The "All about..." articles are meant to give
the interested player of free reed instruments a chance to learn
information on specific concertina related subjects.
Unfortunately, probably due to the limited literature on the subject in English
(most of the literature is
in German, French and Russian), much of the general
knowledge is not based on facts, but rather on beliefs,
which are often
misleading. The following article is a short introduction into the subject of free reeds, as I
taught it for over 20 years at several music institutions.
Sound generation in free reed instruments
Free reed instruments are wind instruments. Unlike other wind instruments, where
is produced by air columns, the sound in a bellows driven (e.g.
accordion, concertina, etc.) free
reed instrument is generated by the cutting
of an airflow in small air waves, not by the
vibration of the reed.
This method of sound generation is actually quite uncommon in
concertina reed and frame
This cutting or ‘chopping up’ of the
airflow is done by a so called 'free reed', or 'tongue' or, as
Wheatstone called it, a 'spring'. This is a small strip of steel, brass
or German silver, which is
attached on one end, either by means of screws or a
rivet, to a brass or aluminum frame.
The frame is slotted, allowing the reed to
move freely ‘through’ the frame.
modern concertina reed,
early square top frame, aluminum and brass frame
early accordion reed,
These reeds are mounted in a small
chamber over an opening which is connected to the bellows.
In order to activate
a reed, an air flow is needed.
The airflow in a concertina is generated
by expanding and contracting the bellows. The
amount of air pressure generated is
determined by the player. The more force the player
applies to the bellows, the higher the air pressure. The size of the bellows also play a role
in the amount
of pressure that can be generated.
If the same amount of force (F) is
applied by the player, smaller bellows will generate more
air pressure than
large bellows. Pressure is the force applied by the player, divided by the
size of the bellows: P = F : S. This formula illustrates that the pressure generated on a
concertina is much greater than on a full size accordion. That’s why we call
high pressure and accordions low pressure free reed instruments.
air flow direction by expanding bellows
In a concertina the air flow is
initiated by pushing down a key. The key is connected to a pad
which opens the
air hole of a reed chamber. When the bellows are expanded (pulled) it creates
airflow which passes through the selected air hole into the reed chamber. From
it will pass through the frame slot, which is obstructed by the reed,
into the bellows. This
obstruction creates a higher air pressure (P1) above the
reed in the chamber than on the other
side of the reed (P2). This pressure
difference is needed to initiate and maintain a reed swing
cycle as we shall see
When the bellows are closed (pushed),
an overpressure is created in the bellows and under
pressure in the reed chamber
and the air flow moves in the opposite direction; from the
bellows into the
chamber and through the air hole. Now the reeds on the bellows side of
the reedpan are activated.
The reed swing cycle
When a free reed is in rest position, it
is almost parallel to the reed frame. The tip is slightly
above the frame. In
this position the reed is free of energy.
When the tip of the reed is lowered or
tension-energy builds up in the reed. the amount
of tension-energy is
determined by the elasticity of the material, and the distance the tip is
moved away (amplitude)
from the rest position. The greater the amplitude, the more
up. The maximum amplitude of a reed is determined by the type of material
and the size and shape of the reed: longer reeds have a larger amplitude.
When the reed is released, the
tension-energy in the reed becomes movement-energy which
causes the reed to move
back towards the rest position and further to the opposite site of the
position. When it moves past the rest position, it builds up tension-energy
movement-energy is replaced by tension-energy, and the motion of the
reed is reversed. The
reed will swing back again in the direction of the rest
position, and the swing cycle will be repeated.
During every cycle the reed will loose
energy because of inner friction and surrounding air. If a
reed is to maintain a
constant ‘stationary’ swing motion, energy will need to be added to the
In free reed instruments a flow of air activates the reeds. This airflow will
not only initiate
the swing cycle, but it will also supply the extra energy
needed to maintain the stationary swing
motion to the reed. The amount of the frame slot obstruction by the reed (fit of the reed in the
has a considerable effect on the amount of airflow needed to maintain the
stationary swing motion.
In other words, a reed with a large gap between the
frame and reed will need more airflow
(faster/more bellows movement) to sustain
Starting the swing cycle: ‘fast’
versus ‘slow’ reeds
The start of the swing cycle of a reed
is one of the most important aspects of the playability of a
free reed instrument. Preferably the reed should start its cycle the moment the key is
and the air flow is generated. The size of the reed plays an important
role in this. In general,
larger reeds need more time to get up to maximum
amplitude than smaller reeds.
Besides the air flow described earlier,
there are other air turbulences inside the concertina that
affect the performance of the reed. Turbulences around the reeds are inevitable because of
shape of the reed chambers, the sharp edges of the reeds and the sudden
jolts of air that occur
There are two main currents around a
reed that start the swing cycle. Besides the pressure P1
on the top of the reed,
there is another air flow that plays an important role.
