The Guitar and its Woods

Fine classical guitars traditionally are made with rosewood back and sides, spruce or cedar tops,
necks of mahogany, fingerboards of ebony. This is, however, is only the beginning of a complex story.
Such woods come in various varieties and grades of quality. Their behavior as tone woods also
depends on how they are cut, dried, and aged.

Wood for the Top
As Antonio Torres (1817-1892) proved over a century ago, when he made a guitar with papier-mache
back and sides, the top is critical to the guitars sound. Of the several "tone woods" available, spruce
is the most widely used. There are several varieties of spruce used in building musical instruments.
By far the first choice for top quality classical guitars is Alpine spruce (picea abies), commonly
called German spruce.   This European spruce, which comes from thinning forests in Switzerland,
Germany, and the former Yugoslavia, has in recent years become increasingly hard to come by.
Although Sitka or Englemann spruce from North America is inferior to European spruce for classical
guitars, it is widely used to construct steel-string guitars because its slightly different fiber structure
helps dampen the harsh harmonics produced by steel strings. Hokkaido spruce has been used
Japanese makers  in their guitars.

In the 1960s, high quality German spruce became increasingly expensive and difficult to obtain.
Jose Ramirez III (1922-1995) began to explore the possibilities offered by Western red cedar
(thuya plicata), commonly called Canadian cedar. Its close, straight grain, dimensional stability
even under changing temperature and humidity, and tonal responsiveness made it an ideal
substitute for spruce. Following Ramirez, many famous luthiers such as Ignacio Fleta (1897-1977)
and Daniel Friedrich (born 1932) began building guitars with cedar tops.

Although some guitar makers are able to achieve good results with cedar, others cannot make it
work for them. In my opinion, the choice between spruce and cedar (other things being equal) is a
matter of taste, much like the difference between vanilla and chocolate ice cream.  Cedar guitars
tend to be more responsive to low-frequency resonance's, and so are often sweeter, mellower,
yet makers are also able use it  to produce bright, clear guitars. On the whole, I find that cedar
guitars have a darker tonality, and that the sound is less direct, more enveloping than spruce.
The sound of a well-aged fine spruce top has an unmatched openness, clarity, directness,
and edge like an arrow.

One of the raps directed at guitars with cedar tops is that unlike those of spruce they do not improve
with age. The other spin, of course, is that they are responsive from the start, and one doesn't need
to play them in for years to achieve the openness of aged spruce. This does not mean, of course,
that a poor sounding instrument will become a good one with time. The rap against spruce is that it
is much more subject to changes in humidity than is cedar. This is precisely why it is so vital that
such woods be well-aged and properly dried.

From the start, the older the spruce used by the maker, the better.  Spruce is a very hydroscopic
wood,that is to say it tends to absorb the same degree of humidity as the surrounding air,
breathing moisture in and out with changes in humidity. Wood cellulose is of two types: one which
is amorphic and absorbs and returns humidity; and the other which is crystalline and does not
absorb humidity.
Once wood is cut, and begins to dry out returning the moisture it absorbed in its life to the air,
the crystalline form begins to replace the amorphic form, reducing its tendency to absorb humidity,
and increasing its rigidity and capacity to vibrate with greater amplitude.
In short, as it slowly ages and dries, its tonal characteristics improve. While there are wood
suppliers who guarantee the woods they provide have been aged 50 years, woods  once they reach
their optimum of dryness, will not improve no matter how much time passes.
Air-drying is preferred by luthiers to kiln-drying methods as it allows time for chemical changes to
occur which "cure" the wood.  
If woods are properly air dried, wood may be seasoned in as little as three to five years.
Luthiers,  however, may cure their tops for much longer-- often twenty to thirty years.

