ACOUSTICS

• Acoustics


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


  The human ear's response to pressure fluctuations in the air caused by vibrating objects
• Types of sound


  • Speech
  • Music
  • Noise
• Frequency (f)


  The number of sound ripples generated in unit time. The number of cycles that the air particles move back and forth in one second in a sound wave
• Unit of frequency is cycles per second (c/s) or Hertz (Hz)
• Frequency bands in room acoustics

  • 63 Hz
  • 125 Hz
  • 250 Hz
  • 500 Hz
  • 1 kHz
  • 2 kHz
  • 4 kHz
  • 8 kHz
• Speed (c)


  The speed of sound in air, measured as 344 m/sec (1,130 ft/sec)
• The speed of sound in air does not vary with the frequency of sound or its loudness
• Wavelength (λ)


  The wavelength and the frequency of sound are related as c = speed, f = frequency, λ = wavelength
• Wavelength of sound at center frequencies

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


  The amount of sound power falling on (or passing through, or crossing) a unit area. Unit is watt per square meter (W/m2)
• Loudness


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

  
• Pitch


  The frequency of sound wave perceived by the human ear. A high-pitched sound has a high frequency
• Noise control


  • Control of airborne noise through insulation or shutting out unwanted sounds
  • Control of structure-borne noises through isolation of machines
• Prolonged reverberation

  • Long reverberation time (RT) due to large amounts of highly reflective surfaces and/or large volume of space
  • Causes blurring which is harmful to both speech and music
  • Influenced by volume of the room, sound absorbing qualities of the room's surfaces, and number of people and furniture in the room
• Echo


  • Distinct reflection of original sound when the path of reflected sound is 20 m (65 ft) or more than the path of direct sound
  • If the difference is less than 20 m, the reflected sound will reinforce the direct sound which is desirable
• Recommended that the surfaces of the front part of an auditorium must be highly reflective to reinforce direct sound and throw it to the rear, while the rear must be highly absorptive
• Resonance


  • Reinforcement of certain sound frequencies due to sympathetic vibrations, especially in enclosed rooms with highly reflective surfaces
• Flutter echo


  • A rapid but repetitive succession of sounds caused by highly reflective parallel surfaces
• Undue focusing of sound


  • Caused by concave surfaces which causes sound to converge at certain points with resulting loss of energy in other parts of the room
• Intensity level is measured on a logarithmic scale called decibels (dB).
• In solids, the particles vibrate back and forth along the direction of wave propagation.
• Sound waves are longitudinal waves that require a medium through which they can travel.
• Sound intensity refers to the amount of energy per unit time that passes through a given area.
• The human ear is sensitive to sound waves with frequencies between about 20 Hz (hertz) and 20,000 Hz.
• The human ear is sensitive to sound waves with frequencies between approximately 20 Hz (hertz) and 20,000 Hz.
• Lower frequency sounds are perceived as lower pitch or tone.
• The human ear can detect sound waves ranging from about 20 Hz to 15 kHz.
• Higher frequency sounds are perceived as higher pitch or tone.
• The human ear has three types of hair cells responsible for detecting different frequencies of sound.
• Pitch is determined by the rate at which vibrations occur, measured in hertz (Hz).
• Loudness is determined by the amplitude of the wave, measured in decibels (dB).
• Loudness is subjective and depends on factors such as age, hearing loss, and individual perception.
• Decibel level is calculated using the formula dB = 10 log(I/I0), where I is the intensity of the sound being compared to a reference intensity of 10-12 watts per square meter.
• Intensity is measured in watts per square meter (W/m^2).
• Sound intensity refers to the amount of energy carried by a wave per unit time.
• Loudness refers to how intense a sound wave is, measured in decibels (dB).
• Sound intensity increases exponentially with distance from the source.
• Intensity level is expressed in decibels (dB) and is calculated using the formula dB = 10 log(I/I0), where I is the actual intensity and I0 is the reference intensity.
• Decreasing the volume of a sound reduces its loudness but does not change its pitch.