When the reed is in rest position, the
tip is not exactly parallel with the frame, but slightly bend
between the frame and the tip of the reed allows air to flow past the reed to
This air flow will pull the tip of the reed downwards towards the frame,
just like two pieces of paper
hanging parallel which, when you blow air between
them, will move towards each other. The fact
that the gap decreases when the reed moves down towards the frame is important for the start of the
the reed starts to move, tension energy is built up which replaces the
suction of the airflow.
The suction of the airflow decreases as the gap gets
Setting or voicing of the reed
The distance between the tip of the reed
and the frame has to be adjusted. Factors that play a role
are the reed material, size of the reed, larger reeds need to be set higher than small reeds
their bigger amplitude, and valves and chamber size.
When the tip of the reed is set too
high, the suction mechanism will not start right away. It will take
some time for the reed to be pulled into the frame slot. A reed that is set too high will
the key has been pressed and quite often air can be heard passing
before the tone starts sounding.
On the other hand, if a reed is set too
low, the suction flow will not generate enough tension energy
for the reed to
come to full amplitude right from the start. Reeds that are set too low will
away with low or moderate air pressure, but will produce a ‘thin’
sound, which misses some of the
lower harmonics due to insufficient reed swing.
If the air pressure is high at the moment the key is
pressed, the reed won’t
speak at all.
There is no standard for ‘setting’ the
reeds. Besides size, elasticity and reed material, the fit in the frame
the reed plays an important role.
The shape and thickness of the reed also
affect the effectiveness of the swing cycle, because they
determine the maximum
amplitude of the reed. If a reed is too thick for its size, it will not be able
get enough energy from the air flow. It will have too much inner friction to
maintain the stationary
swing motion effectively.
A complete swing cycle of a reed can be
divided into 4 steps:
The first step starts with the tip of
the reed in the highest position (maximum amplitude).
The direction of the airflow is from P1
to P2. The air flow coming from above, pushes on top of the
reed, but also
passes through the open slot. In this position, the reed does not obstruct the
much, but when the reed starts moving in the direction of the frame,
the slot opening becomes smaller
and the air flow obstruction will increase.
When the reed is in the 2nd
position it closes of the frame slot and obstructs the flow of air almost
In doing so the reed causes the
pressure P1 to increase considerably. At a certain point the pressure
becomes too much for the reed and a sudden jolt of pressure forces the reed to go down
into the slot.
This is the moment that the reed gets the necessary energy from
the air flow which is necessary to
maintain a stationary swing cycle.
The actual fit of the reed in the slot
determines the amount of energy supplied to the reed. When the
reed does not fit
exactly in the slot, the gap between the frame and the reed will diminish the
effect of the reed and consequently less energy will be supplied to the
When the reed is in the 3rd
position, maximum amplitude downward, the opening between the reed and
allows the pressure to diminish.
Because the air slot opening is smaller
than in the 1st position, the pressure difference is smaller. The
reed now starts to move back up against the direction of the air flow.
When the reed is in the 4th
position it again blocks the air flow completely.
But, the pressure P1 build up is less
than it was in the 2nd position, and because of this it will allow
reed to continue up to the first position. If the airflow obstruction would
have been the same as in
the 2nd position, the swing cycle could not
A reed swing cycle is not symmetrical.
The amount of obstruction in position 2 is larger than in position
4. Also, the
rest position of the reed is not exactly parallel to the frame. The tip is
slightly above the
frame. This means that the tension energy in the reed helps
it move through the blockage. Every time
the reed blocks off the airflow it
generates sound waves.
Reed shapes and
The reed actually ‘chops up’ the air
flow in small air waves. Unlike other reed instruments (e.g. clarinet,
etc.) the vibration of a concertina and accordion reed itself hardly produces
any sound. In fact,
laboratory tests have shown that the sound produced by the
reed itself is neglectable.
The frequency of these ‘air waves’ is determined by the
size of the reed. the larger the reed, the lower
Reeds swing in their typical
frequencies, decided by both size and the material of the reed. For instance,
reed that plays the note ‘C’ made out of steel will have different dimensions
than a reed of the same
pitch made out of brass or German silver.
The length and thickness of the reed
determines its frequency. The width of the reed does not play a
role in this.
fact, two reeds of the same length, material and thickness, but one of them
twice as wide as the other,
will swing in the same frequency. The width does
however have an effect on its swing cycle, because the
larger surface of the
reed increases the air flow pressure (P1).
