Verslag conferentie laagfrequent geluid en trillingen LFN2012

Carel Ostendorf, Cauberg Huygen, Cauberg-Huygen Raadgevende Ingenieurs BV, 27 mei 2012

Stratford-upon-Avon in Engeland was de gastheer voor de 15e internationale conferentie over laagfrequent geluid en trillingen. De conferentie streek tussen 21 en 24 mei 20120 neer in het historische Legacy Falcon hotel. Rond de 80 deelnemers waren op de conferentie afgekomen. In het totaal hielden 30 sprekers een presentatie verdeeld over 3 dagen.

Naast aandacht voor geluid en trillingen was er ook aandacht voor Shakespeare en ontspanning.

Eerste dag: windturbines, windturbines en nog meer windturbines

De Deense Discussie

De eerste dag was volledig gewijd aan laagfrequent geluid door windturbines. Een hot topic met de nodige discussiepunten. Een belangrijke discussie vond plaats tussen de Deense universiteit van Aalborg en het Deense ministerie van Milieu. De Denen beschikken sinds januari 2012 over wetgeving op het gebied van laagfrequent geluid door windturbines. Men gaat uit van het frequentiegebied tussen 10 en 160 Hz. Afhankelijk van de windsnelheid, mag het geluidniveau buiten niet meer dan 44 dB(A) bedragen en binnen 20 dB(A). Omdat het meten van dergelijke geluidniveaus moeilijk is als gevolg van wind, stoorlawaai, steeds wisselende windcondities en onvoorspelbare staande golfpatronen binnen in de woning, is de beoordeling gebaseerd op een overdrachtsberekening. De methode vertrekt vanuit een bronvermogen op basis van metingen en een aantal overdrachtsfactoren. Een belangrijke overdrachtsfactor is de laagfrequente geluidisolatiewaarde voor de gevel. In de wetgeving is 1 serie van waarden opgenomen. Natuurlijk is dit niet passend voor alle huizen. Ongeveer 33% van de Deense woningen zou op basis van onderzoek een slechtere isolatie tegen laagfrequent geluid bezitten dan de waarden die in de wetgeving zijn opgenomen. Tot zover de methode.

De discussie tussen de Denen ging over de wijze waarop de isolatiewaarden waren vastgesteld. In de wettelijke methode is uitgegaan van meetposities in de woning die gebaseerd zijn op de waarneming van laagfrequent geluid door de mensen. Dit hoeft niet automatisch te leiden tot de hoogste waarden in een ruimte omdat je als mens je meestal niet ophoudt in alle hoeken en gaten in een ruimte. De mensen van de universiteit van Aalborg vinden dat je uit moet gaan van de hoogste geluidniveaus in een ruimte. In het eerste geval zijn de geluidniveaus binnen lager, waardoor de geluidisolatiewaarden hoger zijn ten opzichte van de metingen van Aalborg. Een berekening met de wettelijke waarden leidt tot een lager binnenniveau en de vraag is of dat wel recht doet aan de aard van de klachten. Helaas kwam de discussie niet geheel uit de verf omdat de voorzitter de kwestie vrij snel afbrak in verband met de tijd. Aan het einde van de dag bleek, onder het genot van een drankje, dat beide partijen toch erg vasthielden aan hun eigen standpunt. Overeenstemming zal nog wel even op zich laten wachten en de vraag is dan ook of deze methode zonder aanpassingen ook in Nederland moet worden gevolgd.

Japanse accenten

De dag kende ook de nodige Japanse bijdragen die niet allemaal even duidelijk waren. Opvallend was bijvoorbeeld de lezing van de heer Ito over het effect van lichtflikkeringen op de beleving van laagfrequent geluid. Het duurde even voordat de toehoorders doorhadden dat de flikkering veroorzaakt kon worden door de schaduwwerking van de ronddraaiende wieken van de windturbine. De heer Ito kon geen invloed aantonen van het licht op de beleving van laagfrequent geluid.

Meten bij windturbines

Een aantal presentaties behandelden de wijze waarop het geluid van windturbines moet worden gemeten en geanalyseerd. De sprekers benadrukten dat er niet alleen gekeken moest worden naar het spectrum maar vooral naar het verloop van het geluidniveau in de tijd. Door middel van correlatietechnieken lieten zij zien op welke wijze het laagfrequente pompende geluid “gevangen” kan worden. Voor deze meetmethode heb je meer dan een geluidniveaumeter nodig. De techniek maakt gebruik van meerdere microfoons die worden aangesloten op 1 analyzer of pc.

Rekenmodellen

De laatste presentatie (mevrouw Kamali uit Canada) behandelde een vergelijking tussen geluidoverdrachtmodellen en hun bruikbaarheid voor berekeningen met windmolens. De vergelijking betrof ISO 1996, het Nederlandse model (HMRI 1999) en het Nieuw-Zeelands rekenmodel. Omdat de invloed van windturbines vaak tot over grote afstanden reikt, waren de vergelijkingen berekend tot een afstand van 10 km. Het is dan niet zo vreemd dat deze modellen onderling tot relatief grote verschillen komen. In de presentatie werd met name ingegaan op de invloed van de bodem en de luchtdemping in de overdracht. Een opmerking vanuit het publiek was dan ook dat de gebruikte modellen nooit gevalideerd waren voor deze grote afstanden en de grote bronhoogten die horen bij windturbines.

Na 14 presentaties was het publiek aardig moe geluisterd. De einddiscussie kwam dan ook niet uit de verf.

Tweede dag: Japanse les en een uitstapje naar de country site

Tijdens de tweede dag bestond het programma in de ochtend uit lezingen en in de middag uit een bezoek aan Shakespeare’s geboortehuis, de cottage van Ann Hathaway (vrouw van Shakespeare) en een boottocht over de rivier de Avon.

