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Acoustics

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Title: Acoustics


1
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.

2
  • 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.

3
  • 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.

4
The human ear is capable of hearing sounds within
a limited range.
5
Animals have varied hearingranges
6
Hearing range of some animals
7
  • 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.

8
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

9
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.

10
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

11
An anechoic chamber is a space in which there
are no echoes or reverberations. The surfaces
absorb all sound, and reflect none.
12
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.

13
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!!)

14
Sound Waves amplitude frequency (cycles)
15
Radio signals am fm
16
  • 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.

17
Bonded acoustical cotton recycled cotton, class
A non flammableMelamine Foam Acoustical Panels
fiber free, Class A fire retardent
18
Fabric wrapped panels provide good acoustical
absorption
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20
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)

21
  • 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.

22
  • 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.

23
  • 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.

24
an example of books dedicated to the study of
architecture and acoustics
25
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.

26
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

27
  • 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

28
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.

29
  • 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

30
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

31
  • 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."

32
  • Acoustics should be considered very early in the
    design process and the aesthetic concept
    developed in accordance with those requirements.

33
'Stradia' a sound simulation program
34
Sound ray diagram of New National Theatre, Tokyo
(May 1986
35
Concert halls demand very carefulacoustical
analysis
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The Sydney Opera House concert hallbuilding
designed by Jorn Utzon
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