Bss Assignment.docx

Discussion: 1) Sound can either diffracted, reflected, absorbed and transmitted. Explain the difference between these 4 sound paths. Diffraction of sound is one of those less-obvious wave behaviors that play a big role in our perception of waves. Diffraction describes the change in a wave's direction as it travels between or around barriers. It's similar to reflection and refraction in that it involves a change in the direction of waves when they encounter a change in medium. Diffraction is different. In diffraction, waves actually bend around objects that they encounter in their path or bend through openings in between two barriers. You may have seen diffraction occur when water waves travel through a gap in a wall or a jetty. Reflection of sound is the angle of incidence does prove equal to the angle of reflection. In addition, sound rebounds from the surface of either solid or liquid similar to a billiard ball. For successfully experiencing the reflection of sound, it is important that the surface should be polished or rough, and that too of a considerably large size. Reflection involves a change in direction of waves when they bounce off a barrier. The definition of sound absorption is property possessed by materials and objects of converting sound energy to heat either by propagation in a medium or when sound strikes the boundary between two media. Sound energy can be absorbed by ‘acoustically soft’ materials that sound waves encounter, as opposed to being reflected by ‘acoustically hard’ materials. A sound wave is an organized vibration which passes energy from particle to particle through any molecular structure. The energy bouncing off of your home and remaining outside is sound reflection, while the energy traveling through the structure and into your home demonstrates is called sound transmission. In conclusion, the difference between theses 4 sound paths is diffraction of sound changes in a wave's direction as it travels between or around barriers. Reflection of sound is a change in direction of waves when they bounce off a barrier. Sound absorption is the sound energy converts to heat energy by propagates through a medium or strikes the boundary between two media. Sound transmission is sound waves are created by a disturbance that then propagates through a medium.

2) What is transmission coefficient, T? What is sound reduction index, R or SRI? How are they related? Sound transmission can be measured using a metric known as the Sound Transmission Coefficient (STC). The transmission coefficient is used in physics and electrical engineering when wave propagation in a medium containing discontinuities is considered. A transmission coefficient describes the amplitude, intensity, or total power of a transmitted wave relative to an incident wave. The sound reduction index (SRI) is a measure of reduction in the intensity of sound when it passes through part of a building, in other words, the level of sound insulation provided. It is the difference between the sound intensity that hits one side of an object such as a wall, door, window, partition, and so on. The sound intensity measured on the other side, expressed in decibels (dB). The sound reduction index is in turn defined in terms of the transmission coefficient. It equals to 10 times the common logarithm of the reciprocal of the sound transmission coefficient of the surface. The sound reduction index of an element is measured in a laboratory by placing the element in an opening between two adjacent reverberant rooms.

3) Three principles for good sound insulation are heaviness, completeness and isolation. Give ONE (1) example for each of these principles that are applied in building construction. Heaviness Massive, heavyweight barriers will block more sound energy than lightweight barriers. (Less noise will go through it.) This is because the high density of heavyweight materials suppresses sound vibrations inside the material, to a degree that the inside wall of a room, vibrates with less movement. Therefore, the amplitude of the sound waves re-radiated into the air inside the room, so the loudness will minimized. For example, the average sound reduction of a brick wall increases from 45 dB to 50 dB when the thickness is increased from 4 inch to 8.4 inch. This doubling of mass does not have to be achieved by a doubling of thickness, as the mass of a wall for sound insulation purposes is specified by its surface density measured in lbs per square foot (rather than per cubic foot). Similar sound reduction can be achieved by adding thinner, but heavier materials Completeness Areas of reduced insulation or small gaps in the construction of a wall have a far greater effect on overall insulation than you might think. The effective soundproofing of a structure depends on air-tightness and uniformity For example, if a brick wall contains a hole or crack which in size represents only 0.1 per cent of the total area of the wall, the average sound reduction of that wall is reduced from 50 dB to 30 dB by about 40% (!). Isolation Sound transfers through any medium air, structural elements of buildings such as floors, walls. As the sound converts to different wave motions at the junction of different materials, energy is lost and an incremental amount of insulation is gained. This is the principle behind the effectiveness of air cavities in windows, of floating floors, of carpets and of resilient mountings for vibrating machines. Sound isolation can be easily ruined by strong flanking transmissions through rigid links, even by a single nail. For example, Cavity constructions must be sufficiently wide for the air to be flexible, otherwise resonance and coincidence effects can cause the insulation to be reduced at certain frequencies. In small air gaps in conjunction with rigid walls air gaps couples with the walls and separation effect gets lost.

4) From the 3 building material (plywood, cement board and gypsum board). Which offers the best sound insulation? Why? Based on the result that we measured, in 3 of the building material (plywood, cement board and gypsum board) the best sound insulation is cement board because the heaviness will affect the sound insulation. Heavyweight structures with high mass transmit less sound energy than lightweight structures. Heavyweight barriers will block more sound energy than lightweight barriers. Cement board is the heaviest between the 3 building material.

