Environmental "noise industry" is not fit for purpose...

www.invc.co.uk
Noise Control Best Practice noise
TThhee EEnnvviirroonnmmeennttaall NNooiissee
IInndduussttrryy iiss NNoott FFiitt ffoorr PPuurrppoossee……
PPeetteerr WWiillssoonn MMSScc.. MMIIOOAA
Industrial Noise and Vibration Centre: www.invc.co.uk

www.invc.co.uk
In Summary
The “Noise Industry”
• Generally displays a woeful ignorance of both diagnostic
techniques and modern noise control methods
The Victims
• Thousands of people are therefore needlessly exposed to stressful
noise from industrial / commercial premises over prolonged periods
• Many unnecessary deaths consequently (BMJ and WHO reports)
• Companies waste a fortune on inappropriate mitigation
The Best Practice to Avoid the Problems
• The diagnostic procedure that must be followed to evaluate any
potential noise nuisance problem
• Case studies illustrating poor practice in attempted mitigation
(and failed mitigation) of common noise problems
• Examples of best practice

www.invc.co.uk
Noise Kills…
WHO Report: 2011
• Europe: c3% of deaths from heart attacks is attributable to long
term exposure to (mainly nighttime) environmental noise
• 2% of the population suffer from severe sleep disturbance
• 15% suffer from serious annoyance
• UK noise complaints increased by x5 over the last 20 years
• Learning abilities of children badly affected
BMJ Report: 2013
• Environmental noise increases the risk of stroke and coronary
heart disease due to raised blood pressure and hypertension
• Near Heathrow, 24% increased hospital admissions due to stroke;
21% increase due to coronary heart disease; 14% increase for
cardiovascular disease cf low noise areas
All dB(A) based – but many noise issues are low frequency,
so these figures seriously underestimate the problem…

www.invc.co.uk
BS 4142 – technically…
BS 4142 is almost ubiquitous, largely because it exists…
However, it is often (badly) applied to situations where it is not suitable.
• BS 4142 is supposed to assess the likelihood of complaints from
people inside a building by measuring dB(A) outside
• inside rooms, the T.L. of windows shapes the spectrum, reducing mid
and high frequency components - almost un-'A' weighting the sound
• does not work well for noise containing low frequencies
• 5dB(A) correction for noise with tones
• tonal noise at 5dB(A) below non-tonal noise should be equally
disturbing
• should not be used where background noise levels are very low
(<30dB(A))

www.invc.co.uk
Environmental Noise Control is ....
…not just about the overall level…
• Effective noise control must be based on an accurate
diagnosis that relates noise features to subjective impact, not
just on assumptions about overall dB(A).
• Although dB(A) may also be an additional planning /
specification requirement, this is often a completely separate
issue.
• Noise control is an engineering problem that should be solved
by engineering means at source wherever practical.
• All the options must be considered, not just the high cost
conventional palliatives of barriers, enclosures and silencers.
http://www.invc.co.uk/noise/noise-control/environmental-noise-control/

www.invc.co.uk
Attitude, Attitude, Attitude - Placebo Silencers

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Best Practice Elements
• Attitude
• Diagnosis - understand the cause of the subjective problem
 based on detailed diagnosis, objective evaluation linking noise
features to complaints – temporal and tonal components
 link problem noise features to specific mechanical / aerodynamic
plant elements.
• Assess the Noise Control Options
 based on current best practice. The majority of noise control
recommendations that we see are either not fit for purpose or are
far more costly than necessary.
• Recommend / Implement Best Practice Noise Control Option
 typically reduces noise control costs by 50% - 110%!
 reduces the time required to solve problems (often from years to
weeks)

www.invc.co.uk
Diagnosis, Diagnosis, Diagnosis…
You’re just guessing…
The approach taken to mitigate noise problems is often
based on guesswork.
There should be no guesswork involved.
•Temporal Diagnosis
Events, intermittency, turn plant on and off, variation over
time…
•Frequency Content
Broadband: octaves
Tones: narrow band frequency analysis
Note: 1/3 octaves are largely a waste of time. This is the
21st century - FFT is available free on smartphones…
•Audio Recordings
Any SLM can be used to produce calibrated audio files
that can then be analysed by ear and by software
Play back modified audio to the complainant

