards or backwards along the mouthpiece.

waveform	sonogram	Audio
		CL_Bocchini2.mp3 CL_Bocchini2

waveform	sonogram	Audio
		CL_Bocchino.mp3 CL_Bocchino

Timbre and registers

The clarinet is an extremely versatile instrument in terms of timbre. The section musical features gives a brief overview of how the qualities of the instrument are used in music. In this section, instead, we have tried to isolate the individual characteristics and analyse their sound quality independently of the musical context.

The first sample immediately reveals the clarinet's characteristic of having a bore open at one end and closed at the other. Acoustically, this results in a strong suppression of the even-order harmonics. Looking at the sonogram of a B♭₄ at 466 Hz, you will notice that the even harmonics are not completely absent, as would be the case ideally, but are much weaker than the odd harmonics. When looking at the sonogram, remember that it is drawn on a logarithmic scale. The power difference between the first and second harmonics in the B♭₄, for example, is about 20 dB, corresponding to a factor of 100 on a linear scale.

waveform	sonogram	Audio
		CL_SIb.mp3 CL_SIb

Let us now see what happens when B♭ is played in different octaves. The sonogram shows that, in the high octaves, the even harmonics gain proportionally more strength, and this already causes a change in the timbre of the instrument in passing from the low to the high register. To highlight the change, alongside we show the time-averaged spectrum of the first and second notes an octave apart (B♭3 and B♭4) played in the following example, with their frequencies rescaled so that they overlap and their overall amplitude rescaled so that the amplitudes of the fundamentals are equal. The base frequency is 232 Hz. What appears between zero and the first peak is just noise.

waveform	sonogram	Audio
		CL_Ottava.mp3 CL_Ottava

The range of the instrument goes beyond the three octaves shown in the previous example, and changes continuously in character. Here are the extremes of the three registers in which the instrument can play. (See also the musical features.)

waveform	sonogram	Audio
		CL_Registro.mp3 CL_Registro

Harmonics

As with other instruments (oboe, violin, trumpet, etc.), the player can play single harmonics instead of the full spectrum of the instrument. This happens when, by virtue of the particular nature of the excitation and of the boundary conditions imposed by the player, a particular normal mode of oscillation of the air column is selected. One way of obtaining harmonics is to impose a pressure node at a particular point by opening a hole at the desired position. In the following examples the player goes from the base note to the third harmonic (an octave and a fifth above) and to the fifth harmonic (two octaves and a major third above) respectively.

waveform	sonogram	Audio
		CL_Armonici1.mp3 CL_Armonici1

waveform	sonogram	Audio
		CL_Armonici2.mp3 CL_Armonici2

Double sounds

In this example double sounds are produced in two different ways. In the first case, starting from a C₄ at 267 Hz, an A₅ at 871 Hz appears briefly, then gives way to a higher resonance of the bore (roughly an E₆) at 1286 Hz: it is not exactly the fifth harmonic of the C (5 × 267 = 1335 Hz), because the resonances of a real bore are not exactly harmonic.

waveform	sonogram	Audio
		CL_Armonici3.mp3 CL_Armonici3

In the second case, instead, the spectrum is dominated by two pure harmonics at 342 Hz (F₄) and 526 Hz (C₅).

waveform	sonogram	Audio
		CL_SuoniDoppi.mp3 CL_SuoniDoppi

Effects

waveform	sonogram	Audio
		CL_PianoForte.mp3 CL_PianoForte

waveform	sonogram	Audio
		CL_ColpoDiLingua.mp3 CL_ColpoDiLingua

waveform	sonogram	Audio
		CL_Crescendo.mp3 CL_Crescendo

waveform	sonogram	Audio
		CL_Frullo.mp3 CL_Frullo

waveform	sonogram	Audio
		CL_Glissato.mp3 CL_Glissato

waveform	sonogram	Audio
		CL_Vibrato.mp3 CL_Vibrato

Musical features

Introduction

The clarinet is one of the most versatile instruments in terms of timbre, producing a full, warm sound in the low register (called chalumeau) and a penetrating, even shrill one in the highest range (called clarino).

