Micky Yang9/3/15

Department of Mechanical Engineering

Practical Work Report

Marshall Day Acoustics84 Symonds Street, Grafton

Dates Worked: 1/12/14 – 26/02/15

Summary

Marshall Day Acoustics is a consultancy firm that provides advice concerning noise and vibration for various types of activities. The company is fairly small when compared to other big consultancy firms such as Beca, and many of the staff are spread around the world. I have performed many different tasks on different projects. These include data analysis, noise and vibration measurements, and maintenance of databases. My knowledge of acoustics was reinforced and I have learnt how a consultancy firm operates and this experience has been vital for my professional growth.

Acknowledgements

I would like to thank Professor George Dodd of the University of Auckland who made me aware of an internship position at Marshall Day Acoustics. I would also like to thank Keith Ballagh of Marshall Day Acoustics for extending me the opportunity to work at the consultancy firm, and everyone else at the firm for being friendly and welcoming.

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Table of Contents

Summary......................................................................................................................................................... i

Acknowledgements......................................................................................................................................... i

Introduction....................................................................................................................................................1

Company Overview........................................................................................................................................2

Other Services............................................................................................................................................2

Staff Structure............................................................................................................................................3

Equipment..................................................................................................................................................4

Work Undertaken...........................................................................................................................................5

Comments on the Experience........................................................................................................................8

Conclusions....................................................................................................................................................9

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Introduction

Marshall Day Acoustics (MDA) is a leading New Zealand firm of acoustic consultants. Founded in 1981, MDA has worked with architects, lawyers, engineers, local authorities, planners, and developers to deliver a high standard of environmental and architectural acoustical consulting. MDA works from the early stages of the design process with different groups of professionals to produce a solution that meets the client’s requirements while maintaining a cost effective solution.

Acoustics encompass all that involve a transmission of energy through a medium using waves as the mode of transport. This means that projects range from the sound design of a performing arts centre to structural dynamics and vibration analysis of buildings. MDA has worked on a wide variety of projects both nationally and internationally in many countries such as the USA, Australia, China, Malaysia, China, Hong Kong, and the Middle East. For example, a recent project that MDA has consulted on is the Philharmonie De Paris in France (figure 1). This concert hall is a 2,400 seat multi-purpose concert hall which opened in January, 2015 with wide acclaim from critics. MDA worked alongside a 2008 Pritzker Prize winner, Jean Nouvel, a French Architect, to design the space.

Figure 1: Philharmonie De Paris (source: http://marshallday.com/project/philharmonie-de-paris-france)

MDA has also consulted on the acoustics design of the lecture theatres of the University of Auckland Business School (figure 2). A range of key skills were required for this project; designing the room acoustics so that the sound within the room was conducive to learning, sound insulation so that no unwanted noise filters into the room or out of it, and mechanical services selection (HVAC, hydraulics, lifts and electrical) so that any noise or vibration does not negatively impact on a lecture.

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Figure 2: University of Auckland Buisness School (soruce: http://marshallday.com/project/university-of-auckland-business-school-complex-auckland-new-zealand)

Company OverviewOther Services

Besides consulting services, MDA has also developed a wide range of software that aids in the design process. These have been distributed to acoustics professionals around the world for their use. Below is a list and a brief description of the software that MDA has on offer.

dBSea – A powerful tool used for the prediction of underwater noise in a wide variety of settings. IRIS – A powerful, user friendly, and simple to understand system used in room acoustics

measurements. The program works in conjunction with a kit assembled by MDA to capture and analyse room impulse responses in 3-dimensions.

Insul – A tool used to predict the sound insulation of floors, walls, ceilings, and windows. Zorba – A tool used to predict the absorption performance of porous walls with a perforated

façade. SoundPLAN – A modelling software that offers a full visual spectrum of noise and air pollution for

evaluation.

These programs are continually updated to provide the best and most accurate predictions possible to ensure that any acoustician has the best tools available to use in the design stage.

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Staff Structure

MDA has staff in many different countries including New Zealand, Australia, France, the UK and Ireland, China, and Hong Kong. There is approximately 100 staff spread across these countries. The staff structure can be seen in the chart below.

