Acoustics

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Acoustics

• a science that deals with the production,
  control, transmission, reception, and effects of
  sound.
• definition from the Merriam-Webster Online
  Dictionary
• acoustics is addressed in the text Interior
  Construction Detailing on pages 259 - 282.
  These pages will be used for questions on Exam 2.

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• Sound is reflected, transmitted, or absorbed by
  the materials it encounters.
• Soft surfaces, such as textiles, and batt
  insulation, tend to absorb sound waves,
  preventing them from further motion.
• Hard surfaces, such as ceramic tile, gypsum
  board, or wood, tend to reflect sound waves,
  causing echo. Reverberation is the term used to
  describe sound waves that are reflected off of
  surfaces.
• Dense, massive, materials, such as concrete or
  brick, tend to transmit sound waves through the
  material.

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• High frequency sound waves (think of a high
  whistle) are not capable of being transmitted
  through massive, heavy, material.
• Low frequency sound waves (bass) are transmitted
  through massive materials.

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The human ear is capable of hearing sounds within
a limited range.
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Animals have varied hearingranges
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Hearing range of some animals
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• Many animals hear a much wider range of
  frequencies than human beings do.
• For example, dog whistles vibrate at a higher
  frequency than the human ear can detect, while
  evidence suggests that dolphins and whales
  communicate at frequencies beyond human hearing
  (ultrasound).
• Frequency is measured in hertz, or the number of
  sound waves a vibrating object gives off per
  second. The more the object vibrates, the higher
  the frequency and the higher the pitch of the
  resulting sound.

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Decibel levels

• 0 The softest sound a person can hear with normal
  hearing
• 10 normal breathing
• 20 whispering at 5 feet
• 30 soft whisper
• 50 rainfall
• 60 normal conversation
• 110 shouting in ear
• 120 thunder

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Decibel levels

• The human ear's response to sound level is
  roughly logarithmic (based on powers of 10), and
  the dB scale reflects that fact.
• An increase of 3dB doubles the sound intensity
  but a 10dB increase is required before a sound is
  perceived to be twice as loud.
• Therefore a small increase in decibels represents
  a large increase in intensity.
• For example - 10dB is 10 times more intense than
  1dB, while 20dB is 100 times more intense than
  1dB.
• The sound intensity multiplies by 10 with every
  10dB increase.

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Decibel levels

• 130dB - Jack Hammer (at 5ft)?
• 120dB - Rock Concert / Pain threshold?
• 110dB - Riveter or a Heavy Truck at 50ft?
• 90dB - Heavy Traffic (at 5ft)?
• 70dB - Department Store or a Noisy Office?
• 50dB - Light Traffic?
• 30dB - Quiet Auditorium?
• 20dB - Faint Whisper (at 5ft)?
• 10dB - Soundproof room / anechoic chamber

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An anechoic chamber is a space in which there
are no echoes or reverberations. The surfaces
absorb all sound, and reflect none.
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Acoustics sound

• Sound is a mechanical wave and therefore requires
  a medium in which it can travel.
• Acoustics is classically divided into sound and
  vibration.
• Sound refers to waveforms traveling through a
  fluid medium such as air
• Vibration describes energy transmitted through
  denser materials such as wood, steel, stone,
  dirt, drywall or anything besides a fluid.
• It is not heard as much as felt, due to its
  extremely low frequency, which is below the range
  of most human hearing.

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The speed of sound versus the speed of light

• sound travels at 1130 feet per second at normal
  room temperature.
• light travels at 299,792,458 meters per second,
  which is roughly 974,325,489 feet per second (974
  million feet per second!!)

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Sound Waves amplitude frequency (cycles)
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Radio signals am fm
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• am means amplitude modulation the height of
  each wave changes
• fm means frequency modulation the length of
  each wave changes
• FM signals have a great advantage over AM
  signals.
• Both signals are susceptible to slight changes in
  amplitude.
• With an AM broadcast, these changes result in
  static. With an FM broadcast, slight changes in
  amplitude don't matter -- since the audio signal
  is conveyed through changes in frequency, the FM
  receiver can just ignore changes in amplitude.
  The result no static at all.

