Musical Instruments Flashcards
Define Resonance.
The storing of energy in an oscillation; the energy coming from an external source matches the natural frequency of the system and forces it to vibrate more.
Define Natural Frequency.
All objects have a frequency at which they naturally ‘vibrate’ at – it is determined by the number of half wavelengths (harmonics) that fit within it’s boundaries.
Define Force Frequency.
this describes the frequency of the incoming wave (the one that causes the object to resonate). The closer the forcing frequency is to the natural frequency, the bigger the resonance. It is also known as the driving force.
Give an example how Resonance take place.
When 1 tuning fork is struck, the other tuning fork of the same frequency will also vibrate in resonance.
The periodic “driving force” here are sound waves.
When do harmonics occur?
Harmonics occur when ‘Half Wavelengths’ fit exactly between two fixed points.
Describe the link between open strings in string instruments and harmonics.
The strings vibrate at all, its harmonics at the same time.
The open strings can vibrate at all these frequencies at the same time.
Describe how harmonics act in string instruments.
When a string is touched lightly at a certain spot, only the harmonics that have a node exactly at that spot can still vibrate.
A string that is touched lightly exactly at its midpoint can only vibrate at the frequencies that have a node there.
So it will have a thinner sound than the open string.
It will also sound 1 octave higher than the open string.
What is the equation of the Speed of Waves on Stringed Instruments?
In a stretched string, the speed that the wave travels down the string is determined by the following:
𝑣=√(𝑇/𝜇)
v = speed of the wave (m/s) T = tension on the string (N) 𝜇 = mass per unit length - m/L (kg/m)
What is the fundamental harmonic?
The fixed ends of the strings are nodes because they are points of no vibration. So the harmonic with the lowest frequency (the FUNDAMENTAL harmonic)has just one antinode between the fixed points and a wavelength equal to twice the length of the string.
What is a open-ended cylinder?
An open-ended cylinder has anti-nodes at both it’s open ends (due to maximum pressure).
The fundamental harmonic will correspond to ½ wavelength.
COUNT THE NODES FOR THE HARMONIC.
What is a close-ended cylinder?
A closed-ended cylinder instrument has one end closed but the other open to let sound out.
This creates a node at the closed end and results in LOWER sounding notes as the fundamental harmonic will have just ONE QUARTER wavelength in the tube.
COUNT THE ANTINODES FOR THE HARMONIC.
What’s the solution to change the frequency of the note?
You cannot change the speed of sound through the air in the tube so the only way to change the frequency of the note it to change the length of the tube!
