The bellows of a
free reed instrument have been called the ‘soul’ of the
instrument. Just like the bow on a violin, the bellows play an
important role in the sound and performance of a concertina.
At a basic level, the bellows supply the air to the reeds and
control the dynamics: the amount of pressure on the bellows
determines the loudness of the sound.
At a higher level of playing technique, the bellows determine
the intensity of the sound. They can actually shape the notes
you’re playing, determining the attack (e.g. bellows vs. finger
attack) the ‘shape’ of the sound (e.g. increasing intensity and
harmonic overtones) and the ending of the note (e.g. a simple
cut off of the sound, or a rounded or tapered ending by means of
reducing/stopping airflow without removing playing fingers).
Advanced bellows technique is much like bowing technique on a
violin.
The level of performance determines the quality requirements of
the bellows. A beginning player is mainly concerned with basic
dynamics. He/she aims for dynamic consistency and maybe basic
dynamics like forte, piano, etc. For a beginner instrument, the
bellows requirements are stability, consistency in tension, and
of course air tightness.
At the other end of the spectrum, an advanced player needs to be
able to shape the sound by intensity fluctuations and perform
intricate bellows articulations. At this level, the bellows need
to have very low base tension, consistent over the full
expansion range, be very sensitive in order to translate small
fluctuations, and be very stable.
Because of these different requirements, there are different
types and qualities of bellows available, with different
structural designs, materials and construction methods.
Bellows
evaluation
There is a standard method to measure the performance of
bellows. This method measures tension (in grams), bellows travel
(in percentage), stability (in pressure) and airtightness
(airflow per minute).
Tension
In order to measure the bellows travel tension, you need to
remove them from the instrument. We measure 2 values: Closed
Tension (CT) and Open Tension (OT).
Closed Tension is the force required to close the bellows all
the way.
Open tension is the force required to open the bellows all the
way. Tension is measured in grams.
Bellows
travel
Besides the amount of tension generated, we also want to know
when the tension starts to build up. For example, with the
bellows in the ‘dead’ position (natural position, without
tension), we measure the distance they have to expand to fully
open and fully closed. The distance from fully closed to fully
open is the maximum bellows travel (BT). Next, we measure when
(the distance from ‘dead’) tension starts to build up. For
instance, if the maximum BT is 20 cm, and at 15 cm the bellows
start to pull back, the tension free travel for these bellows is
15 cm or 75%.
Stability
bellows stability is a requirement for bellows control. You
cannot perform intricate movements if the bellows are not
stable. Instability is usually the result of stretch in both top
and bottom hinges and the gussets. For instance, if the panel
cover and inner hinges are made out of sheepskin or another type
of leather with poor stability, chances are that over time
bellows folds will collapse under higher pressure. Stability is
measured in psi.
Airtightness
Airtightness is the amount of air escaping thru the bellows
material under a constant pressure. For this test the bellows
are removed from the instrument and mounted on closed stationary
covers with a pressure gauge. Pressure is provided by a dead
weight. With the bellows under pressure, a ‘sniffer’ is used
to locate air escaping through the gussets and
glue lines.
Because of the way sheep hair grows, sheepskin does leak under
pressure. Cement type glues, often used on bellows, do not
harden all the way and stays flexible. Under pressure these glue
lines can be stretched too far and cause leaking. Common leak
locations are gussets (porous leather), gusset tips and panel tops.
Leakage is more common on ‘rig made’ bellows because of the base
tension in the hinges.
Bellows
design
The shape of the bellows and the number of sides have a
considerable effect on the performance.
Fewer sides result in sharper corners. E.g. the angle between
the sides on 6 sided bellows is double that of a12 sided set.
The sharper the corners, the more tension is created within the
bellows when opening and closing them. This tension is caused by
hinges (both outer and inner hinges) being pulled and
compressed, movement between panels, panel tip separation and
gusset stretch.
Hexagonal (6 sided) bellows have a measurable higher base
tension than octagonal (8 sided) bellows, which have a
measurable higher base tension than dodecagon (12 sided)
bellows.
Because of the little movement in the bellows structure, 12
sided bellows allow for a much higher level of bellows technique
than 6 and 8 sided designs.
Preferably, bellows should have shallow corners (high number of
sides), are made out of thin (less compression tension)
airtight, stretch free (stable) non-porous leather, using low
volume hard glue, hard linen (non-stretch) inner hinges, panel
tip support (usually silk), and are tension free constructed.
Concertina bellows can be divided into 3 classes:
Basic bellows
Basic bellows are of the ‘accordion’ type. They consist of
folded cardboard panels with leather or synthetic gussets, no
inside hinges, linen fold covering and leather or synthetic
bindings.
Because the cardboard is folded, there is a certain amount of CT
base tension in the bellows. Basic quality bellows are great
for basic bellows control. You can control dynamics and they are
air tight. Because of the construction and materials, they will
get suppler with time, but will also lose some of their
stability.
Intermediate bellows
Intermediate bellows are of the traditional concertina design.
They consist of individual cardboard panels, often connected
with leather top and bottom hinges, leather gussets, panel
covers and leather bindings. The leather is often sheepskin,
which has a lot of ‘stretch’. Glues used are often of the
cement type, which have a strong hold but do not fully harden.
These bellows are (almost) always made on a ‘rig’. This is a
‘maximum stretch’ or ‘50% stretch’ mold on which the panels
positioned before they are
connected with the hinges and gussets. After the glue dries,
the bellows are removed from the rig and placed in a press or
under weights. Because the bellows are made in the open
position, they tend to have a lot of CT, caused by tension in
the hinges panel tip movement and gusset tension. Pressing the
bellows in the closed position stretches the leather hinges and
gussets. Rig made bellows usually require a case with blocks to
keep the bellows in closed position because the they will always
want to open a little.
High end
bellows
High end bellows are also of the traditional concertina design.
They consist of individual skived card panels, connected with
leather top hinges and hard linen bottom hinges, leather
gussets, silk tip reinforcement, leather or leatherette panel
covers and leather bindings.
The leather for the gussets and bindings is selected goatskin,
which has no stretch, can be skived very thin without losing
strength or becoming porous. Natural water based glues are used
which harden fully with no shrinkage.
Besides the materials, the big difference is the way they are
constructed. No rig is used for high end bellows.
Each set of bellows is measured individually to fit with a
perfect ‘waist’ on the bellows frames. The waist determines the
panel size. No two sets of bellows are identical in size.
All panels are connected by hand on a flat surface, not a rig, and before the glue sets,
moved in the maximum open and fully closed position. Based on
the tension feedback, the bellowsmaker will determine the drying
position for each set of panels, compensating for slight
variations in leather thickness.
This
results in hinge connections without ANY tension. Panel tip
spacing and gusset angle is determined by the maker and varies
for each set of bellows. Other varying factors are the number of sides
(6,8,12), thickness of the leather, type of concertina (anglo
bellows are different from English and duet bellows), and
maximum bellows travel.
Bellows constructed this way have very little travel tension.
High end Dodecagon bellows have a tension free travel of >96%. Standard
values for concertina bellows is between 70-80%.
Making high end bellows requires a lot of knowledge, skill and
experience. It will take several hundred sets of bellows before you’ve
developed any repeatable skills.
Our shop makes on average 100+ high end Wakker Bellows per year for new and
vintage concertinas, in 6, 8, and 12 sides, with 4-10 folds.
Sizes range from 8 key miniatures to 80+ key duet concertinas.
Copyright ©
2001-2021 Concertina Connection Inc8, All rights reserved.