As a relatively small consultancy firm, it is important to foster inter-office relationships and this is done by a company-wide conference session that is held over four days. All the consultants across the country come together and meet to have a discussion on issues related to acoustics from their own experiences on projects and ways in which MDA can improve its business. Also this is the time for everyone to get to know each other in a more informal and social setting. The most recent conference was the beginning of

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MARSHALL DAY ACOUSTICS Board of Directors

Principal

Directors (Keith Ballagh)

Associates

Senior Consultants

Consultants

Intern

this year which was held in Australia. Besides these inter-office conferences, MDA also attends other internationally held acoustic conferences.

Equipment

MDA has a variety of specialist equipment required to conduct vibration and noise measurements. For noise measurement, there are sound level meters called the Type 2250 (figure 3) or Type 2260 designed by Brüel & Kjær. These are used in conjunction with tripods. Each sound level meter also has their own calibration device which is used before each measurement to check that the sound level meter is in good working condition. MDA also has two large speakers, and a specialised tapping machine, used to simulate impact noise, for other noise measurement requirements.

For vibration MDA has three Instantel Minimate (figure 4). A minimate consists of a recording device and a measurement device called a geophone. These geophones are capable of measuring in the three axes, longitudinal, vertical, and transverse.

These pieces of equipment are calibrated frequently to ensure that any readings are accurate. If calibration was not undertaken then any report written using those readings is invalid. Each type of equipment also has a program that is required to download the data off of the monitor. For the 2260, there is a program called Evaluator for environmental noise measurements, and Qualifier for room acoustics. The 2250 uses Measurement Partner Suite - BZ-5503, which is more modern and sophisticated than the two used for the 2260. For vibration, Instantel Blastware is the program used alongside the minimate. The capabilities of this program depends on what features are purchased. To unlock more powerful analytical tools, a dongle is required to be purchased and plugged into the USB port of a computer. There are also various other items such as sandbags (for vibration), binoculars, wind meters, tape measures, range finders, and other smaller items. MDA also has licences to programs such as Matlab, Labview, Google Earth Pro, and AutoCAD.

MDA utilises an intranet system called HAL. It is a database of conference papers, standards, and other useful information. It also serves as a forum for internal matters such as company-wide announcements related to the staff, new procedures, new tools, an idea on how to improve MDA and other news related to acoustics. This database is easily accessed by anyone within MDA across the world.

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Figure 3: Type 2250 sound level meter (source: http://www.bksv.com/Products/handheld-instruments/sound-level-meters/sound-level-meters/type-2250.aspx)

Figure 4: Instantel Minimate (source: http://www.instantel.com/products/MinimatePlus.aspx)

Work Undertaken

At MDA I performed many different tasks for a number of different projects. A majority of the tasks was to perform a noise or vibration survey. A noise or vibration survey consists of taking 15 minutes of continuous measurements. For each noise measurement, I had to fill out a survey sheet detailing the initial and final calibration level of the sound level meter, the date and time of measurement, any significant details about the terrain/environment, and the levels measured by the sound level meter while noting any significant noise events. I also took pictures of each measurement site to corroborate my survey sheet. For vibration, there was no specific survey sheet; however I did take a pad to note down any significant vibration events (these were usually caused by commercial heavy vehicle).

For a noise measurement, I did traffic noise measurement to monitor the ambient levels or the levels that the façade of a building will see. This allows proper design of the façade to achieve a desired noise reduction level using appropriate insulation materials, framing solutions, and wall panelling. The sound level meter was mounted on a tripod which was set at 1.2m at microphone height which is required by the standards. For the ambient noise level monitoring, there were times when I had to measure in a crowded area such as Queen Street. This means that inevitably, any noise from conversation was captured. However, the traffic low, which is of low frequency, is expected to be dominant over the 15 minute period so the conversation noise is generally not much of a concern. In most cases, the conversation was not loud, or significant enough to cause large measurements of noise. There were times, however, when I had to pause my measurements because there would be people who are talking too loudly or too close to the microphone. This was done so that the higher frequency of conversation noise would not affect the over 15 minute average too much. The sound level meter was capable of displaying the noise spectrum, instantaneous sound level, and a waveform in real time. There are also numerical values which are calculated instantaneously as the measurement is going on. These are Leq (equivalent level – the logarithmic average of all the measured levels), L10 (the level that is exceeded 10 percent of the time), L95 (the level that is exceeded 95 percent of the time), and Lmax (maximum measured level). These levels are usually weighted according to how the human ear perceives loudness over the frequency range. This weighting is called A weighting and is usually applied to the equivalent level so that the Leq becomes the LAeq.

