Architectural Acoustics Lesson 2 PDF

Architectural acoustics sounds ACOUSTICS “A Science that deals with the product, control, transmission, reception, and effect of sound” Sound is reflected, transmitted, or absorbed by the materials it encounters Soft surfaces, such as textiles, and batt insulation, tend to absorb sound waves, preven...

Architectural acoustics sounds ACOUSTICS “A Science that deals with the product, control, transmission, reception, and effect of sound” 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 gypsum board, ceramic tiles or wood, tend to reflect sound waves, causing “echo”. Reverberation is the term used to describe sound waves that are reflected off of surfaces ACOUSTIC: SOUND Sound is a Mechanical wave and therefore requires a medium in which can travel Acoustics is classically divided into sound and vibration Sound refers to waveforms travelling 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 fluidIt is not heard as much as felt, due to its extremely low frequency, which is below the range of most human being SOUND ABSORPTON COEFFICIENT α The sound absorption coefficient describes the property of the material to convert incident sound into other forms of energy ex. Thermal to kinetic energy- and thus to absorb it The sound absorption coefficient of a material indicates the amount of absorbed portion of the total incident sound. if α= 0 means that no absorption occurs; the entire incident sound is reflected. If α= 0.5, 50% of the sound energy is absorbed and 50% is reflected. If α= 1, the entire incident sound is absorbed, there is no longer any reflection ABSORPTION COEFFICIENT The sound absorption coefficient of a material is α= (1-r), where r, the sound energy reflection coefficient, is the ratio of sound energy reflected from the surface of the material to that incident upon it What is frequency in sound Frequency is the speed of the vibration, and this determines the pitch of the sound.... Frequency is measured as the number of wave cycles that occur in one second. The unit of frequency measurement is Hertz (Hz for short). A frequency of 1 Hz means one wave cycle per second. RESONANCE ABSORBER Resonance absorber: This term comprises all types of absorbers using a resonance mechanism such as an enclosed air volume or a vibrating surface. Resonance absorbers are mainly suitable for absorbing sound of medium to low frequencies REVERBERATION TIME The reverberation time is the basis for ratings of room acoustic quality The following table provides an overview of the typical reverberation times of different room types REVERBERATION TIME The reverberation time depends mainly on three factors: 1. The volume of the room 2. 3. The surface of the room The furniture in the room A room usually becomes more reverberant with increasing height. Absorbing surfaces- such as carpets, curtains and sound absorbing ceilings, but also furniture or people present in the room- reduce the reverberation time REVERBERATION TIME The reverberation time of a room can be derived from the calculated total equivalent sound absorption area using the Sabine formula T= 0.163 x V/A Where: T= Reverberation time V= Volume of the room A= Total equivalent sound absorption area noise Every day we encounter sounds that annoys us, that interfere with our hearing and communication, or that may be hazardous to our health. Any such unwanted sounds are called noise. This can be observed in private as well as in working environments A- weighted decibels, abbreviated dBA is an expression of the relative loudness of sounds in air as perceived by the human ear. TYPES OF NOISE  Continuous Noise – if the magnitude of the noise does not vary over time  Intermittent Noise – if the noise stops and starts at intervals  Impulsive Noise – if the noise is large in magnitude but short in duration  Varying Noise – is the magnitude of the noise changes over time NOISE CONTROL To approach the solution to any specific noise problem, we need to: 1. Understand the basic physics of acoustics and how noise- unwanted soundis produced, how it propagates, and how it is controlled. 2. Learn the basics of noise control, and how to approach the problem from the three standpoints: the source of noise, the path it travels and the point of reception. 3. Become familiar with, and discover how to apply in both new and remodeling construction, the acoustical products and system that control noise- products that contribute to the creation of acoustically comfortable, productive and healthful environment THREE WAYS TO CONTROL NOISE There are only three basic ways to attenuate or reduce sound, whether at the source, at the listener’s location, or along the path it travels from the source to the receiver. 1. Replace the sound source with a quitter one 2. Block the sound with a solid heavy materials that resists the transmission of sound waves 3. Absorb the sound with a light porous materials that soaks up sound waves CONTROLLING NOISE ALONG ITS PATH Reflected sound may be reduced by placing sound absorbing materials on surfaces from which sound will be reflected CONTROLLING NOISE AT THE RECEIVER If source control is not practical, another approach would be to treat the problem at the receiver “Temporary” sound control: Direct ear protection (earplugs or earmuffs) is often used to protect workers’ hearing when source and path noise control are not practical or possible