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The wood data arranged here originate from different
building timber materials data bases. Some few missing data became
estimated partly on basis of own wood samples. Only species with a
“Roh”density up > 500 kg/m³.were taken.
In order to compare the properties of European species with Australian
Eucalyptus species, some Australian species are deposited in the
red-brown marked lines. Since for the
typical species hollowed out by termites the materials dates were not
available, some other industrial used Eucalyptus species are
represented. These should differ in the wood properties only
insignificantly. The yellow marked lines
shows south-European and the green marked
lines central-European wood species.
Description of the properties:
Darr density (Darr-Dichte): Density of the dry wood
“Roh” density (Roh-Dichte): Density of the wood after
cutting or storage with residual moisture
E-module (E-Modul): Elasticity (as far wood can be
deformed flexibly without lasting deformation.)
Speed of sound
(Schallgeschwindigkeit): Compute/estimated speed
of sound (from E-module and density) in the material wood
Hardness (Härte): Which strength opposes the wood
to a penetrating foreign body.
Decrease (Schwund): Percentage change of the
tangential and radial dimensions when drying wood. The likewise
represented difference from tangential and radial decrease can be
consulted as measure for the inclination to tearing or cracking. I.e.,
wood in tangential direction substantially more shrinks itself than in
radial direction must tear or strongly warp.
Influence of the wood properties on the sound:
The denser and harder the wood is (greater stiffness),
the less the resonances of the air column in the higher frequency
range will be dampened. The sound becomes clearer, richer in overtones
and “harder”. Fewer material resonances form in the deeper frequency
ranges. With hard woods, a reduction of the wall thickness
additionally improves the material resonances in the higher overtone
area. Hence more sound energy is emitted there, which, given the same
basic key, can produce a markedly higher timbre (sound characteristics).
Be careful with using woods that are too soft! An over-thin wall can
cause sound absorption by the material and produce a “dull” sound
characteristic.
Here the art and experience of the didge maker is required, in working
out these additional material resonances.
The greater the ratio of elasticity module to wood density, the higher
is the speed of the sound in the wood and the faster the material
responds to changes in sound, i.e. the responsiveness improves.
Despite the influence of the wood properties on the sound, the form
and resonances of the vibrating air column play the far greater part
in shaping sound characteristics!
Remark on the roughness of the interior
surface: The smoother
and harder the interior surface is at the microscopic level (e.g.
instead of coarse polishing, a hard lacquer), the less the sound
energy of the higher overtone oscillations of the air column is
dampened by friction. The sound characteristic becomes clearer and
richer in overtones. But this does detract somewhat from a typically
soft, earthy sound character. A side effect of this friction on rough,
unworked surfaces can lead to the ringing tones becoming as much as
1-3% higher after polishing and hardening.
The shape of the internal surface in the non-microscopic area (e.g.
coarse chisel marks) tends to play a subordinate role in terms of
physics.
Interpreation of the wood data:
The wood data arranged in the following table
represent average values and are therefore only a rough orientation.
Often the wood properties are determined substantially more by the
growth conditions.
So the density of slowly grown trees on nutrient-poor and dry soils
and in addition still a short annual vegetation period (e.g. in the
mountains at lower temperatures) is substantially higher than for fast
growing trees of the same species on nutrient-rich optimal soils and
long annual vegetation period.
For the density also the minimum and maximum measured values are shown.
It is good to recognize, how largely partly the dispersion can be
within a species.
So e.g. a birch in the mountains, grown slowly on nutrient-poor soil,
can exhibit a higher density, than an oak in warmer environment, grown
fast on nutrient-rich soil. The density stands also in the direct
connection with the yearly ring width. The smaller the yearly ring
width is the higher the density of the wood is. I.e., by investigation
of the growth conditions and the yearly ring width can be done a
selection of suitable trees of a species.
Felling time:
Felling time:
The time for cutting should lie in the winter, because in this season
(vegetation break) the trees have the smallest water content. It is
still better to depend additionally on the moon calendar since the
water content of trees is also affected by tides by the moon position.
More details can be found on the Website of Johannes Schildkamp -->
yedaki.de
Table: Wood dates/properties:
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