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Acoustics 101 - and the NZ Building Code
NZAS 39th Annual Conference 2-4 July 2015
George Dodd and James Whitlock on behalf of ASNZ
To cover –
• What is an acoustician?
• Phenomena and techniques used in the control of
sound
• The special case of dwellings and the New Zealand
Building Code requirements
• Some current research and a look to the future.
The job of an Acoustician
– TO CONTROL OBJECTIVE SOUND SO THAT THE
ASSOCIATED SUBJECTIVE SOUND BENEFITS PEOPLE
Formal noise complaints - Christchurch
0
2000
4000
6000
8000
100001991
1992
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1994
1995
1996
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2000
2001
2002
2003
2004
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2006
Year
Num
ber
of com
pla
ints
Residential noise
Commercial noise
Total cmplaints
Christchurch complaints – analysed by source
12000
13000
14000
15000
16000
17000
18000
19000
20000
2002
2003
2004
2005
2006
2007
2008
Year
Nu
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Auckland City
Noise complaints investigated for Auckland City - data only available since 2002
(Courtesy of Armourguard)
More recent data only provided if requested under OIA and time paid for!
Noise arising from activities within zones Residential zones Except where other more specific controls apply, the LAeq(15 min) noise level and maximum noise level (LAFmax) arising from any activity in the residential zones measured at or within the boundary of an adjacent property site in the residential zones must not exceed the following levels limits. Monday to Saturday 7am-10pm 50dB LAeq(15 min) Sunday 9am-6pm 50dB LAeq(15 min) All other times 40dB LAeq(15 min)
75dB LAFmax
An example of the form of a ‘noise limit’ from the Auckland Council submission to the Unitary Plan Hearings where the objectives include – 1. People and activities sensitive to noise are protected from unreasonable levels of noise. 2. The amenity of residential areas is protected from unreasonable noise, particularly at night.
What is the purpose for a dwelling?
The fact that it is PRIVATE makes it different from a hotel,
hostel, hospital, or other building providing amenities for
humans.
What do we mean by PRIVACY – and especially what
acoustical conditions are required to give you Acoustic
Privacy?
A Definition for Acoustic Privacy –
The condition where no information about you or your
neighbour (including your, or their, presence!) is
communicated by sound.
Tools/Techniques acousticians use for controlling noise –
DISSIPATION =
REFLECTION
DIFFRACTION =
REFRACTION
SPECTRUM CHANGE =
REDIRECTING THE SOUND
ENERGY AWAY FROM A SPACE
SHIFTING THE FREQUENCY
CONTENT SO WE CAN’T HEAR IT
CHANGING THE SOUND
ENERGY INTO HEAT
What would be a good material to insulate sound?
Neighbour’s Noise CAC 1
CAC 2
CAC 3
Shouting Voice intelligible generally intelligible generally unintelligible
Raised Voice generally intelligible generally unintelligible unintelligible
Normal Voice generally unintelligible unintelligible inaudible
Footsteps generally annoying generally not annoying not annoying
Sanitary Noise unacceptable annoyance generally avoided
occasionally annoying not or seldom annoying
Home Music, Loud Radio/TV , Parties
clearly audible clearly audible
generally audible
Subjective Response to Noise from Neighbours
Subjective Response to Noise from Neighbours for the “Classes of Acoustical Comfort (CAC)” in German Guideline VDI 4100 “Noise Control in Housing”
assumimg background level of 20 dB(A) and normal size rooms
NZ’s current Building Code requirements match those of CAC 1
NB: safeguard from loss of
AMENITY as a result of undue
noise …..
Amenity means an attribute of a building
which contributes to the health, physical
independence, and well being of the
building's users but which is not associated
with disease or a specific illness.
Insulating material A material that has a thermal conductivity of less than 0.07W/mK.
Health is a state of complete physical,
mental and social well-being and not merely
the absence of disease or infirmity.
Sound Insulation
• Transmission Loss (TL) is a measure of the energy loss through an element
• Indicates the Sound Insulation value
• Normally quoted as Sound Transmission Class (STC)
TL = 55 dB
50 dB
STC – Sound Transmission Class
• Transmission Loss is measured over a frequency range (low sounds and high sounds)
• STC enables a single figure rating • Obtained by comparison with a
standardized ‘curve’
• Emphasis of curve is on the ‘speech’ frequencies
Transmission Loss vs Noise Reduction
• TL is a property of a building element
e.g. “This wall has a TL of 57 dB”
• NR is the difference in sound level either side of a building element
e.g. “This wall has an NR of 57 dB… when it is X m2 and has room Y with a reverb time of Z on the other side of it.”
