1. Low-frequency noise A biophysical phenomenon
Dr Mireille Oud
medical physicist / consultant
(Congress “Sound, Vibrations, Air quality, Field & Building”, 6 November 2012, Nieuwegein, The Netherlands)
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2. Contents Sources low-frequency sound
Biophysics perceptibility (neurobiologist A.N. Salt, Washington University)
Health effects
Conclusions
Advices
References
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3. Sources low-frequency sound (<<150 Hz)
Via air: up to 1 km
Wind turbines
Gas transport
District heating
Industry
Difference tones …
(Ref.: Kohlhase 2011)
Via ground: up to 100 km  cumulation sources
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4. Sources low-frequency sound
Wind turbines
Gas grid
(Ref.: Kennisportal Wind energy)
(Source.:
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5. Biophysics perceptibility
Organ of balance
______ 
___ 
Cochlea
(Ref.: Chittka & Brockmann 2005)
(Ref.: Prasad)
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6. Biophysics perceptibility
__________
Cochlea
(Ref.: Encyclopaedia Brit. 1997)
(Ref.: Madhero88)
Outer hair cells: pre-amplifier
Inner hair cells: to brain
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7. Biophysics perceptibility
test animal
test animal
(Ref.: Salt 2011)
Can become
audible
Audible for every-one
(Ref.: Pedersen 2008)
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8. Biophysics perceptibility
Occlusion helicotrema  20dB increase sensitivity for low frequencies
Endolymfatic hydrops (swelling middle tube)  dizziness
(Ref.: OpenLearn LabSpace)
(Ref.: Salt & Lichtenhan 2012)
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9. Biophysics perceptibility
response cochlea test animal
5 Hz
Audible cochlea-activity (500 Hz) interacts with inaudible cochlea-activity (5 Hz)  low tone audible through amplitude modulation
500 Hz
audible 5 Hz
(Ref.: Salt & Lichtenhan 2011)
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10. Biophysics perceptibility
Low frequencies audible for everyone: beat, difference tone Superposition of nearly equal, audible, tones (a and b) this amplitude modulation can be acoustic (c) and neural (d)
(Useful application: tuning musical instrument)
a. mono 220 Hz
b. mono 222 Hz
c. mono Hz
d. stereo: left 220, right 222 
(Click here, in presenting
mode of powerpoint.
Use head phone.)
(Source: M. Oud 2012)
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11. Biophysics perceptibility
G-weighting: ISO 7196:1995
(Ref.: Cedric 2004)
weighted wind-turbine spectra
(Ref.: Van den Berg 2006)
 dBC and dBG more realistic
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12. Health effects Still more people perceive LFN (hearing / feeling)
Health effects LFN:
Dizziness
Continuous, pulsing pressure on head
Disturbed sleep
Stress
Raised blood pressure
Heart rhythm disorders …
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13. Why is low-frequency sound experienced as nuisance?
Health effects
Why is low-frequency sound experienced as nuisance?
Directionless, lacks spaciality  seems “within the head”
Character (monotonous or pulsing) & duration
Lack of autonomy (uncontrollable): ear plugs no effect: entrance is via bone conduction
Affects physiology (structure cochlea)
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14. Conclusions
Perception low-frequency sound been demonstrated objectively (audiograms)
Perception low-frequency sound biophysically explicable
Significant part NL-population experiences damage
Low-frequency sound requires different way of assessment: minimally dBC instead of dBA , preference dBG
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15. Advices Systematic investigation health issues
More scientific research (medicine & physics)
Defining measurement and assessment methodology
Formulate norms for low-frequency sound
International approach
Makes sources low-frequency restricted
Adjustment home environment?
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16. Referenties
Dutch low-frequency noise vigilance group:
Dr Mireille Oud:
Prof. A.N. Salt:
ISO norm dBG: (ISO.org) and (DiracDelta science eng. enclyclopedia)
Berg, G.P. van den (2006), “The sound of high winds: the effect of atmospheric stability on wind turbine sound and microphone noise” Ph.D. thesis, Biomed. eng. dept. Rijksuniversiteit Groningen
Cedric R. (2004), “Ecoaccess guideline for the assessment of low frequency noise“, Proc. of Acoustics 2004, 619– 624, Gold Coast, Australia
Chittka L, Brockmann A (2005) Perception Space – The Final Frontier. PLoS Biol 3(4): e137. doi: /journal.pbio
Encyclopaedia Britannica (1997) “Cochlea”
Kennisportal Wind energy on land (2011), “Bestaande windparken”, Min. Infrastructuur and Environment e.a.
Kohlhase S (2011), “Explaining buried pipeline induced LFN hum and gas turbine flutter …” Brookfield Ct, USA
Madhero88:
OpenLearn Labspace, “Hearing – section 3.3 The role of the basilar membrane in sound reception”
Pedersen C.S. (2008), “Human hearing at low frequencies with focus on noise complaints”, Ph.D. thesis, Acoustics dept. of elec. systems, Aalborg University, Denmark
Prasad, “Mechanical cochlea”, senior design project, Stevens Inst. Techn.
Salt A.N. (2011), “Processes underlying homeostasis of cochlear fluids”, Washington univ.
Salt, A.N. & Lichtenhan J.T. (2011), “ Responses of the inner ear to infrasound”, 4th Int. meeting on wind turbine noise, Rome
Salt, A.N. & Lichtenhan J.T. (2012), “Perception-based protection from low-frequency sounds may not be enough”, inter.noise 2012 New York
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