Lecture 2 Acoustics PDF

Acoustic in indoor space Lecture-02 Topic - Acoustics  LEARNT TILL NOW Lecture 1: 1. What is Wave and its type (mechanical wave and non mechanical wave) 2. What is sound 3. What is acoustics 4. Objectives of the acoustic 5....

Acoustic in indoor space Lecture-02 Topic - Acoustics  LEARNT TILL NOW Lecture 1: 1. What is Wave and its type (mechanical wave and non mechanical wave) 2. What is sound 3. What is acoustics 4. Objectives of the acoustic 5. Behavior of sound speed of sound in different medium Reflection Absorption Refraction Diffusion Diffraction Transmission Interference Wavelength Frequency Loudness Pitch of sound  LEARNT TILL NOW Lecture 2: 1. What is noise and its effect on health 2. Type of noise (Air borne and structure borne noise) 3. Sound isolation Site selection (Location wrt. Other structure) building orientation / overall form on the site Acoustical zoning Vegetation, barrier wall, earth berms (mound) Sound masking room orientation within the building design, detailing, specification Construction inspection  Objective of acoustics Noise Sound Privacy reduction intelligibility  NOISE Proper sealing of window (gaskets) STRUCTURE AIRBORNE BORNE curtains NOISE NOISE OUT DOOR AIR BORNE NOISE TYPE OF NOISE and its TRANSMISSION TYPE OF NOISE and its TRANSMISSION 4 3 1. DIRECT TRANSMISSION 2. NOISE VIA CONDUIT / PIPING 3. NOISE VIA LEAKAGE, CEILING VOID / DUCT WORK 4. NOISE VIA CONCRETE SLAB 5. BACK GROUND NOISE (OUT DOOR OR INDOOR) 4 DESIGN CONSIDERATION 1. Flaking noise via conduit 2. POSITION OF DOOR and voids can be minimize by gestating, filling of insulating material, and false ceiling 3. HVAC DUCTING Acoustical Zoning Acoustical Zoning CREATING BUFFER ZONE Acoustical Zoning CREATING BUFFER ZONE  Objective of acoustics Noise Sound Privacy reduction intelligibility Sound intelligibility In speech communication, intelligibility is a measure of how comprehensible speech is in given conditions. Unintelligible speech: incomprehensible, difficult to understand Sound Intelligibility Depends on: Minimize or vanish Noise reduction the acoustical defects Sound intelligibility Out door noise Indoor noise Occupant control (air borne or structure borne) Minimize or vanish the acoustical defects The presence of acoustical defects can contribute to poor intelligibility and general discomfort in rooms. Minimize or vanish the acoustical defects Followings are the type of acoustical defect; i. Reverberation. ii. Formations of echoes. iii. Sound foci. iv. Dead spots. v. Insufficient loudness. REVERBERATION Reverberation is the persistence of sound in the enclosed space , after the source of sound has stopped. Reverberant sound is the reflected sound , as a result of improper absorption. Reverberation may results in confusion with the sound created next.  It is a desirable property of space to the extent that it helps to overcome the drop-off of sound intensity with distance in the enclosure However, if it is excessive, it makes the sounds run together with loss of speech intelligibility. As per Prof.W.C. Sabins reverberation time ‘t’ is given by formula: 𝑉 t =0.16 𝐴 Where V=volume of room in cubic meters A= total absorbing power of all the surfaces of room/ hall. What is a desirable reverberation time? The optimum reverberation time for an auditorium or room depends upon its intended use. Around 2 seconds is desirable for a medium-sized, general purpose auditorium that is to be used for both speech and music. A classroom should be much shorter, less than a second. a recording studio should minimize reverberation time in most cases for clarity of recording.  Reverberation time should remain within limits as per Indian Standard Code: 2526- 1963. Sr. No. RECOMMENDED TIME IN SECONDS ACOUSTICS 1 0.50 to 1.50 Excellent 2 1.50 to 2.00 Good 3 2.00 to 3.00 Fairly good 4 3.00 to 5.00 Bad 5 Above 5.0 seconds Very bad Formation of ECHO Not all sound that hits matter is absorbed. Some of it is reflected. That means sound bounces off the solid matter the way a tennis ball bounces off a wall. Sound reflected back to its source is an echo. An echo is produced when the reflected sound wave reaches the ear after the original sound from the same source has been already heard. Thus there is repetition of sound. The sensation of sound persists for 1/10th of a second after the source has stopped. This defect can be avoided by selecting proper shape for the hall. Use of splayed side walls instead of parallel walls greatly reduces the problem and enhance the acoustical quality of the hall. Echoes may be avoided by covering the opposite walls and high ceiling with absorptive material.  Difference between Reverberation and ECHO Reverberation is the persistence of sound after On the other hand, an echo occurs when a pulse the sound source has been stopped. It results of sound can be heard twice. It is normally from a large number of reflected waves which assumed that if there is a delay of 50ms or more can be perceived by the brain as a continuous between the first and the second sound reaching sound. the ear, then they will be perceived by the brain as separate events rather than one extended event  Sample sound for reverberation.MP3 “Many Factors Influence Speech Intelligibility” SOUND FOCI Some times shape of the hall makes sound waves to concentrate in some particular areas of hall creating a sound of greater intensity. These spots are called sound foci. This defect can be removed by: Geometrical design