Acoustics Reviewer

Acoustics Reviewer ACOUSTICS IS ALREADY PRESENT IN ANCIENT TIMES FREQUENCY THEATER OF EPIDAURUS 20-20,000 Hz-approx. audio frequency range of human hearing. Considered as an architectural marvel 600-40,000 Hz-critical frequency for speech communication The theatre of Epidaurus through its production and presentation of drama, plays and recitals therefore became an important contributor to the progress of Greek arts. Speed of sound in various media: Media Air Air Water Salt Water Rubber Iron Temperature (C) 0 20 25 25 25 25 Speed (m/s) 331 343 1493 1533 1550 5130 Acoustics of the Epidaurus theater are so good you can hear a pin drop from the back seats Spectators’ capacity: 11,750-14,700 Measurements: CAVEA: 119 mts, ORCHESTRA 24,65 mts WHAT IS ARCHITECTURAL ACOUSTICS? -technology of designing spaces, structures, and mechanical systems to meet hearing needs. -with proper design, "wanted" sounds can be heard properly and "unwanted sounds or "noise' can be attenuated to the point where it does not cause annoyance. HEIGHT: approx. 59 mts WHAT ARE THE FACTORS THAT CONTRIBUTED IN THE PROPAGATION OF ACOUSTICS? 1. SEATS ARE MADE OF LIMESTONES & MARBLE 2. THE SEMI-CIRCULAR SEATING OF THE THEATER 3. UNENCLOSED DESIGN OF THE THEATER DEFINITION OF SOUND 4. STEEPNESS OF THE THEATER - Form of energy propagated in waves which continue to subsist until filtered through a material turning into heat by friction - Vibration that travels through a medium HOW SOUND TRAVELS REFLECTION Sound hits a surface and bounces back off of it ABSORPTION Sound hits a surface and some of it is absorbed TRANSMISSION REVERBERATION -is the persistence of sound after the cause of sound has stopped -a result of repeated reflections. SOUND PATH - Every listener in a lecture hall, theater, or concert hall should hear the speaker of performer with the same degree of loudness and clarity. 1. REFLECTIONS - The occur when sound hits a surface that is neither predominantly absorptive nor sound transparent at the specific frequency. Non absorptive surfaces that are large, as compared to the wavelength at a given frequency, reflect sounds Sound that isn’t absorbed or reflected passes through the material, such as a wall. 2. RAY DIAGRAM - Ray diagramming is a design procedure to analyzing reflected sound distribution throughout a hall, us first reflection only. Basic elements in an Acoustic situation 4. ECHOES - a clear echo is caused when reflected sound at sufficient intensity reaches a listener approximately 70 msec or more after hears the direct sound, echoes even if not distinctly discrenable are undesirable in rooms. they are annoying and make speech less intelligible, the relative annoyance is dependent on the time delay, and loudness relative to the direct sound which, in turn, are dependent on the size, position, shape, and absorption of the reflecting surface. 1. Source 2. Transmission Path 3. Receiver The ABC of acoustic design Absorb Block Cover TYPES OF ACOUSTICS Psycho Acoustics-deals with the reaction of human beings to audible sound Environmental Acoustics-deals with the effects of the environment upon audible sound waves, may be broken down to Architectural Acoustics and Landscape Acoustics Electro Acoustics-deals with the generation and detection of audible sound waves Sonics-deals with the technical application of mechanical waves in basic scientific research, industry, and medicine. 5. FOCUSING - Concave domes, vaults, or walls will focus reflected sound into certain areas of rooms. This has several disadvantages. For example, it will deprive some listeners of useful sound reflection and cause hot spots at other audience positions. 6. CREEP - This describes the reflection of sound along a curved surface from a source near the surface. Although the sound can be heard at point along the surface, it is inaudible away from the surface. 7. ABSORPTION- The rate which sound is absorbed in a room is a prime factor in reducing nose and controlling reverberation. All the materials used in the construction of buildings absorbed some sounds, but proper acoustical control often requires the use of materials that have been especially designed to function primarily as sound absorbs. Such materials are popularly known as "acoustical materials. These are also used for reduction of noise in office buildings, hospitals and restaurants. 1. Combustible Or Fire Resistant? 3. ACOUSTICAL BLANKETS 2. How Much Might It Will Reflect? - Blankets are made up chiefly of mineral or wood wool glass fibers, kapok batts, and hair fell. The physical characteristics of the materials in each of these categories will now be considered. 3. What About Its Structural Strength, Absorption of Water, And Attraction for Vermin? 4. How Foolproof Is It? 5. Cam Its Application Be Entrusted to The Average Journeyman? -The materials use most commonly in the fabrication of acoustical blankets are mineral wood, hair, felt, wood fiber, and glass fiber, although, the thickness of these blankets is generally between 11⁄2 and 4 inches, blankets of greater thickness are sometimes used in special applications. 6. What Are Its Appearances, And What Are Its Decorative Possibilities? PRE FABRICATED UNITS 7. How Much Does the Material Cost? TYPE II -Units having perforated surface; the perforations to be arranged in a regular pattern. 