The quality of a top is judged by three aspects of its wood's grain: straightness, density, and medullar
rays. The straightness of grain is very important in determining sound quality and timber. The wood grain
should be totally straight with each grain parallel to the others. Since sound travels along these long
fibers, any deviation from straight grains reduces its strength. Density is likewise important. The great
the density (number of grains per cm) the finer the top. Here it is important to observe whether or not
the density is uniform. Irregular spacing indicates that the wood has not been cut along the grain, and
is of an inferior grade. Generally, in premium grade woods the distance between grains is less than
2 mm. One of the feature's of fine spruce tops is the presence of medullar rays, fibers which grow
at right angles to the grain. While their natural function in the wood is to circulate starch and resin,
they improve the tonal quality of the soundboard by providing links between the long fibers of the grain.
Light medullar rays also may be found in cedar, but they are not as marked nor do they seem as
important to sound as for spruce.

In recent years, some guitar factories have attempted to imitate the appearance of fine instruments
by building instruments with laminated tops. Naturally, they sound like the plywood the are made from.
Buyer beware. Make sure the instrument top is made of solid wood.

Woods for back and sides

Rosewood

Two types of rosewood are commonly used in classical guitars and so-called flamenco negras:
Brazilian rosewood   (dalberia nigra) and Indian  (dalbergia latifolia) rosewood.
Both woods are dense, resinous, and very handsome. Brazilian has highly figured grain, and
many consider it the more beautiful of the two, but it is more brittle and difficult to work than
Indian rosewood. By contrast, Indian rosewood tends to be straighter-grained, and often
contains purplish streaks. Brazilian has become increasingly expensive and rare. In the mid-1960s
the Brazilian government,  with the aim of diverting more work to their sawmills, banned the export
of logs. In 1992 dalberia nigra was declared an endangered rain forest tree, and requires a CITES
license, and so is no longer being exported period.  Indian rosewood, on the other hand, grows
on plantation, and so remains plentiful. Indian rosewood also has the advantage of being
dimensionally more stable, and of being less affected by changes in humidity and temperature
than Brazilian rosewood..

Tonally the woods have slightly different characteristics. Brazilian rosewood is less fibrous,
and a somewhat harder, denser wood, and so tends to reflect sound more, and thus produces a
bit brighter sound than does Indian. This difference, however, can only be perceived by playing
identically made instruments by the same maker. Or, to put it slightly different way, there are much
greater differences in sound between makers using the same woods than between different woods
by the same maker. A well made Indian rosewood guitar may be infinitely better than a fancy-expensive
Brazilian rosewood guitar by a luthier of lesser talent.

Figured Rosewoods

Adding to the confusion, there are many species of dalbergia (botanically "true" rosewoods) from
Brazilian and elsewhere that are marketed as Brazilian rosewood. These figured rosewoods are
very similar in appearance and character to dalbergia nigra and include dalbergia stevenonii
(Honduran rosewood), dalbergia retusa (Cocobolo), dalbergia cearensis (kingwood),
dalbergia frutescens (Pau rosa, Jacaranda Rosa). In this family of similar woods from Brazil,
we also find Machaerium spp. (Caviuna or Fau Ferro), and Dalgberia palo-escrito (Palo escrito).  
In fact, there are literally hundreds of species of dalbergia worldwide. Because of this confusion
and hype overBrazilian rosewood I prefer simply to call these species figured rosewood, and to
refer to Brazilian rosewood as Dalbergia nigra.

Laminated woods

Unlike the top, some fine makers have chosen to build guitars using laminated materials with excellent
results. Jose Ramirez, for example, lines his traditional 1a model rosewood guitars with cypress.  
He believes that this lamination lend greater stability to the back and sides, preventing warping and
twisting, and providing them with their distinctive dark sound. Henner Hagenlocher, similarly lines the
sides of his guitars with cypress.


Maple
For centuries maple has been used in instrument making because its cross-grained structure allows
it to be planed down to make light, but strong instruments. In the nineteenth century, it was widely used
to make both fine classical and flamenco guitars. In fact, up to the 1930s,  fine flamenco guitars
continued to be made of maple which like cypress can be planned very thin, yet produces a
somewhat fuller sound than cypress without being as mellow as rosewood.  Some modern luthiers,
such as Paulino Bernab  Pedro de Miguel, and J. A. Pantoja Martin among others are again using
maple to produce instruments with a sweet vivacious tone.