www.invc.co.uk
Source Identification and Ranking
Identification Techniques
• run each source separately - measure in far field at reference
points
• measure each source close in and predict noise levels (sound
power and propagation)
• use narrow band frequency analysis - compare far field and close
in signatures
Rank the Sources
• …by the subjective impact, NOT just dB(A)

www.invc.co.uk
Cooling Towers

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Rank Multiple Sources Cooling Towers
Ranked sources
• large cooling tower
• small cooling tower
• main pumps (5)
• lift pumps (13)
Ranked local sources for
dominant contributor:
Large cooling tower
• tower air outlets (3)
• tower air inlets (3)
• fan motors

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Rank Multiple Sources Cooling Towers
Ranked sources
tower air outlets (3)
tower air inlets (3)
main pumps (5)
lift pumps (13)
Conventional:
3 sets of silencers (outlets) + noise barrier at boundary at c
£30,000; 56dB(A)
Detailed Diagnosis
Modify outlets and inlets, silence main pump cooling fans, local
screening for lift pumps at c £5000; <50dB(A)

www.invc.co.uk
Cooling Tower: Untreated / Treated

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Cooling Tower Pumps: Untreated / Treated

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Battery Stack Diagnosis

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Battery Factory Stacks
Diagnostic measurements
• synchronise recording time and engineer's watch
• define shut-down and start-up sequence for stacks
• engineer notes time of each operation
• record whole period
• analyse recording - use timings to identify sources
Solution
• purpose designed silencer inserts dropped into 4 of the 5
stacks
• 12 - 15 dB(A) reduction in stack noise

www.invc.co.uk
Press Shop Noise Complaints
• £12k wasted on factory end wall treatment,
£65k additional roof improvements planned
(no guarantee) and £40k+ legal fees spent…
• 3 presses required treatment - c£12k solved
problem.
http://www.invc.co.uk/noise/noise-control/environmental-noise-control/#casestudies

www.invc.co.uk
Air Handling / Chiller Units
The Problem
Several chillers and 2 large AHUs installed at the
rear of a high tech facility were causing serious
environmental noise complaints (more than
10dB(A) above background with tonal content).
£100k spent on ineffective noise control - one
chiller fitted with silencers, simple noise barrier
erected (which also caused air-flow problems) -
but with no effect on complaints….
The Solution
The primary requirement was to carry out an
accurate diagnosis that would allow the sources
to be ranked in terms of their contribution to the
environmental noise and then to rank the noise
sources within each of the significant
contributors.
http://www.invc.co.uk/noise/noise-control/environmental-noise-control/#casestudies

www.invc.co.uk
AHU Diagnosis and Noise Control
Diagnosis
• 2 existing acoustic louvres on each unit for extract and supply air.
Detailed noise measurements were carried out inside each
plenum and outside each louvre over the operating range of the
unit.
- top louvre (extract) 4dB(A) noisier
- poor design due to potential for air recirculation
Noise Control
• turn top louvre round (also improve performance)
• line plenums with acoustic absorbent
• fit baffle to extract fan outlet to reduce noise transmission down
into supply plenum and out through louvre
• plenum lining and baffle reduced noise by 5.5dB(A)
• total noise reduction just over 10dB(A)

www.invc.co.uk
Air Handling Unit: Re-directed Extract
Extract
Supply

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Diagnosis Outside Plenums

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AHU Modifications
complainants
before
after
extract
supply
84dB(A)
louvres
80dB(A) filter
absorbent
baffle
78dB(A)

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Chiller Silencers and Barrier
Intake and exhaust silencers fitted by supplier. Exhaust silencers have some
benefit, intakes none as the chiller is open at the far end. The barriers have
only a small effect for similar reasons.

www.invc.co.uk
Dry Chiller: Impellor Change
noisy impellor
quiet impellor

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Panel Vibration Reduction
damped
undamped
Total 8dB(A) noise reduction under
chiller (damping + absorbent)

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Source Ranking and Target Level
Overall target at complainant: 40dB(A): (35dB(A) + 35dB(A) + 35dB(A))
Eliminate tonal components

