Concertina Reeds





          The "All about..." articles are meant to give the interested player of free reed instruments a chance to learn
          basic 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
          have 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 the sound
          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
          musical instruments.

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


accordion reed,                     early accordion reed,                     harmonium 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.


          Bellows pressure
          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 concertinas
          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
          an airflow which passes through the selected air hole into the reed chamber. From thereon
          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 later.




          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 raised, 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
          tension-energy builds up. The maximum amplitude of a reed is determined by the type of material
          used, 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
          rest position. When it moves past the rest position, it builds up tension-energy again. The
          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
          cycle. 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 slot)
          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 a note.


          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 depressed
          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 the 
          shape of the reed chambers, the sharp edges of the reeds and the sudden jolts of air that occur
          when playing. 

          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 
          upwards.  The gap between the frame and the tip of the reed allows air to flow past the reed to P2.
          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
          cycle. As 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 smaller.


          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 because of
          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 ‘speak’ after
          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 speak right
          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
          slot of 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 to
          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 airflow too
          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 blocking
          effect of the reed and consequently less energy will be supplied to the reed.

          When the reed is in the 3rd position, maximum amplitude downward, the opening between the reed and
           the frame 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 the
          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 be completed.

          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 frequencies
          The reed actually ‘chops up’ the air flow in small air waves. Unlike other reed instruments (e.g. clarinet,
          sax, 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
          the frequency. 

          Reeds swing in their typical frequencies, decided by both size and the material of the reed. For instance,
          a 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.
          In 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
          because 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 cycle.

          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 frequency will 
          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
          frequency will decrease when the weight at the tip is increased.


          Sound spectrum
          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 more
          harmonics the brighter the sound.  

          The swing cycle of the reed creates these complex sound waves by rapid changes of the airflow. The way
          the airflow 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 the sound.

          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 superior
          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
          (swing 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.
          Compared to accordion reeds the second part of the swing cycle of a concertina reed is a lot less effective.
          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
          now in 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 closed
          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 valve that
          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
          played with 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.


          Reed chambers
          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 sound
          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 higher  


           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
          maintain the swing cycle. The goal in concertina construction is to find a balance between air flow
          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
          pressure. In 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 of far
          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 air supply
          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
          two objectives possible. 

          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 case the
          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
          notes need 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 absorbing
          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 
          different ways. 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
          reeds, which produce very little high frequencies. Later, when steel reeds became standard, which
          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. There
          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.