Cypress  
The flamenco guitars are usually made with Spanish cypress, an attractive blond wood that is
extremely light, and can be worked much thinner than rosewood. It is the use of thin, light cypress
for the back and sides that helps give flamenco guitars their vibrant and distinctive sound. The choice
of cypress over other woods, nonetheless, appears to have been a question of building affordable
guitars. Few flamenco players could afford anything else, and cypress was abundant and cheap
in Spain. In recent years, however, high quality cypress has become increasingly difficult to obtain.

Coral
Coral is another wood that is occasionally used to make flamenco guitars. A handsome reddish wood
like cypress coral can be worked thin, to make light vibrant instruments. Harder than cypress, it
produces very bright guitars. Both Pedro de Miguel and JosRuiz Pedregosa have used it to make
outstanding flamenco guitars.

Mahogany

Mahogany is one of the woods widely used to make affordable guitars. While it is much cheaper
than rosewood, its tone is thinner and less resonant than rosewood.

Other woods

Makers have experimented with a number of other woods as alternatives to rosewood.  
Paulino Bernab for instance, has used pear wood in the bodies of high quality classical and
flamenco guitars. Paul Fisher has experimented with a Figured rosewood wood, Santos Palisander,
with good results   In their quest to find more affordable woods guitar builders have also used
sapele, an African wood in the mahogany family, sycamore from central Europe, American walnut,
Koa wood from Hawaii, and Bubinga a reddish brown wood from Cameroon and Gabon.

Woods for the Neck  

The wood for the neck needs to be strong and dimensionally stable or it will warp or twist under
the pull of the strings with changes in temperature and humidity. The wood also should be light to
maintain the balance of the guitar. Because Honduran cedar or Honduran mahogany are straight
grained, and when they are properly seasoned are both light and stable, they are the woods of
choice for classical and flamenco guitar necks. Even so, to prevent warping, many makers reinforce
the necks of their instruments with a bar of ebony running the length of the neck, at 90 degree angle
to the grain.

Woods for the Fingerboard

The fingerboard requires a wood that is very hard as the constant striking by fingers and rubbing
of the strings will rapidly wear groves in softer woods. Two woods are commonly used for fingerboard:
rosewood and Guinea ebony. Although rosewood is a more stable, ebony is much harder wood.
As a result, ebony is universally used for fine guitars; and, rosewood only for entry level instruments.


http://www.azstarnet.com/public/commerce/zavaletas/greene/woods.htm

시더와 스프루스 - (새솔님 작성글입니다)

다음내용은 위 web site에 있는 FAQ와 article에서 관련내용을 발췌하여 정리한 것입니다.
(*주 1) 및 (*주 2)는 제가 설명을 덧붙인 것입니다.
참조 site;
http://www.azstarnet.com/public/commerce/zavaletas/greene/index.htm
  
1. 취향의 문제, 음질의 특징과 반응성
스프러스와 시더의 선택은 취향의 문제이다. 마치 바닐라 아이스크림과 쵸코 아이스크림의 차이처럼.
대체로 시더는 낮은 진동수, 즉 저음영역에서 잘 울림. 그래서 상대적으로 달콤하면서도 더 부드럽고
풍부한 소리를 내는 경향이 있다. 약간은 어두운 느낌의 음색이 특징. 그러나 제작가에 따라서 시더를
써도 얼마든지 밝고 소리가 또렷한 기타를 제작할 수 있다.

시더는 일반적으로 약간 상대적으로 어두운 음색이면서 원달성은 덜하지만 부드러운 톤을 갖고있다. (*주1)

