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• 4tmuspheric Ultrasound • 'nstrllmenf Performance « Scienceilnd the StradivariUs

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- Time __ ~ _ -',_" , -, KINGDOM PTY LTl and Q1uch more;' -;..; ::~:.:;:;;~ ~ Phone: 02 9975 327~ EDITORIALCOMMIITEE: NevilleRetcher Marlon Burgess Vol 28 No 2 CONTENTS August 2000 JosephLai BUSINESSMANAGER: ARTICLES Mrs LeighWallbank

Acoustics Australia Atmospheric General Business (subscripbons,extra copies,bacl< A. Bedard Jr. and T. Georges . ••.• Page 47 issues,advertising, etc) Mrs Le1ghWallbank The Physiological Demands of Wind Instrument Performance POBox.579 CRONULLANSW 2230 ... Page53 Tel (02) 952B 4362 Fax(02)95239637 Science and the Stradivarius walibankOzipworld.com.BU AcousticsAustralia C. Gough •• ...... Page 57 All Edllorlal Matters (artJcles,repol1s, news, bookrelliews. newprodUGts, etG) CONSULTING NOTE Tile Editor, Australia Acoustics& VibrationUnit Solving a Baffling Problem at Warrlngah Aquatic Centre AustralianDefence Force Academy CANBERRAACT:2tlOO J. Andrew and O. PrItchett ••.•••.••.• ...... •...... Page65 Tel (02)S2688241 Fax(02) 62688276 email:acoust-aust®adfa.edu.au htlp1iwww.users.bigpond.comlAwustics Australian Acoustical Society Enquiriessee page 76

AcouslicsAustralia is publishedby the AustralianAcouslical Sociely New Members (A.G.N.OOO712658) Responsibilrtyfor the contents of al1lClesrests upon the authorsand not the Australian Acoustical Society. Articlesare copyright, by the Auslfalian AcousticalSOCiely. All articlesare sent Diary to referees for peer review belore acceptance.Acoustics Australia is abslractedant!indexed in Engineenng Acoustics Australia Information Index, Abstracts, Acoustics Abstracts & Noise: Abstracts and RlJIIiews. Australian Acoustical Society Information 76 Printedby CronuliaPrintingGof'tyl\d, 16 GmnuliaPlaza, Advertiser Index CRONlJLLA2230

Tej (02)952359~, Fax (02) 95239637 email:print@cronul~pfint.com.auCOVER ILLUSTRATION; Schematic cross-section of a violin. See article by Gough ISSN0814-6039

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42 - Vol . 28 (?oo::J) NO.1 Acoustics Australia In my last column on thc need for 'good members who are luminaries witltin the AAS. So our members are lobbying Authorities acoustics' I referred to the distress being By WIlY of inlerest to our wider for clumge, other mernbers are serving of experienced by purchase ofap>irtments with membership, the AAAC has prepared a Standards committees, scrving of State POPl" isolation. My practice rece'Yes a submi.sion which highlights the shor!_ committee. or Federal Conncil or organising call almost daily from "omeOne who is comings of the present building code system national and intcmational confcrcnces and experieneingthisdiffieultya.s1SU'P"ctare andmakesrecommen

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46· VOl. 28 (2QC()) No_ 1 ATMOSPHERIC INFRASOUND'

Alfred J. Bedard Jr' and Thomas M. Georges'

J National Ckeanic and Atmospherk Administration's Environmental Technology Laboratory, in Boulder, Colorado. , NOAA/Colorado State University

Cooperative Institute for R~searehin the Atmosphere, also in Boulder.

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Vol. 28 (2000) NO.1 - 47 NOISE BECOMES SIGNAL Uncovering the of natural phenomena Ihal were formerly someone '"noise" is a recurring theme in scicnee. Since the 1970s. the science of atmospheric infrasonies has focused on understanding the structure of natural infrnsound where it comes from. and how it travels through the atmospherc. II" wc listen to these ultra-low rrequcncies with witabk instruments, we find a vinual symphony ofnaturul and

humao-made rounds whosc intensiti es are comparahl~with

those 01" audihk sounds and whose ,i!:nat\!re~"ften reveal

distant goophysical events. What we have learned abo ut tni~

"geophysical n()is~"may now become an important part ofth~ strategy behind tho CTBT monitorin!: Tlctwork

As an example "r th~richness of the near-iTlfnlwund these waves propagate long distances through the atm"'l'here, environment. rigure 2 is a ha1t~llpheric acoustic methods. An adVllOCcdinfrdSOnic Even using direction-finding microphones, the sources have monitoring nct\\-urk Vias designed but never deployed. With proven more dilficult to locate than one would C>

atrnosphet~with nuclear cxplosiOlls:" By that lime, however, fluctuations on our eardrum, exerted by ordinary conversation

48 - Vol. 28 (2QlO) No.1 ast hc sqnarc of the frequeocy. Ninety-perccnt of the energy of n " ",holdofp.in a 1000 Hz tone is absmbe

The tempcr.lture and wind .~truetureof the atmosphcre bend, infhlsonic waves in the same way that lenses rcfracTlighT w'lIYcs. The temperature of The atmosphere decreascs and Spccch increases with alTitude in a complicated way, causing reflection

and channeling of infrasound wave~ove r great distanceS (see !'igure 4). Waves from an explo,ion, fot example, can arrive at a sensor by way of many dill"crelll paths lhat bounce bctween atmospbcrieiayersandthegrouud. Seasonal and geographic variatiollS in global and limitofprcssurcocnsorscmiti

k.iJomete~throughtheatmo"plNrc,The curve attbe lo ....-er left lhe design of an infrasonic L'TBT monitoring nctwork roughly indicalCs the p","CTlI lin>ilofdctcctahilily impo5<'d by UNHEARD SYMPHONY atmospileric windsandturbnlence Just as we recognile the special qualities of each instrument in

One of The most interesting and useful properties of an orehestra, w~ lell one infrdsound ~oun;~from another by the infrasOlmd is lhal it travels ""ith relatively undiminished frequency-versus-time signature of tho sound, the direCli(m it slr~gthover global distances. Even our iiCnscs tell oS that low comes from, and how long illasts. Onc difference, hov.1:Ver, is that the urchestra we UIC' listening to here contains some frequencies can he heard farther aW

"'Y;I~ Ilct=~ ....,.,tion.dqrth.ncl"" .tKaoo lypC

~OOD DaCT1T1lnc 31tkulk>nr:uC1l,<"OIumctrlcmctcor.u",",,'lln.lb Impa<:t!o<.'ation

1.oc:IC ".~'"rIn ..,&tlon ~,.,~~;drl;ctminc "'",,.. magntmde.md.pccl ... ~~~:-_~i::..'c;=3I>C.1;"udy f .• cI""'le)torm"""""ion3nd c

Ue'l.... .Uon , Iocallon,3l1d"~Ing;pd"""le.~"()« SIlor-ma'lon ~;Iook (Of r:od;u.;lnull"funndoh:t.pc at ..t>on r.lJ'lNO Infr...... k:pret:utllOfl.

