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Why does a saxophone make its sound?

Tenor Viol

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All wind and brass instruments are fundamentally similar: a column of air is made to vibrate. An airstream from the player is disturbed by splitting it over an edge (flute/recorder), by the lips (brass) and by making a reed vibrate against something (mpc single reed, other reed double reed). The length of the vibraitng air column gives you the basis of pitch. Holes in the instrument enable you to change the length of the resonating column and hence the pitch.

The shape of the instrument, its bore, and to some extent what its made from, affect the timbre of the sound.

There are threads on here about the physics and maths of it all somewhere.
 

nigeld

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The postings above are more scientific, but here is how I look at it.

When a column of air gets excited, it stands and waves.
Little columns of air are more excitable than big columns, so they wave faster.
If you make a hole in a big column, it's ego is deflated and it behaves like a little column.

The best way to get a column of air excited is to beat two sticks together very quickly at one end of the column while blowing on them. This is called a double reed. Our ancestors discovered fire when one of them mistakenly rubbed the sticks together instead of beating them together. Later, people found out that it is possible to beat a single stick against a lump of metal or plastic. This is called a single reed. The more expensive the piece of metal or plastic, the more satisfying the process is for the beater.

Saxophones are shaped like ice cream cones. The bottom of the cone is cut off in the factory so that the ice cream can melt and run out. This makes the saxophone much easier to play, but less tasty. Some Italian saxophones are filled with multi-coloured ice cream. The very best saxophones have been re-filled with cryogenically frozen yoghurt. If you blow hard into a cone, it gets over-excited and behaves like two little cones.

Clarinets are tube-shaped. The centre of the tube is removed in the factory and sold as a pencil. If you blow hard into a clarinet, it gets oddly over-excited and behaves like three little clarinets.

Edit: @BigMartin pointed out an error in the previous paragraph. I have corrected it so as not to mislead the less technically knowledgeable members of the forum.
 
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David Dorning

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Hello,
Why does the sax make its sound and how does a clarinet or oboe make its sound?

This is my basic understanding of how it works with a single reed. I'd be interested to hear if it corresponds to anyone else's.....

Blowing into the mouthpiece creates high pressure on the player side of the reed and lower pressure on the other side. This closes the reed which claps against the mouthpiece. A pulse of energy passes down the instrument, compressing air molecules as it goes, until it reaches the first open tone hole. The energy pulse then returns to the mouthpiece as the compressed molecules rearrange themselves, equalising pressure on the reed and enabling it to open again, at which point the sequence repeats. The energy travels back and forth at the speed of sound, therefore the tube length governs the frequency of the cycle, of the reed vibration, and hence the pitch of the note sounded.
 

BigMartin

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Clarinets are tube-shaped. The centre of the tube is removed in the factory and sold as a pencil. If you blow hard into a tube, it gets over-excited and behaves like three little tubes.
I must pick you up there, as your otherwise astute analysis has a flaw. It does not apply to flutes. Flutes are tube-shaped but open at both ends so they can breathe more easily, which makes them more relaxed. An excited flute only behaves like two lilttle flutes.

They should give away a free matching pencil with every clarinet, I think. It would look really chic to have one of those behind your ear at rehearsals.
 
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jbtsax

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For the sax, oboe, and bassoon which are conical woodwinds the wavelength of each note is twice the physical length of the instrument to the first opening since each wave travels down and back. The formula is λ = 2L.

For the clarinet which is a cylindrical woodwind the wavelength of the note is four times the physical length of the instrument to the first opening since each wave travels down and back two times. The formula is λ = 4L.

As others have pointed out, the length of the tube to its first opening determines the pitch or the frequency of the note. That formula is λ = F/C where λ is the wavelength, F is the frequency, and C is the speed of sound which is generally considered to be about 346 meters/second in the warm, moist air inside a woodwind.

That is the "pitch" part of the story simplified. The "color" or timbre of the sound is determined by its "harmonic footprint". Each note on a saxophone, oboe, or bassoon contains in addition to its fundamental frequency, harmonics which are whole number multiples of the frequency of the fundamental. It is the strength or weakness of these various harmonics that give the note its tone color. The cylindrical bore clarinet exhibits only the odd numbered harmonics, giving it a different tone than the soprano sax which is nearly the same length.
 