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Chiller Plant Noise Reduction

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bedroom
window
open/shut
Cooling Tower Tonal Source ID
cooling towers 1 / 2 at 2m
grinder 5m

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Cooling Towers: Detail
Only 71.3Hz blade pass of fans in tower 1 matches bedroom
spectrum - grinder and tower 2 are eliminated as sources

www.invc.co.uk
Remote Control of Noise
video
sound
photos
email
-internet
Specialised analysis
BPM
BAT
Costs
database
experience
@
@
http://www.invc.co.uk/noise/noise-control/remote-control-of-noise/

www.invc.co.uk
Roof-top fans
£50k wasted on acoustic lagging – no effect
Aerodynamic modifications
135Hz reduced by 17dB
270Hz reduced by 22dB
http://www.invc.co.uk/noise/noise-control/remote-control-of-noise/

www.invc.co.uk
Noise Complaints from Industrial Premises
Source: National Physical Laboratory

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Fan Noise Control Options
Techniques by priority and cost effectiveness….
•Control at source
engineering modifications
efficiency – lowest fan noise coincides with maximum efficiency
vibration isolation and vibration damping
Only if the above are not practical should you consider…
•Silencing
•Enclosures
•Lagging
•Barriers
•Building modifications
Conventionally, these
high cost techniques
have been the only
measures that are
considered….
http://www.invc.co.uk/noise/noise-control/fan-noise-reduction/

www.invc.co.uk
Innovative Noise Control Technology
These are some of the innovations we use as part of current best practice
in environmental noise control.
• Quiet Fan technology (QFt)
 typically 10% - 20% of the cost, no effect on fan efficiency
• Chiller / HVAC noise control
 <20% of the cost, free cooling unaffected, higher efficiency
• Fan / combustion stacks
 retro-fit, low cost, fast
• Burner / combustion noise
 source control technology – typically <5% of the cost
• Acoustic Camouflage
 psychological electronic silencing

www.invc.co.uk
London: Office A/C Plant…
• Chillers on top of high-rise office block caused noise complaints in an
adjacent street
• Noise consultancy carried out BS 4142 assessment and
recommended replacing one of the chillers
• Chiller replaced at cost of £100k, several dB(A) quieter at 1m
• Complaints unabated as the noise nuisance was caused by low
frequency tonal noise from a different chiller…
http://www.invc.co.uk/noise/noise-control/fan-noise-reduction/#chiller

www.invc.co.uk
Diageo Chiller
Cooling tower noise experts report conclusion:-
• “A “pure tone” is extremely difficult to eradicate as it requires changes
to the mass being excited and as indicated is a direct result of the
noise power at a primary frequency being amplified and combined
with other harmonics across the frequency band.
• There is no quick fix or simple change that can cure such
phenomena. In order to cut the generated noise level from this
cooling tower we believe the only solution is to correct the fault at
source with a fan change out but while doing so install a low sound
fan i.e. wide cord, sophisticated profile, larger diameter and run at
slower speed.”
• £30,500 plus downtime of several days.

www.invc.co.uk
Diageo Chiller
Diagnosis
•£30k recommendation made with no frequency analysis…
•Analysis of video soundtrack via email – 10 minutes
•670Hz tone is gear-mesh frequency of motor pinion
•Recommended replace gear
•Whole gearbox replaced <£3,000, downtime c one day
Video soundtrack analysis

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Dryer Fan
The recommendation from the first noise specialist was the following:
• Replace impeller or whole fan if practicable to prevent tone being
generated. A cost estimate for a replacement fan and discharge
silencer was obtained at approximately £100k and would require an
extended shutdown to install and modify the existing duct-work to suit.
• Fit attenuators to fan if necessary to reduce noise levels at stack by 5
- 10 dB. The proposal was to add a top conical section to the stack to
increase the exit velocity. This was not pursued as it had high
installation cost as the stack could not self-support the new section.

www.invc.co.uk
Dryer Fan
Diagnosis
•£100k recommendation made with no frequency analysis…
•An internet search by the Precipitates Plant Manager led company to
approach us about our Quiet Fan technology…
•The noise control measures reduced the tone by 20dB, cost <£7k and
paid for themselves in around 9 months as they reduce power
consumption…
Noise analysis