AJ,erJl a,~e :otimalealtll"'-"'.,u"fI/Clh,3nd t>btlngi'lbh:utlOC'l!loc\""'41~CT.Ilh"'l'f"CC»O;

spat\;lltxtcnl ""''''lop pr.>ctk:a1 tk'It"<"tJon ~)... CfI'I>

. ~ Ib)-Idt.;h wi,..,.; me-Duri OOund (" ,,,, Look for Infr,uQfl1c prc-ciIl>oOn;"trtIc""~nd inlern,~diateradi.tionl'oint";me"'lJTto.suur,d .el/.mlc-;u:,,,,,,,'" Cf'upllng fmm thr cpiccn,cr "Esd""ueloca,l aJ

Vol. 28 (2000) NO. 1 - 49 infrasonic monitoring netv.:orks for short-term warning, as wdl as forcollec ling regional avalanche statistics ANJ.I\'lAL INI'RASOU!'IfD

An almost continuou8 but relativdy w"ak hackground of It i~w'CIl known llIat MU usc ultnl.<;Oo.mdfor L"ChoJocation atmospheric infrasound lies in th'" 5-10-7-llecond range of an<.lliut dogs and cats hL'\U sounOlJnd? believed to be genernted by nonlinear ocean-wave interadions The songs or $(KIle wltale~extend inlo the infi-asonic in ncean stmms around the world. Wh ile nearly monochro­ r:lnge. apparently for long-distance conununiClltion. Bising matic in trequency. Ih",~infnl8nnic wa""" which have been concerns about int",rfercnce from human acli,·iti~that h,'l: called ·'the voice ofth" s~a,"arc rdati~dyin cohU"ent in space, increJ.Sedthcle.'elofooekgTQl.ln<.looiwinthcsea.llwn411 suggesting a spatially extendcd sourec. One model f()r tlk: activities havc ceruin ly m~dc~uch collimunic:J tion more 80uod generation process involves trains of interfcring ocean dilTIcull. Kat:' hync, in hcr book Silem Thunder,

infr.asound largc ;mim"I~would greatly C.\tL-OOlhe range of

these SIgnals. Some pn..'d3.tors may ~'"\"l-nb.wc c\"Q h·~-d from th e infl".l$Ound·,.,nsing ')'1'tnns In dctt-ct the bn.:athing or can help heartbeals of prey, but moo: research i$ nc..'lkd 10 find out whether this ;$p05Sib!e a~insrIhebackgroun<.lofnJ!ural Auroral activity and magnetic dismrbanccs in thc polar inlT.!sonicoois.e_ up)JC'r atmosphere al80 generate infra80und dcteded on the In .Jdditton. there are many ane«lotal reports ofunu$U:t1 animal n..'1pot1Sd pn..'Croing eat1hquah-s. The warning ground. Robert Service showed a poet\ "'n~itivily tn the potenlial ofthesc respons.es h.l.'I bttn lhesubjcrt ofintensc nalural ",orld in his Ballad of (he Northern Light~:' research m Chiru. 'nfra.'tOund is one of many candidate

mcrluni:s.ms. all of ".. hith rul,uirc more rigol"OU!l ~tudy-"

Furth.,.. wllrk at NOAA in the 1980s and I ms monitored

se,·ere stonn.~at ncar-infrasonic rrcqu~H~i~,around 1 Hz and found a stronger connection with tornadoes thcmselves.

Coincident Doppler radar mcasl.ln:rncnL~of tornadoes have rcvealedarelationshipbeD,veenfumreldiamcterandinfrasoum. SEVERE-STORM INFRASOUND frcquency that stlggested an infrd"'l.Ind gent:rdtion model In thc 1970s, the National Oceanic and Atmosp heric Radi al modes of vibration in vorticcs can radiate ",mnd wuv<:s Administration began a study of atmospheric infrasound to whosc frequency is inversely proportionH I to the diameter of lhc find out whether it could be used io improve warnings of vort"x core. For examp le, radial vihrations of a 400 m diameter

:;evere wcath.,.. event8, ~u~has IOrnadoes'o We found that core would theoretically radiate at about I Hz. M easurem~ms m any of thc strong~stth understorms, particularly those of the sound gencrated by laboratory vortices and aireraft-wake pow~rfllle nough to reaeh IS kill altitudes, radiated infra sound with wave periods in the tens of 8eeonds, which could be vortices are coru;istent with this1Tl<)(jel. One tOflllldo that passed detccted by multiple observatnrie, more th an a thou8and within 3 km of our Boulder. Colorado, ob:;ervatory k ft a kilometers away. We found that ~evere-stnrminfra>nund wJ.s signarure thm permitted us to usc this model 10 "image" thc n<)t simply a low requency kind (hundcr. Triangulation -f of innea8e in the lornado'~diameter with altitude, using the shows that it exhibits di fferent spatia l and temporal statistics observed decreasc in the dominant infnl:;ound fr<:queue)" at than lightning, and tcnds to come mainly from the subset of storms that 8pawn tornadoes. By on" ",ti mate, the infrasonic highcr elevation angles ofarril'lli. This work shows promise for power rJdimed by the ' tmngest SlOnT18 is <:qui valent to the infrasonic tornado (kt~clion 8ystems Ihat could complement el...::ttie P OW

so - Vol. 28 (2000) NO.1 > mllch larger than the ~ ~:;!l;::U;crts:~~~~rc~a~~~::~~ rI~~=-~--~-===----~= ...a pressure fluctuations are partially b~ ~§i'l~~~~~~~~~~~~;;J1 avemged out Noise reducers with I dimensions greatcr than 1(){l0 feet Source have also bccn used. _~ __ ~ ___=,,,, ,oo::..:,,,,,..,,,,_==="-__ _ ....._ A similar kind of spHtial filter

~;patial aTTay Figure 4. Computer ray trace nlodels how inf.. so~ndat a frequency of I Hz is refracted and consists of a larger of charmeled over long distances by the temp"'rarure and wind strucrure of the annosphere. A 60 such sen,ors 10 sample the wave­ mlsjctofwind bl""'ing: 10 ihe righl at 60 km altitude " simuloteci tQshow the diffc"'"Il"e associated pressure fluduations al hclwec"Tlupstream and d""nslTCam p~ on.Rays that ~ndabn,ptiy arC abs<>rbcdby spaccd locations. Modem digital atmo""ncricvisco.ityandthermalconduction array-processing algorithms" then search in "wavenumber spacc" for MEASURING INFRASOUND combinations of timc delays over the array that match Sound (and infraoound) waves are longitudinal air waves of infrasound waves with different speeds and that come from compression and expansion. Modern 10w-frcqlJel1cy pressW"ll different directions. The design of the spatial filtering arrays is alway' a compromi,;e between angular tewlution and >patial sensors, call~dmicrobawgraphs or \ow-ji"equCll<:y microphones, Can record l"""ure changes of less than 10-' dccorrelation lnfrasound "'"3~c1cngthsarc so long that mOSI sensors are pascals, or 10-< atmospheres. This is still 45 time~I",s deployed at grouod level in two-dimensional arrays. (The s~nsiti\'ethan the human car is at audio freqUtmcies! (Th" SI wavelength at a frequency of I Hz is 340m: at 0.1 lIz, it is 3.4 unit ofprcssure is the ncwt,m per square m~ler,orp;c;ca l. One standard atmusphere is about I (){l000 Pa. The threshold of km.) Wben only two-dimensional array processing is practical, human hearing, which acousticians call 0 decibels, is about 20 the clevatinn angk of ani val ofa wave must be infcrred from micropascals.) One type of far-infras'lllnd senw.r u;;es a t~ sjlI:et! Ihat it travel, across Ihe army. For nampk, a ....m· c sensitive diaphragm open 10 the air on one side and ba<:ked by traversing the array at 340 mls is aniving eS!IL'Iltiallyalong the ground: a wave travcrsing the array at 4HOmls is illl~rpretedas a large. th~rmallyinsulatedreferelMl volurne on th.,uther. A arriving from about 45" abovc horizontal. calibratoo How resistor, ()f leak, acros, the diaphntgm filters oUI very-low-frequency barometric pre,sure changes G~NI<~R..4..TlNGINFRASOUND The ability of pressure sensors to detect infrasonic waws Historically, low-frequency sound propagation has been sludioo is usually limited not hy their sensitivity, but by k><.:ulpressure using e.xplo,ive ,,)ur~es:but this is pra\:tical only in remote fluctuations in the atmosphere that have nothing 10 do with areas. To study infrnsound and its propagation thrclllgh the sound "'"3.\'t::S. These may be causoo by winds and turbulence atmosph",e in a controlled and unobtrusivc \\"3y. or to measure ncar the sensor, or by weather-rclatet! changes in barometric the dircctional response of receiving sensors, it would ~ useful pressure. (T~ pressure amplitude of a typical infra,ound lobeablet"g~nern!eeoherent,narrowhant!infrasoundatwill. signal from a distant sourec is 0.1 Pa, which i, ~quivalenttt) Practical uses for such sources would include inaudible probing the barometric pressure chang~due to a one-centimder of propagation paths where noise pollution is a conccrn and change inaltitudc.) as,essing atmospheric conditions (like temperature inversions) A single pressure sensor often cannot ten the dilfcrence where audible sound could be harmfully trapped or ducted. But bct\VCen the pressure fluctuations caused by a passing wav~"f infras.ound is difficult to gcncrate artificially, because sources infrasound and the non-acoustic pressure changes. On~WdY to ofmanageablc size arc small compared to Uw