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Bonded acoustical cotton recycled cotton, class
A non flammableMelamine Foam Acoustical Panels
fiber free, Class A fire retardent
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Fabric wrapped panels provide good acoustical
absorption
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Advanced Study of Acoustics

• Acoustics is the subject of formal, advanced
  study, including the fields of engineering,
  architecture, and psychology.
• For example, the School of Architecture at
  Rensselaer Polytechnic Institute offers a formal
  program for a Masters of Science degree in
  Building Science (Concentration in Architectural
  Acoustics)

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• The Graduate Program in Architectural Acoustics
  offers an intense curriculum in acoustics for
  effectively shaping sonic environments to achieve
  optimum acoustic performance and sound quality.
• The Program offers studies toward both Master of
  Science and Ph.D. degrees.
• Further doctoral degree studies offer a unique
  program in architectural acoustics, providing the
  knowledge for next-generation acousticians
  involved in room acoustics, psychoacoustics,
  acoustic and vibration measurement techniques,
  and sound reinforcement.

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• Researchers in the acoustics program in the
  School of Architecture are investigating how the
  design of a classroom can affect how easily
  students hear.
• The researchers believe that if more attention is
  paid to classroom acoustics when designing the
  space, students will have an easier time learning
  and understanding what's going on.

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• Research of this kind could lead to the
  development of new standards for classroom
  acoustics.
• Regulators for the Americans with Disabilities
  Act are currently working on such standards,
  which exist already in countries such as Germany
  and the United Kingdom.

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an example of books dedicated to the study of
architecture and acoustics
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Music and Drama Theater Acoustics

• The acoustical characteristics of a venue for the
  live performance of music or drama are an
  important part of the audience experience.
• For music performance, the room becomes part of
  the instrument, helping define the character of
  the musical sound that the audience hears.

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Reverberation Time

• Reverberation time refers to the amount of time
  required for the sound field in a space to decay
  60dB, or to one millionth of the original power.
• In simple terms this refers to the amount of time
  it takes for sound energy to bounce around a room
  before being absorbed by the materials and air

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• Reverberation time is important because it can
  affect how well you understand speech, and it can
  change the way music sounds.
• The effect on speech intelligibility is
  noticeable in a gymnasium or arena, where you
  often can't understand someone who is only 10 or
  15 feet away from you

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Useful Reflections

• Reflections are an important part of acoustical
  design for music performance venues.
• For effective musical acoustics, the reflections
  have to arrive within the correct time window,
  and from the correct direction.

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• The reflections help to boost the level of
  acoustic instruments and human voices in the
  audience area.
• They also influence timbre and help define the
  apparent size or perspective of the instruments.
• The critical time interval we're talking about is
  a very brief 0.3 seconds

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Acoustics Consultants May Provide

• Architectural Acoustics
• Sound Isolation Testing
• Impact Isolation Testing
• Mechanical (HVAC) System Noise and Vibration
• Environmental/Community Noise Assesment
• Computer Physical Acoustical Modeling
• Field Testing
• Industrial Noise Control
• Sound Masking Systems Desig

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• A properly designed acoustical environment
  provides a good listening experience for the
  audience by enhancing the performance or
  presentation.
• Even and natural sound coverage, freedom from
  intruding noise and a sense of presence from the
  performer or presenter are all-important aspects
  of "good acoustics."

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• Acoustics should be considered very early in the
  design process and the aesthetic concept
  developed in accordance with those requirements.

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'Stradia' a sound simulation program
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Sound ray diagram of New National Theatre, Tokyo
(May 1986
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Concert halls demand very carefulacoustical
analysis
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The Sydney Opera House concert hallbuilding
designed by Jorn Utzon
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