Taalproblemen

In het totaal 6 lezingen waarvan 5 door Japanse deelnemers. De Japanners doen veel onderzoek naar de waarneming van geluid en trillingen onder laboratorium omstandigheden. Daarbij wordt niet alleen gekeken naar het wel of niet kunnen waarnemen maar ook naar lichamelijke reacties (zweten, hartslag, bloeddruk) en psychologische invloeden. Zo bleek dat 5 tot 15% van de testpersonen concentratieproblemen kreeg als ze werden blootgesteld aan een waarneembaar laagfrequent geluid. Het was goed dat de papers van de Japanners al waren opgenomen in de proceedings. Dat maakte de soms moeilijk verstaanbare presentaties beter te volgen. Discussie met de Japanse deelnemers is altijd moeizaam vanwege taalproblemen. Ze worstelen zich nog wel door de presentatie heen maar kunnen daarna de vragen niet verstaan en een antwoord niet formuleren. Dat is jammer en doet geen recht aan de nuttige onderzoeken die vaak uitgevoerd worden.


Cottage van Ann Hathaway

De boottocht over de Avon bracht een heerlijke verkoeling en het zachte avondlicht zorgde voor veel fotogenieke momenten die dan ook ruimschoots werden benut. De dag werd afgesloten met het algemene diner voor alle deelnemers van de conferentie. Hoewel het diner rond 22.30 uur was afgelopen, zetten veel deelnemers hun geanimeerde gesprekken nog tot laat voort in de tuin van het hotel.

Laatste dag: horen of voelen? Dat is de vraag

Afwisseling

De laatste dag van de conferentie is vaak een moeilijke dag. De avond ervoor eist dan zijn tol en de eerste sprekers kijken dan ook vaak tegen een half lege zaal aan. Dat was nu echter niet het geval. Bijna iedereen was keurig op tijd aanwezig voor het gevarieerde slotprogramma. In deze dag veel aandacht voor laagfrequent geluid, de manier waarop mensen laagfrequent geluid waarnemen of beleven en een beetje aandacht voor trillingen (microscoop in een operatiekamer), geluidreductie door anti-geluid en CABS. Het laatste onderwerp was een vervolg op de lezing in 2010 tijdens de conferentie in Aalborg (zoek op WAF) waarbij de deelnemers verrast werden op een bijzonder geslaagde demonstratie in de testruimte van de universiteit.

Belangrijke bijdragen over de psychologische kant van het omgaan met hinder door laagfrequent geluid, waren er van Andy Moorhouse (Engeland) en Geoff Leventhall (Engeland). Zij waren betrokken bij projecten waarbij gezocht werd naar therapieën om de negatieve relatie tussen het waarnemen van laagfrequent geluid en hinder of gevoelens van stress, te doorbreken. Deze gedachtegang is niet nieuw. In 2008 vertelde Dion Scheijen (Audiologisch Centrum Hoensbroek) tijdens een NSG bijeenkomst op 8 december over een vergelijkbare therapie die hij had ontwikkeld voor mensen die hinder ondervonden van laagfrequent geluid. Ook de universiteit van Maastricht heeft recentelijk een therapie ontwikkeld om te leren omgaan met ongewenst geluid zoals tinnitus.

Slotdiscussie

De slotdiscussie aan het einde van de dag is soms moeizaam. De deelnemers zijn moe, het deelnemersveld uitgedund en de motivatie om er nog wat van te maken laag. Organisator en nestor Geoff Leventhal had deze keer echter geen moeite de discussie op gang te brengen waarbij met name het onderwerp “waarnemen en beleven van laagfrequent geluid” in relatie tot windturbines weer naar voren kwam. In het gezelschap was nog een aantal deelnemers aanwezig met uitgesproken (en vaak goed onderbouwde) meningen en dat leidde tot een leuke discussie. Strijdpunt was of waarneming alleen via de oren plaatsvindt of ook via de huid. Verschillende deelnemers betoogden dat als bepaalde laagfrequente geluidniveaus worden overschreden, receptoren in de huid geactiveerd worden die daardoor een sensatie veroorzaken. Als deze receptoren eenmaal zijn geactiveerd, zijn daarna lagere geluidniveaus voldoende om weer dezelfde sensatie op te wekken. Tijdens de laagfrequent geluid conferentie in Bristol (2006) kwam dezelfde discussie ook al aan bod. In zes jaar tijd is er kennelijk nog geen duidelijk antwoord gevonden.

Afsluiting

LFN2012 was een geslaagde conferentie die dankzij een prima organisatie, een goede locatie en het gevarieerde deelnemersveld veel waar bood voor zijn geld. Het zou prettig zijn als tijdens de volgende conferentie (2014 in Duitsland) ook de onderwerpen trillingen en maatregelen tegen laagfrequent geluid en trillingen wat meer aan bod zouden komen. Daar heeft de organisatie echter geen invloed op. Dat is aan de deelnemers zelf.

De inhoud van de proceedings staat helemaal onderaan dit artikel. De proceedings met alle papers alsmede meer informatie over de conferentie zelf, zijn te vinden via de conferentie website.

Hieronder de abstracts van de conferentie.

LF 2012 ABSTRACTS - These are in alphabetical order of first authors.

Power to the People

Norm Broner SKM, 452 Flinders Street, Melbourne, 3000, Australia, Email: nbroner___AT___globalskm.com

Summary

Peaking power plants are being developed around Australia to supplement electrical power demand and often are located quite close to either commercial or residential areas both in cities and in rural areas. Low Frequency Noise (LFN) from these plants need to be controlled in order to ensure that neighbours are not acoustically impacted. This paper will report on the experience of one plant where the LFN from the exhaust stacks of two OCGT’s caused nausea and headaches in office workers in a building some 50 metres away from the exhaust stacks. It will also report on another site where a residence was over 1 km away and the residents were experiencing significant LFN annoyance. The solutions required and the implications will be described.