Another type of noise measurement that I help conduct was testing room acoustics. This involved taking the ambient level, a reverberation time test, and an impact noise test. One site that I went to was a construction site where some new housing had just been finished. To test for compliance, the tests described above was done. An impact test uses a tapping machine, seen in figure 5, which consists of a number of known masses driven to hit the floor by a cam system. This is placed at 45 degree angles to walls. This is done to avoid placement along cross beams under the floor, otherwise the impact would be absorbed and the noise transmitted less and not representative. The tapping machine was placed on the floor above while the measurement was taken directly below. The tapping machine was placed in three different places to give an average. There are guidelines set out in the standards which specify acceptable levels of impact noise and if these criteria are not met then mitigation measures are needed. Usually this is done by adding further insulation material or thicker carpet.

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Figure 5: Tapping machine (source: http://www.acoustiblok.com/acoustical-testing.html)

Reverberation is the amount of late incoming sound (after the initial direct sound from the source) that you hear. If it is sufficiently late then it is classed as an echo. The reverberation time is the time taken for the sound with in a room to drop by 60 dB. To conduct this test, a loud speaker is placed near an edged of a wall and pointed at the upper corner. The speaker is usually turned up to around 100dB and pink noise (all the frequencies are present with each band having the same energy) is played through it. The speaker is played for a few seconds to let the noise build up then is switched off. The measurement begins as the speakers starts and finishes around 5 seconds after the speaker is turned off. Three measurements are taken within the room at different locations to get an average.

The ambient noise test measures the sound within the room to see if proper insulation is installed. A certain sound level is specified within the standards and must be met for compliance. This is also done to ensure that traffic noise is properly insulated from entering the room.

There was one instance during a reverberation time measurement within a classroom where a sound level meter was not used to measure the noise level. The sound within the room was recorded using a sound recorder. I then had to download the wav files off the recorder and play it back through the computer to have it analysed within the sound level meter. To do this, there was a special adapter that had to be placed into the preamp (the top section between the microphone and body of the sound level meter) and attached by a special cable to another adapter plugged into the sound output port of the computer. The purpose of this is so that the sound level could be measured from the wave file. There was 13 files of measurements, and after each was played back this was processed within Qualifier. Within the program I was able to see how the level of the sound changed as the speaker was turned off and this was used to determine the reverberation time. The slope of the decay of sound level was used and the reverberation times was reported to the consultant in charge of the project.

For vibration, I took various measurements near buildings or to measure the effects of surface unevenness on vibration, while noting down any significant cause of vibration such as buses and trucks. The geophone has an arrow which points in the direction of the longitudinal measurement and I aligned this perpendicular to a building wall. If I was measuring the surface unevenness then the arrow was pointed in the direction of the defect. The standards require a 12 kg sandbag to be placed on top of the geophone to ensure good coupling with the ground. The minimate is capable of manual or automatic recording and the measurements can be recorded as a histogram (with the value as the highest measured) or a waveform. I conducted all my measurements as a waveform. The building measurements were measured in a 15 minute period while the effects of the surface unevenness was manual recorded each time a heavy vehicle, such as a truck, travelled past.

From this data, I analysed the building measurements while the surface unevenness data was processed and stored in an Excel spread sheet for future reference. The values of interest in the latter was the peak particle velocity (ppv) and will be used later to derive a regression curve. Measurements for the building were a part of a project. From my analysis of the building vibration data in Blastware, I determined the ppv and calculated the average ppv over the 15 minute period using 3 minute windows. That is to say that, I calculated the peak ppv in each 3 minute window within the 15 minute period, then averaged these peak ppv’s. These were used to determine a range, maximum and minimum values for comparison within the report.