When one of the dimensions of a reed is
altered, the frequency will change accordingly. For example,
when the mass at
the tip of a reed is reduced, by filing or scraping, the frequency will
increase. It does
not matter whether the reed is shortened or filed on top. The
frequency chance will be the same. It is of
course better to file on top than to
shorten the length of the reed. the latter will affect the swing cycle
the reed/slot gap will be increased. A larger gap will diminish the ability of
the reed to take
energy from the airflow and affect the attack of the swing
The frequency will increase when a reed
is filed at the top, because the mass at the tip, compared to the
base of the
reed, has diminished. On the other hand, when a reed is filed at the base, the
decrease, because now the mass of the tip compared to the base,
has been increased.
This principle is easier visualized with
a spring mounted on a surface and a weight attached to the other
end. When the
weight is pushed, it will swing in its specific frequency, decided by the
strength of the
spring and the weight at the tip. Now, if the weight is replaced
by a lighter one, the frequency of the reed
will increase, because the balance
between the tip (weight) and base has shifted. For the same reason the
will decrease when the weight at the tip is increased.
Every time the reed goes into the frame
it cuts the air flow and creates a multitude of air waves which,
if their frequency is within the audible range, are perceived as sound waves.
Free reed instruments produce a very
high number of harmonics. In fact, they produce more harmonics
than string and
wind instruments. These harmonics determine the ‘brightness’ of the sound; the
harmonics the brighter the sound.
The swing cycle of the reed creates
these complex sound waves by rapid changes of the airflow. The way
is cut differs between free reed instruments. It is one of the aspects that
contributes to the
sound differences between them.
Looking at the swing cycle again in
relation to the production of harmonics, we see that the fit of the
reed in the
frame, and the shape of the frame slot play a major role in the brightness of
In the first part of the swing cycle,
the reed moves down in the direction of the frame. When the reed
gets closer to
the frame the air flow diminishes greatly. When it enters the frame the air flow
is at its
minimum. The more the airflow is reduced, the stronger the ‘chopping’
effect of the reed will be, and
because of that, the production of harmonics.
It will not stop all together because
the gap between the reed and frame will always allow some air to
pass. When we
compare accordion reeds with concertina reeds, we see that because of the
production methods, the minimum airflow in accordion reeds is generally
less than in concertinas.
The second part of the cycle also plays
an important role in the difference between accordions and
cycle position 2-3). In an accordion the airflow will stay at
its minimum level until the reed
comes to its maximum amplitude.
At that time the opening between the
reed and frame increases for a short moment and more air is
allowed to pass.
In this part of the cycle the shape of
the concertina frame plays an important role.
Unlike the slots in accordion
frames, which have parallel sides, concertina frame slots widen at the
bottom. The exact place depends on the size and frequency of
the reed. The slots of the higher reeds
widen only a little or not at all.
This widening of the slot allows the
airflow to increase again when the reed moves down into the slot.
accordion reeds the second part of the swing cycle of a concertina reed is a lot
Because of the less effective cutting of the airflow,
concertina reeds produce less harmonics.
In the third part of the cycle the reed
starts to move back up. This part is identical to the second, but
reversed order. Part four is a mirror image of the first part of the cycle.
Valves and pitch
For every key on a concertina there are
two reeds, either of the same pitch, as in English and duet
concertinas, or of
different pitches, as in anglos.
2 reeds in each chamber
Each reed swings only on one air flow
direction as explained earlier. Because the two reeds that
correspond with the
same key are in the same chamber, the reed that is not activated needs to be
off. Otherwise air will pass through its frame which diminishes the
required pressure difference
P1>P2 for the activated reed.
The material used for valves must be
both flexible and firm. When a reed is activated, the valve needs
to open as
much as possible, allowing a maximum airflow to pass. If the material is too
light, it will open
sufficiently, but the airflow will cause it to vibrate. A
vibrating valve produces a gurgling sound at the
same time the reed sounds.
If the opposite reed is activated, the
valve needs to close of the air slot as much as possible. Traditionally
leather, both sheep and goat, has been used for this purpose in free reed
instruments. Leather is both
flexible enough to open the air slot sufficiently,
and firm enough not to vibrate on the air current itself.
The requirements for valve leather are
very high. It should be very fine grained to guarantee even tension
and of the
correct thickness. Usually only part of a hide is suitable for valves.
Larger reeds need thicker valves than
smaller ones because the airflow is stronger. In order for a
concertina to produce even dynamics over the whole compass, the valves will have to be
adjusted to the
size of the reeds. Normally 4-5 valve sizes are needed for a
standard concertina. Each size varies in
length, width and thickness.