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Eoe

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So am I right in saying when you hit the octave key you are pulling out a harmonic ?. I have been pondering how to separate the harmonics . easy to do on the guitar. I have been trying to squeak on purpose and control it. A squeak is a harmonic also I am assuming. Or am I wrong about that.
 

Tenor Viol

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Controlled squeaks aka altissimo aka harmonics
 

jbtsax

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Some squeaks are just squeaks which represents the natural frequency of the reed itself without the dampening of the lower lip.
 

kevgermany

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So am I right in saying when you hit the octave key you are pulling out a harmonic ?.
You need to be careful with wording here, the terminology is confusing.

The fundamental is also called the first harmonic.

First overtone is the second harmonic and is an octave above the fundamental, double the frequency of the fundamental.

Second overtone is the third harmonic and is three times the frequency of the fundamental.

As said above, clarinets only have the odd numbered harmonics, 1,3,5,... Saxes have all.

When you hit the octave key, it stops the fundamental/first harmonic from sounding. So the lowest note that sounds on a sax is the first overtone/second harmonic, an octave higher than the fundamental.

On clarinets it's the same principle, but the first overtone isn't there either, so the lowest sounding note is the 3rd harmonic/second overtone, an octave and a fifth higher than the fundamental.
 

nigeld

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Blowing into the mouthpiece creates high pressure on the player side of the reed and lower pressure on the other side. This closes the reed which claps against the mouthpiece. A pulse of energy passes down the instrument, compressing air molecules as it goes, until it reaches the first open tone hole. The energy pulse then returns to the mouthpiece as the compressed molecules rearrange themselves, equalising pressure on the reed and enabling it to open again, at which point the sequence repeats. The energy travels back and forth at the speed of sound, therefore the tube length governs the frequency of the cycle, of the reed vibration, and hence the pitch of the note sounded.

I'm definitely not an expert on acoustics, but I don't think this is right. And it doesn't explain how flutes and recorders make their sound. @David Dorning seems to be describing a shock wave, which I presume is different from a standing wave. My belief is that the turbulent airflow created by the reed and mouthpiece provides a constant supply of energy to make the column of air inside the saxophone resonate, like bowing a violin string. (If a string under tension is plucked or struck, it will resonate briefly, but the bow keeps the energy going.) A simple version of this effect is blowing across the top of a bottle. The nature of the turbulent airflow and the design of the body of the saxophone determine the harmonics created, and thus the tone.
 

Jeanette

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Why?

Because I breathe gently down the mouthpiece and will it to sound a beautiful note and just sometimes my wish is granted......

It's magic just like @Tomasz said :)

Jx
 

kevgermany

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I'm definitely not an expert on acoustics, but I don't think this is right. And it doesn't explain how flutes and recorders make their sound. @David Dorning seems to be describing a shock wave, which I presume is different from a standing wave.

Simplistic version:
Airflow between reed and mouthpiece lowers the pressure, causing reed to bend closed from air and lip pressure. Closing stops the airflow, causing a drop in pressure, creating low pressure part of sound wave. Wave is reflected by first open tone hole back to mouthpiece. High pressure pulse opens reed. Frequency of reed vibration matches frequency of note, so the pressure oscillations maintain/reinforce the standing wave.

Flutes use an unstable airflow over the edge of the fipple/lip plate which passes into/over the hole as it oscillates. You see the same effect when a flag moves from side to side in the wind. This has the same effect as the vibrating reed.

NB. Under normal playing the reed does not close completely, it oscillates causing different amounts of obstruction to the airflow and so giving the pressure changes that are the sound wave. Once complete closure starts happening, a form of clipping occurs, affecting the sound/causing the reed to stay closed in some cases.
 
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Eoe

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Having done extensive research on this subject the above poster is right it is about pressure and not airflow. It is all about the pressure before and after the read. There are a few sites you can Google about the science involved. I forgot the name of the valve the Reed acts but the Reed and mouthpiece is essentially a certain type of pressure valve
 

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