ACOUSTICS INTRO

• Sound


  The human ear's response to pressure fluctuations in the air caused by vibrating objects
• Wave motion


  The way sound travels in space, similar to the motion of a ripple produced by dropping a pebble into a water pond
• Acoustics


  • The science which deals with the production, control, transmission, reception and effects of sound in an enclosed space
• Types of sound


  • Speech
  • Music
  • Noise
• Frequency (f)


  The number of sound ripples generated in unit time, measured in cycles per second (Hertz, Hz)
• Wavelength (λ)


  The distance between two adjacent compressions or rarefactions in a sound wave, related to frequency by the equation c = fλ
• Speed (c)


  The speed of sound in air, measured as 344 m/sec (1,130 ft/sec), which does not vary with frequency or loudness
• Octave frequency bands

  • 63 Hz
  • 125 Hz
  • 250 Hz
  • 500 Hz
  • 1 kHz
  • 2 kHz
  • 4 kHz
  • 8 kHz
• Intensity


  The amount of sound power falling on, passing through, or crossing a unit area, measured in W/m2
• Threshold of audibility


  The sound intensity that is just audible, 10-12 W/m2
• Threshold of pain


  The sound intensity that corresponds to the sensation of pain in the human ear, approximately 10 W/m2
• Loudness


  A measure of the intensity of sound, expressed in decibels (dB)
• Pitch


  The frequency of a sound wave perceived by the human ear, with a higher pitch corresponding to a higher frequency
• Noise control


  1. Control of airborne noise through insulation and shutting out unwanted sounds

  2. Control of structure-borne noise through isolation of machines from the room/building structure
• Reverberation time (RT)


  The time it takes for sound intensity to decay by 1 millionth of its steady state value after the sound source has been terminated
• Reverberation time is influenced by the volume of the room, sound absorbing qualities of the surfaces, and number of people and furniture
• Reflected sound should reinforce direct sound in the front of an auditorium and be absorbed in the rear
• Resonance


  The reinforcement of certain sound frequencies due to sympathetic vibrations, especially in enclosed rooms with highly reflective surfaces
• Acoustics


  is a science which deals with production, control, transmission, reception and effects of sound in an enclosed space.
• Sound


  is the human ear's response to pressure fluctuations in the air caused by vibrating objects.
• Wave motion

  1. a phenomenon where sound travels in space
  2. is similar to the motion of a ripple produced by dropping a pebble to the pond
• 20 hz


  Human hearing range
• Speed of light

  300,00 km/sec
• threshold of audibility

  10^-12 W/m2
• 10 W/m2


  intensity that corresponds to the sensation of pain in the human ear
• LOUDNESS 


  is a measure of the intensity of sound and is expressed in decibels (dB).
• decibels 


  measure for loudness
• Prolonged Reverberation


  long reverberation time (RT) due to large amounts of highly reflective surfaces
• Echo


  distinct reflection of original sound which results when the path of reflected sound is 20 m (65 ft) or more than the path of direct sound
• Flutter Echo


  a rapid but repetitive succession of sounds caused by highly reflective parallel surfaces (wall to wall, or ceiling to floor).
• Undue Focusing of Sound


  is caused by concave surfaces which causes sound to converge at certain points with resulting loss of energy
• absorption coefficient


  the fraction of the incident sound energy absorbed by a surface.
• anechoic chamber


  a sealed room in which all the surfaces are designed to completely absorb all sound produced in the room.
• attenuation


  a reduction in sound level. Sound attenuation in air-conditioning is specified in terms of dB per meter
• background noise


  ambient noise
• break-in noise


  transfer of noise from a space surrounding the duct into the duct through duct walls.
• break-out noise


  transfer of noise from the interior of a duct through duct walls into a space outside the duct.
• dead room


  a room containing an unusually large amount of sound absorption..
• decibel


  a unit of measurement for sound pressure level, sound intensity level or sound power level.
• diffraction


  a change in the direction of propagation of sound as a result of bending caused by a barrier in the path of a sound wave.