ACOUSTICS: branch of physics concerned with sound. 1. SOUND SOURCE – generation of sound 2. TRANSMISSION PATH – airborne, structure borne, waterborne 3. RECEIVER (RECEIPIENT) – accepts the sound whether wanted or unwanted What is the difference between sound and noise? Sound is what we hear. 1. WANTED SOUND – Speech, Music 2. UNWANTED SOUND – Noise (objectionable or not desired) ARCHITECTURAL ACOUSTICS Effect of building design on sound control in buildings Principles of acoustics to create a satisfactory acoustical environment Types of sound control for Architectural Acoustics 1. Acoustical environment in a room: positioning sound sources to the listeners, and arranging appropriate absorptivity or reflectivity levels for all interior surfaces 2. Isolation of unwanted sounds: insulating building occupants from intrusive noise Three aspects of acoustical design of buildings 1. Planning to keep noise sources as far as possible from quiet areas 2. Internal acoustics of rooms 3. Structural precautions to reduce noise penetration Three degrees of acoustic treatment 1. Site (landscape as sound barrier) 2. Architectural Elements (building materials, furniture, furnishings) 3. Acoustic Materials (specifically rooms needing special acoustic treatments) SOUND WAVE: Longitudinal pressure wave in air or an elastic medium especially one producing an audible sensation 1. Sound wave 2. Increased volume sound wave 3. Increased frequency sound wave PITCH and FREQUENCY Frequency is the number of times per second that a vibrating body completes one cycle of motion Unit for frequency is hertz (Hz = 1 cycle per second) Low pitched or bass sounds have low frequencies High-pitched or treble sounds have high frequencies Normal person can hear frequencies from roughly 20 to 20,000 Hz Human speech is mainly in the range 300 to 3,000 Hz DECIBEL (dB) - a logarithmic scale applicable to any parameter. SOUND PRESSURE LEVEL (Lp) Sound pressure converted to the decibel scale SOUND PRESSURE The amount of air pressure fluctuation a noise source creates. We "hear" or perceive sound pressure as loudness. Sound pressure is usually expressed in units called pascals (Pa) SOUND POWER The sound energy transferred per second from the noise source to the air Power is expressed in units called watts (W) Like sound pressure, sound power (in W) is usually expressed as sound power levels in dB. SOUND POWER LEVEL Sound power level, Lw, the total sound energy radiated per second. LOUDNESS The human impression of the strength of a sound How is vibration isolated and controlled? to reduce the problem to a single mass supported by a spring and a damper REVERBERATION Prolongation of the sound in the room caused by continued multiple reflections REFLECTION and ABSORPTION REFLECTION, DIFFUSION, AND DIFFRACTION REFLECTION – the repetition of a sound resulting from reflection of the sound waves Concave Reflector Concave sound-reflecting surfaces (barrel-vaulted ceilings in churches and curved rear walls in auditoriums) focus sound, causing hot spots and echoes in the audience seating area Flat Reflector Flat, hard-surfaced building elements (large enough and oriented properly) effectively distribute reflected sound. The reflector is tilted slightly to project sound energy toward the rear of an auditorium. Convex Reflector Large convex, hard-surfaced building elements are the most effective sound-distributing forms. The reflected sound energy from convex surfaces diverges, enhances diffusion, desirable for music. Reflected sound from convex surfaces is more evenly distributed across a wide range of frequencies. Flat Ceiling Hard, sound-reflecting flat ceiling provides useful sound reflections covering the entire seating area in a lecture room Sloped Ceiling For concert halls: long reverberation, high ceilings, sound-reflecting walls are preferred; ceilings that are diffusing can improve audibility of lateral sound by diminishing the strength of ceiling reflections ECHOES The distinct repetition of the original sound and is sufficiently loud to be clearly heard above the general reverberation and background noise in a space. FLUTTER ECHO Repetitive inter-reflection of sound energy between opposing parallel or concave sound-reflecting surfaces heard as a highfrequency ringing or buzzing To prevent flutter echo, avoid parallel surfaces, provide deep sound-absorbing treatment, or break up smooth surfaces with splayed or ‘scalloped” elements. DIFFUSION – Scattering or random redistribution of a sound wave from a surface; occurs when the surface depths of hardsurfaced materials are comparable to the wavelengths of the sound. DIFFRACTION – Bending or “flowing” of a sound wave around an object or through an opening Noise reduction coefficient (NRC) a single-number index for rating how absorptive a particular material is. Sound Transmission Loss (TL); A door’s ability to reduce noise is called its sound transmission loss (TL) effectiveness. TL is a value given in decibels, which is determined by measuring sound pressure levels at a certain frequency in the source and receiving rooms. Sound Absorption Coefficient (SAC) The fraction of the randomly incident sound power which is absorbed, or otherwise not reflected. Sound Transmission Class (STC) is a single-number rating of a material’s or assembly’s barrier effect. What is the difference between insulation & absorption? Sound insulation is required in order to eliminate the sound path from a source to a receiver such as between apartments in a building, or to reduce unwanted external noise inside a concert hall. Sound absorption occurs when some or all of the incident sound energy is either converted into heat or passes through the absorber.