For the same project above, I also had to interpret design drawings drawn by Beca which showed the plan view of Auckland city. It had markings on it which I used to determine how many buildings would be within 5m or 10m of the road side. Address were also required to be given and these were found using GIS map view, located on the Auckland Council website, in conjunction with the design drawing. The count was given to the report writer.

I also developed an Excel spreadsheet model that utilised empirically derived formulas to predict vibration levels as a function of distance. This will be used to quickly ascertain if what vibration level is

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acceptable given a distance from a building. These empirical formulas were derived from data from construction vehicle or operations such as compaction, piling, and rolling, and can be found in the standard BS 5228:2:2009. I learnt new Excel skills to develop the model such as using drop down lists, using hyperlinked buttons, and form controls. The Excel model allowed quick calculation of distance and vibration values given set parameters. Graphical representation of the formula was also shown and the curve could be manipulated easily by changing certain parameters, the same ones used to calculate a single distance or vibration value. I designed the interface to be intuitive and user friendly so that anyone at MDA should be able to use it easily. I also added explanations where applicable to aid the user.

In a Norwegian standard, there is a calculation method described used to determine the maximum statistical value of weighted vibration level. This value is then used to classify the building where the measurement was taken. This method has been adopted by the New Zealand Transport Agency (NZTA) for use. Because there are a few different methods that different consultancy firms use to measure and to calculate this parameter, the NZTA sent out a round robin survey to find out what capabilities and how accurate each firm were when finding this value. MDA did not complete the round robin by the due date, however, James Whitlock, who was the point of contact with NZTA, felt that it might be interesting to see what MDA could do so he tasked me with developing a model to calculate this. For this, I had to learn how to use Labview. NZTA provided some test cases in an Excel file which I had to convert into an ASCII input for Labview. From there I process the vibration data into its spectrum and 1/3 octave bands. The 1/3 octave bands are a range of frequency values. There are 33 bands ranging from the lowest frequency of 14.1 Hz to 22390 Hz. For reporting purposes, the centre frequency between the lower limit and upper limit of a 1/3 octave band is shown. The value of interest in these bands was the peak value. These values were extracted from Labview and the post processed in Excel. The test cases that was provided by the NZTA also had some expected values. There were 6 saw tooth cases and from my results, I was able to calculate the last case to an accuracy of ~100%. However, for the previous 5, the accuracy was only ~25%. I was unable to find the cause of this as the laptop which had Labview on it had to be used by a consultant in Queenstown during the last two weeks of my placement.

MDA is involved with the noise planning for Queenstown Airport and each year a report is written detailing the noise level of the airport in operation. The airport needs to meet noise requirements set out by the council in the form of noise contours (imaginary lines around the airport that dictate acceptable or maximum allowable noise levels) and MDA advises the airport if these are breached. MDA has a noise monitor in Queenstown that constantly monitors noise levels and these measurements can be assessed online. I was required to acquire three months that represented a high amount of air traffic, these were October through to December 2014. The day by day data that I downloaded was represented as 1 second Leq values and each day was recorded from midnight to midnight the following date. Therefore there was a significant amount of data. Fortunately, there is a program called Aircraft Noise Analyser (ANA) that helped in the data analysis. I uploaded each day’s data into ANA which graphically displays the waveform of noise level over 24 hours. The required output from this program is called the Ldn (combined level over daytime and night time) and the Ldn,aircraft. To do this I had to specify a trigger level, the level which when exceeded is counted as a significant noise event, and the duration of the event. I had to justify my choices and upon discussion with the supervisor of the project, the choices that I made was reasonable. I had chosen a trigger level of 58dB and a duration that was longer that 1 second but less than 3 seconds. For most days, these parameters was acceptable and the number of Ldn and Ldn,aircraft events was found. However for some days, the events was greater than 200, due to just things as high wind speed or adverse weather, which the program did not allow. Therefore I had to adjust my trigger levels and duration time. First I changed the trigger level to 1 dB higher, then I adjusted the greater than time. I kept adjusting until the greater than time was 3 seconds. I limited the event duration to only 3 seconds as I reasoned that any event longer than 3 seconds would capture noise that was not part of the

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event. My supervisor agreed with me, so therefore when the limit was reached I adjusted the trigger level accordingly to find less than 200 events.