Attached 10 th~pre8sure S<:tlsm ,hown in figure 5 are 12 Hz and sealed with a rupture disk. When prcssurized to I T"ddialarms with ports at one-fill,t intervals, covering an area atmosphere and ruptured, it emitted a consistent pulse 50 feet in t!iameler. Wave' of near-infrasound (with wJveform that could be rccognized morc than a kilornct~raway

Vol. 28 (2tXXJ) NO.1 - 51 and detected al 30 kilomders. Figure 1 ~h()wsthi~ resonator. The dcsign of a practical coherent source of infiasound rcmainsclus ive, but device, such as very large organ pipes, slrings, and drum~have been ,uggested. Such an "orchestra" would haw dimen,ions of hundreds offeet and require a huge amount of huffing and puffing to produce a useful infrasound level, which novertheless would go unheard. ACOUSTlC-GRAVITY WAVES Far_infra,()und behaves physicaJly ju,t like ordinary sound until its wave pericod exceeds about 1 minute (0.017 Hz frequency). in a dcn'!ity-stratified atmosphere, the buoyancy forces on a parcel of air bccom~cumpardble to pressure­ gradient force" and the wave-associated air motion is no Figure 5. Noise_reducing microphone. The la,!:c device uscs longer exactly longitudinal. As frequency decreases, ~patiala~"ragin g to !illlooth ont .mall-.cale ""'''UTechange,; propagation of Thcse Haoc(Iustic_gmvity \I,'3.\'CS" becomes more eam.cu hy winds and turtmlencc, thus enhancing its =ponse t(} dispersive (frequency supporl Comprehen'i>'I! Nudear Te.,'1 Ban ]h,my monitoring, Xational even underground ones. Another kind of long-period Academy Pres." Washinglon, DC (1997) inlrasound radiated bydistanl explosions is guided along the 2 L. Stmus;;, Men nnd Decisions, Douhleday, Garden City, NewYorl< Earths ~urfaceand is calkd a Lamb wave.' The ersT (1962) monitoring network will have to be "smart" enough to distinguish the long-period signatures of nuclear tests from many natuml sources ofacoustie-gravity waves. Among those that baw been studied are earthquakes, weather fhmts,jet ,\reams, and clear-air turhulence in the upper atmosphere. WHAT NEXT? 4 W L Donn. D. M. Shaw. Rev. Grophys. S, 53 (1%7) OUT present understanding of Earth's natural infrasonic envi­ ronm""t is largely phel\(lmeoological and lach qLJaJltitative, R. K.Cook,Soundl.l1(1962) testable physical models for how the various observed infra­ 1 W. Tempo.t. cd. , Infmsound and low-frequrncy vibration. soood soorecsactua!1yradiatc. The wavc tbeorists have their Academic P, N~'WYork (1976). work cut oul for Thcm and shGUld be able to find support in thc 7 R. W. Service, C"I/ulfd Po~m.

52 - Vol. 28 (2CXXJ)NO.1 Acoustics Australia THE PHYSIOLOGICAL DEMANDS OF WIND INSTRUMENT PERFORMANCE' Neville R. Fletcher Research School of Physical Sciences and Engineering Australian National University, Canberra 0200

Summary: Requirements on blowing pressure and lip tensi'>n in the piaylllg of woodwind and brass il1lltruments are examined an drelated tothesound_producingmechanismineacbcasc_ Loud playing ofhiJlhnotes on brass instrnmentsis found 10 belhe moot pbysiolngic ally demanding situation, but all instruments havc particular reqmrernents forpreclJle physiological cont.oi

1. INTRODUCTION To fIrst order, this is all that is required, and the instrument by 1n The playing of musical wind instruments goes back to the will sound whatever note is dictated the fingering. dawn of hwnan history, but it is only recently that we have practice there are a few subtleties. In the fIrst place, thc begun to understand in detail the physical principles production of high notes is aided if the player adjusts the lips so that the vibrating part the reed is shortened, and there is governing sound productIOn and the physiological variables of also an associated reduction of the mouth volllIIle by raising that must be controlled by the player during perfonnance. the tongue. This generally increases the closing pressure a Along with this goes a better understanding of the design and little, so that nonnal blowing pressure is also a little raised. To construction of the instruments themselves, but that, as they reducr: the loudnes~of the ~ound,the player tenses the lips so say, is another story. that the reed aperture is reduced and le~sair flows through into Setting aside the pipe organ, we can divide musical wind the instrument. This also causes a small decrease in closing instruments into three classes: reed-driven instruments such pressure, and so in optima! blowing pressure. as the clarinet, oboe, bassoon and saxophone; lip-driven bras~ AE, shown in Figure 1, for normal clarinet playing, the instrumenls such as the trumpet, trombone and tuba; and air­ blowing pressure is typically 2 to 3 kilopascals (kPa) for soft jet driven instruments of the flute family. In all of these, the playing, and 4 to 4.5kPa for loud playing over the whole pitch player must learn to control the pitch of the note being played range of the instrument (Fuks and Sundberg, 1997), though by manipulating finger Ireys, valves or slides, and then nrust jazz players may sometimes use a higher blowing pressure to carefully control the actual sound-producing mechanism to produce an incisive or even rough tone quality. These produce a satisfactory result. This requires deliberate control pressures should be compared with nonnal sub-glottal of physiological variables such as lip position and tension, pressures of about 300Pa for speech and perhaps lkPa in blowing pressure, and perhaps vocal-tract configuration. It is singing, and are not so high as to cause much physiological the purpose the present paper to describe what is known of of stress. (For those not familiar with these pressure units, lkPa the requirements on each of these variables. Details of the is equivalent to about lOcm water or 7.5nun mercury. A scale acoustics of the instrwnents themselves can be found in translation is given in each figure.) Fletcher and Rossing (1998). Playing technique for the saxophone is in many ways 2. REED-DRIVEN INSTRUMENTS similar to that fur the clarinet, !lIld jazz players often switch between the two instruments. The saxophone also has a single The clarinet is perhaps the simplest and most studied of the flat reed but differs from the clarinet in having a wide­ woodwind instruments, because it has an essentially mouthed conical bore. Blowing pressure for the alto cylindrical tube and a single flat reed with simple geometry. saxophone is typically about 2kPa for soft playing, but may The player's lips enclose the reed and the mouthpiece against rise as high as 8kPa in the middle register for very loud which it is clamped with a gap of about lnun at thc tip, and playing where a harsh tone quality is desired, as shown in the player applies air pressure that tends to close the reed Figure 1 against the mouthpiece. Analysis of the physics of this Double-reed instruments, such as the oboe and bassoon, situation shows that the reed will begin to vibrate, and thus have a very narrow conical bore and a narrow reed with two cause oscillations in the air flow through the aperture between vibrating tongues bound together. The reed aperture is much it and the mouthpiece into the instrument tube, once the smaller than in the single-reed instruments and, because tho blowing pressure exceeds one-third of the value required to reed is curved across its width and there is significant flow completely dose the reed agairu;t the mouthpiece face. Th resistance in the narrow reed channel, a higher blowing ensure stable playing, the player ordinarily uses a pressure that pressure is required to make it vibrate. The blowing pressure is one-half to two-thirds this closing pressure. of used by skilled players increases by about a faGtor two between soft and loud playing, and rises by about a factor two across 'Orig:inallypublishedas""l4~physiologiquelorsduthe compass of the instrument, as shown in Figure 1. Pressures joudesin.trumentsavc:nt"'in~desAm(2000)of around lQkPa, as required for high loud notes on the oboe

