Topic 1 - musical instruments Flashcards
Resonance
Storing energy in an oscillation
Energy coming for an external source match’s the natural frequency of the system and forces it to vibrate
Natural frequency
All objects have a frequency at which they naturally vibrate at
Determined by the number of half wavelengths (harmonics) that fit within its boundaries
Forcing frequency
Describes frequency of incoming waves (the one that causes the forcing object to resonate)
the closer the forcing frequency is to the natural frequency the bigger the resonance
Also known as the driving force
Harmonics
Occur when half wavelengths fit exactly between 2 fixed points
Stringed instruments: open string
The strings vibrate at all it’s harmonics at the same time
The open string can vibrate at all these frequency at the same time
Stringed instruments: harmonics
When a string is touched lightly at a certain spot only the harmonics that have a node exactly at the spot can still vibrate
A string that is lightly touched exactly at this midpoint can only vibrate at the frequency’s that have a node there. So it will have a thinner sound than the open string. It will also sound one octave higher than the open string
Speed of waves on stringed instruments
V m/s = square root tension on the string N / mass per unit length kg/m
Fundamental harmonics
Fixed end of strings are nodes because they are points of no vibration
So harmonic lowest frequency (the fundamental harmonic) has just one anti node between the fixed points
And a wavelength = to twice the length of the string
Close ended cylinders
One closed end but one open end to let sound out
This creates a node at the closed end and results in a lower sounding notes
As the fundamental harmonics will have just one quarter wavelength in the tube
Count the anti nodes for the harmonic
Open ended cylinder
Has anti nodes at both it’s open ends (due to maximum pressure)
The fundamental harmonic will correspond to 1/2 wavelengths
Count the nodes for the harmonic
