A general overview on how sound is produced
Generally, sound is produced through the buzzing of a player's lips, and this buzzing is amplified by the instrument.
In terms of the standing wave pattern that forms within the closed air column, the vibration of the lips produces a wave across the tube and is then reflected back onto itself once it reaches the end of the column. Thus, the incoming waves and reflected waves produces a standing wave. |
This is an example of a standing wave pattern that you might see within a trumpet. Noticed how the closed end is an anti-node and the open end is the node.
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Buzz, buzz, buzzing!
To further expand on the features of the standing wave pattern, we have to clear this particular misconception.
Although the air column of the trumpet is special, (as one end is closed and the other is open) an anti-node forms at the closed end or at the mouth piece, not a node. This is because the mouth changes the pressure of the air as the lips vibrate. When the lips are closed, the pressure is built inside the mouth until it reaches a point where the lips burst open; releasing a high pressure pulse. Then the lips closes again and the pressure drops. This process is then repeated.
As for the open end, a pressure node forms. This is due to the fact the the pressure at this end remains constant and close to the atmospheric pressure.
Although the air column of the trumpet is special, (as one end is closed and the other is open) an anti-node forms at the closed end or at the mouth piece, not a node. This is because the mouth changes the pressure of the air as the lips vibrate. When the lips are closed, the pressure is built inside the mouth until it reaches a point where the lips burst open; releasing a high pressure pulse. Then the lips closes again and the pressure drops. This process is then repeated.
- Lip tension plays a role in buzzing. The tension keeps the lips together; the more tension there is, the higher the pressure is needed to buzz and the resonant frequency increases. This means that a player can adjust lip tension so that it vibrates to match one of the natural frequencies of the instrument.
As for the open end, a pressure node forms. This is due to the fact the the pressure at this end remains constant and close to the atmospheric pressure.
Diagram shows process of buzzing as explained in the green text
The video above shows the buzzing in action!
As mentioned in the "sound" Section, because the trumpet has a closed air column, the harmonic frequencies are odd multiples of the first harmonic. Described below, are the parts of the instruments that fix this irregularity.
Trumpet bellThe bell of the trumpet is capable of bringing those odd frequencies closer together. But how does it do this?
Well, the bell works by raising the frequency of the standing waves.
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A trumpet bell
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Mouth-piece
The mouthpiece of the trumpet is capable of lowering the highest frequency of the trumpet, essentially doing the opposite of the bell.
In combination, these parts (the bell and mouthpiece) work together to bring the odd harmonics closer, thus it forms a complete harmonic series (with the exception of the fundamental). Therefore, the instrument is more musically capable. |
A trumpet mouthpiece
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Working with the valves
We already know the basics on how the trumpet can produce music and the harmonic series it can play, but there is just one problem. It is very difficult to rely only on lip tension to select the correct harmonics.
Thus, valves are put into place to resolve this issue. -Essentially, valves manipulate the length of the air column the sound waves travel in. Where the longer the air column, the lower the frequency and thus a lower pitch. This is because the frequency of the air column is inversely proportional to the length of the column. These devices work by redirecting the air flow into extra length of tubing. The valves work through the depression of the pistons, where when they are not pressed down, the air goes through the device. When depressed, air is redirected into another air path to change harmonic frequency. |
As you can see above, the piston consists of different openings, where depending on whether they are depressed, air can travel through several path ways.
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Factors affecting sound quality
To conclude, based on the information in this page, there are several factors that affect the quality of the sound made in a trumpet. These are...
NOTE; the frequency itself is not affected as that is determined by the source, however, the fundamental frequency will be affected as it depends on the length of the tube.
To counter the change in temperature of the air, the instrument can be adjusted by increasing the length, or decreasing the length of the air column (adjusting to the wavelength) through sliding the main tuning slide shown below;
- The tension and geometry of the players lips; determines the pitch played
- The shape of the bell; determines the maximum frequency the trumpet can play
- The mouthpiece; enclosed volume and constriction of device lowers frequency of the highest resonances.
- The length of tubing; the longer the air column, the lower the pitch
- The temperature of the air: this determines the speed that the sound wave will travel in the medium, thus (according to the universal wave equation) the wave-length will be affected, and in extension, the fundamental frequency of the air column.
NOTE; the frequency itself is not affected as that is determined by the source, however, the fundamental frequency will be affected as it depends on the length of the tube.
To counter the change in temperature of the air, the instrument can be adjusted by increasing the length, or decreasing the length of the air column (adjusting to the wavelength) through sliding the main tuning slide shown below;
Trumpet Main Tuning Slide