Acoustics Assignment
Please view the file 'Excel Spreadsheets for Acoustics' which provides spreadsheets required for the Acoustics Assignment. Please also view the file 'Acoustic solutions to Personal Feedback questions'.
General Advice -
Question 1 - Question 1 of the assignment is concerned with calculating the noise levels inside a rooms. This involves repetitive calculations and it is recommended that you use a spreadsheet in order to undertake these calculations. You should also look to incorporate the data from the CDROM in order to help your calculations. However, please not that it is vital that the logic of your technical workings can be easily followed, therefore it should be accompanied by a brief and clear explanation of what you have done.
Question 2 - In Question 2 of this assignment, you will be asked to make use of the general knowledge which you have gained in the Acoustics part of the module to advise on some aspects regarding the acoustics design. You should present your discussion in the form of a short executive report, including diagrams where appropriate. In the context of this assignment, the people who will consider the findings of your report have no other background data and are not experts in environmental design. You will therefore need to write your answer as a carefully structured explanation which leads up to each of the key technical points. Do not forget to acknowledge the source of information provided in the report where appropriate.
Timescale
It is intended that this assignment should take around eight hours to complete. If you have done the spreadsheet examples in the text, the calculations should not take more than four hours. Planning and writing the report (Question 2) should take up to four hours.
The Assignment -
A new crematorium is proposed for the town of Eastmouth on the South Coast of England. A shortage of land has dictated that a site only 45 m from a residential housing estate is to be used. The aim of Question 1 in this assignment is to establish the expected sound pressure levels within the chapel in the crematorium. The aim of Question 2 is to investigate and discuss whether noise from the crematorium will be of concern to residents in the housing estate and to recommend any remedial action if necessary.
Question 1 - Inside the new crematorium, the noise level in the chapel is considered to be a critical factor. Accordingly, the reverberant sound pressure level in the chapel is to be limited to NR35. There are two significant noise sources in the chapel: (i) a ventilation system driven by a mixed flow fan; and (ii) a cremator furnace in an adjacent plant room (called here the "furnace room").
The ventilation system for the chapel is shown in Fig 1 (see end of assignment). In addition to serving the chapel, the ventilation system also serves a waiting room and an office. There are three bends in the system; each bend is a mitre bend that is unlined. Each outlet from the ventilation system terminates in the centre of the ceiling of the room into which it supplies air.
Using the data supplied below
a) Establish the reverberant sound pressure level in the chapel due to the ventilation system acting on its own (i.e. with the furnace installation turned off)
b) Establish the reverberant sound pressure level in the chapel with the ventilation system working and the furnace installation turned on (i.e. you need to account for the noise from the furnace room when estimating a final value for the sound pressure level in the chapel).
c) Establish whether the sound pressure level in the chapel meets the NR35 design requirement. Discuss any issues or problems with the design; is any further action required, if so, what action would you take? Note that you have two (identical) acoustic attenuators at your disposal - these attenuators may be placed within the ducting system to attenuate the sound power emitted by the fan. The characteristics of the attenuator are listed below.
Question 2 - You have been retained by the local authority to prepare a report on any potential noise problems at the Eastmouth Crematorium. In the report you should examine all potential sources of noise problems, as well as discussing any remedial action that may be necessary. You should also discuss any general utility advice suitable for the ventilation installation.
DATA
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Sound power levels
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Octave band centre frequency (Hz):
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125
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250
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500
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1k
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2k
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4k
|
|
SWL of fan (dB):
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94
|
99
|
93
|
85
|
74
|
68
|
|
SWL of furnace (dB):
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86
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86
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88
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90
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68
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58
|
Area of terminal grille A = 0.2500 m2.
Area of terminal grille D = 0.1225 m2.
Area of terminal grille G = 0.1925 m2.
Area of terminal grille J = 0.1600 m2.
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Sound Attenuator
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Octave band centre frequency (Hz):
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125
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250
|
500
|
1k
|
2k
|
4k
|
|
Attenuation delivered (dB)
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12
|
25
|
38
|
39
|
23
|
16
|
You have been given two of these attenuators to use where you wish.
Attachment:- Acoustics Assignment.rar