A ' sufferer's ' perspective of Annoyance from Low Frequency

Disturbances - and why the lack of a U.K. Standard prevents the resolution of disputes.

John Burton hjrjeburton___AT___yahoo.co.uk

From the exhibition at the Anatomical Museum of Basel, Basel, Switzerland :-

Summary

“ Skin separates our interior life from the external world, but it also brings us into contact with it. Various sensory structures in the skin allow us to sense pressure, texture, temperature, and pain. Among these the Pacinian corpuscles (shown stained red and blue and magnified 400 times) are so sensitive that they can detect the floor vibration caused by a passerby.”

Deconvolution Beamforming Analysis of Low Frequency Wind Turbine Noise

Robert P. Dougherty OptiNav, Inc, 1414 127th PL NE #106, Bellevue, WA 98004, USA rpd___AT___optinav.com

Summary

Two simple, field deployable phased arrays of microphones were used to evaluate their capability for locating low frequency and audio frequency wind turbine noise. The low frequency array was a 10 m triangular arrangement of three microphones on plywood boards the ground. The second system was a commercial 24-channel planar array with an aperture of 0.7 m, placed on the ground in the center of the triangle. By combining the two systems and applying advanced beamforming algorithms, wind turbine sound sources were located over the range of 2 Hz – 4 kHz. A low frequency source was found in a location that is consistent with an interaction between the blade tip vortex and the tower.

Infrasonic measurements, pre- and post-commissioning, Ontario wind farm

Brian Howe, Nick McCabe, Sean Ferguson, HGC Engineering, 2000 Argentia Road, Plaza One, Suite 203, Mississauga, Ontario, Canada, L5N 1P7, E-mail: bhowe___AT___hgcengineering.com nmccabe___AT___hgcengineering.com

Summary

A campaign of sound level measurements made at infrasonic frequencies was undertaken at a wind farm in Ontario, Canada. A series of attended measurements were conducted indoors at two residences, and a longer series of automated measurements were conducted outdoors, using an in-ground subsurface windscreen technique. The measurements were made prior to commissioning of the wind farm, and then repeated after production began. Similar trends with wind speed and wind turbine operation were observed in the indoor and outdoor data.

Influence on Hearing of LFN by Fluctuation of brightness

ITO Tatsuya University of Yamanashi, Takeda 4-3-11, Kofu, Yamanashi 400-8511, JAPAN, E-mail : g11mm003___AT___yamanashi.ac.jp,

HARA Atsushi University of Yamanashi, Takeda 4-3-11, Kofu, Yamanashi 400-8511, JAPAN E-mail : g12mm029___AT___yamanashi.ac.jp

KITAMURA Toshiya University of Yamanashi, Takeda 4-3-11, Kofu, Yamanashi 400-8511, JAPAN Email : kitamura___AT___yamanashi.ac.jp

Summary

A wind-power-generation equipment has problems of psychological and physiological influences on the person by a low frequency sound or a shadow flicker. Many researches on the influence of a low frequency sound and a shadow flicker were done separately. However, some complaints are annoyed by both of its. Therefore, we conducted exposing examinations on subjects with low frequency sound under the fluctuating brightness of a light. A hearing threshold and a psychological influence of beating low frequency sound on subjects under the fluctuating brightness condition or steady brightness condition were evaluated. The psychological influence was evaluated by a questionnaire under 0dB, +5dB or +10dB over their own hearing threshold level with variant or steady brightness condition. By the fluctuating of brightness, dispersion of the threshold grew. Though, there are no changes on a hearing threshold averaged by all subjects. From questionnaire, unpleasant feeling grew especially. An influence on annoyance was greater than by low frequency sound.

Options for assessment and regulation of low-frequency noise

Jan Jabben, National Institute for public Health and Environment (RIVM), Box 1, 3720 BA Bilthoven, The Netherlands. E-mail: Jan.Jabben___AT___rivm.nl

Edwin Verheijen, dBvision Consultants, Groenmarktstraat 39, 3521 AV, Utrecht, The Netherlands. E-mail: Edwin.Verheijen___AT___dbvision.nl

Summary

Dutch legal limits for Lden noise levels are different for road traffic, railways, industry and airports. A justification for these differences might be found in the difference between doseresponse relationships for noise annoyance. Nevertheless, frequently situations occur where people severely complain of low frequency noise, even when Lden levels amply comply with limits. So far, an effective regulation specifically for low frequency noise is not available. This paper discusses some options for improving the protection for LFN annoyance from Lden legislation. A potential solution might be to penalize Lden levels based on low versus high frequency ratio and tonality. This is demonstrated by examples for a number of LFN cases in the Netherlands.

Danish regulation of low frequency noise from wind turbines.

Jørgen Jakobsen. Danish Environmental Protection Agency, Strandgade 29, DK-1401 København K, Denmark email: jojak___AT___mst.dk

Summary

The Danish statutory order on wind turbine noise was revised in order to establish new rules for low frequency noise [1]. The new regulation entered into force January 1st, 2012, and it applies to wind turbines notified to the municipalities from this date. The new regulation complements the previous noise limits for wind turbines with a new mandatory limit for the low frequency noise, which is 20 dB A-weighted level of the indoor sound level in the 1/3- octave bands 10 - 160 Hz. The purpose of the new regulation is to ensure that neither the usual noise nor the low frequency noise will annoy the neighbours when the wind turbines start to operate.