Valves also have an effect on the
frequency of the reed. If they are too heavy they will not open
sufficiently and will interfere with the airflow and reed amplitude. The pitch of a reed with a
is too heavy can drop as much as 10-15 cent. This is because the reed
will not be able to develop the full
swing motion. Selecting the right
size/thickness valves can be done by comparing the pitch of a reed
and without a valve. The pitch difference of a reed with the right size valve
and without one s
should not be more than 5 cent.
Leather valves will not last
forever. Humidity and use will harden them and cause them the curl up, away
from the reed pan. Curled up valves affect the attack of the reed, because it affects
the first part of the
cycle, the suction of the reed towards the frame.That is why valves should be
checked and replaced
Because of the limited
lifespan of leather valves, the accordion industry developed a type of foil to
replace the leather. Valves made out of this material are uniform and constant
in quality and will not
deteriorate. Instruments with these type of valves will
stay in tune much longer.
A negative aspect of the foil
valves is that they affect the sound quality of the instrument. Because the
material is much harder and smoother than leather, it does not absorb the higher
sound waves as much
as leather does, resulting in brighter sounding reeds.
So far we discussed the tone generation
in free reed instruments. The sound waves created by the reeds
will not all reach the outside of the instrument.
The first obstacle is the reed chamber.
The sound waves produced by the reed will literally bounce of
the walls of the
chamber. The walls of the chamber can act as a filter or amplifier of particular
waves. A course surface will absorb more of the higher frequencies that a
smooth and hard surface.
The size of the chamber also has an
effect on the reed performance. In a large and deep reed chamber
the sound waves will reflect more than a shallow one and therefore will absorb more of the
early reed chambers
modern 'shortened' reed chambers
As explained earlier, a reed needs a
certain amount of air pressure and air volume in order to start and
swing cycle. The goal in concertina construction is to find a balance between
economics with regard to the stationary swing motion and the quality of
the sound produced.
The sound waves will leave the chamber
through the air hole and enter the action space. The size of
the hole also plays
an important role in the performance of the reed.
It decides the amount of air that is
allowed in the chamber and how fast it enters. If the hole is too
small the pressure build up in the chamber takes too long, which results in a slow reed
attack. A low
air supply can even affect the reeds capability of maintaining a
stationary swing motion.
On the other hand, if the hole is too
large, too much air enters the chamber at one, creating too much
this case the reed won’t be able to complete the cycle or will perform poorly.
The distance of the pad to the hole when
opened, which is decided by the amount of key travel, has the
same affect on the
reed performance as the size of the hole. For instance, if the pad does not lift
enough the effect is the same as a small air hole.
This problem is quite common nowadays
because of standardized pad sizes which are too thick for
certain instruments. Many concertinas, especially the early ones, suffer from a lack of sufficient
due to the wrong size pads. The instruments were designed for very
thin pads because of the limited
space in the action space. When new pads are installed that are about twice the thickness of the
originals, there is not
enough room for the pad to open sufficiently. The result is a slow and poorly
sounding instrument. Most people blame this on the reeds, but it is
actually just a matter of wrong
adjustment and parts.
The last part of the journey of the
sound waves in the instrument is the action space. Basically there are
The first one is to try to produce as
much of the harmonics that are left. Because sound reflection
diminishes the higher frequencies, there should be as little reflection as possible. In this
fretwork will be very open.
If the goal is to amplify the higher
harmonics, which produces a very bright sound, metal ends are used.
These ends reflect the sound waves
better than other materials because of the hard and smooth surface.
The openness of the fretwork determines how much the waves will reflect before
leaving the instrument.
In most metal ended concertinas the
fretwork is adjusted to the specific frequency of the tone. The lower
more reflection, which produces a somewhat warmer sound, than the high notes.
If you look
at the top models with metal ends, you’ll see that they adjusted the
fretwork to the specific frequencies.
The other objective can be to produce
a round warm tone, filtering more high frequencies. This is done
by increasing the
sound reflection with wooden ends with little fretwork. Wood is perfect for
the higher frequencies and amplifying lower ones. The openness of the
fretwork decides again how long
the waves will be kept in the action space.
In the 19th century it was
custom to install baffles, to filter the high frequencies. This was done in two
In early instruments they used spruce
wooden baffles to amplify the lower and middle
frequencies rather than cutting
the high ones. These instruments usually had German silver or brass
produce very little high frequencies. Later, when steel reeds became standard,
produce more higher frequencies, they used leather baffles which do not amplify any frequencies, but
only cut the higher ones.
The type of wood used for the ends plays
only a small role it the sound quality of a concertina. The
sound produced by
the vibration of the ends is nihil compared to the sound reflection they cause.
is a difference between instruments with hard and soft wooden ends, but
again, it is the absorbing effect
that causes the difference, not the vibrating
of the ends.