Versatility of timbre

Given its characteristic waveform, practically free of even harmonics, the timbre is sometimes a little "woody" and lends itself well to "pastoral" settings (such as L. van Beethoven's 6th Symphony, the Pastoral, which, especially in the 5th movement, abounds in melodic phrases given to the clarinet), but also to simple and intense expressiveness (as in the Andante of W. A. Mozart's Clarinet Concerto, made famous by the film Out of Africa), or to disconsolate resignation (as in the first song of the cycle Lieder eines fahrenden Gesellen by G. Mahler), up to a strongly nostalgic and even heart-rending character (see the famous letter scene from La Traviata by G. Verdi, where a melancholy clarinet solo guides the heroine's pen as she writes a painful farewell letter to her lover).

New trends: jazz articulation

These are just some of the countless shades of timbre (and therefore of character) that the instrument can offer, taking advantage above all of the marked difference in colour between the two characteristic registers mentioned above. In the same way, though in a completely different musical language, jazz too has taken up the instrument, making it the solo centrepiece of the big bands: the sound is often very breathy, almost dirty (but no less expressive for that) in the middle-low range, and shrill, almost "screamed" in the very high range, pushing the most peculiar timbral features of the clarinet to their extremes. Here we offer a rather exceptional example: a solo by the actor and director Woody Allen, a great blues enthusiast as well as a capable clarinettist, who recently took on a long tour with his New Orleans Jazz Band.

The most recent inventions

Naturally, the extreme versatility of the instrument could not fail to attract the interest of the musical avant-garde, which has carried out research above all on timbre and articulation. In the third piece of Les murs de Jean for seven instruments, Luca Antignani gives the clarinet a long solo that "falls", at the end of each musical phrase, on an easily played double stop (going against the essentially monophonic tradition of the instrument). In his Germogli di vetro II for clarinet and piano, Paolo Boggio invents for the clarinet a very special descending glissando that imitates a kind of fierce howl, a desperate cry, while Lachenmann, in Dal niente (Interieur III), explores nearly all the articulation capabilities of the instrument, from breath to sound, from staccato to pizzicato, up to the "kiss" of the reed, and Sciarrino, in the composition Let me die before I wake, focuses once again on the borderland between silence and sound, dwelling at length on tremolos of harmonics.

Remarks

• Clarinet and saxophone: although the body of the saxophone is almost always made of metal rather than wood, the saxophone belongs to the woodwind family, because this classification refers to the mechanism of sound production rather than to the material the instruments are made of. In brass instruments the primary vibration is always produced by the oscillation of the player's lips, while in woodwinds it is produced by a reed (clarinet, saxophone, oboe) or by the oscillation of the air flow breaking against an edge of the instrument (flute).

• In real instruments the pressure node at the open end does not coincide exactly with the end of the bore, but falls slightly beyond it. The real bore therefore behaves like an ideal bore of slightly different length: an "effective length". This effect, however, depends on the frequency, and also occurs for all the holes of the instrument. If the clarinet were perfectly cylindrical, therefore, it could not be in tune in all registers. Construction techniques have evolved to compensate for this variability through small variations of the cross-section of the instrument along its length.

Check your understanding

Further reading and links

• We invite you to read the fundamental page Sound and resonance, which sets out the general principles of how a musical instrument works. Reading it will help you better appreciate the peculiarities of the instrument described on this page.

• In our virtual laboratory you can experiment with the formation of reflected waves and their dependence on the shape of the bore and on the position of the holes of the instrument. The page experiments on sound tubes illustrates some guided experiments.
• In the guided path clarinet and oboe you can use the TubeLabLight app to find out why the clarinet, with its cylindrical bore, sounds much lower than the oboe, whose conical bore is almost the same length.