Acoustics Australia Vol. 28 (2000) No.1 - 53 figure!. 1'ypicalbl(IW;ngpreSS\lrerang~sacrossthe",w;;caleompassforc1arinet,altoS.1X"I'hone,oboe,and bassoon, for piano andfo".. playing. [Data from fukll andSundbell! (199ti).] or bassoon. impose a signifieant physiological stmin on the and this eonccms the larylJ)[. Mukai (1989)made obscrvations player if the condition mustbc maintaincd fora long section of the larynx of many wind instrument players during of music, but this usually results only in facial reddening. For perfonnanc.: in the laboratory, using a nascndoscope, and less-skilled players. there may be significant difficulty in found that, while novice players typically had wide open maintaining thc lips in position on the reed, because moulll larynxes. experienced players of all varieties of wind pressure tends to blow tile lips open. There is no remedy for instruments mostly adducted their vocal folds to constrict this except regularpraClice, preferably begun al an early age, greatly the laryngeal opening. In the case of players using lostrcngthentllclipmusc1cs vibmto.thevoea l foldstendcdtovib11ltein synchronywilhlhe The reed woodwinds. and particularly the double rccds. do vibrato. There do not appear to have been further not require a large air flow 10 produce a moderately loud investigatiollsofthis finding in the ease of reed instrument sound, and p!ayt-rscan therefore play quite long passages. up players to perhaps SO seconds in duration. witllout requiring to take a breath. This, too. imposes a physiological strdin on Ihe player 3. LlP~DRIVEN BRASS INSTRUMENTS bccauseofthe build-up of carbon dioxide ooncentration in thc While the playcrs lips takc tbc plaee of the recd inbl1lSS lungs. Nonnal1y such a build-up triggers a breathing reflex, instruments, Iheiroperation is very different. The reason is but experience players are able to suppress this toa that, while pre~~urein the player's mouth tends to close a reed considerable extent. It has recenllyhc<;;omc oommon practice valve, it tends to QpCn a lip valvc. The C)(act motion ofa for woodwind players 10 become adept at the tec hniques of player's lips isoomplex and to some extent undcre onseious 'cireularbreathing: in which the throat and mouth are filled control, although the player does not gcncrally realise what with air from the lungs under pressure to maintain the changes arc being made. The lips may either blow outwards instrument sound, and then sealedolffrom the traehea and lowards the instrument, like an outward-swinging door, or nasal passages at the soft pa late so tltat a quick breath may be move laterally like a sliding door. More realislically thcy may taken through the nose. 1ltis technique. which has becn used combine both these movements or may even have a wave-like by Australian Aboriginal didjcridu players for thousands of motion (Yoshikawa. 1995; Adachi and Sato. 1996). years. allows the player to continue playing without The important thing acoustically is that the lips are able to

interruption for an indefinite time act as a sound-generating valve only very close to their natur~ It has already been mentioned that the volume of the al resonance frequency. This means that lip muscle tension mouth is typically reduced for playing high notes and must be adjusted very carefully by the player to match the increased for very low notes, as is dear from the lowered chin pitch of each note, and must be increased greatly for high of bassoon playcrs. There is anolher aspect of respiratory tract nMes. The accuracy of tcnsion adjustment requircd increases physiology that also appears to enterperfonnance tc.:hniquc, in the upper range of the instrument whcrc the frcquencicsof

54-Vol. 28 (2000) No. 1 Acoustics Australia , Trumpct m! '''I

" Il ff 11O.! I~~

~~ ~ '00 ·5 " '" l ".1 .~ . , ,,! "j pp . zj"' .04 F4 C6 F6 a ~

Figun:2. l'ypkalblowingpr=;Ufl'rangea\:fQSIlhcmUll;cal Figure 3 TYl'ical blowingpre5sure rangcacrosll the musical comp""" for the trumpet in pilJlli.

Acoustics Australia Vot 28 (2000) No. 1·55 frequency of 5 to 6Hz. The result is not so much a regular three classes of wind instruments, and some musical demands oscillation in sound level or in frequency, both of which may impose quite extreme physiological stresses. It is 10 be remain almost unaffected, but ratheI an oscillation in tone hoped that, by understanding what is required and the reasons quality caused by variation in the amplitude of the upper for it, players may improve both their tochnique and their hannonics of the sound playing comfort. It is not immediately clear how this vibrato is REFERENCES accomplished, and indeed it may vary from one school of Adachi, S. and Saw, M. (1996) "Trumpet SO\Ind sirnulaticn using a playing to another. It could be by rhythmic oscillation of the twc·dimensicnal lip vibraticn model,~J. AOOII.It. Soc. Am. 99, abdominal muscles, by similar changes in lip tension and thus 1200--1209. in lip aperture, or by oscillation of the vocal folds if they are ,ignificantly adducted. Mukai (1989) found a narrowing of the Fletcher, N.H. (1975) "Acoustioal correlates of flUle performance technique,"J.Acousl. Soc. Am, 57.233-237 airway by the vocal folds for experienced flute players as for other instrumentalists, and an oscillation in airway area in Fletcher, NR and Rossing, T.n. (1998) The Physics of Mu"froj synchrony with the vibrato, but recent studies have suggested instruments, (second edition) Springer·Vedag, NewYcrk, pp.401-SS1 that there may be more variation in tochnique from one FJetcher,N.H. and Tamopolsky, A. (1999) "Blowing JD""""Ill"e,powI:!", individual to another than found in his work. and spectrum in trumpet playing,"J. Acoust. Soc. Am. lOS, 874-881. 5. CONCLUSIONS Puh, L and Sundberg, J (1997) "Blowing pressures in reed woodwinds," Proc. i .... l. A.:m.rl. ISMA'97, 273-278. As set out in this brief review, the production of a well controlled sound from a musical wind instrument involves Mllkai,S. (1989) "Laryngeal mcvementduringwind i""trwnent play," precise control of a number of physiological variables, J. Oto/aryngcl. Japan 92, 260-270. particularly blowing pressure and lip configuration. The Yoshikawa, S. (1995) "Aconstka} behavior oflmtss-player'. Hps," J. requirements on these vdriables are very different between the Acousl. Soc. Am. 97, 1929-1939.

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56 - VoL 28 (2000) No.1 Acoustics Auslralia SCIENCE AND THE STRADIVARIUS' Col.in Gough School of Physics and Astronomy L'nivcrsityofBirrniogham Edgbaston, Birmingham 015 ZTT

~mail:[email protected]

I=::~~o!j::~ :''':~~~o7:\:~;:::eft:~d:':i1:.:a7=i~ i:/:.";c~;I!~i:'::i~:::::,:~1 thatmalo. aSlmlivarius

Is there really a lo~ts~cret that ~etsSlnldiv-,u;lIs violins apart a hal f, many famous physicists have bt:cn intrigued by the from the best instruments made After more than a workings of the violin, with Helmholtz, Savart and Raman all hundred years of vigorous debate, qucstlon TCmatnS making vital contrihutions highly contentious, provoking strongly held hut divergent It is important to recognize that the sound of" the great views among players, violin makers and scientists alike. AI! of Italian instrumeuts we hcar today is very different from the the greatest violinists of modern timcs certainly believe it 10 sound they would have made in Stradivari's time. Almost all be true, and invariably perform on violins by Stradivari or Cremonese instruments underwent extensive restoration and Guarneri in preference to modem instruments "improwmenf' in the 19th cemury. You need only listen to Vio lins by the groat Italian makers arc, of COUfllC, beautiful "authentic" baroque groups, ill which most top perrmmers

\mrksofaTlin their own right, and are covcted by collectors play on fine Italian instnnncnls restored to their formcr stat~, as well as players. Particularly outstanding violins have to recognize the vast diffcrence in loue quality bern'een thcse reputedly changed hands for over a million pounds. In restored originals and '·modem" versions of the Cremonese contrast, finc modern instrumcnts typically cost about violins

