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Secret of the great violins? The wood, study suggests

July 1, 2008
Courtesy PLoS One
and World Science staff

The long-sought se­cret to the great Ital­ian vio­lins of old, with their un­par­al­leled sound, may lie in their wood, a sci­ent­ist claims.

Ra­diolo­g­ist Berend Stoel of Lei­den Uni­ver­s­ity Med­i­cal Cen­ter in the Neth­er­lands ran med­i­cal scans on sev­er­al of the vi­o­lins by famed crafts­men such as An­to­nio Stra­di­va­ri (1644-1737). Stoel found that their wood is more uni­form in dens­ity than that of mod­ern in­stru­ments.

"Strads," as admirers call them, have fetched up­wards of $2 mil­lion at auc­tion. (Image cour­tesy Li­brary of Con­gress)

Stra­di­va­ri and a se­lect few con­tem­po­rar­ies work­ing in Cre­mo­na, Italy are con­sid­ered to have brought fid­dle­mak­ing to its high­est apex. His vi­o­lins, of which about 600 are be­lieved to sur­vive, have fetched more than $2 mil­lion at auc­tion. 

But ex­pe­rts re­main di­vid­ed and largely puz­zled over what ex­plains the in­stru­ments’ superb qual­ity, which mod­ern tech­nol­o­gy and craft, by gen­er­al con­sen­sus, have failed to re­pro­duce.

Stoel used CT, or com­put­ed to­mog­ra­phy, scans, a meth­od of ex­am­in­ing ob­jects with X-rays and a com­put­er that builds a se­ries of cross-sec­tion­al scans. He worked with the mod­ern luthier, or violin-maker, Ter­ry Bor­man to com­pare in­stru­ments by Stra­di­va­ri, the only slightly less known Guar­ne­ri del Gesu (1698-1744) and mod­ern vi­o­lins.

Stoel said he found marked dif­fer­ences re­gard­ing the dens­ity, or weight per un­it vol­ume, from point to point in the wood of clas­si­cal vi­o­lins com­pared to mod­ern ones.

A giv­en tree pro­duces wood of dif­fer­ent dens­i­ties de­pend­ing on the sea­son. Spring­time growth ty­pi­cally yields wood that con­tains most of the wa­ter trans­fer chan­nels. Thus it’s light­er than wood pro­duced lat­er in the year, which serves more for struc­tur­al sup­port. 

The av­er­age wood dens­ity of the clas­si­cal and mod­ern vi­o­lins did not dif­fer sig­nif­i­cantly overall, Stoel said. But the “dif­fer­entials,” or dens­ity dif­fer­ences from point to point, af­fect the ef­fi­cien­cy of vibra­t­ion and thus the sound. This could ex­plain the an­cient in­stru­ments’ ton­al qual­i­ties, Stoel and Bor­man wrote in re­port­ing their find­ings in the July 2 is­sue of the on­line re­search jour­nal PLoS One.

The an­cient luthiers seem to have sought out si­m­i­lar types of wood as are cur­rently chos­en for vio­lins, the pair wrote. It’s un­clear how the mas­ters ob­tained the spe­cif­ic wood dens­ity qual­i­ties found in the stu­dy, they added, but some wood treat­ment might have done the job. One cu­ri­ous pos­si­bil­ity, they wrote, is a treat­ment called “pond­ing”—placing the wood in­to streamwa­ter and let­ting bac­te­ria al­ter the ma­te­ri­al prop­er­ties by eat­ing away at it. 

But al­though pond­ing is spo­rad­ic­ally men­tioned in con­nec­tion with the Cre­monese vi­o­lins, re­search has shown they were probably not ponded, Stoel and Bor­man wrote. Still, they added, pond­ing might lead to some changes in the di­rec­tion of a si­m­i­lar wood qual­ity.

To de­ter­mine dens­i­ties, Stoel de­signed a com­put­er pro­gram to be used to­geth­er with the CT scans. The de­sign drew on pre­vi­ous work he had done in help­ing to cre­ate a pro­gram that cal­cu­lates lung dens­i­ties in em­phy­se­ma pa­tients.

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The long-sought secret to the unparalleled sound of a few eighteenth-century Italian violins may lie in their wood, a scientist claims. Radiologist Berend Stoel of Leiden University Medical Center in the Netherlands ran medical scans on several of the violins by celebrated craftsmen such as Antonio Stradivari (1644-1737). Stoel found that their wood is more even, in terms of density, than that of modern instruments. Stradivari and a select few contemporaries working in Cremona, Italy are considered to have brought fiddlemaking to its highest apex. His violins, of which about 600 are believed to survive, have fetched more than $2 million at auction. But experts remain divided and largely puzzled over what explains the instruments’ unrivalled quality, which modern technology and craft by general consensus have failed to reproduce. Stoel used CT, or computed tomography, scans, a method of examining objects with X-rays and a computer that builds a series of cross-sectional scans. He worked with noted modern luthier, or violin-maker, Terry Borman to compare instruments by Stradivari, the only slightly less known Guarneri del Gesu (1698-1744), and several modern violins. Stoel said he found marked differences regarding the density, or weight per unit volume, from point to point in the wood of classical violins compared to modern ones. The findings focus on the fact that a given tree produces wood of different densities depending on the season. Springtime growth yields the wood that contains most of the water transfer channels. Thus it’s lighter than wood produced later in the year, serves more for structural support. The average wood density of the classical and modern violins did not differ significantly overall, Stoel said. But the “differentials,” or density differences from point to point, affect the efficiency of vibration and thus the sound. This could explain the ancient instruments’ tonal qualities, Stoel and Borman wrote in reporting their findings in the July 2 issue of the online research journal PLoS One. The ancient luthiers seem to have sought out similar types of wood as are currently sought out for the purpose, the pair wrote. It’s unclear how the masters obtained the specific wood density qualities found in the study, they added, but some wood treatment might have done the job. One curious possibility, they wrote, is treatment called “ponding”—placing the wood into streamwater and letting bacteria alter the material properties by eating away at it. But although ponding is sporadically mentioned in connection with the Cremonese violins, research has shown they were probably not ponded, Stoel and Borman wrote. Still, they added, the treatment might lead to some changes in the direction of a similar wood quality. To determine densities, Stoel designed a computer program to be used together with the CT scans. The design drew on previous work he had done in helping to create a program that calculates lung densities in emphysema patients.