Wind instrument

The wind instruments or aerophones are a family of musical instruments which produce sound by the vibration of the air content inside, without the need for strings or membranes because it only requires air vibration. Metal aerophones produce a loud ringing sound. In this case, the musician vibrates his lips in a mouthpiece that generates the acoustic frequency. Among the metal aerophones we can name the trumpet, the tuba and the trombone, among others.

Description

Wind instruments are those that emit sounds by exhaling air in a convenient and different way to make sound.

Methods for obtaining different grades

• Use different air columns for different tones, as in the bread flute. These instruments can play several notes at once.
• Changing the length of the vibrant air column by modifying the length of the tube through coupling valves (see rotary valve, piston valve) that direct the air through additional tubes, thus increasing the total length of the tube, lowering the fundamental tone. This method is used in almost all metal instruments.
• Change the length of the vibrant air column by lengthening and/or shortening the tube through a sliding mechanism. This method is used in the trombone and in the Flood Flate.
• Change the vibration frequency by opening or closing the holes on the side of the tube. This can be done by covering holes with fingers or pressing a key that then closes the hole. This method is used in almost all wood wind instruments.
• Make the air column vibrate in different harmonics without changing the length of the air column (see natural tube and harmonic series).

Almost all wind instruments use the latter method, often in combination with one of the others, to broaden their range.

Classification

Depending on the material

Examples of Metal Wind Instruments

Wind instruments can be classified into two categories. These categories are divided according to the material with which the timbre is produced:

1. Metal instruments . The bell is usually strong, bright and with metallic sound. The sound in these instruments is produced by the vibration of the lips in a cup-shaped metal nozzle, which produces acoustic frequency.
2. Wooden instruments. The bell of these instruments is softer and melodious than metals. The sound occurs when blowing over a hole (bezel mouth) or making a double or simple tongue reed vibrate.

According to its shape

Wind instruments or sound tubes can be classified according to three different criteria:

The tubes can be conical, cylindrical or prismatic:

• Chronicles: saxophone, fagot, fiscorno, tuba, oboe...
• Cylindricals: transvender flute, clarinet, sweet flute...
• Prismatics: primitive instruments and some organ tubes.

According to the excitation mode of the air column

The tubes are classified as mouthpiece, tongue (single or double) and mouthpiece tubes:

• Embo
  • Directa: Naughty.
  • Indirecta: Tip flute and organ tubes
• Lengüeta
  • Free: Acordeón, harmonic, melodic.
  • Batiente:
    • Simple: clarinet, saxophone, organ tubes.
    • Double: oboe, fagot.
• Nozzle: trumpet, trumpet, trumpet, tuba...

Physics of sound production

Sound production in all wind instruments depends on air entering a flow control valve attached to a resonant chamber (resonator). The resonator is usually a long, cylindrical or conical tube, open at the end. A high pressure pulse from the valve will travel down the tube at the speed of sound. It will be reflected from the open end as a low pressure return pulse. Under suitable conditions, the valve will reflect the pulse back, with increased energy, until a standing wave forms in the tube.

Reed instruments, such as the clarinet or oboe, have one or more flexible reeds on the mouthpiece, forming a pressure-controlled valve. An increase in pressure within the chamber will decrease the pressure differential across the reed; the reed will open further, increasing airflow. Increased airflow will further increase the internal pressure, so a high pressure pulse reaching the mouthpiece will be reflected as a higher pressure pulse back to the tube. The standing waves inside the tube will be odd multiples of a quarter wavelength, with an antinode pressure at the nozzle, and anode pressure at the open end. The reed vibrates at a speed determined by the resonator.

In the case of Lip Reed (brass) instruments, players control the tension of their lips so that they vibrate under the influence of the air flowing through them. They adjust the vibration so that the lips are most closed, and the airflow is the lowest, when a low pressure pulse reaches the nozzle, to reflect a low pressure pulse back down the tube. [Standing waves inside the tube will be odd multiples of a quarter wavelength, with a pressure node at the nozzle and a pressure node at the open end.

In air reed instruments (flute and fipple-flute), the thin sheet of grazing air (flat jet) that flows through an opening (mouth) of the tube interacts with a sharp edge (lip) to generate the sound. The jet is generated by the musician, by blowing through a fine slit (duct). In the case of recorders and fireplace organ pipes, this indentation is made by the instrument maker and has a fixed geometry. In a transverse flute or a panpipe, the slit is formed by the musicians between their lips.