8. Will it Be Expensive to Install and Maintain? HOW IS SOUND ABSORBED? A. FIBROUS MATERIALS-occur naturally, from both animal (hair, wool, silk) and vegetable (cotton, fax, hemp) sources B. PANEL RESONATORS is an enclosed system of air side a panel, that communicates with the outside through small openings. CLASS A- Units having perforated surface which acts as a covering and support for the sound absorbent material to be strong and durable and substantially rigid. CLASS B- units having circular perforations extending into the sound absorbent materials CLASS C- units having slots or grooves extending into the sound absorbent material TYPE III- units having a fissured surface TYPE IV- units having a felted fiber surface C. VOLUME RESONATORS Class A-Units composed of long wood fibers HOW LONG IT WOULD TAKE FOR NOISE TO DAMAGE YOUR EARS? 30 dB 85 dB 88 dB 91 dB 94 dB 97 dB 100 dB 115 dB 120 dB 125 dB 140 dB will not cause damage Higher than this level is the beginning of hearing damage (esp after 8 hrs of exposure) Lawn mower, City Traffic (damage in 4 hrs) such as hairdryer, garbage disposal (damage in 2 hrs) such as electric drill (damage in 1 hr) such as motorcycle (darnage in 30 mins) such as mp3 player, snowmobile (damage in 15 min) such as leaf blower stadium football game (damage in 30 sec) such as rock concert, ambulance siren (damage in 6 seconds) such as fire alarm, firecracker) such as jet engine at take-off, gunshot (damage in immediate hearing) Class B-Units composed of fine felled vegetable fiber or wood pulp Class C- Units comprised of mineral fibers 2. ACOUSTICAL PLASTERS AND SPRAYED MATERIALS -On materials, these materials comprise plastic and porous materials applied with a trowel, and fibrous materials, combined with binder agents, which are applied with (sprayed on) air gun blower. TYPE I-Acoustic Plaster TYPE II-fibrous materials combined with a binder agent and which are applied by being sprayed on with an air gun or blower Absorptive Barrier Quilted Curtain (ABQC) - They are made from materials that are specifically designed to block or absorb sound waves, such as fiberglass or rock wool. Sailcloth and Vinyl Encapsulated Baffle (SVEB) - Cost effective, lightweight, high acoustical performance, moisture and chemical resistant. Any large area where noise and reverberation need to be reduced Porous Expanded Polypropylene Wall Panel (PEPP) - They are typically made from porous materials that are designed to absorb sound waves, rather than reflect them TYPES OF ACOUSTICAL MATERIALS ACOUSTICAL DEFECTS 3 CATEGORIES 1. Echo-sound waves which have been reflected to a listener with sufficient magnitude and time delay so as to be perceived separately from those communicated directly from the source to the listener. 1. PRE FABRICATED UNITS- These include acoustical tile, which is the principal type of material ds, and absorbents sheets. available for acoustical treatments; mechanically perforated units backed with absorbent material: and certain TYPE 1-CAST UNITS HAVING A PINED OR GRANULAR APPEARING SURFACE CLASS A-Mineral nits composed of small granular of finely divided particles with Portland cement binder CLASS B-Mineral units composed of small granules or finely divided particles with lime or gypsum binder CLASS C-Unit composed of small granules or finely divided particles of mineral vegetable origin with incombustible mineral binder 2. Long-Delayed Reflection - similar to echo except that the time delay between the perception of direct and reflected sounds is somewhat less. 3. Sound Shadow-occurs when an area does not receive an adequate amount of direct and reflected sound. 4. Sound Concentration-sound reflections from concave surfaces concentrating in an area sometimes referred to as hot spots. The intensity of sound at hot spots are always at the expense of dead spots. 5. Flutter Echo-a rapid succession of noticeable small echoes observed when a short burst of sound is produced between parallel sound reflective surfaces. 6. Coupled Spaces-two rooms adjacent to each other by means of open doorways, with at least one space being highly reverberant. 7. Distortion-an undesirable change in the quality of musical sound due to the uneven and excessive sound absorption of the boundary surfaces at different frequencies. 8. Room Resonance- also called Coloration. Occurs when certain sounds within a narrow barrier of frequencies tend to sound louder than other frequencies. Vegetation - Trees and vegetation are normally NOT effective as noise control barriers. It is because attenuation from trees is mainly due to branches and leaves, which is why sound energy near the ground will not be significantly reduced. - Deciduous trees will provide almost no attenuation during the months when their leaves have fallen. - A single row of trees has no value as an acoustical barrier. Thin planting of trees can provide visual, but not acoustical shielding. - Many rows of trees have some value as an acoustical barrier. 