£10,000, whil~fac tory-mack violins for beginners can be Prominent among the 19th-<:e!ltury violin restorer, was th~ bought for under £100. Do such prices really reflect such large French maker Vui1laume, whose copy ora Guamcrius violin is diffcronces in quality? showu in figure la. Vuillaumc worked closely wi1h Felix Sa­ The violin is the most highly developed and vart, \)c,st kno\oTl to physicists for the Biol--8avan law in most sophisticated of all stringed instruments. It emerged in electromagnetism, to enhance the tone of early iosrruments. Northern Italy in about 1550, in a fonn that has remained Vuillaume, Sa\'arl and oth~rswanled to produce more essentially unchanged ever since. The lamolls Crcmonesc powerful and brilliant sounding instruments that could stand violin-making families of Amali, StrauiYdri and Guarneri out in the larger orchestras and concert halls of the day. 1m­ formed a continuous line of succession that f10urished from provem~ntsin instnmlent design ",,-ere also introduccd to ,upport the technical demands of great violin virumsi like about J600 to 1750, with skills being handed down from Paganini father 10 son and from master tu apprentice The popular belief is that their Wlsurpassed ,------;==---- -, skills, together with tbe magical Stradivarius secrct,werclostbylhcstartortheI9thccntury. Every violin, whether a Stradivarius Or the cheapest factory-made copy, has a distinctive "voice" of its own. Just as any musician can

immediately fCcognize the differene~between Domingo and ravarotti singing the same operatic aria, so a skilled violinist can distinguish bt.twcen different qualities in the

sound prooUC<'d hy individual Str~divarior Guarneri violins. The ehaUenge for scicntists is (a) A e<.>pyofa Guam~riu,viotin made by tho to chamch;:ri:re such differences by physical 19\h-ccnlUry Frroch violin maker Vuillaume, measurements. Lndeed,ovcrthela,icenturyand .h(l\\T1fmmthcpiaycr·Sp"n-pcctive. (b) A "chem.tic cros,,-se

Vol. 28 (2000) NO.1 - 57 BACK TO BASTCS: THE COMPONENTS OF The front plate ofttle violin is carved from a solid block of A ViOLIN fine-grained pine. Maple is uSllillly used for the back plate and for the sides. 1\1.'0 expertly carved and elegantly shape.:! "I~ To lUldcn;tand the factors that determine the quality of ~oumJ holes" arc also cut into th~liu nt plate. The earving of the produced by particular instruments. we must first recall how f-holes ollen helps to identify the maker of a valuable the violin work> (figure Ih). Sound is produced hy drawing a instrument: never rely on the label inside the violin to spot a bow across one or more of the four stretched strings. The fake instrument as the lahel will probably have been forged as string tensions are adjusted hy tuningpeg.s at one end the of well. string, so that their fundamental frequencies are about 200, The f-holes play a mUllbcr of imponant acoustic rolos. By 300,440 and 660 Hz - which cOrTel>-pondto the notes G, D, A breaking up the area of tbe front plale, th")' affect its vi­ and E. However, the strings themselves produee almost no bmlilmal mO

Fig"'" 3 (al Drawing" bow ovcr the ' Irillgs of a violin g"""Tate, "nearlyideal.awroothlbrceonthetopofthe hridge."Thcforcc can COIl8ist of"" many a, 40 ,'ourier components. with the amplit.ude of Ihe ntl1 component uccrc",ing smoothly in proportion 10 -lin (main figure). (b) Thc bridge. wh.ieh transfomlS energy from the vibrating strings to Ihe vibralional

moocsofwundbo~,h""are.JlOn,.thal,-arieswithfrequency.

The n:sun:mre, al about 3 kH~'IOd 4.5 kHz boo,t the outp~' the bridgo is ]mown .., Ih~ "sticking oound while the dip berv,,,en lhem rcduec. the·'na>al"qualitic. regime" At the IX"ilioo wh.re the string is beingbo"",d the in Ihe tone. (c) A mathematically modelled acoustic OIllput of . Iring move< with the same speed, and inth~ ",me dilTiCtion, as the vio1in. The output increase.>; dramalically wh.nevor the Ih~ bow. (b) The ,hap" ofth. string al fin equally spaced time e'~itingfrequmcycoincideswithonecftbemaTIyv;br"tiona1 il\tcrval,forthe~slippingregime",whon the lcinkis InlYelling modc.ofthc instroment. (dl The Fourier OO1I1poncnlSof the botw~el\the bow and the bridge, and back. The string !\OW mnlli-reoonanceacouslicoutput,prooucedbybowinglheIO\\".,t moves in Ihe opposite direction to the bow. (el Tbe note on the in,mullent at 200 Hz. The main fl.gure show. rhe d;'pla£c!1J<."llt oflh" Siring al too bowing: l"';"t. (d)T"" force calculated OUtpUIwaveform prod"~~dby the iJctlli~odinput

T,;nec~erICdby the

wh~1"CTi, thel~n,ionoflheming input, the Fourier components of the output will vary

dramatically in amp~'udefrom one note to the next.

58 - Vol. 28 (2CXXl) No. I Acoustics Australia the other side ofthc plate to vibrate with a larger amplitude. of sound produced by great violinists is mainly due 10 the fact

Thi.~increases the radiating volume oftbe violin and produces that they can control the Helmholtz waveform with the bow. a much stronger sound. The quality of sound produced by any violin therefore depends The violin also has a "bass bar" glued underneath the top as much on the bowing skill of the violinist as on the physical pl!!le, which stops energy being dissip!!led into acoustically properties. One of the reasons that the great Cremonese inefficient highCl'-order modes, The has~bar and sound post violins sound so wonderful is because we bear them played by were both made bigger in the 19th century to strengthen the the world's greatest players! instrwnentandtoincreascthesoundoutput. SOUNDS GOOD: HOW A VIOLIN MAKES A GETTING KINKY: HOW STRINGS VIBRATE NOISE In the 19th century the German physicist Hermann von The sawtooth force that is generated on the top of the bridge Helmholtz showed that when a violin string is bowed, it by a bowed string is the input signal ilia! forees the violin to vibrates in a way that is completely different from the vibrate and radiate sound-rather like the c1ectrical input to a sinusoidal standing waves that are familiar to all physicists. , albeit with a much more complicated frequency Although the string VlbrateS back and forth parallel to the response. The input sawtooth waveform has a rich bowing direction, Helmholtz showed that other transverse content, consisting numerous Fouriet" components. vibrations of the string could also Ix: excited, made up of of Since the violin is a linear system, the same Fourier straight-line sections. These are separated by "kinks~that H travel back and forth along the string and are reflecled at the components or "partials appear in the ontput of the violin, ends. The kinks move with the nonnal 1Tansven;c-wave The amplitude of each partial in the radiated sound is velocity,c = (Tim)"', where Tisthetensionandmthemassper determined by the response of the instrument at that particular unit length of the string. The bowing action excites a Helm­ frequency. This is largely determined by the mechanical holtz mode with a single kink separating two straight sections resonances of the bridge and by the body of the instrument. (figure 2). These resonances are illustrated schematically in figure 3, When the kink is between the bow and the fingered end of where typical responses have been mathematically modelled the string, the string moves at the same speed and in the same to simulate their influence on the sound produced. direction as the bow. Only a small force is needed to lock the two motions together. This is known as the "sticking regime" (figure 2a). But as soon as the kink moves past the bow - on its way to the bridge and back - the stcing slips past the bow and starts moving in the opposite direction 10 it. This is known as the "slipping regime" (figure 2b). AllhDugh the sliding friction is relatively small in the slipping regime, energy is continuously transferred from the strings to the vibrational modes of the instrument at the bridge. Each time the kink reflects back from the bridge and passes underneath the bow, the bow has to replace the lost energy. It therefore exerts a short impulse on the string so that it moves again at the same velocity as the bow.

This procc~sis known a~the "slip-stick" mechanism of string excitation and relies on the fact that sliding friction is much ,mal1er than sticking friction (figure 2c). The Helmholtz wave generates a transverse force Tsin6 on the bridge, where 9 is the angle of the string at the bridge. This force increa:tQ; linearly with time, but its amplitude reverses sud

Acoustics Auslralia Vol 28 (2000) No.1 - 59 Figure S. Timc-averagedinterfi:renc<: holOJlrnIllSshowingtwo­ Figure 6. A rUlit~lemenTmconstruction sbowing one of lhe

dimensional flexural Sianding wa~c.on the front plale of a aco"sticallyimportantstructuralmodesofthebodyofa~iolin guitar. The interference patterns. which indicate contours of The snapshol vi,,"" ~hows,on a m""h cxagg~T1Itedscale, the cqual-amplitudc vibrations, are much mOte symmetrical than highly asymmetric ~ertiealdisplacemen ts and flexural vibration, the instrumenL The results were obtained wh"n the tboseobservcd fortbe~iolin.The conlOurs in a violin cross the of cdgc,ofthein,u llmcnl-inotw",ords, the ,ides ofa violin displacemcnt was a\ its ma"imum. Note that vibrations of aU transfer significant vibraTions from the front to the back parts of the instrum"n! are involved in the ,""oonantmode. In Unfortunalcly,ili.nntClll;y loobt.in similachigb"'l""lity particuiar, the resonanccs of the front nnd back plales c.nnot be considcrcdin iSf>latioo fmm ilic.,,,t of the instrument, as has interf"rellCe patterns fOr a violin. which has Slnall"r, more often been ossumed in the pa.

