Frequency,Hzsound intensity level,dBwooden boardegg trayclothcardboard

10070646568

20074687073

30080737879

40085808384

50089838585

60093899092

70088848586

80090879088

90095899193

AbstractThis research is about the audibility of sound. There are many factors will affecting the audibility of sound like distance, type of material as a reflector and so on. We will conduct an experiment which is about the effect of the type of materials based on audibility of sound. In the experiment, we will use different type of material such as cloth, cardboard, wooden board and egg tray. We carry out the experiment to identify which material is the most suitable to be used in our school hall. Besides, we will determine which material is the good reflector and good absorber of sound. We will use the noise meter to measure the intensity level of sound.

Introduction2.1 TheorySound is a vibration that propagates as a typically audible mechanical wave of pressure and displacement, through a medium such as solid, water, and air. Sound wave are longitudinal waves propagated in the form of compression and rarefaction in air. During propagation, waves can be reflected, refracted or attenuated by the medium. We always need a public address system (PA system) to amplify sound so that the audiences can listen to every announcement clearly.There are some factors affecting the audibility of sound like distance, frequency, amplitude, type of material as a reflector and so on. Intensity of sound is defined as the energy per second incident on a unit area perpendicular to the direction of sound propagation. The intensity level of sound can be measured by using decibel meter or just by ear. Frequency is the number of cycles per second the sound wave itself produces, and it determines the pitch of the sound we hear. Frequency is measured in hertz.The range of human hearinggoes from 16 to 20,000 Hz, with 16 being the lowest detectable pitch, and 20,000 is the highest. Wavelength is the distance between the start and the end of a sound wave cycle. Amplitude is the perceived loudness of the sound.Reflection of SoundReflection is the change in direction of a wavefront at an interface between two different media so that the wavefront returns into the medium from which it originated. Common examples include the reflection of light, sound and water waves. The law for reflection is the same as that of light, ie., the angle ofincidenceof a sound waveequals the angle of reflection, just as if it were produced by a 'mirror image' of the stimulus on the opposite side of the surface. The sound waves that travel towards the reflecting surface are called the incident sound waves. The sound waves bouncing back from the reflecting surface are called reflected sound waves. For all practical purposes, the point of incidence and the point of reflection are the same point on the reflecting surface.A perpendicular drawn on the point of incidence is called the normal. The angle which the incident sound waves makes with the normal is called the angle of incidence, "i". The angle which the reflected sound waves makes with the normal is called the angle of reflection, "r".

Application of Sound Absorptive Materials:Acoustical material plays a number of roles that are important in acoustic engineering such as the control of room acoustics, industrial noise control, studio acoustics and automotive acoustics. Sound absorptive materials are generally used to counteract the undesirable effects of sound reflection by hard, rigid and interior surfaces and thus help to reduce the reverberant noise levels (Beranek Leo L., 1960; Bruce, 1981). They are used as interior lining for apartments, automotives, aircrafts, ducts, enclosures for noise equipments and insulations for appliances (Knapen and Lanoye, 2003; Youn Eung Lee, Chang Whan Joo, (2004). Sound absorptive materials may also be used to control the response of artistic performance spaces to steady and transient sound sources, thereby affecting the character of the aural environment, the intelligibility of unreinforced speech and the quality of unreinforced musical sound Frank Fahy, (2001). Combining absorptive materials with barriers produces composite products that can be used to lag pipe or provide absorptive curtain assemblies. All noise control problem starts with the spectra of the emitting source. Therefore, sound absorbing materials are chosen in terms of material types and dimension, and also based on the frequency of sound to be controlled Francisco Simon and Jaime Pfretzschner, (2004) Sound AbsorptionSound absorption is the capability of a surface, or building material, to absorb sound instead of reflecting it. Sound waves will continue to bounce around a room for a time after they are created if the majority of surfaces in a roomis reflective. Surfaces that absorb sound better will not allow for reflections to bounce around as much, and will deaden the sound wave more quickly. Many common building materials, such asgypsum board, wood, concrete, brick and tile, are fairly reflective and do not absorb much sound. Softer materials, such ascarpet, foam padding, and fiberglass insulation, are far better at absorbing sound.The use of absorptive materials can be helpful in controlling sound. Fiberglass insulation is very absorptive and can be used where sound control is a concern. Thick carpet with padding is also very absorptive, and acoustical ceiling tilesare designed to absorb rather than reflect sound. Even in cases where these options are not viable, absorptive materials can be added to finished rooms in other ways: furniture with thick cushioning is extremely absorptive, as are thick and heavy curtainsand drapes. Itemssuch asthese can be added or arranged in ways that will allow for greater sound absorption. Acoustical baffles with absorptive materials can be purchased for use in areas where sound is a major concern, and most are designed to be unobtrusive and visually nondescript so as to allow for installation without drastically altering the aesthetics of a room.

