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.
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!!)
‘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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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 vibrationmeasurement 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.
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.