At low frequencies!h~bridge s imply acts as a mechanical rede~ignof t he bridge in the 19th century. Violinists often lever. since the response is independent of frequency. How­ plaec an additiorml mass (the "mute") on the top of the bridge, ever, betwecn 2.5 and 3 kHz the bov.in£ action excites a effectively 10000'Cringth e frequency of lhe bridge resonances slr,mg resonance of Ihe bridge, with the tep rocking about its This re~ult,in a mu-ch quieter and ··warmer" sound that narrowed w

"ensitiv~,and gives greater brightness and carrying power to major importance "fthe bridge in detennining the over the body. Thankfully Ihi, dip decrca~stlte - rather like the way in which a Car engin~is tuned to get the amplitude oftlte partials attltese frequencies, whidt tlte ear ~stpetfonnanee . Violini~tswill, forexanlple, carefully adjust associates wilh an unplcasantshrillness in musical quality. the bridge to suit a panicular instrument - Or even <;elect a

The sinw'oidal lilrce exert~dby the bridge tm the top plate difftm:nt bridge altogelher. The sound quality of many modem produces an acoustic output that can t>e modelled violins could undoubttXIly be improved by taking just as much mathematically. th e output increases dramatically whenever earcinsclectingandadjusting thebr idge the exciting frequency coincides with one of the many The transfer of energy from the vibr every time a resonance is e"cite<.i. The must n,1t be too ,trong, otherwi'e th e instrument becomes modelled response is very similar to Jllany recorded examples difficult to play and the viulinist has to work hard to maintain madc on real instrumc!Ils tlte Helmholtz wave. Indeed, a completo breakdown can <>ccur In practice, quite small changes in the arching, thickness when a Siring resonance coincides with a particularly strongly and mass of the individual plates can result in big changes io coupled and ligh.tly damped structural resonancc thc resonant frequencies of the violin, whiclt is why no two 'Wben Ihis happtms the sound suddenly changes from a instruments ever sound exa~""\ly alike. The multi-resonant smooth tone to a quasi-periodic, IUlcontrollablc, gruming responsc leads to dramatic variations in the amplirndes of sound - the ··wolf-note". Players minimize this problem by individual partials for any note played on tlte violin. wedging a duster against lhe top p lale to dampen the Sueh factor<;mU-Slhaveuncon'ciou!;ly guided the radical vibrational modes. or by placing a resonating mass, the '·wolf-

60 - VoL 28 (2CXXl)No.1 Acoustics Australia note adjuster", on one of the strings on the far side of the contribute to a certain shrillness in thcirquality. hridge. However, this only moves the wolf-note to a note that In pmctice it is extremely difficult 10 distinguish hetween a is not played as often, rather than eliminating it entirely. particularly fine Stnldivanus instrument and an indifferent The Hc1mhollz motion of the string and lhe wolf-nute mOlk'TD copy on the basis of the measured response alone. The problem were extensively studicd by the Indian physicist ear is a supreme dctcction dcvicc and the brain isa far more Chandrasekhara Raman in the early years of the 20th century. sophisticated analyser of complex sounds than any system yet His results were published in a series of elegant theoretical and dcveloped to 3SSCSSmu,ical quality. experimental papers soon after he founded the Indian Although such measurements give the li"Cquencies of im· Academy of Scie~sand before the ""lrk on optic> that porlant acoustic resonances, they tell us nothing about the way carned him thc Nobel Prize for Physics in 1930 a violin actually vibrates. A powerful teehniquc for in­ vestigating such vibrations is called timc-averagcd interference GOOD VIBRATIONS: THE ROLE OF holography. Bernard Richardson, a pbysieist at Cardiff RESONANCES Univef':>ity in the UK, has made a number of such studies on The existencc of so many reSl.mance'l at alTIlO'>t ramlom the guitar and violin. Som~particularly beautiful examples for frequencies means that thcre is simply is nu such thing as a the guitar arc shown in figure~.Unfortunately , it is not easy to "typical" v,1lVcform or spectrum lor tlte sound from a violin. obtain similar high-quality images for the violin because it is Indeed, there is just as much variation between the individual smaller, the vibrations of the surface arc smaller, and the notes on a single instrument as there is between the o.ame note surfaces of the violin are more curved and less reflcctivc than played on different instruments. This implie> lhat the thQ~of the guit.ar. perceived lime ofa viulin must be related to overall design of Another powerful approach is modal analysis: a violin is the instrument, rather than to tile freqllCllcies of particular lightly struck with a calibraled hammer at several positions and resonances on an instrument. tllc transicm rcsponse at various points is measured with a very An interesting attempt to 1001: for such global properties ligbt accelemrneter.lb ese responses an: then analysed by was =tly made by th", violin mal:.,. Heinrich Diinnwald in computer tu give the resonant frequencies and stru.. : tural Gcnnany. He measured the acoustic output of 10 Italian modes ofvihratioll of the whole instrument. This technique has violins, 10 fine modcm eopics and iO factory-madc violins, been used to teach students about violin aeoosties at thc aU ofwbich were cxcited by an electromagnetic driver on one famous Mittenwald school of violin making in Gennany and side of the bridge (fib'1ln' 4). Between 4(lO and 600 fu, the by Ken Marshall in the US. Marshall has also shown that tbe fa<.:tnry-madc violins were round - surprisingly - to be <.:l()~crway the violin is held has linle effect on it.- resonant response. to thc Italian instruments than lhc modem copics. At Similar infonnalion can be obtained hy finite-dement frequencies above 1000 Hz, hov.-ever, the factory-madc analysis: the violin is modelled as a set of masses that are instruments had a rather "'eak resporu;e - in contrJst to thc connected by springs, which makes it relatively over-strong response of the m()(iern violin', which may str.l.ightforward to cy""luate the resonant modes and f\l;sociated

Figun:7.Whong!itteri'pol.lrcdonlOviolinpJatc.thata",freclysu'pcndeJ above a loudl;peakcr, the glitterboonces up and dO\",n, and moves (owards the nodal Jines ofimpo'"tOnt 10w-fmJuency rCWMnces. Tn an attm1p' to comp<."1Isatcfor tbe DatumJ v"JIiation in the proper­

ties of the uscd (0 makc a violin> many sciontifically minded violin makers adjllSt tno arenin~and ( hicln"ss ofllle lOp and bouom plat., to achievo particular rc,;onant tr.quencies and noJaJ p"tlems in an instnnnem