(*주1) 음파를 오실로스코프를 통해 파형을 관찰하면 진동수가 많은 고음성분은 파형의 형태가 날타로운
형태를 갖고 진동수가 낮은 저음성분은 완만한 곡선을 그린다. 같은 음정이라도 그 음정에는 그 기본 진동수의 2배, 3배, 4배… 의 배음(harmonics)이 포함되어 있으며 이 배음의 함량이 음색을 결정하는 요소이다.
높은 진동수의 배음이 많이 포함될수록 파형의 형태는 날카로와 지며 음색은 명확해지고, 밝아지며,
극단적인 경우에는 폰티첼로 같은 금속성 소리가 난다.
스프러스가 밝은음을 낸다는 것은 높은 진동수의 배음에 대해 잘 반응한다는 것이다.)
스프러스는 충분한 시간이 지나 건조가 잘 되어있는 경우 대단히 명확하고, 원달성이 뛰어나며 화살촉같은
선명한 음의 분리도를 가지며 트인 소리를 낸다. 스프러스 앞판의 기타는 제작된 이후 수년정도 연주를
많이 해 줄수록 소리가 더 트인다.
반면 시더는 스프러스에 비해 시간이 지나더라도 소리가 크게 좋아지지 않는다. 그러나 처음부터 반응성이
좋아서 처음부터 큰 음량과 트인 소리를 낸다.

2. 수분과의 상관관계 및 건조에 따른 나무조직의 변화
또 스프러스는 시더에 비해 습기에 변형되기 쉽다. 그래서 잘 건조된 오래된 것을 선택해야 한다.
스프러스는 주변 공기의 습도에 따라 수분을 흡수하거나 배출한다. 즉 공기의 습도가 높으면 수분을
흡수하고 습도가 낮으면 수분을 배출한다.
나무의 섬유소는 두가지 종류가 있는데 그 하나는 비정형성 섬유소로 수분을 흡수, 배출하는 것이고 또
다른 하나는 결정성 섬유소로 수분을 흡수하거나 배출하지 않는 것이다. 나무가 잘려져서 마르기 시작하면
비정형성 형태가 결정성 형태로 바뀌어지게 되는데 흡수성은 점점 없어지고 단단해지게 되면서 더 큰
진폭으로 진동할 수 있게 된다. 한마디로 시간이 지나고 건조될수록 음질이 더 좋아진다. 그러나 일단
최적상태로 건조된 나무는 더 이상 시간이 지나더라도 음질이 더 좋아지지는 않는다. (* 주2)

(* 주2) 단, 이것은 연주를 하지 않고 건조된 상태만을 가지고 이야기 한 것이다. 최적상태로 건조된 나무이더라도 연주를 함으로써 더 소리가 좋아질 수 있다. 아래에서 설명 되어있다.)

4. 수질선과 음질
좋은 스프러스 앞판 나무의 특징중에 하나는 수질선(medullar ray)이 있다는 것이다.
수질선이란 나무결에 직각방향으로 자라는 섬유질을 말한다. 나무에서 수질선의 역할은 녹말과 수지를
순환시키는 것이지만 앞판으로 쓰일경우 수질선은 나무결을 이루는 긴 섬유들 간의 통로가 되어서
음질을 개선시킨다. 수질선은 시더에서도 약간 보이기는 하지만 뚜렷하지 않고 스프러스 만큼 소리에
중요한 역할은 하지 못한다.

5. 기타의 소리가 트인다는 것
스프러스는 시더에 비해 수지(resin) 성분이 많아서 소리가 트이는 데 시간이 더 많이 걸린다.
시간이 지날수록 수지는 더욱 더 부서지기 쉬운 상태로 되고 연주를 자꾸 하면 이 수지들이 소리의
진동에 의해 부서지게 된다. 그렇게 되면 기타는 더욱 더 반응성이 좋아지고 음질은 더욱 익게 된다.
얼마나 빨리 소리가 트이냐 하는 것은 앞판의 나무가 얼마만큼 잘 건조되었는가 하는 것과 얼마나
자주 연주를 해 주느냐에 달려있다. 당연히 잘 건조된 것일수록, 자주 연주를 할수록 소리가 빨리 트인다.
스프러스의 종류에 따라서도 차이가 난다. 보통 독일산 스프러스는 대체로 소리가 트이는데 1~2년 걸리고
이후 수명이 다할 때까지 지속적으로 소리가 개선된다. 북미지역에서 나는 엥겔만 스프러스는 독일산
스프러스 보다 수지성분이 적어서 상대적으로 빨리 소리가 트인다.