Masonry vs Plasterboard
150mm Concrete 2 x 10mm Noiseline
STC 55 200mm cavity with insulation
1 x 10mm Noiseline
STC 55
IIC – Impact Insulation Class
Not measured as a TL
The actual sound level is measured over a frequency range
Standardised Impact Source
Tapping Machine
The New G6
There is change in Philosophy from;
Performance of the materials to
Performance of the building
Change from TL to NR - from STC to Rw and DnTw
… and more.
The New G6
Overall improvement of 3 – 8 dB
stay tuned…
Neighbour’s Noise CAC 1
CAC 2
CAC 3
Shouting Voice intelligible generally intelligible generally unintelligible
Raised Voice generally intelligible generally unintelligible unintelligible
Normal Voice generally unintelligible unintelligible inaudible
Footsteps generally annoying generally not annoying not annoying
Sanitary Noise unacceptable annoyance generally avoided
occasionally annoying not or seldom annoying
Home Music, Loud Radio/TV , Parties
clearly audible clearly audible
generally audible
Subjective Response to Noise from Neighbours
Subjective Response to Noise from Neighbours for the “Classes of Acoustical Comfort (CAC)” in German Guideline VDI 4100 “Noise Control in Housing”
assumimg background level of 20 dB(A) and normal size rooms
NZ’s current Building Code requirements match those of CAC 1
Elastic Meta-Materials are materials which are internally engineered to create -
• Properties not available in nature
e.g.Negative density and/or stiffness
• Properties which are determined by their
internal structure rather than their chemical
composition
(so the fundamental equations governing their
behaviour need modifications to Newton’s
Law!!)
Application: sound barrier
• Changing the effective density of wall or partition
• First practical application!
• Exceptional performance but limited frequency band (for
now)
Acoustic Invisibility and Black Holes with ‘Indefinite Materials’
• Cloaking: guiding waves around an object
• Super-absorbers: guiding waves in a lossy object
July 8, 2013
Redesigned Window Stops Sound But Not
Air, Say Materials Scientists By exploiting some exotic acoustic techniques, researchers have
built a window that allows the passage of air but not sound
Wind Turbine Syndrome (Pierpont, 2009)
• Sleep disturbance, • Headache, • Dizziness, vertigo, unsteadiness • Tinnitus • Ear pressure or pain • External auditory canal sensation • Nausea • Memory and Concentration deficits • Irritability, Anger • Panic episodes • Fatigue • Loss of motivation
What could be causing health effects?
• Dominant source of sound is the aerodynamic noise caused by the flow of air past the turbine blades
• Sound produced is a broadband sound present across a range of frequencies, from the audible to the sub-audible.
• Audible sound limit set in New Zealand by wind farm noise standard NZS 6808:2010 (recommended limit of 40dB).
• Symptom reporting has coincided with public
speculation about alleged health effects (Chapman et
al., 2013).
• Media reporting about wind farms and health effects
contain factors likely to induce fear, anxiety and
concern (Diegnan et al., 2013).
What could be causing health effects?
Negative health information
and symptom reporting Warnings about health effects may
trigger health complaints even when no
actual risk is posed (Faasse et al., 2012)
Such information can create anxiety,
health concerns and related symptom
expectations, priming people to notice
and negatively interpret common
physical sensations and symptoms (Petrie
et al., 2005)
The Role of Expectations
Might symptom expectations created from negative
health information explain the link between wind
turbines and health effects?
A sham double-blind provocation study
54 participants
High infrasound symptom
expectations video
Low infrasound symptom
expectations video
Infrasound (<40db at 5Hz)
Sham infrasound (no sound)
counterbalanced
10 mins
10 mins
Number of symptoms
0
2
4
6
8
10
12
Before Infrasound During Infrasound Before Sham During Sham
Nu
mb
er o
f Sy
mp
tom
s
Low Expectancy
High Expectancy
Symptom Intensity
0
5
10
15
20
25
Before Infra During Infra Before Sham During Sham
Sym
pto
m I
nte
nsi
ty
Low Expectancy
High Expectancy
Conclusions
• Negative health information readily available to people living in the vicinity of wind farms may create symptom expectations, providing a possible pathway for symptoms attributed to operating wind turbines.
• Framing health information in a positive way may provide a way to reverse, reduce, or protect against the experience of noise annoyance and symptom reporting.
The design is relatively simple and relies on two exotic acoustic phenomenon. The first is to
create a material with a negative bulk modulus.
A material’s bulk modulus is essentially its resistance to compression and this is an
important factor in determining the speed at which sound moves through it. A material with a
negative bulk modulus exponentially attenuates any sound passing through it.
Kima and Lee’s idea is to design a sound resonance chamber in which the resonant forces
oppose any compression. With careful design, this leads to a negative bulk modulus for a
certain range of frequencies.
