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.

• 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 hearingranges

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

• 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

• 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

• 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

• ‘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.

Bonded acoustical cotton; recycled cotton, class A non flammableMelamine 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

Vibration and resonance of high building

Vehicles and Transports

Planting: Butches, flowers and treesReduce noises 5-10dB

Double or MultilayerDoors and Windows

Suitable Plane=Noise reduction

buffer area reducing noise impact

Noise reduction:Extra Glass boxes, doors and windowsPartitioning 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:

• 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 all-important 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 SystemAVRS 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 carefulacoustical 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 hallbuilding 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 0-

50ms 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 reverberation level should increase below 500Hz.

Geometry of HallsTRAPEZOID