Analysis of Models for Audible and Low Frequency Noise Prediction for Wind Turbine

Case Studies

Mahtab Kamali*, Siva Sivoththaman* and Stephen McColl**

*Electrical and Computer Engineering Department, University of Waterloo, 200 University Avenue West, Waterloo, Ontario, Canada N2L 3G1

**Department of Public Health and Health Systems, University of Waterloo, 200 University Avenue West, Waterloo, Ontario, Canada N2L 3G1

Summary

Wind power is a rapidly growing renewable energy technology with an annual growth rate of more than 25% over the last 5 years. By the end of year 2010, about 198 Gigawatts (GW) of electricity was produced worldwide by wind turbines. This number is predicted to reach 575 GW by year 2020 (Renewables’21 2011 and IEA 2011). With the rapid growth of this technology, there have also been some concerns of potential safety and health effects from wind turbines. One of the topics being actively debated is the noise generation from wind turbines.

Helping sufferers to cope with noise using distance learning cognitive behaviour therapy

Geoff Leventhall: Noise Consultant geoff___AT___activenoise.co.uk

Donald Robertson: CBT Practitioner don.robertson___AT___live.co.uk

Steve Benton: Westminster University bentons___AT___westminster.ac.uk

Lyn Leventhall: E-Learning Consultant lyn___AT___brookesweb.co.uk

Summary

Unresolved noise complaints cause considerable distress to sufferers, and a deterioration in quality of life as a consequence of failure to cope with the noise stress. The environmental noise control structure is directed towards higher frequency noises, which can be assessed by use of A-weighted measurements and this results in some low frequency noise problems receiving an inadequate evaluation. A number of countries now have limits for low frequency noise, but these are not yet well known or widely used. (Leventhall, 2009). Is there a solution to the problem of what can be done to help the small number of people who are adversely affected by perception of a low frequency noise, which it has not been possible to control? This paper describes how Cognitive Behaviour Therapy can be a solution.

Measurement of Psychological Response and Evaluation of Task Performance on Lowfrequency

Sound

Hiroshi MATSUDA College of Science and Technology, Nihon Univ. 7-24-1, Narashinodai, Funabashi city, Chiba, Japan. E-mail: matsuh_0604___AT___yahoo.co.jp

Nobuo MACHIDA College of Science and Technology, Nihon Univ. 7-24-1, Narashinodai, Funabashi city, Chiba, Japan. E-mail: machida___AT___eme.cst.nihon-u.ac.jp

Hoshito OHI Graduate School of Science and Technology, Nihon Univ. 7-24-1, Narashinodai, Funabashi city, Chiba, Japan. E-mail: hoshihoshi01071990___AT___yahoo.co.jp

Summary

Low-frequency sound of frequencies below 100 Hz has been an environmental problem in Japan since the 1970's. However, Japan has not yet established any regulatory standards regarding low-frequency sound for general environments or industrial workplaces. Lowfrequency sound is classified into either steady low-frequency sound (SLFS) or fluctuating low-frequency sound (FLFS). Generally, the influence of low-frequency sound on the human body is analysed using a SLFS generated from fixed sound sources. Therefore, nor has it  established any methods for measuring low-frequency sound generated from a moving sound source or a FLFS. We examined the influences of the SLFS and FLFS above the sensation threshold level based on the task performance in this study. The psychological response in the tasks was measured by using a seven-grade rating scale. We found from the experimental results that the task performance decreased about 5-10% when a SLFS and FLFS above the threshold level were present. In addition, for almost all the experimental conditions, the task performance under SLFS and FLFS do not appear to differ based on the frequency and sound pressure levels. In addition, the results of the psychological response to SLFS and the amplitude modulated low-frequency sound (AMLFS, carrier composed of sinusoidal wave frequency is constant) measured by whole-body exposure are described.

Effect of noise on the low frequency vibration sensation

Hisao MIURA Graduate school of Science and Technology, Nihon University, 7-24-1 Narashinodai, Funabashi city CHIBA JP. E-mail: cshs11038___AT___g.nihon-u.ac.jp

Nobuo MACHIDA College of Science and Technology, Nihon University, 7-24-1 Narashinodai, Funabashi city CHIBA JP. E-mail: machida___AT___eme.cst.nihon-u.ac.jp

Hiroshi MATSUDA College of Science and Technology, Nihon University, 7-24-1 Narashinodai, unabashi city CHIBA JP. E-mail: matsuh_0604___AT___yahoo.co.jp

Summary

In this study, the effect of whole-body vibration sensation was examined through exposure to subject vibration and noise. The vibration stimulation consisted of the low frequency wholebody vertical vibration, and then noise stimulation using white noise, musical tones, and a fluctuating sound synchronized with the body vibration. The evaluation method for the vibration sensation used the magnitude estimation method, the semantic differential method. The experimental results showed that the vibration sensation was changed, such as a decrease in sensible strength of vibration, when the human body was simultaneously exposed to both the vibration and noise stimulation.

Experience of adapting tinnitus and hyperacusis treatment techniques for LFN perception

Andy Moorhouse. University of Salford. Email: a.t.moorhouse___AT___salford.ac.uk

David Baguley. Cambridge University Hospitals NHS Foundation Trust.

Tim Husband. Dewsbury and District Hospital.

Claire Banks. North Devon District Hospital.

Pam Comiskey. Victoria Hospital, NHS Fife.

Tony Kay. Aintree University Hospitals NHS Foundation Trust.

Alan Kenyon. Blackpool Victoria Hospital.

Don McFerran. Colchester Hospital University NHS Foundation Trust.

Faye Penney. Torbay Hospital.

Karen Smith. Manchester Royal Infirmary. Christine Whalley. Torbay Hospital.