Their resonance chamber is actually very simple—it consists of two parallel plates of
transparent acrylic plastic about 150 millimetres square and separated by 40 millimetres,
rather like a section of double-glazing about the size of a paperback book.
This chamber is designed to ensure that any sound resonating inside it acts against the way
the same sound compresses the chamber. When this happens the bulk modulus of the entire
chamber is negative.
An important factor in this is how efficiently the sound can get into the chamber and here
Kima and Lee have another trick. To maximise this efficiency, they drill a 50 millimetre hole
through each piece of acrylic. This acts as a diffraction element causing any sound that hits
the chamber to diffract strongly into it.
The result is a double-glazed window with a negative bulk modulus that strongly attenuates
the sound hitting it.
Kima and Lee use their double-glazing unit as a building block to create larger windows. In
tests with a 3x4x3 “wall” of building blocks, they say their window reduces sound levels by
20-35 decibels over a sound range of 700 Hz to 2,200 Hz. That’s a significant reduction.
9th International Conference on Advanced Building Skins, 28-29 October 2014, Bressanone, Italy The main objective of the conference is to contribute to a multidisciplinary, integrated planning approach among architects, engineers, scientists, energy managers, manufacturers and the building industry, with the aim to reduce energy consumption while improving the comfort of the building's occupants. This year's topics include: - Design Methods for Sustainable, High-Performance Building Facades - The Future of Advanced Building Skin Design - High-Tech, Low-Tech, Lightweight Building Envelopes - Thermal Performance of Phase Change Materials for the Building Skin - Thermal and Environmental Performance of Eco Materials for the Building Skin - Smart Materials for Intelligent Building Skins - Architectural Membranes for High Performance Building Skins - Shading Systems for Enhanced Daylight Control - Building Skins for Tropical Climates - Adaptive Hortitecture: Building Envelopes as Micro Climates and Productive Environments - Integrating Photovoltaics into the Building Envelope - Cost Optimization for Solar Energy Systems, NZEB and Façade Renovation - Optimization Techniques for the Refurbishment of Building Envelopes - Performance Simulation of the Building Envelope
“So close? Cooper wondered if the Chadwicks knew what
it was actually like to have neighbours living practically
on top of you, packed in cheek by jowl, so close that you
could hear them clearly through the walls on either side of
you. There were lots of people … who knew what that
was like. His own ground-floor flat in Welbeck Street
sometimes echoed to the slam of a door from the tenant
upstairs, the clatter of feet on the stairs, the blare of old
Mrs Shelley’s TV set next door.”
“Many of these people would have come here from the
city seeking peace and quiet, looking for a refuge from
noise and traffic ..”
Excerpt from The Devil’s Edge, by Stephen Booth, Sphere Books, 2011
There has been a 5.25% increase in the total number of complaints received this year
compared to last year and a 45.21% increase since 2003/04 when numbers of complaints were
first recorded.
Many neighbour noise problems are a result of incompatible lifestyles and a lack of
consideration for the rights of others. The Department of the Environment considers that
better education is one way of tackling the problem and is keen for the councils to continue
their efforts to raise noise on local agendas.
Factors Influencing IIC
The IIC is dependent on:
• The floor structure (material, thickness, etc.)
• The floor covering (carpet, vinyl, parquet tiles)
• The ceiling beneath (isolated, layers etc.)
The acoustic benefit of each factor can be separated.
IIC factors
Concrete Floor
Thickness (mm) IIC
75 16
100 21
150 28 Unlike airborne sound, we cannot
achieve Building Code G6 requirement using mass alone
Improvements: Floor Coverings
Vinyl +4 Cushioned Vinyl +15 Parquet +16 Cork +18 Tiles with underlay +0 to +24 Carpet +44
Improvements: Ceilings
Ceiling fixed directly to slab +4 13mm Gib suspended ceiling on battens +13 Gib on resilient hangers +20
[nothing beats carpet]
The NZ Building Code
Clause G6 addresses
Airborne and Impact Sound
• Airborne Sound: STC 55 for walls and
floors/ceilings
• Impact Sound : IIC 55 for floors/ceilings
• 5 point relaxation for field testing on site i.e. FSTC 50 and FIIC 50.
• Both laboratory performance and field performance must be complied with.
Scope of G6
Performance requirements are for habitable spaces of household units.
Habitable spaces are: Bedrooms
Living rooms and lounges Kitchens
Studies
Is Compliance Enough?
• G6 is the Building Code minimum. Often not sufficient for owners expecting high quality
• Complaints received with FSTC 55 & FIIC 57 i.e. 5 - 7 points above G6
• Owner expectations, neighbours’ behaviour and background noise all have an influence on satisfaction
• STC and IIC are rather old criteria, based on 1950 noise sources and brick walls
• Modern entertainment systems produce significant low frequency energy, which is not catered for by STC
