The reed assembly comprises of a slotted brass frame, a clamping bar held by two small screws and a reed tongue. The brass reed frame is tapered so that it slides firmly into the matching tapered cut out in the reed pan. The frame has a slot cut through it over which the tongue is clamped; at rest the tongue effectively closes off the frame slot to resist airflow. On operating the bellows, the force of air, passing through the gap between the tongue and the slot in the frame, pushes the tongue until it is moved away from its position just above the frame slot and curves into the frame. Airflow takes place and pressure drops; this, combined with the tension in the tongue, enables the tongue to spring back through the slot and then back down again into the slot, and so the cycle recommences with the air flow maintaining the energy of oscillation and the amplitude. or degree of noise the reed makes. The frequency of vibration of the reed determines the pitch of the note produced. which i5 subject to the length, width, and variations of thickness along the length of the reed tongue that is the vibrating part of the reed.
The pictures show the detailed arrangement of the reed pan and reeds. It can be seen how each reed is paired with another in the same chamber space and that opposite each reed is a leather flap or valve that i5 glued to the pan at the valve’s outer end. The valve acts by being blown off the pan reed slot when its corresponding reed is played, and being sucked down to seal the pan slot when air flow is reversed, cutting off air to that reed and thus allowing the other reed in the chamber to take all the airflow and sound both sweetly and immediately. The diagram also shows that on the chamber side, the valves have valve pins set across them.
The slots provide the airways to each reed, aligning with the slots in the reed brass housing shoes (reed frames). The chambers vary in length and width to accommodate the reed size and so form acoustically resonant chambers that contribute to the instrument tone and sound projection. There are no chambers on the inner face of the pan, just the reeds and valves that operate when the bellows are compressed. The reed pan layouts vary between the various systems. Anglos often have a square chamber layout, whilst English tend to be radial in pattern. Irrespective of concertina type, the anatomy is exactly the same.
The chamber upper wall surfaces and round the central thumb hole is covered with a soft chamois leather gasket material, as are the inner faces of the wooden bellows frame. These gaskets are to ensure that there can be no air bleed between adjacent chambers, or around the reed pan edge to effect matching inner and outer reeds. The positioning of the chamber walls is such as to match to the appropriate pad hole in the pad board so that a pad, on lifting, allows air to a single chamber. and thus a single reed pair.