Drumset Mechanics
What
causes the tone?
A drum
is fitted with either one or two heads over the open ends of the shell, with
drum kit this is Mylar, with drum corps Kevlar and on 'traditional' instruments
any one of a range of animal or fish skins. The head is struck which generates
vibrations that are modulated within the drum
and radiate out from it. These vibrations are perceived by the ear as a
fundamental note plus harmonics & overtones. The shell and head properties
dictate the timbre and tone respectively in a manner which will vary in line
with many factors but mostly dependent on the properties of the shell design
viz. bearing edge, diameter, thickness, depth, internal construction, number and
type of laminate plies, internal shaping and also by your choice of heads and how you have tuned the drum.
One
head or two?
The
choice of using a single (batter) head or two (batter and resonant) heads on
rack and floor toms is a personal decision. Using the batter head only will
give you a sound that is very clean and bright with a shorter sustain, the
emphasis on attack rather than tone. Toms with a single head are known as
concert toms and are less common than two headed toms. Concert toms may be seen
in orchestral applications, within larger drum
set-ups
or as drums for that specific sound, however the decision to use single headed
toms should be based on suitability for your own musical requirements.
Using
two heads creates a synergy within the drum which gives an output greater than
the sum of the parts. With two heads you have a surface parallel to the batter
head against which the vibrations caused by striking the drum are reflected back
against the batter head and then back to the resonant head etc etc. Secondly,
as the vibrations are retained within the drum for a longer period, the drum
shell is 'excited' to produce vibrations also which in turn add the existing
vibrations. The other main advantage and the most important aspect of using two
heads is the level of control that the drummer can exert over the movement and
duration of the tone. This is a tuning consideration and is covered in the tuning section of the
site. Basically, with both heads tuned identically, the waves are continuously
reflected in phase with each other with each wave slightly quieter than the
previous until they are dissipated sufficiently to have decayed below the point
of hearing, this gives maximum resonance for that drum in that tuning. With the
heads tuned differently to each other, they will be out of phase, giving a tone
that decays faster and a greater attack. On lower toms and/or at lower tunings
this gives a 'pitch bend' effect.
Most
drummers opt for two heads for all the above reasons.
Thick
or thin?
The
density of the shell has a significant impact on the sound of a drum.
A very
thick drum will, in relative terms, hardly resonate at all and will tend to
project a clear bright version of the head-tone imparting few of its own
qualities into the sound, this is because the vibrations from striking are
reflected by the shell more than they are absorbed by it (although a certain
amount of absorption will always take place with a wooden drum) At lower
tunings, they deliver a 'fat' or 'round' sound. At elevated tunings they tend
to choke up more easily, or as Bob Gatzen describes them, a 'Blunt' or 'Sticky'
sound.
A
thinner drum on the other hand will act like a type of membrane, vibrating and
resonating in greater harmony with the heads, in this scenario, because it is
absorbing vibration, it starts to vibrate itself and imparts its own vibrations
and therefore sound into the overall tone of the drum. At higher tunings, they
are very clear in pitch and cut well through the music,
they deliver greater volume than thicker shelled drums and lower tunings this
may be considered a more 'woody' and warmer sound, overall a thinner shell will
deliver a more pure tone than a thicker drum. In general a thinner shelled drum
will accept all head types and thicknesses and will deliver the optimum tone for
that head type.
One
caveat about using thinner shelled drums is that at high volumes, the vibrations
within the shell of a drum itself can cause the sound to distort. Pick your
shells to match the music you aim to play
Construction variations
Because
by far the majority of drums are of laminate construction, manufacturers also
have the option of using 'cocktail laminates' in their drums whereby they
construct the shells from different types of woods sandwiched together. This an
attempt to address the tone/resonance trade-off situation. The choice is a
subjective one and the major considerations are the number / thickness of plies
and the types of woods used. Different materials impart different qualities of
vibration into the sound of the drum (see shell design) and therefore giving different qualities
or timbres of sound. As a rule of thumb, the softer the construction material
the more 'mellow' the sound, e.g. Maple is 'warmer' than Birch, and because the
softer wood will have more movement and vibrate more easily than a drum made
from harder wood. Maple will also be louder and more bass-resonant, whereas a
harder material such as birch will have a quieter and more focused sound.
A
limited number of manufacturers construct drums using solid shells, these fall
into two types. Stave drums are constructed in a barrel-like manner with
vertical blocks of wood glued together to create a shell, some 'high end' snare
drums
use this construction method. The other and true solid shell construction
involves taking a solid log of wood and machining it to size. In general solid
shell drums are thicker than laminate drums usually 1/2" (10-12mm) as opposed to
5/16 (7-8mm) are heavier and deliver a bright sound balanced with an impressive
low end.
Reinforcements?
If you
look inside the interior of a drum you may see that there is a second layer of
plies at the top and bottom 3/4" - 1"of the shell usually angled to match the
bearing edge cut, with the central vertical area of the shell remaining at the
'proper' shell thickness. These are known as reinforcement rings. primarily
these are used for maintaining roundness and tune .
With the
on-going development of drums, manufacturers have created product lines that are
very thin-shelled to produce warm and woody sounding drums, although
structurally sound, these drums, particularly larger sizes, may distort with the
vibration of being struck, the reinforcement ring acts as a shock absorber and
keeps these excessive vibrations to an acceptable level.
Reinforcement hoops therefore, by restriction, counter the tonal
effect of thin shells to an extent, however as John Van Ness from DW drums says
in his article
on re-inforcing hoops on this site, they taper "off the highs because the column
of air is physically blocked by the re-inforcement hoops at the inside edges."
Certainly you should expect less resonance a more low frequencies from a drum
with reinforcement rings.
Internal surfaces
The
interior surface finish of a drum will also have an effect on the overall sound
of the drum, some drums are manufactured with the same glossy lacquer inside as
out and this will give a more reflected sound, very clean and crisp and because
of the reduced absorption into the shell will be less woody. A drum with a
satin finish, i.e. not a high gloss lacquer, will start to deliver more of the
woody sound and a drum with no interior finishing will have a porous surface and
will deliver even more of the wood sound into the drum. Some high end custom
drum builders carve intricate designs into the internal shell to dissipate the
internal harmonics. These can be pretty subtle differences!
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