Sound, Waves, uh yea.

Sound! Come  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 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  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  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 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-V s /V) for the source approaching the detector (1+V s /V) for source leaving the detector  F detected frequency  Fs emitted or source frequency  V is velocity of the wave and Vs is velocity of the source.

 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.