Transcript Sound, uh yea.

Sound, Waves, uh yea.
Sound! Come on! @!#%#!
 Pitch, loudness, and timbre are all perceived
attributes of sound.
 Pitch is the perceived frequency of a sound
 Loudness is the perceived intensity or
amplitude of a sound wave.
 Timbre is the perceived quality of a sound
and what separates a trumpet from a
clarinet playing at the same pitch and
loudness
Sound, the sound of music
 Sound waves are nothing more than
oscillating patterns of compressed and
decompressed matter, typically air.
 Sound waves vary in speed depending on
the medium and the temperature of the
medium
 The speed of sound is @ 343 m/s (767
mph or Mach 1) at 20 degrees C but can
vary up to .6 m/s for each degree difference
 Reflected waves are called echoes
Sound off
 Sound travels faster through a solid or liquid
than it does through a gas. Sound moves
through steel at roughly 5130 m/s and water
1493 m/s. In most cases the more dense it
is the faster sound travels.
 The speed of sound in air depends on the
square of the Kelvin temp. If temp is
quadrupled then speed increases by 2
Ear stuff, not wax
 We can hear frequencies between 20 Hz
and 20,000 Hz. Below 20 is called
infrasonic and above 20,000 is referred to
as ultrasonic.
 Most animals have a much greater range
than we do and can communicate/navigate
with a greater range as well
Seriously
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The sound level is measured in decibels dB
Decibels are logarithmic
The level depends on the pressure variation.
The lowest detectable variation is 2 x 10-5
This is given a value 0 dB. A sound or variation
10 times greater than this would be 20 dB. 10
times greater than that is 40 dB and so on.
 A 10 dB increase is perceived as twice as loud
Kill me now
 10 dB is barely audible
 50 dB is conversational level
 Lawn mowers and some alarm clocks are
around 80 – 100 decibels. (Most
headphones are in this range)
 Rock concert – 110 dB
 Jet Engine – 140 dB
 Anything over 85 dB for more than 8 hours
can cause permanent hearing loss
Can you hear me
 91 dB for over 2 hours can achieve the
same thing
 115 dB 30 seconds
 140 dB 10-15 seconds
 A ringing in the ears usually indicates a
threshold has been reached.
Sound
 Doppler effect, is the increase in frequency
of sound wave as the object emitting the
sound moves
 Doppler effect, F+= fs(1-Vs/V) for the
source approaching the detector (1+Vs/V)
for source leaving the detector
 F detected frequency
 Fs emitted or source frequency
 V is velocity of the wave and Vs is velocity
 Musical instruments are resonaters, either
closed pipe or open pipe.
 Closed pipe resonators have one end
closed while the other end is open, clarinet,
oboe, saxophone, coke bottle
 Open pipe resonators have both ends open,
flute, trumpet, trombone
 In a closed pipe resonator the sound wave
is composed of high and low pressure, as
the sound wave travels down the tube it is
reflected, if the high pressure point of the
wave hits the emitter while it is at high
pressure, resonance occurs
 With this type of resonance, a standing
wave is produced
 The shortest column of air
that can have an antinode
at the closed end and a
node at the open end is ¼
of a wavelength, after this
resonance occurs at ½
wavelength intervals
 Therefore, 1/4, 3/4, 5/4,
7/4 will be in resonance.
 fn =nv/4L, n =quarter
wavelengths 1,3,5,7,
v=wave speed, L is tube
length
 The shortest column of air that
can have nodes at both ends of
an open ended pipe is ½ of a
wavelength , resonance lengths
are found and ½ intervals from
that.
 Therefore1/2, 1, 3/2, 2 will be in
resonance
 Long story short being either
open ended or closed ended
and varying the length will
produce different frequencies
and thus different sounds for
different instruments
 fn=nv/2L n = half wavelengths
1,2,3, v = wave speed, L = tube
length
 A tuning fork produces a simple sine wave
at a given frequency.
 Musical instruments, your voice, etc produce
a complex sine wave at that same
frequency, more like a compilation of other
waves overlapping the simple sine wave.
 This overlapping is unique to your voice or
musical instrument and is described as
timbre. The quality of sound produced.
 With musical instruments, either closed pipe
or open pipe, they all have a fundamental
frequency, the lowest resonant frequency
 Closed pipe is at ¼ the wavelength, odd
number multiples of the fundamental are
called harmonics.
 Open pipe is at ½ the wavelength, with
whole number multiples of the fundamental
being harmonic.
 Frequencies with a ½ ratio are said to be an
octave. A frequency of 440 Hz versus 880
Hz.
 The first harmonic is an octave higher than
the fundamental.
 If two different instruments play two different
frequencies that are not “harmonious” then
they are called dissonant.
 Harmonious frequencies are consonant.
 Two instruments playing nearly the same
frequency produce what are called beats.
 Instruments are tuned to eliminate the
presence of beats or pulses.