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• Level: GCSE
• Subject: Maths
• Word count: 3003

# Acoustics Assignment

Extracts from this document...

Introduction

Acoustics Assignment Assignment Brief To choose a room and analyse the construction materials and subsequent surface areas of that room, and using the given formula, show an understanding in the calculations involved in solving absorption coefficients, reverb times and standing waves of any given space. Introducing Acoustics Before any formula can be applied, or calculations analysed, a firm understanding must be grasped of the main components involved in this assignment, namely: Standing waves Nodes / Anti-nodes Fundamental frequency Reverberation time Absorption Absorption coefficients Frequency Wallace Sabine Let us consider each heading Standing Waves The modes of vibration associated with resonance in extended objects like strings and air columns have characteristic patterns called standing waves. These standing wave modes arise from the combination of reflection and interference such that the reflected waves interfere constructively with the incident waves. An important part of the condition for this constructive interference is the fact that the waves change phase upon reflection from a fixed end. Because the observed wave pattern is characterised by points, which appear to be standing still, the pattern is often called a 'standing wave pattern.' Nodes / Anti-nodes One characteristic of every standing wave pattern is that there are points along the medium, which appear to be standing still. These points, sometimes described as points of no displacement, are referred to as nodes. There are other points along the medium, which undergo vibrations between a large positive and a large negative displacement. These are the points which undergo the maximum displacement during each vibrational cycle of the standing wave. ...read more.

Middle

0.7 0.8 0.6 0.4 Acoustic tile, suspended 0.5 0.7 0.6 0.7 0.7 0.5 Brick 0.03 0.03 0.03 0.04 0.05 0.07 Brick and plaster 0.41 0.45 0.48 0.56 0.58 0.60 Carpet, 3mm pile height 0.05 0.05 0.1 0.2 0.3 0.4 Chair, small fabric 1.5 3.5 4 4.5 4.75 4.5 Concrete block, painted 0.1 0.05 0.06 0.07 0.1 0.1 Concrete block, unpainted 0.4 0.4 0.3 0.3 0.4 0.3 Concrete, poured 0.01 0.01 0.02 0.02 0.02 0.03 Door, wooden 0.17 0.21 0.26 0.29 0.31 0.34 Draperies, medium velour 0.07 0.3 0.5 0.7 0.7 0.6 Glass 4mm 0.20 0.22 0.28 0.34 0.34 0.29 Gypsum wallboard, 1/2" on studs 0.3 0.1 0.05 0.04 0.07 0.1 Heavy carpet on concrete 0.02 0.06 0.15 0.4 0.6 0.6 Heavy carpet on felt backing 0.1 0.3 0.4 0.5 0.6 0.7 Heavy plate glass 0.2 0.06 0.04 0.03 0.02 0.02 Ordinary plaster, on lath 0.2 0.15 0.1 0.05 0.04 0.05 Ordinary window glass 0.3 0.2 0.2 0.1 0.07 0.04 Platform floor, wooden 0.4 0.3 0.2 0.2 0.15 0.1 Plywood sheet, 1/4" on studs 0.6 0.3 0.1 0.1 0.1 0.1 Person, adult 2.5 3.5 4.2 4.6 5 5 Recliner, leather 3 3.75 3.5 3 2.5 2 Stud wall 0.25 0.32 0.34 0.47 0.39 0.50 Timber floor 0.18 0.25 0.37 0.39 0.45 0.45 Upholstered seating, unoccupied 0.2 0.4 0.6 0.7 0.6 0.6 Upholstered seating, occupied 0.4 0.6 0.8 0.9 0.9 0.9 Vinyl tile on concrete 0.02 0.03 0.03 0.03 0.03 0.02 Wooden seating, unoccupied 0.02 0.03 0.03 0.06 0.06 0.05 Wooden pews, occupied 0.4 0.4 0.7 0.7 0.8 0.7 The Spare Room 2.74 cm 2.70 cm 3.07 cm 1.91 cm Door 1.72 cm Window .81 cm .79 cm Consider a room with floor (and ceiling) ...read more.

Conclusion

= 0.177944381 Tr = 0.17 seconds Analysis of results After carefully analysing the room's absorption coefficients and reverb times, the conclusion was that the room, due to the absorbing properties of the walls, ceiling and floor, suffered from a reduced reverberation time. This causes the sound within the room to appear dull, flat and without much bass. Corrective procedures To enhance the deficient bass, and add a warmer, richer element to the sound of the room, thick velvet curtains could be added to the windows. This would absorb the higher frequencies and reflect the lower end of the scale. The timber floor could be covered with a luxuriously deep pile carpet, again this would soak up the higher frequencies and reflect the lower ones. Acoustic wall coverings, designed for use on most vertical surfaces, could also be considered. These products are predominantly made of man-made polyester and olefin fibres, and are tested for a special sound attenuation rating known as a Noise Reduction Coefficient (NCR) rating. This rating indicates the amount of sound absorbed into the wall. The higher the number, the more noise absorption at the specified frequency; in this case, we would be looking to absorb the high end and reflect the bass. The ceiling could be covered with acoustically reflective tiles, specially designed to reflect a particular frequency whilst absorbing unwanted ones. Furniture also plays an important part in the room's overall acoustics. Bearing in mind the sound field will not be perfectly diffused; it would be advantageous to uniformly place seating, rather than placing items randomly throughout the room. ?? ?? ?? ?? 11 2 Lee Foster Lee Foster ...read more.

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