2.2 Problem Statement In school hall, there is a public address system(PA system). However, the PA system does not function well all the time. During assembly, there are always some students who cannot listen to all the messages or announcement conveyed by teachers and principals clearly especially those who sit at the back. This always causes some miscommunication. These is the sale reasons that we are carrying out this experiment to improve our PA system so that we can produce good quality sound without interference by reflection.

2.3 ObjectiveThe objective of this experiment is to study how the type of materials will affect the audibility of sound.

3.0 MethodologyThe theme of the project (2014/2015) is given as Sound Wave.The title of the project is To Investigate on How Does The Type of Material Affect the Audibility of Sound.The project is planned from November of 2014.After preparing for all the elements which are required to complete this experiment, the experiment is carried out on .The experiment is started at in the physics laboratory of the school, SMK RAJA PEREMPUAN PERAKand the experiment is completed at .After that, the report about the experiment is written and handed it on

Materials and apparatusone wooden board

one piece of cardboard

one piece of cloth

one egg tray

two pieces of manila card

one speaker

one surface on a car plat

one pendrive (frequency generator)

one noise meter apps

one cellophane tape

one protractor

To investigate on How Does The Type of Material Affect The Audibility of Sound we need to prepare some type of material such as egg tray, wooden board, cloth and cardboard. The apparatus is set up as shown in the figure. Two piece of manila card is placed at an angle of 30 and cellophane tape is used to fixed the position. The angle of incidence and angle of reflection is kept constant. After that, a surface on a car plat is placed in the middle of the manila card. A speaker is placed in one end of the manila card and the other end of the manila card is placed a noise meter. Next, we started the experiment by using the wooden board. We turned on the speaker with constant volume and the sound intensity level is recorded by the noise meter. The steps is repeated by using other materials like egg tray, cardboard and cloth by increasing the frequency of 100Hz, 200Hz, 300Hz, 400Hz, 500Hz, 600Hz, 700Hz, 800Hz and 900Hz.

Observation and Discussion

The graph is shows the relationship between the sound intensity level and the type of material as reflectors with different frquency. The type of material that causes the highest sound intensity level is wooden board. It has the highest reading for every frequency. This implies that wooden board is a good reflector of sound and bad absorber. This is because wooden board has hard surface compare to other material that we had use. Egg tray has the lowest reading on sound intensity level because egg tray is a bad refletor of sound and good absorber. This is because egg tray is a porous sound-absorbent materials will be anything that can transmit sound through themselves and then absorb the sound, converting it into a small amount of friction energy. These can be items such as carpet, heavy draperies and open-cell foams. Any item that will allow air to pass into it and then be absorbed by a cellular structure will make a good sound absorber. Therefore, wooden board and egg tray are not suitable to use as reflector in our school hall. For the cardboard and cloth have approximate same reading on sound intensity level. These material are more suitable to use as reflector at our school hall. This is because the cardboard and cloth have the moderate reading on sound intensity level.

ConclusionBased on the experiment, we know that different type of materials will reflect different sound intensity level. We have chosen cloth as the reflector for our school hall. This is due to its moderate abilities of reflection and absorption .We would like to suggest some changes on this experiment like the experiment should be done in a wider empty quite room without any obstacle to reflect the sound. Besides that, we shold fix the thickness of each material at 1cm. By during those changes, we belive that the reading of sound intensity level will be more accurate for the next experiment. In future, we will carry out the experiment like investigate the relationship between the frequencies of sound with sound intensity level.

References