Summary

The paper describes a trial in which modern techniques for alleviating the symptoms of tinnitus and hyperacusis were adapted for use with clients with a complaint about LFN with no obvious origin. A treatment protocol was adapted from modern audiology practice specifically for LFN. The treatment rationale is based on models of tinnitus perception, the key feature being a cycle of increased perception in which anxiety or fear, increased central gain and increased autonomic activity play a role. This model and the associated treatment protocol, which aims at encouraging habituation, are described. Nine audiology centres around the UK were given special training in the protocol. The participating audiologists then accepted referrals from Environmental Health Officers in their area in cases where there was a complaint about LFN with no obvious origin. The aims were to improve quality of life for LFN sufferers and improve the effectiveness of Environmental Health Officers in dealing with cases of this type (which may form up to 70% of LFN complaints). The treatment protocol is described and its effectiveness discussed. Useful insight was also gained about the effective referral of LFN clients and the numbers of LFN sufferers within the health system in the UK.

Active low frequency sound field control in a listening room using CABS (Controlled Acoustic Bass System) will also reduce the sound transmitted to neighbour rooms.

Sofus Birkedal Nielsen. Acoustics, Department of Electronic Systems, Aalborg University, Fredrik Bajers Vej 7, 9220 Aalborg Ø, Denmark, Email: sbn___AT___es.aau.dk

Adrian Celestinos (former at:). Acoustics, Department of Electronic Systems Aalborg University, Fredrik Bajers Vej 7, 9220 Aalborg Ø, Denmark Email:acelestinos___AT___gmail.com

Summary

Sound in rooms and transmission of sound between rooms gives the biggest problems at low frequencies. Rooms with rectangular with hard boundaries have strong resonance frequencies and will give big spatial variations in sound pressure level (SPL). In the source room an increase of 20 dB SPL at a wall can appear at modal frequencies. For that reason the modal frequencies in the source room will also have big impact on the transmission to neighbour/receiver rooms. These low frequency resonance frequencies are very audible in the source room but also in neighbour rooms as a booming bass. CABS (Controlled Acoustic Bass System) is a time based room correction system for reproduced sound using loudspeakers. The system can remove room modes at low frequencies, by active cancelling the reflection from the rear wall of a normal stereo setup. This can be done using cancelling loudspeakers at the rear wall. Measurements in a source room using CABS and in two neighbour rooms have shown a reduction in sound transmission of up to 10 dB at resonance frequencies and a reduction at broadband noise of 3 – 5 dB at frequencies up to 100 Hz. The ideas and understanding of the CABS system will also be given. CABS is controlled by a developed digital signal processing system (DSP).

Microscope attached to the ceiling requires different solution

Carel Ostendorf, Cauberg-Huygen Raadgevende Ingenieurs BV, Postbus 480, 6200 AL Maastricht, The Netherlands, E-mail: c.ostendorf___AT___chri.nl

Summary

In order to increase the efficiency of operating rooms, more and more equipment is attached to the ceiling. This leaves more room for the people on the floor. The technical installations for air, pressure and water are positioned close to the operating room; on the next floor level for example. Computer screens, operating light and microscope are now attached to this same floor, introducing a potential vibration problem. During the design of two new buildings for a large hospital, this vibration problem was taken into account. Measurements had been done, a prediction had been made and measures had been taken. After the building, the first test results with the microscope were alarming. The image the microscope produced was vibrating in such a way that surgery was not possible. Several measurement sessions were carried out. The aim of one session was to measure the movement of the building and find out what kind of frequencies were relevant. In another session the installation of the microscope itself was studied including the influence of different kinds of vibration sources like traffic, technical installations and the movements of people. In this paper the results of the measurements are discussed as well as the solution that was chosen in the end.

Low-frequency noise from large wind turbines – additional data and assessment of new Danish regulations

Christian Sejer Pedersen, Henrik Møller, Steffen Pedersen, Section of Acoustics, Aalborg University, Fredrik Bajers Vej 7, B5, 9220 Aalborg Ø, Denmark, E-mail: [cp] [hm] [stp] ___AT___acoustics.aau.dk

Summary

Previous studies have shown that the noise has more low-frequency content, when wind turbines get larger, and with todays’ megawatt turbines the low-frequency noise may cause annoyance for the neighbours. Therefore, low-frequency noise has been included in the noise regulations on wind turbines in Denmark. In this study, the data material has been increased to include more data on noise from modern production turbines up to 3.6 MW. In addition, the new Danish regulations are assessed. The previous result that the relative amount of low-frequency noise is higher for large turbines (> 2 MW) than for small turbines ( 2 MW) is confirmed. Due to the air absorption, the higher low-frequency content becomes even more pronounced, when sound pressure levels in relevant neighbour distances are considered. Even when A-weighted levels are considered, a substantial part of the noise is at low frequencies, and for several of the investigated large turbines, the one-third-octave band with the highest level is at or below 250 Hz. It is thus beyond any doubt that the lowfrequency part of the spectrum plays an important role in the noise at the neighbours. The new Danish regulations are based on calculations of the indoor noise at the neighbours, but unfortunately, the calculation underestimates the level that would be measured, thus the regulation does not adequately prevent potential annoyance and sleep disturbance effects from future wind turbines in Denmark.

Control of noise – systems for compact HVAC units

Steffen Pedersen, Henrik Møller. Aalborg University, Fredrik Bajersvej 7 B4, 9220 Aalborg East, Denmark. E-mail: [stp],[hm]___AT___es.aau.dk

Summary

This paper discusses noise control systems for implementation in compact HVAC units. The control of low-frequency noise presents different problems than at higher frequencies. This is mainly related to the long wavelength, which means that passive solutions require a significant volume of space, often not available in compact HVAC units. Active control can provide attenuation over a significant frequency range, including low frequencies, while requiring a more limited space. While the concept of active noise control is simple, a number of limitations in the acoustical, electrical and control systems affect the performance of implementations. The source pressure and the impedance of a centrifugal fan were measured, and a number of configurations for noise control were investigated. The performance of a simple analogue feedback control was tested in a physical prototype. An adaptive digital controller (feedback and feedforward using FXLMS with cancellation of feedback to reference) was simulated and implemented on a low-cost TI C55XX DSP platform.

Can Infrasonic Lift Noise from Wind Turbine Rotors Contribute to Audible Sound?

Werner Richarz, Echologics Engineering, 6295 Northam Dr. #1, Mississauga, ON, Canada, wricharz___AT___echologics.com

Harrison Richarz, Clay Allee 336, #306, 14169 Berlin, Germany, hfr___AT___gmail.com

Summary

Autocorrelations of wind-turbine sound measured exhibit periodic ‘pulses’ at the blade passage frequency. Their amplitudes are a direct measure of the overall sound power that can be attributed to the low frequency sound emitted by the wind-turbine. In general this is of the order of 50% or less. As the shape of the auto-correlation is governed by the first few harmonics, one can randomize the relative phase of the higher harmonics without altering the shape of the auto-correlation. This phase randomization mimics propagation through a turbulent atmosphere. Whereas the low frequency pulses are virtually inaudible, phase randomization results an audible swoosh-like sound.

Wind noise estimation functions for low frequency sound measuring in natural wind

Masayuki Shimura, Noboru Kamiakito, Atushi Aoki, Kengo Tateishi and Hisashi Niwa, Civil Engineering and Eco-Technology Consultants Co. Ltd. 2-23-2, Higashi-Ikebukuro, Toshima-ku, Tokyo, Japan,  E-mail: shimura___AT___kensetsukankyo.co.jp

Takashi Nomura and Hiroshi Hasebe, Department of Civil Engineering, College of Science and Technology, Nihon University, 1-8-14, Kanda-Surugadai, Chiyoda-ku, Tokyo, Japan, E-mail: nomura___AT___civil.cst.nihon-u.ac.jp

Toshikazu Osafune, Nippon Expressway Research Institute Co. Ltd., 1-4-1, Tadao, Machida-shi, Tokyo, Japan, E-mail: t.osafune.aa___AT___ri-nexco.co.jp

Shiniti Terazono and Yasuhiko Kawasaki, Aco Co. Ltd., 85-1, Otsuka, Hachioji-shi, Tokyo, Japan, E-mail: aco-info___AT___aco-japan.co.jp

Yoshiki Ito, Takaaki Hayashi and Yoshinori Iwai, Sonic Corporation, 19-6, Higashimatsubara, Hakonegasaki, Mizuho-machi, Nishitama-gun, Tokyo, Japan, E-mail: yoshiki-ito___AT___u-sonic.co.jp

Summary

It is indispensable to distinguish wind noise and target sound for verification of measured sound results since, in natural wind, perturbation by wind is nothing but phenomenon of pressure fluctuation and the pressure fluctuation acts on a microphone as the wind noise. We have conducted wind tunnel experiments to evaluate the main factors of wind noise for a low frequency microphone, and have confirmed that three parameters, evaluation time for wind velocity, mean wind velocity and turbulence intensity, strongly affect wind noise level. Although the wind noise is also affected by incident angle of wind as well as specification of the microphone and the type of wind screen, we have attempted to evaluate the wind noise effects under some particular but typical conditions and have derived a set of regression functions to evaluate the wind noise levels. After these experimental works conducted in laboratory, we have continued to improve the regression functions for wind noise by natural wind based on the sound measurement at various outdoor sites. In the present paper, a prototype of our low frequency measuring system and the new improved regression functions are introduced.

Experiences with the New Danish Rules for the Calculation of Low Frequency Noise from Wind Turbines

Thomas Sørensen • EMD International A/S • Niels Jernesvej 10 • DK-9220 Aalborg Ø • Email:ts___AT___emd.dk • T: +45 9635 4444

Summary

January 1 st 2012, a revision of the Danish Rules for Wind Turbines was published by the Danish Ministry of the Environment. The new rules include a set of requirements for the low frequency noise emissions from wind turbines. These rules includes a propagation model for the calculation of low frequency noise as well as specifying a procedure for measuring the source low frequency noise level from the turbines. Along also has come a guideline to the codes. While implementing the new rules and performing the first studies based on the new rules, it has been clear that calculation of noise in a landscape with existing turbines is by no means a simple matter and that the new low frequency noise requirements do impose additional complexity to the noise analysis. Our study outlines the first experiences with the new Danish noise rules including a number of lessons learned. These cover interesting implications for turbine owners, developers, turbine suppliers, local authorities and consultants alike. Such problems facing the implicated parties are:

  • Access to source noise data

  • How do we deal with existing turbines with no source noise data?

  • How does the low frequency noise impact differ from regular noise?

  • What is the necessary level of documentation?

We have yet to see if the turbines will pass the post installation noise measurements.

Enhanced Perception of Infrasound in the Presence of Low-Level Uncorrelated Low-Frequency Noise.

Dr M.A.Swinbanks, MAS Research Ltd, 8 Pentlands Court, Cambridge CB4 1JN, UK., malcva___AT___msn.com

Summary

In prior work, the author has presented a technique for evaluating perception of infrasound and low-frequency noise, relative to the threshold of hearing, by a cumulative integration process which matches the mean energy of the sound to that of an equivalent sinusoid at the hearing threshold. The author demonstrated that this approach, while rigorous, fails to take account of the crest factor of the sound, which can be very much greater than that of a pure sinusoid. Time domain simulation of the hearing response to real signals near the hearing threshold showed that taking the effect of crest factor into account, low frequency and infrasound may be perceptible at significantly lower levels than those defined by the simple criterion of equating mean sound energy. This analysis has now been developed further, using time-domain simulation to take account of a well-defined hearing threshold, together with the effects of additional, uncorrelated lowfrequency noise present within the same critical bandwidth (1Hz – 100Hz). The results of dynamic simulation show that in the presence of such uncorrelated, low-level noise, unwanted low-frequency sound and infrasound may be perceived at levels which would otherwise be completely dismissed as being well below the threshold of hearing. These conclusions will be shown to be consistent with prior reported peer-reviewed laboratory experimental data, which hitherto has defied immediate explanation.

Audibility of low frequency sounds – Part 1: Experiment on hearing thresholds for pure tones

Hideki Tachibana Chiba Institute of Technology, Tsudanuma 2-17-1, Narashino, Chiba, 275-0016, Japan E-mail: pon-t___AT___iis.u-tokyo.ac.jp

Shinichi Sakamoto Institute of Industrial Science, The University of Tokyo, Komaba 4-6-1, Meguro, Tokyo 153-8505, Japan E-mail: sakamo___AT___iis.u-tokyo.ac.jp

Sakae Yokoyama Institute of Industrial Science, The University of Tokyo, Komaba 4-6-1, Meguro, Tokyo 153-8505, Japan E-mail: sakae___AT___iis.u-tokyo.ac.jp

Hiroo Yano Chiba Institute of Technology, Tsudanuma 2-17-1, Narashino, Chiba 275-0016, Japan E-mail: yano___AT___acoust.cs.it-chiba.ac.jp

Summary

To investigate wind turbine noise problem, the study program titled “Research on the Evaluation of Human Impact of Low Frequency Noise from Wind Turbine Generators” has been planed over the three years from the 2010 fiscal year, under the sponsorship of the Ministry of the Environment, Japan. As a study in this research, subjective experiments on audibility of low frequency sounds are being performed by using an experimental facility consisting of a couple of a reverberation room and an anechoic room using sixteen woofers. As the first step of this study, the hearing thresholds in the frequency range between 10 Hz and 200 Hz were examined by getting participation of 97 subjects in a wide age range from 20’s to 60’s.

The influence of audible background noise on the equal-sensation levels for “vibration perceived in the head” of subjects exposed to low-frequency noise

Yukio Takahashi, National Institute of Occupational Safety and Health, Japan, 6-21-1 Nagao, Tama-ku, Kawasaki 214-8585, Japan. E-mail: takahay___AT___h.jniosh.go.jp

Summary

The results of our previous study suggested that the head was the part of the body most sensitive to the vibratory sensation induced by low-frequency noise. A subsequent study showed that the threshold levels for “vibration perceived in the head” were hardly affected by audible background noise, which suggested that a person exposed to low-frequency noise perceived vibration in the head almost independent of the perception of sound. In the present study, to confirm the previous result, we measured the equal-sensation levels for “vibration perceived in the head” while presenting audible background noise. The background noises, whose A-weighted sound pressure levels were 45 and 55 dB(A), were the same as those used in the previous study. A 50-Hz, 85-dB(Z) tone was used as the reference tone for measuring the equal-sensation level for “vibration perceived in the head”. We found that the audible background noise hardly affected the equal-sensation levels for “vibration perceived in the head”. This result supported our previous finding that a subjective perception of vibration in the head of a person exposed to low-frequency noise was not related strongly to the perception of sound.

The application of DEFRA LFN procedure for LFN complaints and subsequent source identification and resolution

Jon Tofts, Environment Agency, SW Regional Noise Advisor. E-mail: Jon.Tofts___AT___Environment-Agency.gov.uk

Summary

1) The LFN criteria presented in “Proposed criteria for the assessment of low frequency noise disturbance” (NANR45) are suitable for noise regulators, such as the Environment Agency, to determine the presence of LFN pollution from industrial sources. 2) The ideal solution of ‘tackling noise at source’ is achievable with LFN sources, particularly centrifugal fans. If this is not an option, then noise absorbent can adequately abate the noise, given both sufficient quantity and a suitable design. 3) The use of synchronised noise meters allows potential noise sources to be positively discounted.

Study on the evaluation from the propagation of the repetitive vibrations

Masashi UCHIKUNE, Department of Precision Machinery Engineering, College of Science & Technology, Nihon University, Japan. E-mail:uchikune___AT___eme.cst.nihon-u.ac.jp

Summary

The purpose of this study is to make clear the physiological and psychological effects of the subjects with the backrest contact-transmitted vibration for the health effects of guidance. The subjects occurred the health effects in seated position with the passage of time and the work of sitting considered the workload and it measured the difference in the health effects of the duration of the exposures (1800s) and for the threshold value from 0.00111, 0.0326 (0.13Hz) to 0.399 m/s 2 (0.47 Hz) at short durations with the repetitive vibrating and it aimed at the caution guide for the application of frequency-weighting curves with respect to health effects. Concerning the exposure during a short term which is made that causes the function from the backrest contact- transmitted vibration of the whole-body vibration. For seated persons, it examined to find the effect of the whole-body vibration in a very low frequency range, Physiological effects were examined by investigation of the effects on the cardiovascular system, the blood flow system, the respiratory movement, the salivation, the core body temperature, electromyography system, to confirm the effects on the autonomic nervous system, and on postural sways in the normal Romberg’s position. According to a result concerning of the experiment set up by us, effects were seen in acceleration ranging from 0.209 m/s 2 in the horizontal direction (fore-and-aft movements) of the frequency ranging 0.34 Hz, which are then transmitted to a human body.

Time domain analysis of low frequency wind turbine noise

Bruce Walker Channel Islands Acoustics, 676 W Highland Dr, Camarillo, CA 93010 USA. E-mail: noiseybw___AT___aol.com

Summary

A simple field-deployable system has been developed and tested for capturing phaseaccurate waveforms of low frequency and infrasonic periodic and impulsive acoustic emissions. The intent of the system is to provide a data base for subjective evaluation. Secondarily, the system is capable of approximate source location based on cross-correlation functions for multiple pairs of matched microphones. This paper is a progress report on the evolution of the measurement system and its use for examination of field data. Concurrently with this project, an extended low frequency range playback system is being fabricated to allow influences of wave-form parameters to be judged aurally relative to audibility threshold and annoyance potential.

Auditory masking by band noise at low frequencies

Toshio Watanabe Fukushima National College of Technology 30 Nagao, Kamiarakawa, Taira, Iwaki, 970-8034 Japan E-mail: twatanabe___AT___fukushima-nct.ac.jp

Summary

Auditory masking of low frequency sound was measured. Masking sounds are band noise whose central frequencies are 20Hz and 40Hz, and these levels are 70dB and 47dB. They have the same loudness. The measurement frequencies are from 8Hz to 50Hz, 1/3 octave step. The number of subjects is twenty one. To check the masking characteristic cluster analysis was applied to the masking results. They were divided into three patterns and each group had the original characteristic and the each deviation was smaller than the total deviation. The masking frequency characteristic by 20Hz band noise was similar to that of 40Hz band noise in every group. For group A, the masking values increase as the frequency increases. For group B, they are very small at all frequencies. For group C, they are negative at all frequencies. The masking values were measured as the bandwidth of making noise is changed. Eleven subjects were participated in this experiment. They were all engaged in the experiment of masking by 20Hz and 40Hz band noise. The masking results were also divided into three groups and had the different characteristic. The masking characteristic by band noise could be connected with the bandwidth changing. It is clear that the hearing characteristics are divided into three groups and each group has the original hearing ability a tlow frequencies.

Recent examples of field measurements on low frequency sound and complaints by a

non profit organization for supporting noise and low frequency noise complainants in

Japan

Shinji YAMADA, Yukio INUKAI, Kimiaki TAKAGI, TsutaeSEBAYASHI, Shota

KOYAMA, Yukiko TANAKA and Yuji HORIE

NPO for Supporting Noise, Vibration and Low Frequency Noise Complainants, 1-9-3 Shiobe,

Kofu, Yamanashi, 400-0026 Japan

E-mail: shinji-yamada___AT___ae.auone-net.jp

Summary

The number of noise complaints of Japan is around 15,000 a year and there are about 200 complaints of low frequency noise. In our NPO (Non Profit Organization), the specialists as volunteers on noise, vibration, low frequency noise consult with the complaints and measure the low frequency noise. It is difficult to measure the noise in the night by local government, and in such cases we measure the noise in the night for a long-time in complainant’s house. However, sometimes we cannot find the appropriate level of low frequency noise, though the complaint appeals for the serious damage by low frequency noise. Therefore we measured the complaint’s reaction at the same time with low frequency noise in the complainant's house. We analyzed the correlation between the complaint’s reaction and measured low frequency noise. In many cases, we cannot find out the correlation between the measured low frequency noise and complainant’s reaction.

Development of measurement system for wind turbine noise

Hiroo Yano Chiba Institute of Technology, Tsudanuma 2-17-1, Narashino, Chiba 275-0016,

Japan E-mail: yano___AT___acoust.cs.it-chiba.ac.jp

Tatsuya Ohta Chiba Institute of Technology, Tsudanuma 2-17-1, Narashino, Chiba 275-0016,

Japan E-mail: ohta___AT___acoust.cs.it-chiba.ac.jp

Hideki Tachibana Chiba Institute of Technology, Tsudanuma 2-17-1, Narashino, Chiba 275-

0016, Japan E-mail: pon-t___AT___iis.u-tokyo.ac.jp

Summary

To investigate wind turbine noise problem, a study program titled “Research on the Evaluation of Human Impact of Low Frequency Noise from Wind Turbine Generators” has been planed over the three years from the 2010 fiscal year under the sponsorship of the Ministry of the Environment, Japan. As a main study in this research, field measurements are now being performed at a lot of wind turbine sites in Japan. For this aim, a new type sound level meter with a wide frequency range (1 Hz to 20k Hz) and a windscreen system of double skin construction with a high wind shielding performance were developed by considering the convenience at the measurement sites. To examine the performances of the measurement instrumentation and to find the general method of measuring wind turbine noise in the immission areas, various laboratory experiments using anechoic room and a wind tunnel and preliminary field tests were performed.

Audibility of low frequency sounds – Part 2: Audibility of low frequency components in

wind turbine noises

Sakae Yokoyama Institute of Industrial Science, The University of Tokyo, Komaba 4-6-1,

Meguro, Tokyo 153-8505, Japan E-mail: sakae___AT___iis.u-tokyo.ac.jp

Shinichi Sakamoto Institute of Industrial Science, The University of Tokyo, Komaba 4-6-1,

Meguro, Tokyo 153-8505, Japan E-mail: sakamo___AT___iis.u-tokyo.ac.jp

Hiroo Yano Chiba Institute of Technology, Tsudanuma 2-17-1, Narashino, Chiba 275-0016,

Japan E-mail: yano___AT___acoust.cs.it-chiba.ac.jp

Hideki Tachibana Chiba Institute of Technology, Tsudanuma 2-17-1, Narashino, Chiba

275-0016, Japan E-mail: pon-t___AT___iis.u-tokyo.ac.jp

Summary

Human audibility of low frequency components contained in wind turbine noise was investigated by using actual wind turbine noises (on-site recordings) and an artificial model sound representing the general wind turbine noises. In this experiment, the higher frequency components of these sounds were cut off through a low-pass filter of which cut-off frequency was changed from 10 Hz to 125 Hz in 10 steps. The test sounds were produced in an anechoic room through a loudspeaker system consisting of sixteen woofers and one middle/high-frequency-range loudspeaker. To examine the subject’s sensation (audibility) objectively, the Maximum-Length-Sequence (MLS) modulation cross-correlation technique was applied. That is, the test sounds were produced intermittently being modulated by a 5 th order MLS-signal and the cross-correlation between the MLS-signal and the subject’ response presented by a push-button system was calculated. As a result, it has been confirmed that the low frequency components in infrasound frequency range of general wind turbine noises can not be heard by human auditory sense.