Due to the acoustic oscillation of the tube, the air in the tube is alternately compressed and expanded. This results in an alternate flow of air in and out of the tube through the mouth of the tube. The interaction of this transverse acoustic flow with the flat air jet induces a localized disturbance of the jet velocity profile at the tube outlet (origin of the jet). This disturbance is strongly amplified by the intrinsic instability of the jet as the fluid moves towards the lip. The result is a global transversal movement of the jet on the lip.

The amplification of perturbations in a jet by its intrinsic instability can be seen by looking at a plume of cigarette smoke. Any small amplitude movement of the hand holding the cigarette results in an oscillation of the plume that increases with distance upwards and, finally, in a chaotic motion (turbulence). The very oscillation of the jet can be triggered by a gentle airflow in the room, which can be checked by waving with the other hand.

The oscillation of the jet around the lip results in a fluctuating force of airflow over the lip. Following Newton's third law, the lip exerts an opposite reaction force on the flow. This reaction force can be shown to be the sound source that drives the acoustic oscillation of the tube.

A quantitative demonstration of the nature of this type of sound source has been provided by Alan Powell by studying a flat jet interacting with a sharp edge in the absence of a pipe (the so-called edgetone). The sound radiated by the edgetone can be predicted from a measurement of the unstable force induced by the jet flow on the sharp edge (labium). The production of sound by the reaction of the wall to an unstable force of the flow around an object also produces the aeolian sound of a cylinder placed normal to a flow of air (the phenomenon of piped music). In all these cases (flute, edgetone, wind tone...) the sound production does not imply a vibration of the wall. Therefore, the material the flute is made of is not relevant to the principle of sound production. There is no essential difference between a gold or silver flute.

Sound production in a flute can be described by a fixed element model in which the tube acts as an acoustic swing (mass-spring system, resonator) that preferentially oscillates at a natural frequency determined by the length of the tube. The instability of the jet acts as an amplifier that transfers energy from the steady jet flow at the tube outlet to the oscillating flow around the lip. The tube forms a feedback loop with the jet. These two elements are coupled to the smoke outlet and the lip. At the smoke outlet, the transverse acoustic flow of the tube disturbs the jet. At the lip, the oscillation of the jet gives rise to the generation of acoustic waves, which maintain the oscillation of the pipe.

The acoustic flow in the pipe can be described, for constant oscillation, in terms of standing waves. These waves have a pressure node at the mouth opening and another pressure node at the opposite end of the open pipe. Standing waves inside an open tube will be multiples of half a wavelength.

According to an approximation, a tube of about 40 cm. will present resonances near the following points:

• For a tongue or reed instrument: 220 Hz (A3), 660 Hz (E5), 1100 Hz (C#6).
• For an air cane instrument: 440 Hz (A4), 880 Hz (A5), 1320 Hz (E6).

In practice, however, obtaining a range of musically useful pitches from a wind instrument depends largely on careful instrument design and playing technique.

The frequency of the modes of vibration depends on the speed of sound in air, which varies with the density of the air. A change in temperature, and only to a much lesser degree also a change in humidity, influences the density of the air and therefore the speed of sound, and thus affects the tuning of wind instruments. The effect of thermal expansion on a wind instrument, even a brass instrument, is negligible compared to the thermal effect on air.

Bell

The bell of a clarinet in if bemol

The bell of a wind instrument is the round, flared opening in front of the mouthpiece. It is found on clarinets, saxophones, oboes, French horns, trumpets, and many other types of instruments. In brass instruments, the acoustic coupling between the bore and the outside air occurs in the bell for all notes, and the shape of the bell optimizes this coupling. It also plays an important role in transforming the resonances of the instrument. On woodwinds, most notes are vented at the highest open tone holes; only the lowest notes in each register are fully or partially vented in the bell, and the function of the bell in this case is to improve the consistency of pitch between these notes and the others.

Blowing pressure

Playing some wind instruments, particularly those involving high resistance to respiratory pressure, causes increases in intraocular pressure, which has been linked to glaucoma as a potential health risk. A 2011 study focusing on brass instruments noted "temporary and sometimes dramatic elevations and fluctuations in IOP". Another study found that the magnitude of intraocular pressure increase correlates with associated intraoral resistance. to the instrument and linked the intermittent elevation of intraocular pressure from playing high-resistance wind instruments with the incidence of visual field loss. The range of intraoral pressure involved in various classes of ethnic wind instruments, such as Native American flutes, is generally less than that of Western classical wind instruments.

Links

• Wikimedia Commons hosts a multimedia category Wind instruments.
• Wikimedia Commons hosts a multimedia category Wooden wind instruments.
• Wikimedia Commons hosts a multimedia category Metallic wind instruments.