Acoustics
• “a science that deals with the production, control,
transmission, reception, and effects of sound.”
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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.
• 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.
• 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.
The human ear is capable of hearing sounds
within
a limited range.
Animals have varied hearing
ranges
Hearing range of some animals
• 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.
Decibel levels
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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
Decibel levels
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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.
Decibel levels
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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
An anechoic chamber is a space in which
there are no echoes or reverberations.
The surfaces absorb all sound, and reflect none.
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.
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!!)
Sound Waves:
amplitude & frequency (cycles)
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
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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.
Bonded acoustical cotton; recycled cotton, class A non flammable
Melamine Foam Acoustical Panels: fiber free, Class A fire retardent
Fabric wrapped panels provide good acoustical absorption
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)
• 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.
• 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.
• 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.
an example of books dedicated to the study of architecture
and acoustics
Sound Pollution
Vehicles and Transports
Vibration and resonance
of high building
Planting: Butches, flowers and trees
Reduce noises 5-10dB
Double or Multilayer
Doors and Windows
Suitable Plane=Noise reduction
buffer area reducing noise impact
Noise reduction:
Extra Glass boxes, doors and windows
Partitioning with permanent or temporary separators
Using Dampers=Noise reduction
A Modern method of noise reduction:
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.
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
• 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
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.
• 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
Acoustics Consultants May Provide:
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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
• 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 allimportant aspects of "good acoustics."
• Acoustics should be considered very early in the design process
and the aesthetic concept developed in accordance with those
requirements.
• Room Acoustic Modeling Using Ray Tracing
• Using room acoustic modeling software HGC Engineering
demonstrates the paths and reflections of three speakers’ voices
within a uniquely shaped synagogue space. Ray tracing is used to
show visually how the room would theoretically fill with sound from
these speaker orientations, considering room configuration,
reflections, surface material properties
Sound ray diagram of New National Theatre, Tokyo (May 1986)
'Stradia': a sound simulation program
• REFLEX is a room acoustics software application developed in 1989
by MJM ACOUSTICAL CONSULTANTS INC. with the help of the
department of architecture and mathematics of University of
Montréal. With REFLEX one can visualize the spatial distribution of
the first reflexions on the boundaries of a room, and reorient
automatically surfaces to redirect sound reflexions where they are
required. This last feature allows the acoustical designer to address
the spatialization of a room, an aspect of room acoustics which is
often left aside because of the lack of proper tools to adress it.
AVRS - Acoustic Virtual Reality System
AVRS performs spatial 3D-sound processing allowing the arbitrary placement
of sound source in auditory space. The main goal is to develop a genuine
experimental flexible platform, that runs in a general-purpose architecture
computer (standard hardware and software).
ECOTECT (Building Performance Simulation Software)
• Featured design analysis tools include: shadows and reflections,
shading design, solar analysis, lighting design, right-to-light, acoustic
analysis, thermal analysis, ventilation & air flow, building regulations,
and resource management.
Concert halls demand very careful
acoustical analysis
• The analysis in Bernaek’s “Acoustics” assumes uniform
absorption throughout the hall.
– The assumption is OK when predicting the reverberation time.
– But in many halls the assumption does not accurately predict the
reverberant loudness.
• Audience areas are highly absorptive
– ~80% of the energy is absorbed.
– Usually the other surfaces in a hall are entirely reflective.
• Direct sound that hits an audience surface does not
contribute to reflected energy
– either early or late.
– If the view from the stage is almost entirely of people, the direct
sound will dominate for most of the seats.
• Surfaces around the orchestra that reflect sound into the
audience provide strong early reflections.
– But this energy will not be available for later reverberation.
– running reverberation and envelopment will be low.
• Thus we must choose between a strong early sound level,
and the warmth and envelopment of later reverberation.
Loudness of early sound vs late
reverberation
• If we want running reverberation to be
audible, we need to provide many
surfaces that direct sound can hit without
being absorbed.
– And the reflections from these surfaces should also
not be absorbed.
– This is the case in a classical “shoebox” hall.
• But design decisions can still influence
loudness and clarity.
The Sydney Opera House concert hall
building designed by Jorn Utzon
Early vs Late: Shoebox vs
vinyard halls
• The “Vinyard” design is popular as a
concert hall design.
– The audience surrounds the orchestra
– Reflectors on the ceiling and side walls reflect
energy directly into the audience.
– The result is a strong early sound, and low
late reverberation and envelopment.
Shoebox vs Directed Halls
In Boston, the ceiling and side
walls are sound-diffusing, and
not absorptive.
A large percentage of the direct
sound to be trapped in the hall,
becoming late reverberation.
The sound is both clear and
reverberant!
In Los Angeles, the ceiling, vinyard walls,
and the side walls are arranged to reflect
direct sound back to the audience, where it
is mostly absorbed.
Early and middle reflected energy is
increased, and late reverberation is
decreased.
The Ideal Reverberation above 1000Hz
The ideal profile has three distinct slopes.
1. Reflections in the 20ms to 50ms time range
with a total energy of -4dB to -6dB relative to
the direct sound combine with the direct
sound to produce a decay rate under 1
second RT.
2. Reflections in the 50ms to 150ms time range
decay much more gradually – with a slope
greater than 2 seconds RT.
3. Reflections after 150ms produce our perception
of reveberance, and should decay at a rate
appropriate to the music.
Most real rooms (at all frequencies) have
exponential decay
- But then there will be too few early reflections
and the late reverberation will be weak.
If the direct sound above 1000Hz is weak, there
will be too much energy between 50 and 150ms,
and the sound will be MUDDY.
The ideal reverberation profile is
frequency dependent
• For frequencies above 1kHz (speech) the ideal profile has three
distinct slopes
– 1. The early slope – consisting of the direct sound and the 050ms reflections. This slope is steeply down – less than 1
sec RT.
– 2. The middle slope – 50 to 150ms – is relatively flat – can
have an RT of 3s or more. This flat section of the profile
maximizes the late reverberant level while minimizing the
muddiness.
– 3. The slope of the decay beyond 150ms can be around 1.3
seconds RT for opera and up to 2 seconds RT for orchestra
(if the early slope is short enough to maintain clarity.)
• Below 500Hz the decay probably should be single sloped, with
RT of 1.7s or higher.
– This is because in our experience a single slope decay at
low frequencies produces the most pleasing sound on an
orchestra.
• Thus for optimum acoustics the reverberation time and
Geometry of Halls
TRAPEZOID