Vol. 28 (2000) No.1· 61 vibmtiom; of the whole structure (figure 6). Various physical terms of numbers and exact ratios. paralIletelsofthe materials w;edto maketheviolincana1so be Memhcrs of the ''scientific'' school of violin makers might incorpomted in the calculations. It is then possible to construct reasonably claim that this could be the lost Stradivarius secret. a virtual violin and to predict all its vibmtional and a.:oustic However, it mllSt in&ed have been secret, since there is no properties. This might be the first step tuwards designing a historical evidence to support the casco Although many first­ violin with a specified response and hence tona1 quality - eM modem violins have been built based on these principles. once we know how to define "quality" in a m.easurable way. there is little evidence to suggest that they are any bctter than BUILD QUALTIY: HOW TO MAKE A GOOD many fme instruments made with more traditional methods. VIOLIN Howevex, neither traditional craftsmanship nor scientific methmjg can hope to coo:trol the detailed resonant structure of So how do skilled violin makers optimize !he tone of an an instrument in the acoustically important range above instrument during the CODlltruction process? They begin by 1 kHz. Even the tiniest changes in the thiekncs.s of the plates selecting a wood the highest possible quality for the front of will significandy affect the specific resonances in this and back plates, which they test by tapping with a hannner and frequency range, lIS will the inevitable variatiODll in the pro­ judging how well it ''rings''. perties of the wood. Furthermore, the frequencies and The next important step is to skilfully carve !he plates out distribution of the resonant modes of the violin depend on the of the solid wood, taking great care to gct the right dcgrce of exact position of the sound post, which imposes an additional arching and variations in thickness. The crnftsrmm hIlS to learn constrnint on the modes that can he excited. Top players how to adjWlt the plates to produce a fine-sol.Qlding regularly return their instruments to violin makers, who move instrument. Traditional l1llIirers optimize the thickness by the sound post and adjnst the bridge in an effort to optimize the testing the ''feel'' of !he plates when !hey are flexed, and by !he sound. This means that there is no unique set of vibrational sounds produced when the are tapped at different positions characteristics for any particular instrument not even a with the knuckles. This is the traditional equivalent of nndal Stradivarius! analysis, with the violiu maker's bmin providing the interpretative computing power. KNOTTY PROBLEM: THE EFFECTS OF However, in the last 50 years or so, a group of violin WOOD makers has emerged who have tried to take a more overtly Another factor that affects the quality of a violin is the internal scientific approach to violin making. The pioneer in this field damping the wood. This strongly affects tlte multi-resonant was Carleen Hutchins, the doyelUle of violin acoustics in the of response the instrument and the ov

Renaissance view of ''perfection'', which"",", measured in ~wonderfullyexciting, almost deafening, very vibrant It is

62 • VoL 28 (2000) No.1 appears to change in its first few years. Surprisingly, many players still believe that their instruments improve because they are loved and played well, which would be very difficult to explain Qn any ratiQnal scientific basis! THE SECRET AT LAST? MallY other theories have been put folWlU"dto aecount for the Stnldivarius secret. The most popular for well over a century

has been that the varnish had some sort Df ''magic~ composition. The main functiDn Qfthe varnish is to protect the instrument from dirt and to stop it absorbing moisture from the player's hands. The varnish also imparts great aesthetic value 10 the instrument, with its translucent cQating·highlighting the beautiful grain structure of the wood below. However, historical research has shown that the varnish is no different 10 that used by IDllllY furniture mak

The same will obviously be true fQr all old Italian made by ~kiJIedcraftsman today. Indeed, some leading sDlDists instruments. The age ofthe wood may therefore automatically dOl Dccasionally play Qn mQdem instnnnents. However, the contribute to the improved quality Qf the older instruments. really top soloists - and, not surprisingly, violin dealers, who This may alsD cxplain why the quality ora modern instrument have a vested interest in maintaining the Cremonese legend Qf

Acoustics Australia V'll. 28 (2000) No.1 - 63 intrinsic superiority - remain uHcrly uncouvinced. L Cremer 19M The r~ ic.sof lhe Violin (MIT Press, Cambridge, Maybe mere is an essential aspect of violin quality that we /l.la""achusetb) ITiIJl,lation J S Alh.-n - <.!ctailcd mathematic.] are still fuiling to recognize. Many violini.,ts 'XIy th<:y can dcscriptionoflhcosscntialphysicsofviolinacoustics dis tinguish an instrument with a fine "ltalian Crcmoncse N I-l Fletcher and T D Ros,ing ]\198 The Physics of MWlical sound" from one with. say, a more "Fn:nch~tone , such as my In.'lrum,'1l/s 2nd edn (Springer. New York) - a uthoritative book with Vuillaurne violin. But \\'e still donOI know how to chamclerizc alltbe ... levant backgroundscience such properties in meaningful physical terms. C M TTutchiru; 19~1The Acoustics of Violin Plates !X-i~qtific What \\'e need is mon: research, with high-quality ~O\:tobo:rpl70 violinists working with psycho-acolUiticians, scientists anil C Ht*:h;1\J &rodV Ik-n* (ed) 1997 R""nl r<'h Pape'3 in Violin sympalhetic violin makers, to make funher progress in Acoustie.. 1975-93 ;'01, 1 and 2 (The Acoustical Society of Amcri~a. solving this cballenging and fascinating problem. New York) - ,""cellem ovc",iews of all ""pects of violin acoustics

M E Mdn~ and J Woodhou~e198t On \h~funda mentals of bowed FURTHER READING string "YDnmicsAcustica4393 A H Ikoaoe ]916 Fundamental. "f Musical Arou;·h·e.. (o.rord UnivcrsityPrc.";J-non-ruathernatical.butfullofpenetmtinginsights

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c.:tn _150 be defmod di,-"ctly in geometry ~I.,. optiOl'l.,tnn ....u ... 1 ",pJay, multipie ' OOn • • oftw.nI!convo!ution.h .. d- Contact La.... DSP or CATT-Acou.tic pho"" "'Iu.li ....tion. and.n ... .,rtmtnt (~.n .tg.• eI -catt) ford emo dl.ksOl'Lake

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64 . Vol. 28(2CXXl) No.1 Acoustics Australia SOLVING A BAFFLING PROBLEM AT WARRINGAH AQUATIC CENTRE John Andrew' and David Pritchett' 'PKA Acoustic CODsulting 'David Pritcllett Pty Ltd Suite 103,220 Paeific Highway 40 Cambourne Avenue Crows Nest NSW 2065 St Ives NSW 2075

ABSTRACT: Warringah Aquatic Centre has fur 20 years been a major sporting and recreation dmwcard fur ten.~ofthoru;andsof people on thel"""rnorth .horeandlmvernorthem beaches ,,[Sydney. Noise reverberation has always beeo a ooncern al the Centre, even though baffles were installed in the ceiling about 15 years ago. When the baffics beganjo deteriomte over the past ooupJe of years, the

situation became critical. This article describes h

1. INTRODUCTION Inspection of the graphs and figures indicated that the The Waning.th Aquatic Centre at Frerichs Forest on Sydney's highest noise levels were recorded on the evening of Friday,S lower North Shore records about 360,000 visitors a year, trum March, between the time the logger was set up and J Ipm(2300 hours). Tho LA"",(maximum RMS Sound Prcssure Level) was casual swimmers and families to aquarobics and swim class 106.5 dH(A) during this period and the other parameters were: students and, of course, clubs and schools holding sporting L, 102.0 dB(A) camivals. L\O 95,4 dB(A) The building is of conm;:te construction approximately 65 LA", 91.0 dB(A) metres long, 50 metres wide and 9 metres high from the Loo 84.5 dH(A) concourse around the pool to the underside of the effective ceiling which is profiled with roof lighting and high and low Other periods when LA"", reached over 100 dB(A) were levels. Tiered seating is provided on each side and at one end Saturday evening (\03), Monday daytime (102), Tuesday day­ of the pool. time (103), Wednesday daytime (103), ThW"sday daytime (104). Noise levels in the pool had been deteriorating over some From these measurements, it is obvious that noise levels in years and tho problem became critical towards the end of the pool centre were extremely high and close to being 1998. Mr Gary Penfold, General Manager of the Centre unacceptable under the rcquirements of Worksafe Australia, desen"bed the problem: "Aquarobics and swim classes couldn'l namely 8SdB(A) for eight hours. Using the data logger information, the noise exposure level hear their instructors, and school carnivals were chaotic. We was calculawd as follows for representative eight-hourperiods were getting more and more complaints." rlmingeach day. Warringah Shire Council sought an acoustic assessment in 9arn-5pm 2pm-IOpm early 1999. PKA Acoustic Consulting was asked to L"",dB(A) LA,qdB(A) investigate: Saturday, 6 March 76 79 Existingrevcrbcrationtimes Sunday, 7 March 74 73 Existing ambient sound levels Monday, 8 March • Pre-existingreverberationtimes Tuesday, 9 March 82 78 • Recommended -reverberation times Wednesday, 10 March 83 80 The investigation was bal!ed upon site visits, acoustic Thursday, 11 March 83 78 measurements, drawings and photographs provided by On three occasions, employees wcn: exposed to 83 dB(A), Council as well as computer modelling and general acoustic just below the staMory 85 dB(A) LAo"limit. calculatiOl1'l. Reverberation times in the enclosed pool were determined 2. TESTING EXISTING AMBIENT NOISE using large 800mru inflated balioollil that were pricked with a pin, the resulting burst being recor&d through a Sennheiser The old noise baffles were removed before a noioo data logger "Dummy Head" microphone system onto a Sony OAT (Acoustic Research Laboratories type EL-015) was set up on rccordertypeTCD-D7. top of the fIre hose reel cupboard next to the Manager's Office at one comer of a mezzanine level around the pool. The logger 3. ANALYSING THE ACOUSTIC TESTS was set to update every 15 minutes and to operate from 5pm The recordings were analysed by audio input into a computer. (1700 hours) on Friday,S March 1999 until 9.30am (0930 The digital recordings were transferred to computer wave flies hours) on Friday, 12 March 1999. and analysed using SlA Smart-Pro to obtain the octave banded

