Wavelength is dependant on the velocity and frequency of the
sound. You can figure out a wave length by dividing the velocity by the
frequency. At the normal speed of sound
through air and at a frequency of 1KHz the wave length will be 0.333m roughly
the length of a standard ruler. But if you increase the frequency the wave
length will get shorter, so doubling the frequency to 2KHz means the wave
length drops to 0.1665m about half the size from before, and if you half the
frequency to 500Hz the wave length will double up to 0.666m. The relation
between frequency and wavelength is linear in air.
Frequency is used in many different ways when working with
sound, for example there is a concert pitch which is a generic frequency used
to tune concert instruments. The tuning instrument will play an A note at a
frequency of 440Hz, this is the standard frequency but it can also be tuned to
442 or 443 depending on the what was chosen for the piece, a sound at this
frequency though will have a wave length of 0.757m.
Acoustic waves traveling through a solid object find it
easier at a lower frequency than I higher frequency, this is because at a
higher frequency the wavelength is smaller and the material it is passing
through is likely to have within its structure parts roughly the same size as
the wave length which means the wave is more likely to reflect inside the
object and travel less far. The lower the frequency though the larger the
wavelength which isn’t hindered by the material it is passing through and is
carried further along the material ending in a better sound.
A standing wave is a wave that doesn’t move in a direction
yet the wave still pulses up and down. This can occur when two waves of the
same frequency and intensity going opposite directions meet. This can also
happen when a wave is confined within boundaries, an example can be the string
on a violin or a guitar, the string is held in place but can still move up and
down to create the sound. Because there is no velocity the wave is standing.
Constructive interference is an even that occurs when two
waves of the same frequency are travelling in the same direction. If you add
the two waves together you get a wave that is the same as the two waves before
but with a larger amplitude.
Destructive interference is when two waves of the same
frequency are travelling in the same direction but the waves are identical in
placement. The waves join together with an up wave meeting a down wave and they
cancel each other out, the two waves becoming nothing.
The reason Decibels are use to measure the volume of sound
is because the loudness climbs at such a
large rate that the numbers would be too large and inconvenient, because
decibels work in a logarithmic way the difference in loudness can be expressed
with a smaller number. For example 0 decibels (dB) is a value of one in
loudness. 10 dB has a value of 10 in
power, yet 20 dB has climbed to 100. If you go up to 100 dB you are looking at 10000000000.
The scale is used to you can accurately measure the increase in volume of a
sound as it is much easier to use a number with 3 digits than 11.
A sound with a frequency of 1KHz will take exactly the same amount
of time to travel a distance of 20m as a sound with 10KHz or 20KHz, all of them
would take 0.06 seconds to reach 20m.
Sound is known to travel underwater at an even faster speed
than it does through air but this isn’t the only difference between the two. For
example the human ear underwater finds it harder to hear the sounds made, it
requires a higher frequency or loud volume to be heard. The reason sound
travels faster through water than air is because the molecules in water are
much closer together than in air so the vibration passes through much faster.
An interesting fact is that salt water carries sound faster than fresh water
does. This is because the increase in salt molecules in the water give more
particles to vibrate off increasing the speed.
