The reed body is normally aluminium and the reed tongue steel. The tongue is rivetted to the body. The unit has two reed tongues fitted each in its own close fitting slot. One reed serves the bellows action in the inward direction while the other serves the outward direction. The base of the tongues and their inner surfaces are quite often blue in colour and it is understood this is the result of treatment of the metal during its manufacture. The reed valves/leathers normally fitted are not shown in the diagram:-
The natural frequency of a parallel sectioned reed is found from:
f = 1/2pi x X/Lsquared x square root of E/D(1+4.1K) where
pi = Greek symbol (diameter/circumference relationship)
L = length of the tongue (in centimetres)
X = breadth of the tongue(in centimetres)
E = modulus of elasticity of the material (in dynes per square centimetre)
D = density of the material (in grammes per square centimetre).
K = ratio of the mass at the end of the tongue to mass of tongue itself.
Though the formula is largely irrelevant to a repairer’s everyday life it does serve to show the parameters which affect the frequency and that an alteration made to the reed profile (for example by a repairer’s file) would alter ‘K’ in the above formula and frequency ‘f’ as a result. It is also noted that the modulus of elasticity is a factor and this no doubt relates to reed quality (response and sound quality).
Modern reeds tend to be tapered and an extremely complicated formula is required to calculate their frequency. The tapering/shaping process is understood to be an attempt to reduce discordant harmonics and overtones.
On a more practical note repairers (U.K.) identify the individual notes/keys/reeds(for example) on a standard 41 keyed piano accordion as follows:
Similar sorts of identification codes are used for diatonic instruments. (B/C, C/C# tuning etc.).
Italian manufacturers and repairers use the following for reed identification: