home *** CD-ROM | disk | FTP | other *** search
- Path: senator-bedfellow.mit.edu!bloom-beacon.mit.edu!news.starnet.net!news.starnet.net!newspump.wustl.edu!hood.cc.rochester.edu!news.acsu.buffalo.edu!dsinc!pitt.edu!gatech!howland.erols.net!feed1.news.erols.com!dispatch.news.demon.net!demon!mail2news.demon.co.uk!measure.demon.co.uk!Enviro
- From: Andrew Silverman <Enviro@measure.demon.co.uk>
- Newsgroups: alt.sci.physics.acoustics,alt.answers,news.answers
- Subject: Acoustics FAQ
- Followup-To: alt.sci.physics.acoustics
- Date: Sun, 07 Sep 97 20:55:00 GMT
- Organization: EnviroMeasure
- Approved: news-answers-request@MIT.EDU
- Message-ID: <873665061snz@measure.demon.co.uk>
- Reply-To: Enviro@measure.demon.co.uk
- X-Mail2News-User: Enviro@measure.demon.co.uk
- X-Mail2News-Path: punt-1.mail.demon.net!measure.demon.co.uk
- X-Newsreader: Demon Internet Simple News v1.30
- Lines: 1542
- Xref: senator-bedfellow.mit.edu alt.sci.physics.acoustics:6893 alt.answers:28801 news.answers:111778
-
- Archive-name: physics-faq/acoustics
- Last-modified: 7th September 1997
- Version: 0.09
-
- *** ACOUSTICS FAQ ***
-
-
- DISCLAIMER - NO WARRANTY OF ANY KIND WHATSOEVER IS MADE FOR THE FITNESS
- OF THE CONTENTS OF THIS FAQ.
-
- In order to allow maximum compatibility only ASCII symbols are used
-
-
-
- Aims
- ====
-
- * To make acoustics accessible to a wider public
- * To encourage cooperation within the acoustics community
-
-
-
- Changes since previous version
- ==============================
- 1.2 Web site revision & additions
- 1.3 software revisions
- 2.1 addition
- 2.9 added and qs following renumbered
- 2.10 revised
- 2.11 revised
- 6.1, 6.4 revised
- 6.7 musical intervals added, following renumbered (inc ref 6.10)
- 9 address & e-mail additions and revisions
-
-
- 1] Resource Pointers
-
- 1.1 What acoustics related news groups and FAQs are there ?
- 1.2 What World Wide Web sites are there ?
- 1.3 What acoustics software is available on the Net ?
- 1.4 What acoustics books and journals are there ?
-
-
- 2] Basic Acoustics
-
- 2.1 What is sound ?
- 2.2 What is a decibel (dB) ?
- 2.3 How is sound measured ?
- 2.4 What does dB(A) or "A-weighted" mean ?
- 2.5 How do sound levels add ?
- 2.6 How does the ear work ?
- 2.7 At what level does sound become unsafe ?
- 2.8 What is sound intensity ?
- 2.9 How does sound decay with distance ?
- 2.10 What is the sound power level ?
- 2.11 What is the speed of sound in air, water .. ?
- 2.12 What is meant by loudness?
-
-
- 3] Vibration
-
- 3.1 What is vibration?
- 3.2 How is vibration measured ?
- 3.3 How is vibration isolated and controlled ?
-
-
- 4] Architectural & Building Acoustics
-
-
- 4.1 What is reverberation time ?
- 4.2 What is the sound absorption coefficient ?
- 4.3 What is the difference between insulation & absorption ?
- 4.4 How is sound insulation measured ?
- 4.5 How do I improve the noise insulation of my house/dwelling ?
-
- 5] Reserved
-
- 6] Miscellaneous Questions
-
- 6.1 What is active noise control ?
- 6.2 What causes a sonic boom ?
- 6.3 Can you focus sound ?
- 6.4 What is sonoluminescence ?
- 6.5 Why does blowing over a bottle make a note ?
- 6.6 What is pitch ?
- 6.7 What are musical intervals?
- 6.8 What causes "helium voice" ?
- 6.9 What is structural acoustics ?
- 6.10 What is the Doppler effect ?
- 6.11 What is white noise, pink noise ?
-
- 7] INDEX
-
- 8] Various Tables
-
- 8.1 Formula for A weighting
-
- 9] List of National Acoustic Societies
- -------------------------------------------------------------
- -------------------------------------------------------------
-
-
- 1] Resource Pointers
- -----------------
-
- *** 1.1 What acoustic related news groups and FAQs are there ?
-
- news groups
- -----------
-
- news:alt.sci.physics.acoustics - started by Angelo Campanella - now the
- principal group for discussion of acoustics topics. Ang's CV is at URL
- http://www.Point-and-Click.com/Campanella_Acoustics/angelo.htm
-
- news:sci.physics - general physics but occasionally acoustics related
- questions are posted.
-
- news:rec.audio.tech - includes discussion on audio equipment, speakers
- etc. There are other rec.audio groups which may be of interest.
-
- news:alt.support.hearing-loss and news:alt.support.tinnitus - groups
- for sufferers of these complaints
-
- news:bionet.audiology - matters relating to hearing and hearing loss
-
- news:bit.listserv.deaf-l news:uk.people.deaf news:alt.society.deaf
- - usenet seems an ideal communication medium.
-
- news:comp.dsp - the group for people interested in computing digital
- signal processing solutions, FFTs FIRs IIRs etc.
-
- news:comp.speech - speech recognition and simulation
-
- news:comp.sys.ibm.pc.soundcard.misc - various discussion of use of
- internal soundcards in IBM compatible computers.
-
-
- FAQs
- ----
- The main archive site for all usenet FAQs is
- ftp://rtfm.mit.edu/pub/usenet/
-
- A list of sites (including html) for the Acoustics FAQ is at
- http://super.zippo.com/~consult/Acoustics_FAQ_mirrors.html
- --------------
- The Active Noise Control FAQ by Chris Ruckman is at
- http://www.xis.com/~ruckman/
- --------------
- The Tinnitus FAQ deals with a range of hearing disorders. It is
- maintained by Mark Bixby and available at
- http://www.cccd.edu/faq/tinnitus.html
- --------------
- The Audio FAQ, with everything you ever wanted to know about the
- subject, from preamplifiers to speakers and listening room acoustics.
- It is located in the pub/usenet/rec.audio.* directories
- --------------
- The comp.speech faq maintained by Andrew Hunt has information on speech
- processing and some software links
- http://www.speech.su.oz.au/comp.speech/
- --------------
-
- *** 1.2 What World Wide Web sites are there ?
-
- Many acoustical web resources can be found from links in the first two
- locations or the "search engines" listed below.
-
- http://www.ecgcorp.com/velav/index.html
- (virtual lib for acoustics & vibration with useful links)
- http://capella.dur.ac.uk/doug/acoustics.html
- (wide selection of acoustics related links)
- http://www.campus.bt.com/CampusWorld/pub/ScienceNet/first.html
- (science questions and answers)
- http://online.anu.edu.au/ITA/ACAT/drw/PPofM/INDEX.html
- (simple acoustics introduction from David Worrall)
- http://www.mme.tcd.ie/~m.carley/Notes/
- (theoretical basic acoustics lecture notes; difficult stuff like
- the wave equation etc, in hypertext for browsing, or gzipped
- Postscript format for downloading)
- http://asa.aip.org/
- (Acoustical Society of America home page with several links and
- comprehensive career section, book lists and Society info etc)
- http://pcfarina.eng.unipr.it/
- (Angelo Farina has published a variety of papers - some are
- available in zipped MSWord format)
- http://eaa.essex.ac.uk/eaa/
- (European Acoustics Association)
- http://users.aol.com/inceusa/ince.html
- (Institute of Noise Control Engineering home page)
- http://super-highway.net/~wattsup/Audio%20related%20Site%20list.html
- (Steve Ekblad's extensive audio related BBS and Internet list)
- http://www.techexpo.com/
- (Technical societies, conferences etc etc but not specifically
- acoustics related)
- http://www.iso.ch/
- (main ISO standards page)
- http://www.iso.ch/addresse/membodies.html
- (national standards organizations addresses)
- http://www.ansi.org/
- (official ANSI site)
-
- The Digital Equipment Corporation has an extremely powerful Advanced
- Search facility at:
-
- http://altavista.digital.com/
-
- alternatively try searches on:
- http://www.yahoo.com/
- http://www.hotbot.com/
- http://www.infoseek.com/
- http://www.excite.com/
- http://www.lycos.com/
- http://www.dejanews.com/ (can also be used as Usenet posting gateway)
-
- or use your nearest Archie site to look for files you want.
-
- *** 1.3 What acoustics software is available on the Net ?
-
- A range of programs available for downloading from the Simtel archive.
-
- Spectrogram 3.2 - Accurate realtime Win95 spectrum analysis program
- (freeware) by Richard Horne is at a few sites including:
- http://tinker.winsite.com/info/pc/win95/sounds/gram32.zip
-
- The comp.speech faq has several links to speech related software
- including speech recognition and text to speech programs.
-
- There are a few programs for various platforms listed at URL
- http://www.cisab.indiana.edu/CSASAB/index.html
- The programs listed are mainly for sound analysis and editing.
-
- Some software is available for audio systems design at URL
- ftp://ftp.uu.net/usenet/rec.audio.high-end/Software
-
- Odeon is a program for architectural acoustics. A demonstration version
- is available by ftp. The demo includes a large database for
- coefficients of absorption. A web page at URL
- http://www.dat.dtu.dk/~odeon/index.html
- describes the capabilities of the program and gives the ftp address.
-
- Also some interactive acoustics software (eg room acoustics, RT,
- decibel conversion etc) is available at a couple of sites.
-
- *** 1.4 What acoustics books and journals are there ?
-
- There is a large range of books available on the subject. Generally the
- choice of book will depend on which approach and subject area is of
- interest. A few books are listed below:
-
- >>Introduction to Sound
- >>Speaks, C
- Good foundation for acoustics principles
-
- >>Acoustics Source Book
- >>Parker, S (editor)
- Basic introductory articles on many topics discussed in the
- alt.sci.physics.acoustics group. Old book - technology a bit dated.
-
- >>The Science of Sound
- >>Rossing, T
- Introductory book on acoustics, music and audio
-
- >>Fundamentals of Acoustics
- >>Kinsler, L Frey, A et al.
- Good overall coverage of acoustics but includes lots of theory
-
- >>Acoustics ...
- >>Pierce, A
- Classic advanced text - lots of theory
-
- >>Engineering Noise Control
- >>Bies, D & Hansen, C
- Practically biased with examples. Partially updated and corrected.
-
- >>Handbook of Acoustical Measurements and Noise Control
- >>Harris C (editor)
- Comprehensive practical reference book.
-
-
- A list of recently reviewed noise-related books is at URL
- http://users.aol.com/inceusa/books.html
-
-
- Some Journals
- -------------
- Journal of the Acoustical Society of America (monthly)
- Noise Control Engineering (US - every 2 months)
- Acoustics Bulletin (UK - every 2 months)
- Acta Acustica (P.R.China)
- Acta Acustica / Acustica (Europe - 6 per year)
- Journal of the Acoustical Society of Japan (E) (English edn - 2 months)
- Acoustics Australia (3 per year)
- Journal of Sound & Vibration (UK - weekly)
- Journal of the Audio Engineering Society (US - 10 per year)
- Applied Acoustics (UK - 12 per year)
-
- ---------------------------------------------------------------
- ---------------------------------------------------------------
-
-
-
-
- | Definitions used:
- |
- | 10^(-5) indicates 10 raised to the power of minus 5
- | 1.0E-12 indicates 1.0 x 10^(-12)
- | 1 pW indicates 1 picowatt i.e. 1.0E-12 Watt
- | W/m^2 indicates Watts per square metre
- | lg indicates logarithm to base 10
- | sqrt indicates the square root of
- | pi = 3.142
- | Lw is sound power level, the w is subscripted
-
- 2] Basic Acoustics
- ---------------
-
- *** 2.1 What is sound ?
-
-
- Sound is the quickly varying pressure wave within a medium.
- We usually mean audible sound, which is the sensation (as detected by
- the ear) of very small rapid changes in the air pressure above and
- below a static value. This "static" value is atmospheric pressure
- (about 100,000 Pascals) which does nevertheless vary slowly, as shown
- on a barometer. Associated with the sound pressure wave is a flow of
- energy. Sound is often represented diagrammatically as a sine wave, but
- physically sound (in air) is a longitudinal wave where the wave motion
- is in the direction of the movement of energy. The wave crests can be
- considered as the pressure maxima whilst the troughs represent the
- pressure minima.
-
- How small and rapid are the changes of air pressure which cause sound?
- When the rapid variations in pressure occur between about 20 and 20,000
- times per second (ie at a frequency between 20Hz and 20kHz) sound is
- potentially audible even though the pressure variation can sometimes
- be as low as only a few millionths of a Pascal. Movements of the ear
- drum as small as the diameter of a hydrogen atom can be audible! Louder
- sounds are caused by greater variation in pressure - 1 Pascal, for
- example, will sound quite loud, provided that most of the acoustic
- energy is in the mid-frequencies (1kHz - 4kHz) where the ear is most
- sensitive.
-
- What makes sound?
- Sound is produced when the air is disturbed in some way, for example
- by a vibrating object. A speaker cone from a hi-fi system serves as a
- good illustration. It may be possible to see the movement of a bass
- speaker cone, providing it is producing very low frequency sound. As
- the cone moves forward the air immediately in front is compressed
- causing a slight increase in air pressure, it then moves back past its
- rest position and causes a reduction in the air pressure (rarefaction).
- The process continues so that a wave of alternating high and low
- pressure is radiated away from the speaker cone at the speed of sound.
-
-
- *** 2.2 What is a decibel (dB) ?
-
- The decibel is a logarithmic unit which is used in a number of
- scientific disciplines. In all cases it is used to compare some
- quantity with some reference value. Usually the reference value is the
- smallest likely value of the quantity. Sometimes it can be an
- approximate average value.
-
- In acoustics the decibel is most often used to compare sound pressure,
- in air, with a reference pressure. References for sound intensity,
- sound power and sound pressure in water are amongst others which are
- also commonly in use.
-
- Reference sound pressure (in air) = 0.00002 = 2E-5 Pa (rms)
- " " intensity = 0.000000000001 = 1E-12 W/m^2
- " " power = 0.000000000001 = 1E-12 W
- " " pressure (water) = 0.000001 = 1E-6 Pa
-
- Acousticians use the dB scale for the following reasons:
-
- 1) Quantities of interest often exhibit such huge ranges of
- variation that a dB scale is more convenient than a linear
- scale. For example, sound pressure radiated by a submarine may
- vary by eight orders of magnitude depending on direction.
-
- 2) The human ear interprets loudness on a scale much closer to
- a logarithmic scale than a linear scale.
-
-
- *** 2.3 How is sound measured ?
-
- A sound level meter is the principal instrument for general noise
- measurement. The indication on a sound level meter (aside from
- weighting considerations) indicates the sound pressure, p, as a level
- referenced to 0.00002 Pa.
-
- Sound Pressure Level = 20 x lg (p/0.00002) dB
-
- Peak levels are occasionally quoted. During any given time interval
- peak levels will be numerically greater, and often much greater than
- the (rms) sound pressure level.
-
- *** 2.4 What does dB(A) or "A-weighted" mean ?
-
- Noise was not of particular concern at the beginning of the century.
- The first electrical sound meter was reported by George W Pierce in
- Proceedings of the American Academy of Arts and Sciences, v 43 (1907-8)
- A couple of decades later the switch from horse-drawn vehicles to
- automobiles in cities led to large changes in the background noise
- climate. The advent of "talkies" - film sound - was a big stimulus to
- sound meter patents of the time, but there was still no standard method
- of sound measurement.
-
- The first tentative standard for sound level meters (Z24.3) was
- published by the American Standards Association in 1936, sponsored by
- the Acoustical Society of America. The tentative standard shows two
- frequency weighting curves "A" and "B" which were modelled on the ear's
- response to low and high levels of sound respectively.
-
- The most common weighting today is "A-weighting" dB(A), which is very
- similar to that originally defined as Curve "A" in the 1936 standard.
- "C-weighting" dB(C), which is used occasionally, has a relatively flat
- response. "U-weighting" is a recent weighting which is used for
- measuring audible sound in the presence of ultrasound, and can be
- combined with A-weighting to give AU-weighting. The A-weighting formula
- is given in section 8 of the FAQ.
-
- In addition to frequency weighting, sound pressure can be weighted in
- time with fast, slow or impulse response. Measurements of sound
- pressure level with A-weighting and fast response are also known as the
- "sound level".
-
- Some sound level meters can measure the average sound level of a noise
- over a given time. It is called the equivalent continuous sound level
- (L sub eq) and is A-weighted but not time weighted.
-
-
- *** 2.5 How do sound levels add ?
-
- If there are two sound sources in a room - for example a radio
- producing an average sound level of 62.0 dB, and a television producing
- a sound level of 73.0 dB - then the total sound level is a logarithmic
- sum ie
-
- Combined sound level = 10 x lg ( 10^(62/10) + 10^(73/10) )
-
- = 73.3 dB
-
- Note: for two different sounds, the combined level cannot be more than
- 3 dB above the higher of the two sound levels. However, if the sounds
- are phase related there can be up to a 6dB increase in SPL.
-
-
- *** 2.6 How does the ear work ?
-
- The eardrum is connected by three small jointed bones in the air-filled
- middle ear to the oval window of the inner ear or cochlea, a fluid-
- filled spiral coil about one and a half inches in length. Over 10,000
- hair cells on the basilar membrane along the cochlea convert minuscule
- movements to nerve impulses, which are transmitted by the auditory
- nerve to the hearing center of the brain.
-
- The basilar membrane is wider at its apex than at its base, near the
- oval window, whereas the cochlea tapers towards its apex. Different
- groups of the delicate hair sensors on the membrane, which varies in
- stiffness along its length, respond to different frequencies
- transmitted down the coil. The hair sensors are one of the few cell
- types in the body which do not regenerate. They may therefore become
- irreparably damaged by large noise doses. Refer to the Tinnitus FAQ for
- more information on hearing disorders.
-
- http://www.mankato.msus.edu/dept/comdis/kuster2/audiology.html
- http://oto.wustl.edu/cochlea
- ftp://rtfm.mit.edu/pub/usenet/news.answers/medicine/tinnitus-faq
-
- *** 2.7 At what level does sound become unsafe ?
-
- It is best, where possible, to avoid any unprotected exposure
- to sound pressure levels above 100dB(A). Use hearing protection when
- exposed to levels above 85dB(A), especially if prolonged exposure is
- expected. Damage to hearing from loud noise is cumulative and is
- irreversible. Exposure to high noise levels is also one of the main
- causes of tinnitus. The safety aspects of ultrasound scans are the
- subject of ongoing investigation.
-
- There are other health hazards from extended exposure to vibration. An
- example is "white finger", which is found amongst workers who use hand-
- held machinery such as chain saws.
-
-
- *** 2.8 What is sound intensity ?
-
- This may be defined as the rate of sound energy transmitted in a
- specified direction per unit area normal to the direction. With good
- hearing the range is from about 0.000000000001 Watt per square metre
- to about 1 Watt per square metre (12 orders of magnitude greater). The
- sound intensity level is found from intensity I (W/m^2) by:
-
- Sound Intensity Level = 10 x lg (I/1.0E-12) dB
-
- Note: 1.0E-12 W/m^2 normally corresponds to a sound pressure of about
- 2.0E-5 Pascals which is used as the datum acoustic pressure in air.
-
- Sound intensity meters are becoming increasingly popular for
- determining the quantity and location of sound energy emission.
-
-
- *** 2.9 How does sound decay with distance ?
-
- The way sound changes with distance from the source is dependent on the
- size and shape of the source and also the surrounding environment and
- prevailing air currents. It is relatively simple to calculate provided
- the source is small and outdoors, but indoor calculations (in a
- reverberant field) are rather more complex.
-
- If the noise source is outdoors and its dimensions are small compared
- with the distance to the monitoring position (ideally a point source),
- then as the sound energy is radiated it will spread over an area which
- is proportional to the square of the distance. This is an 'inverse
- square law' where the sound level will decline by 6dB for each doubling
- of distance.
-
- Line noise sources such as a long line of moving traffic will radiate
- noise in cylindrical pattern, so that the area covered by the sound
- energy spread is directly proportional to the distance and the sound
- will decline by 3dB per doubling of distance.
-
- Close to a source (the near field) the change in SPL will not follow
- the above laws because the spread of energy is less, and smaller
- changes of sound level with distance should be expected.
-
- In addition it is always necessary to take into account attenuation due
- to the absorption of sound by the air, which may be substantial at
- higher frequencies. For ultrasound, air absorption may well be the
- dominant factor in the reduction.
-
- *** 2.10 What is the sound power level ?
-
- Sound power level, Lw, is often quoted on machinery to indicate
- the total sound energy radiated per second. The reference power is
- taken as 1pW.
-
- For example, a lawn mower with sound power level 88dB(A) will produce
- a sound level of about 60dB(A) at a distance of 10 metres. If the sound
- power level was 78dB(A) then the lawn mower sound level would be only
- 50dB(A) at the same distance.
-
-
- *** 2.11 What is the speed of sound in air, water .. ?
-
- The speed of sound in air at a temperature of 0 degC and 50% relative
- humidity is 331.6 m/s. The speed is proportional to the square root of
- absolute temperature and it is therefore about 12 m/s greater at 20
- degC. The speed is nearly independent of frequency and atmospheric
- pressure but the resultant sound velocity may be substantially altered
- by wind velocity.
-
- A good approximation for the speed of sound in other gases at standard
- temperature and pressure can be obtained from
-
- c = sqrt (gamma x P / rho)
-
- where gamma is the ratio of specific heats, P is 1.013E5 Pa and rho is
- the density.
-
- The speed of sound in water is approximately 1500 m/s. It is possible
- to measure changes in ocean temperature by observing the resultant
- change in speed of sound over long distances. The speed of sound in an
- ocean is approximately:
-
- c = 1449.2 + 4.6T - 0.055T^2 + 0.00029T^3 + (1.34-0.01T)(S-35) + 0.016z
-
- T temp in degrees Celsius, S salinity in parts per thousand
- z is depth in meters
-
- See also CRC Handbook of Chemistry & Physics for some other substances
- and Dushaw & Worcester JASA (1993) 93, pp255-275 for sea water.
-
- *** 2.12 What is meant by loudness?
-
- Loudness is the human impression of the strength of a sound. The
- loudness of a noise does not necessarily correlate with its sound
- level. Loudness level of any sound, in phons, is the decibel level of
- an equally loud 1kHz tone, heard binaurally by an otologically normal
- listener. Historically, it was with a little reluctance that a simple
- frequency weighting "sound level meter" was accepted as giving a
- satisfactory approximation to loudness. The ear senses noise on a
- different basis than simple energy summation, and this can lead to
- discrepancy between the loudness of certain repetitive sounds and their
- sound level.
-
- A 10dB sound level increase is considered to be about twice as loud in
- many cases. The sone is a unit of comparative loudness with 0.5 sone=30
- phons, 1 sone=40 phons, 2 sones=50 phons, 4 sones = 60 phons etc. The
- sone is inappropriate at very low and high sound levels where
- subjective perception does not follow the 10dB rule.
-
- Loudness level calculations take account of "masking" - the process by
- which the audibility of one sound is reduced due to the presence of
- another at a close frequency. The redundancy principles of masking are
- applied in digital audio broadcasting (DAB), leading to a considerable
- saving in bandwidth with no perceptible loss in quality.
-
-
- -------------------------------------------------------------
- -------------------------------------------------------------
-
- 3] Vibration
- ---------
-
- *** 3.1 What is vibration ?
-
- When something oscillates about a static position it can be said to
- vibrate. The vibration of a speaker diaphragm produces sound, but
- usually vibration is undesirable. Common examples of unwanted vibration
- are the movement of a building near a railway line when a train passes,
- or the vibration of the floor caused by a washing machine or spin
- dryer. Floor vibration can be reduced with vibration isolators; however
- there is often a penalty to pay in the form of a slight increase in the
- machinery vibration and its consequent deterioration.
-
-
- *** 3.2 How is vibration measured ?
-
- Vibration is monitored with an accelerometer. This is a device that is
- securely attached by some means to the surface under investigation. The
- accelerometer produces a tiny electrical charge output, proportional
- to the surface acceleration, which is then amplified by a charge
- amplifier and recorded or observed with a meter. The frequencies of
- interest are generally lower than sound, and range from below 1 Hz to
- about 1 kHz.
-
- It is sometimes more useful to know the velocity or displacement rather
- than the acceleration. In the case of velocity, it is necessary to
- integrate the acceleration signal. A second integration will provide
- a displacement output. If the vibration is sinusoidal at a known
- frequency, f, then an integration is easily calculated by dividing the
- original by 2 x pi x f (noting that there is a phase change)
-
- Example: A machine is vibrating sinusoidally at 79.6 Hz with an rms
- acceleration of 10 m/s^2.
- Its rms velocity is therefore 10/(2 x pi x 79.6) = 20 mm/s
- Its rms displacement is 10/(4 x pi^2 x 79.6^2) = 0.04 mm
-
-
- *** 3.3 How is vibration isolated and controlled ?
-
- Vibration problems are solved by considering the system as a number of
- springs and masses with damping. It is sometimes possible to reduce the
- problem to a single mass supported by a spring and a damper.
-
- If the vibration is produced by a motor inside a machine, it is usually
- desirable to ensure that the frequency of motor oscillations (the
- forcing frequency) is well above the frequency of the natural resonance
- of the machine on its support. This is achieved by altering the mass
- or stiffness of the system as appropriate.
-
- The method of vibration isolation is very easy to demonstrate with a
- weight held from a rubber band. As the band is moved up and down very
- slowly the suspended weight will move by the same amount. At resonance
- the weight will move much more, but as the frequency is increased still
- further the weight will become almost stationary. In practical
- circumstances springs are more likely to be used in compression than
- tension, but the principles are exactly the same.
-
- A further method of vibration control is to attempt to cancel the
- forces involved using a Dynamic Vibration Absorber. Here an additional
- "tuned" mass-spring combination is added so that it exerts a force
- equal and opposite to the unwanted vibration. They are only appropriate
- when the vibration is of a fixed frequency.
-
- Active vibration control, using techniques akin to active noise
- control, is now coming into use.
-
- Important:-
- Intuitive attempts to reduce vibration from machinery can sometimes
- instead aggravate the problem. This is especially true when care was
- originally taken to minimize vibration at the time of design,
- manufacture and installation.
-
-
- -------------------------------------------------------------
- -------------------------------------------------------------
-
- 4] Architectural & Building Acoustics
- ----------------------------------
-
- *** 4.1 What is reverberation time ?
-
- Work on room acoustics was pioneered by Wallace Clement Sabine 1868-
- 1919 (see his Collected Papers on Acoustics, 1922).
- The reverberation time, T, is defined as the time taken for sound
- energy to decay in a room by a factor of one million (ie by 60 dB). It
- is dependent on the room volume and its total absorption.
-
- In metric units
-
- 0.161 x room Volume
- T = ----------------------------------------------
- sum of Surface areas x absorption coefficients
-
-
- *** 4.2 What is the sound absorption coefficient ?
-
- The absorption coefficient of a material is ideally the fraction of the
- randomly incident sound power which is absorbed, or otherwise not
- reflected. It can be determined in two main ways, and there are often
- variations in the results depending upon the method of measurement
- chosen. It is standard practice to measure the coefficient at the
- preferred octave frequencies over the range of at least 125Hz - 4kHz.
-
- For the purposes of architectural design, the Sabine coefficient
- (calculated from reverberation chamber measurements) is preferred.
- Interestingly some absorbent materials are found to have a Sabine
- coefficient in excess of unity at higher frequencies. This is due to
- edge effects and when this occurs the value can be taken as 1.0
-
- The Odeon computer program includes a file of absorption coefficients.
-
-
- *** 4.3 What is the difference between insulation & absorption ?
-
- There is often confusion between sound insulation and sound absorption.
-
- Sound insulation is required in order to eliminate the sound path from
- a source to a receiver such as between apartments in a building, or to
- reduce unwanted external noise inside a concert hall. Heavy materials
- like concrete tend to be the best materials for sound insulation -
- doubling the mass per unit area of a wall will improve its insulation
- by about 6dB. It is possible to achieve good insulation with much less
- mass by instead using a double leaf partition (two separated
- independent walls).
-
- Sound absorption occurs when some or all of the incident sound energy
- is either converted into heat or passes through the absorber. For this
- reason good sound absorbers do not of themselves make good sound
- insulators. Although insulation and absorption are different concepts,
- there are many instances where the use of sound absorbers will improve
- insulation. However absorption should not be the primary means of
- achieving good sound insulation.
-
-
- *** 4.4 How is sound insulation measured ?
-
- The measurement method depends on the particular situation. There are
- standards for the measurement of the insulation of materials in the
- laboratory, and for a number of different field circumstances. Usually
- the procedures involve generating a loud sound of a specified type and
- monitoring the transmitted noise.
-
- It is very useful to have a single number to characterize the
- insulation of a partition. Measurements are often conducted in third-
- octaves, and the reduction plotted on a graph. A reference curve is
- then fitted to the measurements using a specified procedure, and the
- value of this curve at 500 Hz is taken as the figure. There is a slight
- difference in procedure between the U.S. and ISO standards, but the
- methods are basically similar. The same is also true for impact noise
- transmission assessment, where a standard tapping machine is in use to
- hammer floors. Sound pressure levels in the room below are monitored.
-
- *** 4.5 How do I improve the noise insulation of my house/dwelling?
-
- This is one of the most commonly asked questions of noise consultants.
- Firstly you should consider whether better insulation is really
- essential. The method of noise insulation will depend on the exact
- situation, so the advice of a competent person should be sought at an
- early stage. Sound insulation is most often asked for in order to keep
- out unwanted noise, but is occasionally requested for the purpose of
- minimizing disturbance to others. The following ideas may serve as
- guidelines.
-
- When the noise is from an external source such as a main road it may
- be possible, if planning authorities permit, to screen with a noise
- barrier. These can be effective providing that the direct line of sight
- between traffic and house is concealed by the barrier.
-
- The weak point for sound transmission to and from a building is most
- often via the windows. Double glazing will usually afford noticeably
- better protection than single glazing, but in areas of high external
- noise it might be preferable to have double windows with a large air
- gap and acoustic absorbent material in the reveals. A drawback of
- improving external insulation is that, for some people, the resultant
- lower background level can itself be disturbing; it can also make noise
- transmission through party walls more apparent. The fitting of new
- windows may reduce the level of air ventilation, and it will be vital
- to compensate for this, if necessary with a noise attenuating system.
-
- You may also need to consider noise penetration through the roof,
- floors, ceilings and walls.
-
- Noise through party walls can be reduced by the addition of a false
- wall. This is constructed from a layer of sound insulating material,
- commonly plasterboard, separated from the party wall by a large void
- containing acoustic quilting. The false wall must not be connected to
- the party wall because that would allow sound transmission paths. The
- quality of construction is an important consideration if optimal levels
- of attenuation are desired. It is advisable to contact an independent
- noise consultant before allowing any building works to commence.
-
-
- -------------------------------------------------------------
- -------------------------------------------------------------
-
-
- 6] Miscellaneous Questions
- ----------------------
-
- *** 6.1 What is active noise control ?
-
- ANC is an electronic method of reducing or removing unwanted sound by
- the production of a pressure wave of equal amplitude but opposite sign
- to the unwanted sound. When the electronically produced inverse wave
- is added to original unwanted sound the result is sound cancellation.
-
- This method of noise control is becoming increasingly popular for a
- variety of uses. It is sometimes considered a miracle "cure-all" for
- noise problems which, at the present time, is not the case. For example
- noise cancellation in 3D spaces, such as living areas, is very
- difficult to achieve. However it can be more successful locally, eg for
- a passenger sitting in an aircraft or car. There are many institutions
- and companies around the world working on the technology to increase
- the circumstances where ANC can be used effectively. The award winning
- Active Noise Control FAQ is maintained by Chris Ruckman and available
- at a number of sites worldwide including:
-
- http://www.xis.com/~ruckman/
-
- *** 6.2 What causes a sonic boom ?
-
- (from "Aircraft Noise" by Michael T Smith, Cambridge, 1989)
-
- " .. When the speed of an aircraft is supersonic, the pressure waves
- cannot get away ahead of the aircraft as their natural speed is slower
- than that of the aircraft. Slower, in this context, means just over
- 1200 km/hr at sea level and about 10% less at normal cruising altitude.
- Because they cannot get away, the pressure disturbances coalesce and
- lag behind the aeroplane, which is in effect travelling at the apex of
- a conical shock wave. The main shock wave is generated by the extreme
- nose of the aeroplane, but ancillary shocks are generated by all the
- major fuselage discontinuities. .. "
-
-
- Ken Plotkin (kplotkin@access2.digex.net) on 24th July 1995 wrote:
-
- [snip] .. A body moving through the air pushes the air aside. Small
- disturbances move away at the speed of sound. Disturbances from a
- slowly moving body go out in circles, like ripples from a pebble in a
- pond. If the body moves faster, the circles are closer in the direction
- of travel. If the body is supersonic, then the circles overlap. The
- envelope of circles forms a cone. The angle of the cone is determined
- by its vertex moving in the body's travel direction at the body's
- speed, while the circles grow at the sound speed. [snip] The
- existence of the "Mach cone", "Mach waves" and the corresponding angle,
- was discovered by Ernst Mach in the nineteenth century. [snip]
-
-
- *** 6.3 Can you focus sound ?
-
- Sound can be focused like light, but in the case of sound the "optics"
- must be much larger because you are dealing with longer wavelengths.
- The effect is heard in some domed buildings such as the Capitol in
- Washington, and St Paul's Cathedral in London providing noise
- background conditions permit.
-
- Large parabolic reflectors can be used very effectively to send and
- receive sound over significant distances. Check out your local science
- museum or exploratorium - there may be a demonstration. It is also
- possible to refract sound and focus it using a lens. The lens is
- constructed from a large thin bubble, say 2 metres across, filled with
- carbon dioxide. The effect is not very pronounced.
-
- Sound can be directed by making use of constructive and destructive
- interference. This idea is used in column speakers, and commercial
- systems for reducing noise levels outside the dance floor area of
- discos.
-
- *** 6.4 What is sonoluminescence ?
-
- In the early 1930s Frenzel and Schultes discovered that photographic
- plates became "fogged" when submerged in water exposed to high
- frequency sound. More recent experiments have succeeded in suspending
- a single luminous pulsating bubble in a standing wave acoustic field,
- visible in an undarkened room. Generally sonoluminescence is light
- emission from small cavitating bubbles of air or other gas in water or
- other fluids, produced when the fluid is acted upon by intense high
- frequency sound waves. The mechanism is not completely understood, but
- very high pressures and temperatures are thought to be produced at the
- centre of the collapsing bubbles.
-
- See "Science" 14 October 1994 page 233, "Scientific American"
- (International Edition) February 1995 Page 32 or "Physics Today"
- September 1994 Page 22, all quite readable articles.
-
- See also the following URLs:
-
- http://ne43.ne.uiuc.edu/ans/sonolum.html
- http://www.wdv.com/Sono
-
- James Davison (TKGN58A@prodigy.com) on 28th June 1995 wrote:
-
- [snip] .. I have been sufficiently interested to reconstruct the
- apparatus for producing this effect -- using a pair of piezoelectric
- transducers, an old oscilloscope and a signal wave generator --
- materials costing only a few hundred dollars.
-
- I am proud to say that tonight I managed to reproduce this effect --
- the tiny bubble has the appearance of a tiny blue star trapped in the
- middle of the flask. It is distinctly visible to the unadapted eye in
- a dark room, and it is a very startling thing to see. [snip]
-
-
- *** 6.5 Why does blowing over a bottle make a note ?
-
- Resonance in acoustics occurs when some mass-spring combination is
- supplied with energy. Many musical instruments rely on air resonance
- to improve their sonority. If you blow across the mouth of a bottle you
- can often get a note. The bottle behaves as a Helmholtz resonator. The
- main volume of air inside the bottle is analogous to a spring, whilst
- the "plug" of air in the neck acts as an attached mass. The resonant
- frequency is roughly given by:
-
- f = { c sqrt (S/LV) } / 2pi
-
- c is velocity of sound
- S is the surface area of the neck opening
- V is bottle volume
- L is the effective length of the neck ie the actual length plus ends
- correction. Ends correction ~ 1.5 times radius of neck opening
-
- Example: A 75 cl (7.5E-4 m^3) wine bottle with neck diameter 19 mm,
- bottle neck length 8 cm, air temp = 20 degC
- calculated resonance = 109Hz (actual resonance was 105Hz)
-
- Helmholtz resonators are sometimes employed as a means of passive noise
- control in air conditioning ducts. They may also be hidden in the wall
- design of auditoria and offices in order to improve the acoustics.
-
-
- *** 6.6 What is pitch ?
-
- The term "pitch" has both a subjective and an objective sense.
- Concert pitch is an objective term corresponding to the frequency of
- a musical note A (at present 440Hz). Using such a standard will define
- the pitch of every other note on a particular musical scale. For
- example, with Equal Temperament each semitone is higher or lower in
- frequency than the previous semitone by a factor of 2^(1/12). An octave
- is a pitch interval of 2:1. Many sounds with no obvious tonal
- prominence are considered by musicians to be of indeterminate pitch;
- for example, the side drum, cymbals, triangle, castanets, tambourine,
- and likewise the spoken word.
-
- Pitch is also a subjective frequency ordering of sounds. Perceived
- pitch is dependent on frequency, waveform and amplitude or changing
- amplitude. Numbers can be assigned to perceived pitch relative to a
- pure frontal tone of 1000Hz at 40dB (1000 mels) thereby establishing
- a pitch scale.
-
- Further info and examples on pitch from URL:
- http://www.music.mcgill.ca/auditory/Auditory.html
-
-
- *** 6.7 What are musical intervals ?
-
- An interval is the ratio in frequency between musical notes. These
- intervals are sometimes called a second, third, fourth, fifth etc.
- which refers to the position on the scale that the note is to be found.
- In the scale of C major: C D E F G A B C, the note 'E' is the third
- note of the scale and the interval from C to E is therefore called a
- third. For the scale D major: D E F# G A B C# D, the third will be F#.
- The term 'interval' can also be used to indicate that the notes are
- sounded together, in which case there are consonant intervals and
- dissonant intervals.
-
- The ratio of frequency intervals for Just Intonation is demonstrated
- below in the scale of C major, though the same ratios apply to all the
- major keys:
-
- C
- (9:8)
- D
- (10:9)
- E
- (16:15)
- F
- (9:8)
- G
- (10:9)
- A
- (9:8)
- B
- (16:15)
- C <- Octave
-
- The interval between E & F and between B & C is a semitone, whilst the
- other intervals are tones. The interval between any two notes above can
- be found by multiplying the intervening ratios; thus if all the above
- ratios are multiplied together the resultant is 2 because an octave is
- twice the original frequency.
-
- The notes of minor scales differ from their major counterparts; one
- important difference being the flattened third. E flat is a minor third
- above the note C.
-
- The use of Just Temperament causes serious problems of intonation when
- music modulates between keys. Equal Temperament is nearly always used
- as a compromise to the problem of tuning (see question 6.6).
-
-
- *** 6.8 What causes "helium voice" ?
-
- Many people, on hearing the voice of someone who has breathed helium,
- believe that the person's speech pitch has increased.
-
- WARNING - Breathing helium can be very dangerous.
- ^^^^^^^
- A cavity will have certain resonant frequencies. These frequencies
- depend on the shape and size of the cavity and on the velocity of sound
- within the cavity. Human vocal cords vibrate non-sinusoidally in the
- vocal tract, giving rise to a range of frequencies above the
- fundamental. The vocal tract mainly enhances lower frequency components
- imparting the recognizable voice spectrum.
-
- The velocity of sound in helium is much greater than in air, so
- breathing helium will raise the vocal tract's resonant frequencies.
- Although the vocal cords' vibrational frequencies are little affected
- by helium, the effect of higher cavity resonances is to alter
- substantially the relative amplitudes of the voice spectrum components
- thus leading to apparent pitch change.
-
-
- *** 6.9 What is structural acoustics ?
-
- Structural acoustics is concerned with the coupled dynamic response of
- elastic structures in contact with non-flowing fluids. (The fluid,
- although non-flowing, undergoes small-amplitude vibration relative to
- some equilibrium position.) For heavy fluids like water, the coupling
- is two-way, since the structural response is influenced by the fluid
- response, and vice versa. For lighter fluids like air, the coupling
- may be either one-way (where the structural vibration affects the fluid
- response, but not vice versa) or two-way (as occurs, for example, in
- the violin).
-
- Structural acoustics problems of interest involving water include the
- vibration of submerged structures, acoustic radiation from
- mechanically-excited, submerged, elastic structures; acoustic
- scattering from submerged, elastic structures (e.g., sonar echoes);
- acoustic cavity analysis; and dynamics of fluid-filled elastic
- piping systems. These problems are of interest for both time-harmonic
- (sinusoidal) and general time-dependent (transient) excitations. Water
- hammer in pipes can be thought of as a transient structural acoustics
- problem.
-
- Structural acoustics problems of interest involving air include
- determining and reducing noise levels in automobile and airplane
- cabins.
-
- Reference (for simple geometry problems):
- "Sound, Structures, and Their Interaction," Second Edition, by M.C.
- Junger and D. Feit, MIT Press, Cambridge, Mass (1986).
-
-
- *** 6.10 What is the doppler effect ?
-
- When a sound source is moving, a stationary observer will detect a
- different frequency to that which is produced by the source. The speed
- of sound in air is approximately 340 m/s (see 2.11). The wavelength of
- the sound emitted will be foreshortened in the direction of motion by
- an amount proportional to the velocity of the source. Conversely the
- wavelength of a receding sound source will increase. The doppler effect
- may be noticed as a marked drop in pitch when a vehicle passes at high
- speed.
-
-
- Example 1: A sound source, S, emits 1000 waves per second (1 kHz) and
- is moving directly towards an observer, O, at a speed of 100 metres per
- second (equivalent to approx 225 miles per hour).
-
- After 1 second the wave front, which is travelling at the speed of
- sound, will have travelled 340 metres from the original source
- position. Also after that second the sound source will have moved 100
- metres towards the observer.
-
- 0 m 340 m
- S | | | | | | | | | O
- <-------------- 1000 waves ------------------>
-
-
- 100 m 340 m
- S | | | | | | | | | O
- <------- 1000 waves --------->
-
-
- Therefore the same number of waves will occupy a space of 340-100 = 240
- metres and the wavelength will be 240/1000 = 0.24 metres.
- To the observer the frequency heard will be the speed of sound divided
- by its wavelength = 340/0.24 = 1416.7 Hz.
-
- Example 2: An observer moving at 100 metres per second directly
- approaches a stationary sound source, S, which is emitting 1000 waves
- per second (1 kHz). In this example there is no change in wavelength.
- In one second, the observer will hear the number of waves emitted per
- second plus the number of waves which s/he has passed in the time
- (1000+100/0.34) = 1294.1 Hz.
-
- Note the interesting result - a stationary observer with moving source
- will not hear the same frequency as a would a moving observer with
- stationary source.
-
- *** 6.11 What is white noise, pink noise ?
-
- The power spectral density of white noise is independent of frequency.
- Since there is essentially the same energy between any two identical
- frequency intervals (for example 84-86Hz and 543-545Hz), white noise
- narrow band FFT analysis will show as flat. However octave band
- analysis will show the level to rise by 3dB per octave because each
- band has twice the frequency range of the preceding octave.
-
- Pink noise is often produced by filtering white noise and has the same
- power within each octave. Narrow band analysis will show a fall in
- level with increasing frequency, but third-octave band or octave band
- analysis will be flat.
-
- see Joseph S. Wisniewski's Colors of noise FAQ at:-
- http://capella.dur.ac.uk/doug/noisecols13.txt
-
- -------------------------------------------------------------
- -------------------------------------------------------------
-
- 7] INDEX
- -----
-
- A-weighting 2.4 2.12 8.1
- absorption coefficient 4.1 4.2
- accelerometer 3.1
- acoustic energy 2.1 2.8 2.10 4.1 4.3
- Acoustical Society of America 2.4 http://asa.aip.org/
- active noise control 6.1
- active vibration control 3.3
- addition of sound 2.5
- air absorption 2.9
- ANC 6.1
- atmospheric attenuation 2.9
- atmospheric pressure 2.1 2.11
- audibility 2.1 2.12
- column speaker 6.3
- concert pitch 6.6
- dB(A) 2.4 8.1
- decibel (dB) 2.2 2.3 2.4
- Doppler effect 6.10
- dynamic vibration absorber 3.3
- ear 2.1 2.2 2.6 2.7 http://oto.wustl.edu/cochlea/
- elastic structures 6.9
- equal temperament 6.6 6.7
- equivalent continuous sound level 2.4
- focusing sound 6.3
- frequency 2.1 2.4 2.12 6.6 6.7
- hearing conservation 2.7 http://www.globaldialog.com/~nhca/index.html
- hearing damage 2.6 2.7
- Helmholtz resonator 6.5
- historical notes 2.4 2.12
- insulation 4.3 4.4 4.5
- interference 6.3
- interval (music) 6.6 6.7
- inverse square law 2.9
- just intonation 6.7
- Leq 2.4
- logarithmic scale 2.2 2.3
- loudness 2.1 2.2 2.12
- loudspeaker 2.1 6.3
- longitudinal wave 2.1
- Lw 2.10
- major and minor keys 6.7
- masking 2.12
- mel 6.6
- musical scale 6.6 6.7
- ocean sound velocity 2.11
- octave 6.6 6.11
- pascal 2.1 2.2 2.8
- passive noise control 6.1 6.5
- peak level 2.3
- phon 2.12
- physical constants http://physics.nist.gov/PhysRefData/contents.html
- Pierce, George W 2.4
- pink noise 6.11
- pitch 6.6 6.8
- resonance 6.5 6.8
- reverberation time 4.1
- Sabine, Wallace C 4.1
- semitone 6.6 6.7
- sone 2.12
- sonic boom 6.2
- sonoluminescence 6.4
- sound 2.1
- sound absorption 4.1 4.2 4.3
- sound cancellation 6.1
- sound decay 2.9
- sound insulation 4.3 4.4 4.5
- sound intensity 2.2 2.8
- sound intensity meter 2.8
- sound level 2.4 2.5 2.12
- sound level meter 2.3 2.4 2.8 2.12
- sound power level 2.10
- sound pressure 2.1 2.2
- sound pressure level 2.3 2.4 2.5
- speech 6.6 6.8
- speaker 2.1 6.3
- speed of sound 2.1 2.11 6.8 6.10
- structural acoustics 6.9
- supersonic 6.2
- tapping machine 4.4
- third-octave band 6.11
- tinnitus 2.6 2.7
- ultrasound 2.9
- ultrasound scans 2.7
- velocity of sound 2.1 2.11 6.8 6.10
- vibration 2.1 2.7 3.1,3.2
- vibration control 3.3
- voice 6.6 6.8
- wave 2.1
- weighting 2.4 2.12 8.1
- white finger 2.7
- white noise 6.11
-
- -------------------------------------------------------------
- -------------------------------------------------------------
-
-
- 8] Various Tables
- --------------
-
- 8.1
-
- A weighting can be found from the following formulae
-
- For A-weighting: A(f) =
-
- 12200^2 f^4
- ------------------------------------------------------------------
- (f^2 +20.6^2) (f^2 +12200^2) (f^2 +107.7^2)^0.5 (f^2 +737.9^2)^0.5
-
-
- The weighting in dB relative to 1000Hz is now given by
-
- A(f)
- 20 lg ------- note: A(1000) = 0.794
- A(1000)
-
- In tables, octave and third-octave frequencies are given as nominal
- values, for example 1250 Hz or 2500 Hz. Ideally weightings should be
- calculated for the exact frequencies which may be determined from the
- formula 1000 x 10^(n/10), where n is a positive or negative integer.
- Thus the frequency shown as 1250 Hz is more precisely 1258.9 Hz etc
-
-
-
- -------------------------------------------------------------
-
-
-
- 9] List of National Acoustical Societies
- -------------------------------------
-
- For standards organizations addresses see section 1.2
-
- Please let me know if any information in this list needs amending.
-
- Argentina
- Argentina Acoustical Association
- Asociacion de Acusticos Argentinos
- c/o Prof A. Mendez, Laboratorio de Acustica, Camino Centenario Y 506,
- 1897 - Gonnet, Argentina
- Tel: +54 21 84 2686 Fax: +54 21 71 2721
- e-mail: acustica@isis.unlp.edu.ar
-
- Australia
- Australian Acoustical Society
- Private Bag 1, Darlinghurst, NSW 2010
- Tel: +61 2 331 6920 Fax: +61 2 331 7296
-
- Austria
- Austrian Acoustics Association
- c/o Prof Ewald Benes, Technische Universitat Wien, Institut fur
- Allgemeine Physik, Wien, Austria
- Tel: +43 1 58801-5587 Fax: +43 1 5864203
-
- Belgium
- Belgian Acoutics Assosciation (ABAV)
- Av. P Holoffe 21, 1342 Limelette, Belgium
- Tel: +32 2 653 88 01 Fax: +32 2 653 07 29
- e-mail: bbri.lim@pophost.eunet.be
-
- Brazil
- Sociedade Brasileira de Acustica
- Attn Prof Samir Gerges, Universidade Federal de Santa Catarina,
- Departamento de Engenharia Mecanica, Campus Univeritario, C.P 476
- CEP 88040-900, Florianopolis - SC, Brazil
- Tel: +55 48 2344074 Fax: +55 48 2341519
- e-mail: gerges@mbox1.ufsc.br
-
- Canada
- Canadian Acoustical Association
- PO Box 1351, Station F, Toronto, Ontario, M4Y 2V9, Canada
- Tel: +1 514 343 7559 or +1 613 993 0102
-
- Chile
- Sociedad Chilena de Acustica
- San Francisco # 1138, Santiago, Chile.
- Tel/Fax: +56 2 555 63 66 or +56 2 551 79 20
- e-mail: acusticos@entelchile.net with copy (Cc) to: crooke@cmet.net
-
- China (PRC)
- Acoustical Society of China
- 17 Zhongguancun St., Beijing 100080, China
-
- Czech Republic
- Czech Acoustical Society
- Technicka 2, 166 27 Prague 6, Czech Republic.
- Tel: +42 2 24352310 Fax: +42 2 3111786
- e-mail: csas@feld.cvut.cz
-
- Denmark
- Acoustical Society of Denmark
- c/o Department of Acoustic Technology, Bldg. 352 - Technical University
- of Denmark, DK-2800 Lyngby, Denmark
- Tel: +45 4588 1622 Fax: +45 4588 0577
- e-mail: atc.das@dat.dtu.dk
-
- Finland
- Acoustical Society of Finland
- c/o Helsinki University of Technology, Acoustics Laboratory,
- Otakaari 5 A, FIN-02150 Espoo, Finland
- Tel: +358 9 451 2499 Fax: +358 9 460 224
- e-mail: akustinen.seura@hut.fi
-
- France
- French Acoustical Society
- Societe Francaise d'Acoustique
- 23 avenue Brunetiere, 75017 Paris, France
- Tel +33 1 48 88 90 59 Fax: +33 1 48 88 90 60
- e-mail: sfa@cal.enst.fr
-
- Germany
- German Acoustical Society
- Deutsche Gesellschaft fur Akustik
- c/o Department of Physics Acoustics, University of Oldenburg,
- D-26111 Oldenburg, Germany
- Tel: +49 441 798 3572 Fax: +49 441 798 3698
- e-mail: dega@aku.physik.uni-oldenburg.de
-
- Greece
- Hellenic Acoustical Society
- Patision 147, 112 51 Athens, Greece
- Tel or Fax: +30 1 8646 065
-
- Hong Kong Institute of Acoustics
- PO Box 7261
- Hong Kong
- Fax: +852 2886 3777
- e-mail: hkioa@hk.super.net
-
- Hungary
- Scientific Society for Optics, Acoustics... (OPAKFI)
- Fo utca 68, H-1027 Budapest, Hungary
- Tel/Fax: +36 1 202 0452
- e-mail (c/o Andras Illenyi): illenyi@sparc.core.hu
-
- India
- Acoustical Society of India
- c/o Dr S Agrawal, CEERI Centre, CSIR Complex, Hillside Road,
- New Delhi-110012, India
- Tel: +91 11 5784642
- e-mail (c/o National Physical Lab): Agrawals%npl@sirnetd.ernet.in
-
- Italy
- Italian Association of Acoustics
- Associazione Italiana di Acustica
- via Cassia 1216, 00189 Roma, Italy
- Tel: +39 6 30365746 Fax: +39 6 30365341
- e-mail: aia@idac.rm.cnr.it
-
- Japan
- Acoustical Society of Japan
- Nippon Onkyo Gakkai
- 4th Floor, Ikeda Building, 2-7-7 Yoyogi, Shibuya-ku, Tokyo, Japan
- Tel: +81 3 3379 1200 Fax: +81 3 3379 1456
-
- Korean Republic
- The Acoustical Society of Korea,
- c/o 302-B, The Korean Federation of Science and Technology,
- 635-4, Yeoksam-dong, Kangnam-gu, Seoul-city, 135-080, Rep. of Korea
- Tel: +82 2 565 1625 Fax: +82 2 569 9717
-
- Mexico
- Mexican Institute of Acoustics
- Instituto Mexicano de Acustica
- c/o Sergio Beristain, P.O. BOX 75805,
- Col. Lindavista 07300 Mexico, D.F.
- Tel +52 5 682 28 30 Fax: +52 5 523 47 42
- e-mail: SBERISTA@vmredipn.ipn.mx
-
- Netherlands
- Netherlands Acoustical Society
- Nederlands Akoestisch Genootschap
- Postbus 162, NL-2600 AD, Delft, Netherlands
- Tel: +31 15 26 92 442 Fax: +31 15 26 92 111
- e-mail: nag@tpd.tno.nl
-
- New Zealand
- New Zealand Acoustical Society
- c/o J. Quedley, CPO Box 1181, Auckland, New Zealand
- Tel: +64 9 623 3147 Fax: +64 9 623 3248
- e-mail: mms@bitz.co.nz
-
- Norway
- Acoustical Society of Norway
- Norsk Akustisk Selskap
- c/o Lydteknisk senter-NTH Sintef Delab, N-7034 Trondheim, Norway
- Tel: +47 73 59 43 36 Fax: +47 73 59 14 12
- e-mail: sverre.stensby@delab.sintef.no
-
- Peru
- Acoustical Society of Peru
- Sociedad Peruana de Acustica
- Garcilazo de la Vega 163, Salamanca de Monterrico, Lima 3, Peru
- Tel: +51 1 4351151 Fax: +51 1 4675625
- e-mail: cjim@net.cosapidata.com.pe
-
-
- Poland
- Polish Acoustical Society
- Polskie Towarzystow Akustyki
- Instytut Akustyki, Uniwersytet Adama Mikiewicz, ul J.Matejki 48/49,
- 60-769 Poznan, Poland
- Tel or Fax: +48 61666 420
- e-mail: ula@phys.amu.edu.pl
-
-
- Portugal
- Portuguese Acoustical Society
- SPA - CAPS/Instituto Superior Tecnico, Av. Rovisco Pais
- 1096 Lisboa CODEX, Portugal
- tel: +351 1 841 9393/39 fax: +351 1 352 3014
- e-mail: capsist@alfa.ist.utl.pt
-
- Romania
- Romanian Acoustical Society
- Societatea Romana de Acustica
- c/o Nicolae Enescu, Universitatea Politehnica Bucuresti,
- Splaiul Independentei nr. 313, 77206 Bucuresti, Romania
- Tel: +40 1 4101615 Fax: +40 1 4104488
- e-mail: enescu@cat.mec.pub.ro
-
- Russia
- Russian Acoustical Society
- 4 Shvernik ul, Moscow, 117036 Russia
- Tel: +7 095 126 7401 Fax: +7 095 126 8411
- e-mail: bvp@asu.acoins.msk.su
-
- Singapore
- Singapore Acoustics Society
- c/o W Gan, Acoustical Services Pte Ltd
- 209-212 Nanyang Ave, NTU, Singapore 2263
- Fax +65 791 3665
- e-mail: chenzhen@pacific.net.sg
-
- Slovakia
- Slovak Acoustical Society
- c/o Prof Stefan Markus, Racianska 75, PO Box 95, 830 08 Bratislava 38,
- Slovakia
- Tel: +42 7 254751 Fax: +42 7 253301
- e-mail: markus@umms.savba.sk
-
- South Africa
- South African Acoustics Institute
- c/o Dr Fred Anderson, P.O. Box 912-169, Silverton, South Africa, 0127
- Tel or Fax: +27 12 832857
- e-mail (c/o Andersen Technology): pak03486@pixie.co.za
-
- Spain
- Spanish Acoustical Society
- Sociedad Espanola de Acustica
- Serrano 144, E-28006 Madrid, Spain
- Tel: +34 1 5618806 Fax: +34 1 4117651
- e-mail: a.perezlopez@mad.servicom.es
-
- Sweden
- Swedish Acoustical Society
- Svenska Akustiska Sallskapet
- c/o Ingemansson AB, Box 47 321
- S-100 Stockholm, Sweden
- Tel: +46 8 744 5780 Fax: +46 8 18 26 78
- e-mail: sas@ingemansson.se
-
- Switzerland
- Schweizerische Gesellschaft fur Akustique
- Societe Suisse d'Acoustique
- Postfach 251, 8600 Dubendorf
- Tel: +41 1 823 4743 Fax: +41 1 823 4793
- e-mail: kurt.heutschi@empa.ch
-
- Turkey
- Turkish Acoustical Society - TAS
- Y.T.U. Mimarlik Fakultesi
- Yildiz, 80750, ISTANBUL/TURKEY
- Tel: +90 212 259 70 70 ext: 2772
- Fax: +90 212 26105 49
- e-mail: takder@ana.cc.yildiz.edu.tr
-
- UK
- Institute of Acoustics
- 5 Holywell Hill, St Albans, Herts, AL1 1EU, UK
- Tel: +44 1727 848195 Fax: +44 1727 850553
- e-mail: Acoustics@clus1.ulcc.ac.uk
-
- USA
- Acoustical Society of America
- 500 Sunnyside Blvd., Woodbury, NY 11797, USA
- Tel: +1 516 576 2360 Fax: +1 516 576 2377
- e-mail: asa@aip.org
-
- -------------------------------------------------------------
- -------------------------------------------------------------
-
- FAQ Contributors
- ================
-
- Note: Please write to alt.sci.physics.acoustics newsgroup, not to the
- contributors.
-
- Michael Carley (mjcarley@maths.tcd.ie)
- Gordon Everstine (geversti@oasys.dt.navy.mil)
- Johan L Nielsen (nielsen@tele.unit.no)
- Torben Poulsen (tp@dat.dtu.dk)
- Larry Royster (royster@eos.ncsu.edu)
- Chris Ruckman (ruckman@xis.com)
- Asbjoern Saeboe (saeboe@tele.unit.no)
- Jesper Sandvad (js@kom.auc.dk)
- Andrew Silverman (Enviro@measure.demon.co.uk)
-
-
- _____________________________________________________________
-
- *** END ***
- -------------------------------------------------------------
-
-
-
-