9. Whispering Gallery-high frequency sounds creeping along large concave surfaces such hemispherical dome. - Addition of shrubs on the ground will provide better attenuation. Polyurethane Foam (PF) Earth Berms - It exhibits good sound absorption since sound wave is absorbed with broadband frequency range starting from 1,000 to 5,000 Hz where the sound absorption coefficient is higher than 0.6. - Earth berms are effective isolators if completely covered by sound-absorbing material, such as plant. Melamine Foam (Wedge/Pyramid) - Is a nitrogen-rich compound. The melamine derivatives possess flame retardant properties, due to the release of nitrogen when burned. Melamine reacts with formaldehyde and produces thermosetting plastic as a product. Acoustic Baffles - sound waves are instead absorbed by the paneling. The baffles' core is vibrated by sound waves on impact, converting the energy into heat before it's given a chance to return. APPLICABLE TREATMENTS ARCHITECTURAL LIMP Fabric Insulator ALL Floor Carpets Sound PLENUM Walling with Airgap HARDWOOD Sprung Floor/HDF POLYURETHANE Foams BONDED Acoustical Panel (BAP) DOUBLE Glazing Windows PANEL & Membrane Absorbers RESILIENT Floor Coupling POROUS Materials EGGCRATES Absorbent ACOUSTIC Fastened at edges with tight seal Reduced floor sound reverberation For dance studios isolating room noise For dance studios isolating room noise Absorbs sound reducing reflections Absorbs sound reducing reflections High end spaces for insulating sound Composed of gypsum sound absorbers Reduce vibration & increase sound isolation Lower band frequency of sound Cheapest sound diffusers FUNDAMENTALS OF NOISE CONTROL • Noise: All sounds that are distracting, annoying. or harmful to everyday activities • Airborne Noise: sound transmitted through the air only, usually through continuous air paths, doors, windows, vents, air shafts, etc. These pathways are called Acoustical Short Circuits. • Structure-borne Noise: radiated sound setting into vibration of solid parts of the building The fundamental objective of noise control is to provide an acceptable acoustical environment. LANDSCAPE ELEMENTS FOR NOISE CONTROL - If there are reflective surfaces along their tops or deciduous trees, the effectiveness is reduced because it can scatter sound energy. Thin Wall Barriers - Elevated roadbed plus shielding of grass- covered earth berm and thin-wall barrier can provide useful attenuation. However, elevated highways more than 500 ft. away can produce almost the same noise levels as highways at grade level because the line of sight will not be blocked. - Roadbeds below grade can interrupt the direct sound path from source to receiver even further, thereby providing greater attenuation by diffraction. Roadbed depressions of 12 ft. or more are usually needed to control highway noise. - Attenuation from thin-wall barrier is more effective where there is greater angle of diffraction. LAND USE PLANNING FOR NOISE CONTROL Zoning - Industrial and commercial areas may act as barriers of noise for the benefit of residential occupancies - Light industry may be completely surrounded by office and research park buildings so that the residential areas are protected from industrial and vehicular traffic noise. Site Planning - Use of concentrated external parking - Use of cuttings - Use of landscape embankments Building Orientation - Orient the buildings such that the building will be shielded from traffic noise. Openings and sensitive areas should be located away from source of noise or near shielded areas. - By angling or staggering the buildings, noise build up from courtyards can be reduced. LECTURE HALLS and CLASSROOMS The most important requirement for lecture halls and classrooms is noise control. - The Optimum Reverberation Time in lecture halls and classrooms is 0.4 to 0.7 seconds. - Lecture halls with volumes of 425-570 cu. m. or an audience of 150-200 persons does not require a Sound Amplification System. - However, non-amplified speech, directly from sound source to receiver is hardly understandable beyond 9-12 meters. - Classrooms with rectangular shapes, level floors, and floor areas normally between 59-93 sq. m. seldom create any acoustical problems, even if rear wall is not treated acoustically. - For such rectangular lecture rooms with a modest capacity, a diagonal seating layout is recommended eliminates parallelism between walls and utilizes splayed front walls as sound reflectors. CHURCHES and SYNAGOGUES - One of the most difficult aspects in the acoustical consideration of churches is RT control. - A long RT is preferred to enhance organ sounds, chorus singing, and even the chanting of words. However, speech intelligibility suffers. - The Chancel and Pulpit, as well as the organ and choir, should be well elevated and surrounded by reflective enclosures. - Churches usually consist of several coupled spaces (e.g., nave, chapel, baptistery, confessionals, etc.). - Coupled spaces must be provided with certain acoustical requirements and need individual reverberation control. MULTI-PURPOSE AUDITORIUMS and COMMUNITY HALLS - The problem with most multi-purpose auditoriums is the unraked or level floor. - Level floors introduce the following: 1. difficulty in providing direct sound 2. flutter echoes between level ceiling and floor 3. lack of absorptive treatment - Community halls and auditoriums found at the basement of large churches offer a lot of acoustical problems, primarily the existence of an excessively long RT (5-8 seconds).