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Corrugation Plant
• Abatement notice - £150k quoted
for building modification - with no
guarantee of success. EHO
suggested our 2nd opinion…
• Diagnosed corrugator roller tones
and defined BPM.
• Reduced tonal content at source
by 12dB – and eliminated PPE
requirement – for cost of £25k…

www.invc.co.uk
Restaurant Fans and Chiller
Kitchen extract exhaust system and chiller on roof
65dB(A) outside bathroom window; 33dB(A) in bedroom
Consultant recommendation: move chiller + build noise barrier;
expensive silencer in duct

www.invc.co.uk
Naked chiller Proposed silencer (£400)

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Bedroom and room
below chiller
Chiller tone at 48.5Hz + harmonics
– previous recommendations
would not have worked….

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Chiller Fans
Low frequency noise
complaints (48.5Hz)
Money wasted on
recommended noise
barrier…
Emailed this video.
Analysed soundtrack to
reveal tonal content…

www.invc.co.uk
Chiller Fans
Aerodynamic modifications reduced
48.5Hz tone by 13dB and other tones by
up to 20dB plus improved efficiency… 8
fans, < £4k

www.invc.co.uk
Schiller Biomass Power Station Fan
• 50MW station (largest in USA)
noise problem: 2 storey ID fan.
• Conventional silencer had a
very big impact on efficiency
• QFt fitted in only 12 hours!
• 10dB reduction in noise
• Fan power consumption
reduced
• No site visit…
“…the 3m wide ID combustion
fan could be heard across the
river… after installation (only 12
hours)…10dB drop in noise,
which is huge…recorded a
reduction in ID fan power after
QFt had been installed.” – Jim
Granger, Senior Engineer

www.invc.co.uk
Scrap Can Extract and Chopper Fans
modified fan
Problem
Occupational + environmental tonal
noise
Conventional
• silencers, lagging and enclosures
• capital cost > c£35000 +
maintenance costs
BPM Engineering
• internal fan modification reduced
tones by 23dB and overall noise
by 22dB(A)
• cost c £3000 - no maintenance
costs (lasts the lifetime of the fans
despite passage of cans)

www.invc.co.uk
Thermal Oxidiser Fans
New plant – supplier suggested earth berm, enclosures etc
CMB asked for a 2nd opinion
BPM – Quiet fan technology, remove “beating”, damper type and location
changed, small secondary silencers: 15dB(A) reduction >£100k saved and
more efficient….

www.invc.co.uk
Axial Vent Fans
8 off axial vent fans with 8m long silencers several stories up
112Hz blade pass problem tone reduced by 20dB by fitting invertors to
change speed slightly to avoid resonant condition.

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Chiller Farm
£300k quoted to reduce fan noise - several stories up – loss of free cooling
Innovative geometries + control systems + control at source
15dB(A) reduction, no loss of efficiency, c £40k…

www.invc.co.uk
Yoghurt-Based Noise Control - Boiler Burner
16dB tonal noise reduction

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Cement Works Stack Noise Control
• Plant update to improve efficiency
had a disastrous effect on stack
noise, causing complaints over a
wide area.
• Planned conventional silencing
would have been very costly and
would have caused unacceptable
down-time.
• We designed tuned inserts that
were installed over a weekend.
• Noise reduced by 19dB with no
effect on system efficiency and at
a small fraction of the cost.

www.invc.co.uk
BP Refinery: $1.25m conventional silencers: $0.25m via engineering
– no impact on efficiency, no site visit

www.invc.co.uk
Noise Control Best Practice noise
QQuueessttiioonnss??
PPeetteerr WWiillssoonn MMSScc.. MMIIOOAA
CCoonnttaacctt uuss ffoorr ffuurrtthheerr iinnffoorrmmaattiioonn
ccoonnssuulltt@@iinnvvcc..ccoo..uukk ++444411775533 6699888800
Industrial Noise and Vibration Centre: www.invc.co.uk

Environmental "noise industry" is not fit for purpose...

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