shapes of the interior faces. Providing highly absorbent materials on critical areas (curved spaces) DEAD SPOTS This defect is the out come of formation of sound foci. Because of high concentration of reflected sound at sound foci , there is deficiency of related sound at some other points. These spots are known as dead spots where sound intensity is so low that it is insufficient for hearing. This defect can be removed by suitably placing diffusers and reflectors and Right proportions of internal spaces. INSUFFICIENT LOUDNESS This defect is caused due to lack of sound reflecting flat surface near the sound source Excessive sound treatment in the wall This defect can be removed by Providing hard reflecting surface near the source By adjusting the absorption of the hall to get the optimum reverberation time when the length of the wall is more it is advisable to install speaker. Characteristics of Good Acoustical Materials Sound Absorbers Sound Diffusers Noise Barriers Sound Reflectors 1. Sound Absorber To eliminate sound reflections oto improve speech intelligibility oreduce standing waves oprevent comb filtering Typically materials are open cell polyurethane form, cellular melamine, fiberglass, fluffy fabrics and other porous materials. A wide variety of materials can be applied to walls and ceilings defending on your application and environment These material vary in thickness and in shape to achieve different absorption ratings defending on the specific sound requirements. Types of Sound Absorber Acoustical foam panels White Paintable Acoustical Wall Panels Fabric Wrapped Panels Acoustical Wall Coverings Ceiling Tiles Baffles and Banners for ceiling Fiber Glass  Acoustical Foam Panel Material-Melamine Acoustical Foam. Features-Color and patterns provide distinctive appearance. Applications-Open office areas, conference rooms, theaters, cafeterias/restaurants, retail stores, medical facilities, auditoriums, hotels, night clubs, assembly areas and radio dispatch centers. Thickness-2-3/8" - 1-3/8" SIZES: 2' x 2' nominal. Natural White. (Custom colors available, 3,000 square foot minimum Natural echo foam quantity). Installations-Adhesive for direct application to walls and ceilings. Acoustic foam Adhesive polyurethane acoustic foam Wall acoustical foam  White Paintable Panel In addition to reduce echo and reverberation, these acoustical panels are used to create unique design and patterns Quick and easy acoustical solution Soft drywall textures appearance Create unique patterns Panel size allows for flexible mounting options 2’ x 2’ Paintable and printable finish  Fabric wrapped panels Used to reduce echo and reverberation in applications, small and large These panels are manufactured from a rigid high density, glass fiber Wall panels Acoustical board and covered with an acoustically transparent fabric Available as Wall Panels, ceiling tiles, hanging baffles, acoustical clouds and bass traps Sizes are 2”thk,2’ x2’,2’ x 4’.  Ceiling tiles Ceiling tiles absorb noise and block sound transmission. Ceilings tiles may also be ordered as a full 24’*24’inch, unbacked for adhesive mounting directly on walls and ceilings and 2”thk. They are there in five different patterns and a non-pattern look to enable “mixed and match” for own design  Wall coverings Acoustical wall fabric features are Lightweight acoustic fabric, easy to install, available in many colors, durable and improve speech intelligibility Sound channels is resistant to moisture, mildew, rot, bacteria and is non- allergenic Its the perfect acoustic fabric for offices, classrooms, conference centers or any area where speech intelligibility is a critical factor  Baffles and banners Baffles Hang Vertically – Parallel With the Walls Clouds Hang Horizontally – Parallel With the Floor Offer Greater Absorptive Surface Area Can Be Used for “Temporary” Installations Many Various Products & Finishes Things to Consider Best Used in Rooms With High Ceilings Possible Interruption of Fire Suppression Sprinklers Possibly Effecting Lighting by Casting Shadows  2. Sound Diffusers These devices reduce the intensity of sound by scattering it over and expand area, rather than eliminating the sound reflections as an absorber. Quadra Pyramid Diffuser Generates a uniform polar responds over a broad frequency range using a pre-rotated pyramidal pattern to create 16 angles of reflection Pyramidal diffuser This traditionally work disperses sound uniformly over a broad frequency range. A quick solution to reduce flutter echo.  Sound Diffusers Double Duty Diffuser This poly cylindrical diffuser do twice the work. They scatter sound and function as a bass trap Quadratic Diffuser A true quadratic residue diffuser designed for uniform broadband scattering and reducing HIGH-Q reflection  3.Noise barriers These material range from dense materials to block the transmission of airborne sound to devices and compounds used to isolate structures from one another and reduce impact noise Sound barrier materials are used to reduce the transmission of airborne sound Composite materials are used to block and absorb sound for machine enclosures as well as blocking airborne sound and impact noise  4. Sound reflectors They are simply panels of wood that have been carve into a convex shape that will allow them to reflect sound directly into the audience in order to hear whatever is on the stage with even greater clarity. Composed mainly of plywood with some gel to make them even more reflective of sound