Acoustics Australia Vol. 28 {2000} NO.1 - 65 rcvcrberationtimcsforthc pool cnclosllTC The rolluwing T($ults werc obtained: Octaveband Cffiltrefreq (Hz) 125 250 500 lk 2k 4k Reverberation lime (soo:mct\) 6.0 6.0 6.4 6.6 6.5 5.0 Reverberation times in the enclosed pool alter barnes were originally installed were e,timated as an average or about 2.5 sel.'onds, based upon descriptions provided by pool staff together with photographs of the original acoustic treatment. lfthc reverberation time could be reduced from 6 seconds to about 2.3 seconds, the ma:-;Dnum sound level would be r~dm:edby ab out 4 dB, from 83 to 79 dB(A). Following this analysis, PKA Acow;tic Consulting submine

Cumputer muddling on a Madnto~h, running Bose MoodIer Version 4.7, was used to a"is! in m,termining the extenl and layout of acoustic absorbing material. Bose Figure t Conlputcr_generated perspective vicw showing Modcllcr is a sound system design program usually used to recommended positions for the baftles at Warringah Aquatic Ccntte. In fae\, som~ly~fI1es were moved from the rear of the place in a room or auditorium. PKA Acouslie huilding and' lJ.rcdthrough the skylight op~,"ingstravel along tracks Each barne, measuring !200mm long by lOOOmm high and below ceiling height. The gantries providC'd 3 safer option for llOmm thick, was covered with 5(}..micron black polythcne in~tanationworker:; than scaffolds Or lifts and allowed work to sheeting 10 prevent deteriormion by moisntre. Deterioration be und

The suece~fultenderer, Alliance Noise & Energy basic spacings werC' approved: two metres and fom metres Management. recommended a number of changes to the along the length of the pool and approximatdy 3.5 metres original concept ootlined by Council. A key recommendation

6ii - Vol. 28 (2OO:J) No.1 AcolJstics Australill Suspem;ion or the haffles was achieved by a system of e(lUld erect with a minimum of fuss. When people arc working spe<:ialJy fabricat~dhrack ets, T-bars and stainless steel wires 10 mctrcs above a concrete floor or pool, safety is a major

fabrication of the majority of components was done off site to issue. Dcvc1Gping the working plalfonns solved IxJth the sar~ly reduce time on site, With corrosion of the original baffles in i~,utand made lhe work much more simpk than scaffolding mind Alliance heavily anodised the aluminium components or hydraulic lifts." and inserted nylon hushes between all aluminil1m and 5. CONCLUSION ACOUST in "The Alli~nceclto'i gn and PKA ic Cons ult g rtlUmed [0 the Centre al lhe end or appropriate for us, hoth in terms of installation metllOds and November to compk te a new set of reverberation the final product," >aid Gary Penfo ld. "Itv.as imporlant to us

- given the other v,ork going on at the same time- that the The teSl demonsTrated lhal lloist 1evel~ w~re eon~islenlly installation teams were professional, thorough and s.olution­ low"r around the pool, with reverberation times averaging oriented. They \\ 'eTC working wilh o[h~rteam, around lh

all times, as well as learns of workers refurbishing all lhe Across the octave hand, reverberalion times ra!\g~drrom 1.4 change rooms aud replacing virUiaJly every door in lhe second~al I 25H:r. in one localion to 2.7 seconds at I ,O()()Hz at Cenlre " another, "The new system has transformed the Ccntre," said Mr Penfold. "Before the ne\\' baffles were installed v,e could not

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70 - Vol. 28 (?OCXl)No, 1 NSW Noise Control cover the relationships 3IId responsibilities constmttcdfordcvelopingtbenoise-redncing Regulations betweenthevarious.mkcllOldern. Tos!M!the materialsnndshapeof!hebaffles,screen',ete process off, the EPA will be inviting required forminimiziogtunnd fan and wind Five yean; ago NSW Noise Control stakeholdern to provide thcir ideas as to wha! noise and turbulence. Those prc:sent inspected Regnlations were substantially improved on The shooldgo into the policy. comp1ex nature the full-scale and small-scale tunnels to see previous legislation and oovereda rangcof ofrail administrntion sugg .. t>; the importance the actual measures used to achieve this noise new issues reflecting the changing sounds ofa very strong liaison component to the tbat our community produces. The idea of development SO that anyoutoome will be regulating for nOIse was to provide the supported by industry as well as the LouisFoury community with important thresholds of community. The general philosophy 10 be behaviour oonsistent with reasonable followed will be the same as that for previous Sound Demonstration harmonious living in medium and high policies - i.e., the establishment 00 an The NSW Division held a technical meeting density settlement situatious where specifie environmental goal and withproeedurcs put on the evening of 21 June 2000 at the situatioll8 could be identified and described. in place to ensure eitber the attainment of the premises of CSWs Commercial Design The.., are ill obvious, dominate any local goal or an approacb to the goal as closely as council. oornplaint registers and inclnde prncticable.ThcvicwW

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72 - Vol. 28 (2000) NO.1 und other ground ba,..,d activities on to pop mlL'iic and tbcme parks. TheflJStpape r by Louis Sutbcnand iCtS the =e by focus:sing on how to measure, evaluate arwl consel"\'l: NSW naturalquicl:.l1tescthreeaspe<:5,asrelatcd MrThomas Mitehell, 10 various types of noise generated by MrGrrutlHaigh Recreational Noise Effects on recrealional activities, are addresscd in thc Q LD Man and on the Environment papers. Six of the papcrs discuss \he efTecu of the noi se thaI is an cs:scntial pan of the International In.timtt of Noise Control cxperienceofa thcm<:park and disoo music. VIC Enllineering, 1999,pp 120, hardcover, Mr JimAnlOnopoulos A special time was set aside in the Distributor INCE(NZ) d, P 0 Bo~~7032, lt Graduate MsEm ily llulce MA NA 6230, Wellington, New ualand. tel symposium program for discussion groups SA +6442332066,f .... +64 4233 20 17, for the main streams. A summary of tile phihlUI@iconz,co,nz, Price, including points raised in thcse discussion groups is MrNeilMackenzie p<.>Slage,NZSl35 or US S75 orA$115 provided in the volwnc along with Ihc list of Mr Lcc Piekarski, attendees MrDcnni.Batg e, Thio bound volume comprises the papers MrRoryllughcs, presented at the lntcmatiolUll symposium on This volume con..isl5 mainly ofco ntributcd MrIanPhillips, Recrcation.aINoi,..,hcldinQueen<1OWn,NZ papcrs and so C3l\not be e.-cpectcd to = all MrDarrenMariooff, following the lntemoise98co nferencc. It tile aspec1s ",nichare relcvantlO recreatioruil MrJohoDunsford, has been published in collaboration with ooise. H~i tdoesformavaluable Ms Maryann , record of the papers and thc discussion a\thc Noise Control Engineering Journal SO tile Ms Margaret Thompson, symposium and would provide useful fomut of the papers iooonsiS\erlt wilh\ MsJcnniferCorkhill, infonnation for those dealing with Joumal\ ""lUiremenll;. This also explains MrMarcSimpson, why the pagination of the volume recreational ooise is.".,. MrKar.Kheel.e., commences from page 79. MarionSI/rgf!SS The 23 papers, each between four and six Mu,*",S..".,nu .. Raf'lll"CItOffiC

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76 - Vol. 28 (2000) No.1 DATA ACQUISITION SYSTEMS NORSONICS

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