In a recording room, if an acoustic wave was measured to have a frequency of 1KHz we would work out the wavelength taking the velocity, which we know to be 333m/s and divide it by the frequency. First we would need to change the 1KHz to Hz = 1000Hz
So 333/1000= 0.333metres.
If you had a 2KHz wavelength, you use the same method of working out except this time it would be 333/2000= 0.166metres.
If the frequency was only 500Hz, this would produce a wavelength of 0.666metres.
There are some circumstances where the velocity may not be 333m/s for example underwater and this would change the equation. Other things that could affect this equation could be if you were in an anechoic chamber as they use frequency absorbers.
VELOCITY = THE SPEED OF SOUND
- Velocity is the distance travelled during a unit of time by a sound wave. It is measured in metres per second (m/s).
- Wavelength is the distance between each successive crest of a wave. It is measured in metres (m).
- Frequency is the rate at which something occurs or is repeated over a particular period of time in a sample.
- 20Hz - 20,000Hz is our audible sound range.It is measured in hertz (Hz).
- Sound travels faster in liquids and non-porous solids than it does in air. In water it travels 4.3x faster.
When all the instruments in an orchestra tune for a concert, they tune to something called CONCERT PITCH. Standard concert pitch is A440Hz or the note A above middle C on a piano.
You can work out the wavelength of the sound coming from the violin by dividing the velocity, which we know as 333m/s, by the frequency, 440Hz. So 333/440= 0.7568m is the wavelength.
Sound travelling through different environments:
If an acoustic wave with a wavelength of 3.33m travels along a workbench we can work out the frequency of the sound wave by dividing the velocity (333m/s) by the wavelength (3.33m) which equals 100Hz.
It is easy for sound to travel through a solid such as this workbench as the energy from the sound waves is transmitted by the particles in the solid colliding with each other.
In solid materials the atoms that make up the workbench are packed very close together, therefore they don't move about as much. Due to them being in this fixed position, they can only vibrate in a fixed position, so sound waves travel through the solid object very fast. For example like a domino effect.
You can work out the wavelength of the sound coming from the violin by dividing the velocity, which we know as 333m/s, by the frequency, 440Hz. So 333/440= 0.7568m is the wavelength.
Sound travelling through different environments:
If an acoustic wave with a wavelength of 3.33m travels along a workbench we can work out the frequency of the sound wave by dividing the velocity (333m/s) by the wavelength (3.33m) which equals 100Hz.
It is easy for sound to travel through a solid such as this workbench as the energy from the sound waves is transmitted by the particles in the solid colliding with each other.
In solid materials the atoms that make up the workbench are packed very close together, therefore they don't move about as much. Due to them being in this fixed position, they can only vibrate in a fixed position, so sound waves travel through the solid object very fast. For example like a domino effect.
- Sound travels through air at 333m/s
- Sound travels through water at 1500m/s
- Sound travels through solid steel at 5000m/s
It travels more slowly through air compared to a solid because the air particles are a lot further spread apart, so when they vibrate, they move freely in all directions and have to move further in order to collide with other particles. So even though sound doesn't move as fast in air, it does travel in all directions as the air surrounds you.
STANDING WAVES:
Decibels
Decibels are used in the measurement of relative loudness in acoustic waves because the loudness of sound is based on intensity level, using a logarithmic scale. It is relative to the weakest sound the human ear can hear (by ratio).
The formula for sound intensity is:
http://www.noisehelp.com/decibel-scale.html
When sound travels underwater, it travels faster than it does in air, this again is due to the water molecules being closer together as they are a liquid (rather than a gas like the air) so it is easier for them to collide and vibrate.
It is interesting that if you have ever listened to someone talk whilst you are underwater in a swimming pool, the noise sounds sort of distorted and it is not always clear what the person is saying to you. I came across this article which goes further into why this happens.
https://ccrma.stanford.edu/~blackrse/h2o.html
STANDING WAVES:
- A standing wave is a wave that remains in a constant position.
- It occurs because the medium is moving in the opposite direction to the wave.
OR
If a stationary medium interferes between two waves of equal amplitude travelling in opposite directions. - physics.info/waves-standing/
- For example, a standing wave can be compared to the string of a guitar, it is joined at both ends but it can still move/vibrate only up and down rather that traveling forwards and backwards as the medium is in a fixed position.
- Constructive Interference occurs when two waves combine by the superposition principle.
eg Amplitude = A
A1 + A2 = A total
http://zonalandeducation.com/mstm/physics/waves/interference/constructiveInterference/InterferenceExplanation2.html - Destructive Interference occurs when the crest of one wave interferes with the trough of another. The amplitudes are subtracted.
The amplitude of an acoustic wave determines its loudness.
The amplitude of a wave is its maximum disturbance from its undisturbed position.
(not the difference between the the top and bottom of the wave)
(not the difference between the the top and bottom of the wave)
Decibels
Decibels are used in the measurement of relative loudness in acoustic waves because the loudness of sound is based on intensity level, using a logarithmic scale. It is relative to the weakest sound the human ear can hear (by ratio).
The formula for sound intensity is:
http://www.noisehelp.com/decibel-scale.html
When sound travels underwater, it travels faster than it does in air, this again is due to the water molecules being closer together as they are a liquid (rather than a gas like the air) so it is easier for them to collide and vibrate.
It is interesting that if you have ever listened to someone talk whilst you are underwater in a swimming pool, the noise sounds sort of distorted and it is not always clear what the person is saying to you. I came across this article which goes further into why this happens.
https://ccrma.stanford.edu/~blackrse/h2o.html