References: (3 behavior of sound waves, Date Viewed:5 November 2018) https://www.physicsclassroom.com/class/sound/Lesson-3/Reflection,-Refraction,-andDiffraction (Reflection of Sound Waves, Date Viewed:5 November 2018) https://www.toppr.com/guides/physics/waves/reflection-of-sound-waves/ (Sound absorption, Date Viewed:5 November 2018) http://www.acoustic-glossary.co.uk/sound-absorption.htm (Sound Wave Transmission Through Surfaces, Date Viewed:5 November 2018) https://www.streetdirectory.com/travel_guide/119163/science/sound_wave_transmission_thr ough_surfaces.html (Sound reduction index (SRI), Date Viewed:5 November 2018) https://www.designingbuildings.co.uk/wiki/Sound_reduction_index_(SRI) (Principles of Soundproofing, Date Viewed:5 November 2018) https://www.vocalboothtogo.com/soundproofing-6/ (SOUND INSULATION, Date Viewed:5 November 2018) http://www.ode.com.tr/sound-insulation/ (Diffraction: Relation to Sound & Light and Effects of Wavelength, Date Viewed:5 November 2018) https://study.com/academy/lesson/diffraction-relation-to-sound-light-and-effects-onwavelength.html

Name: Clarence Koay Introduction: A sound wave is the pattern of disturbance caused by the movement of energy traveling through a medium (such as air, water, or any other liquid or solid matter) as it propagates away from the source of the sound. The source is some object that causes a vibration, such as a ringing telephone, or a person's vocal chords. A vibrating object compresses the surrounding air molecules (squeezing them closer together) and then rarefies them (pulling them farther apart). Although the fluctuations in air pressure travel outward from the object, the air molecules themselves stay in the same average position. As sound travels, it reflects off objects in its path, creating further disturbances in the surrounding air. When these changes in air pressure vibrate your eardrum, nerve signals are sent to your brain and are interpreted as sound. The waves are classified mainly two types that are longitudinal wave and transverse waves. The sound waves are good example of longitudinal wave which is travelled medium with the use of force. This force is exerted between molecules of the medium. The electromagnetic radiations are transverse waves which also include the light waves. These waves show displacement in the perpendicular direction of the field intensity vector. The quantum theory gives the description of wave properties which includes wave intensity, wave number, wave frequency, energy of wave, wavelength etc. the motion of wave and its full study is physical phenomena. Let’s discuss wave properties and some examples of waves.

Diagram 1 (Waveform,5 November 2018)

Plywood Board A structural material consisting of sheets of wood glued or cemented together with the grains of adjacent layers arranged at right angles or at a wide angle. When layers like this

are put together it produces a very sturdy and durable wood. It is important the type of glue used to put the layers together, when a professional adhesive is used the plywood becomes resist to cracks, shrinking, twists and warps, making it a better wood than many other plain woods on the market. Plywood has been used in building many homes and commercial constructions and is often used for walls, ceilings and more.

Cement Board Cement board is a building material made of a mixture of glass fibres and cement, usually formed into 4 by 8 foot sheets, 1/4 or 1/2 inch thick. It is typically used as a backing for tiled walls and floors, or on the exterior of buildings. If used on building exteriors, cement board may either be stuccoed, or simply painted as the final exterior surface. Cement board is rigid and very strong and can be cut to desired sizes, because it is cement-based the cutting tools and saws need to be carbide-tipped. Unlike sheet rock or paper-backed gypsum board, when attached to studs, floors or exterior walls cement board forms a strong, impact-resistant surface, strengthening the structure it is attached to. Gypsum Board Gypsum board, also known as drywall or wallboard, is a type of sheathing used for interior walls and ceilings. Since the mid-1940s, it has been the primary wall construction in most houses. Vertical wooden pieces frame a room providing support for the sheets of wallboard. These sheets are connected to the framing by either screws or nails, and seamed together using a special drywall compound, which leaves an even and flat surface. The result is a wall that is smooth and easy to finish.

References: (Diagram 1, Waveform, Date viewed: 5 November 2018) http://www.planetoftunes.com/sound-audio-theory/sound-waveformdiagrams.html#.W-j-tpMzZPY (Sound waves, Date viewed: 5 November 2018) https://physics.tutorvista.com/waves.html (Plywood, Date viewed: 5 November 2018) https://www.merriam-webster.com/dictionary/plywood (Cement Board, Date viewed: 5 November 2018) https://www.wisegeek.com/what-is-a-cement-board.htm (Gypsum Board, Date viewed: 5 November 2018) https://www.wisegeek.com/what-is-gypsum-board.htm