After I had acquired the Ldn values for all the days, I created a table within Excel to find the logarithmic average over the three months. I also correlated each day with wind and weather information to determine if the wind direction and speed had an effect on the measurement. Queenstown Airport had two runways, one in the north-east direction, and the other orthogonal to this main runway. The noise monitor is aligned with the latter one. The north-west runway is used when the wind is predominantly in this direction and I found that the higher trigger levels that were required occurred when this runway was used. I presented graphs showing the Ldn values over the 3 months, Ldn values in the north-west direction only over the three months, and Ldn values in the other direction only over the three months. Logarithmic averaged values were also presented for each. However the one of interest was the overall Ldn average value and it was found that over those three months, the noise level did not exceed the noise contours.

Other less project specific work that I did was maintaining and updating databases and spreadsheets which MDA regularly uses in their design work. One example of this is inputting experimental data into a program called Sound Absorption Database. This allows quick access to all available test data digitally. I updated a spreadsheet used in estimation reports as the previous estimations were less accurate. The estimations are calculated in Insul and I created the Insul model to update the calculated values in the estimation spreadsheet. I also updated other worksheets used to determine which ventilation system should be used by inputting the latest data or new models.

Keith is the programmer for Insul and I created many different testing models for him using experimental data. Insul has a graphically output to show the calculated curve and the experimental reference curve can be shown on top of that. These were created so that he had reference models to prove that his changes to Insul yielded correct or accurate calculations.

Comments on the Experience

I have thoroughly enjoyed my time at MDA. The people who work there are friendly and open. They have been very welcoming of my placement. I have made friends while observing how a consultancy firm operates.

Through the work that I have done, I have gained a greater awareness and appreciation of the field of acoustics. It is still an evolving field of science with new discoveries are constantly being made and MDA’s involvement in conferences is a good way to keep up to date of these discoveries. My knowledge of acoustics has been reinforced, although, I was only exposed to a small part of it. However I do feel that through my experience I am getting a feel for what is acceptable from just listening/feeling to the actual calculated results.

A possible improvement opportunity that I observed at the company concerns an internal element of the company. Searching documents on HAL could be improved. At the moment, the search string is performed so that it searches the title of the data entry, the title of the attached document, author, keywords of the data entry, and any text within the document itself. This leads to a large number of irrelevant entries being returned which means that your desired document is not found. To improve, I think it would be better if the search was limited only to the keywords of the entry, the title of the entry, the summary of the entry, author, and the title of the document attached. This should eliminate any wrongly pulled results. Another area of improvement is that on HAL, there a multiple entries of the same document. Removing duplicates improves searching capabilities and removes clutter on the server.

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Because MDA has a limited number of equipment, it is essential that bookings are made in advance. This is done on Excel. However, there were times that Excel did not allow editing because someone had not closed the document or Excel itself. This is a cause of inefficiency and a possible solution may be to use Google Docs which allow simultaneous editing at a time.

Being a small company, MDA does not have managers as such. You are expected to self-manage with the expectation that the deliverables are prepared in time. The junior consultants can choose when they want to go take measurements and perform other duties. If they encounter a problem, there are many senior consultants who are willing to mentor them. I feel that because of this, MDA is a very pleasant place to work at. There is still the expectation to perform but you are given more freedom without a manager having to constantly monitor your work.

Conclusions

MDA has been a very enjoyable working atmosphere and I felt right at home from the first day of work. I have gained a better understanding of acoustics and how an acoustics consulting company operates. The experience has been invaluable and I have now know the type of work a consultancy firm, in general, does, which I can take into my future work in a consultancy firm or otherwise. I have gained new skills in Excel and particularly in acoustics measurements and analysis. The acoustics consultancy industry is certainly a career path that I would pursue.

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