Just as it is important to choose the right wood for string instruments, the metal is important to the steel pan. The choice of metal is even more crucial for the pan, as the steel is the primary source of the sound in the pan, not only acting as an amplifying resonator as the wood of string instruments.
First, the quality of the metal is vital to steel pan fabrication. The steel that is used for the drums is a compound that, besides the iron, contains small amounts of carbon (0.1-0.2%) and manganese (0.4-1.4%). The concentration of these added substances determines the mechanic and acoustic properties of the steel.
One major problem for the community of panmakers seems to be their lack of control over the raw material. The reason is that, during the evolution of the pan, the tuning has come to put more extensive requirements on the steel quality than the drum's original purpose as a container does.
A first step towards a solution to this problem would be to analyse the metal of a well-sounding instrument. A documentation of the exact content of carbon and other substances in the steel would be of good help in the choice of raw-material. I have taken some samples, but I have not had the opportunity to analyse them yet.
The next step would be to get a steel mill to deliver raw material according to this specification and have a steel drum factory to produce high quality drums especially for steel pan making.
Further measurements, stating within which ranges the content of the various substances could vary and still make a good instrument, could also give clues to which factors in the properties of the metal that are important to the tone generation.
The thickness of the steel affects the resonance frequency of the note. Thicker metal is stiffer and therefore it produces a higher pitch in a note with constant measures. But thicker metal is also heavier. This lowers the frequency, which will counteract the effect of the stiffness. The acoustic effect of changes in thickness has to be measured to reveal what the net result will be. Suitable experiments would be to add chromium or grind off material successively and do measurements of the frequency spectrum.
Another important acoustic effect of the thickness is that an increased mass can conserve a larger amount of energy. Notes with thicker metal can take harder hitting without "breaking" in sound. This means that they are capable of receiving and radiating more sound energy - the instrument will be more powerful.
But thicker metal also means that it will be more difficult to get the notes to vibrate - to excite them, which can result in a problem for the small notes in tenors and double tenors. Measurements show that the sinking of a tenor makes the metal about 30% thinner in the middle. The thinning in the middle is of benefit for the higher note that will be located there, because the reduced stiffness will make it easier to get them to vibrate. This might be one of the reasons for sinking the higher pans deeper and putting the higher notes in the middle.
The acoustic effects of the crafting work are shaping the metal, making it softer and forcing tensions into it. The softening of the metal occurs because the initial crystal structure of the metal is destroyed when it is re-shaped. A new crystal structure is later established by the tempering, and this restores some of its former hardness.
One reason for doing the backing, besides the shaping of the note dents, could be to force a tension into the notes by compressing the metal in them. This possible tension could later be conserved by the groove in the metal and by the tempering. If there is a conserved tension introduced by the backing, it would presumably result in an expansion force, acting to push the sides of the note outwards. According to acoustic theory such a tension lowers the pitch, see the chapter about tone generation above.
If the effects of the manual crafting work could be neglected, it would be possible to use machines and do the sinking and the backing with mechanised methods. The sinking has already been mechanised at MIC - Metal Industries Corporation, and some claim that it works, while other say the opposite.
It is practically impossible to do any laboratory experiments on the acoustic effects of the crafting. Future field experiments will have to determine if it is possible to press-form the whole pan.
Another source of problems for the tuners seems to be the rather un-controlled method for tempering and the lack of theoretical knowledge of what happens to the metal during the heating. The most important effects of the tempering are presumably an anneal (removal of tensions) and a hardening.
The crafting introduces many tensions and local differences in hardness in the metal due to an effect that is called a cold-hardening. When the metal is hit with a hammer it gets hot in the spot where it is hit. But the heat is quickly led to the surrounding metal, which results in a fast cooling of the heated spot, which has a hardening effect.
The most significant effect of the tempering is presumably the anneal, which removes this cold-hardening and the uneven tensions put into the metal during the grooving and the backing. If they were left, they would disturb the delicate physical conditions in the note and make proper tuning impossible. The anneal should result in notes with an even tension over their whole surface. This anneal is presumably the main reason why quality steel pans can't be made without heating.
Beside the anneal, the steel also seems to be affected by two other processes during the heating: First, it is hardened by the reorganization and fixation of the new crystal structure in the metal by the heating and the cooling. Second, there seems to be an oxidation of some of the carbon content of the steel, making it more stretchable. Carbon is initially put into the steel to make it hard.
The most critical part of the tempering is to balance the two processes against each other. If the pan is heated too little, it will not be tempered enough, making it soft and unstable during the tuning. This problem can be solved by heating the pan again, this time a little longer.
If the pan, on the other hand, is heated too long, too much of the carbon will oxidise, making the metal too stretchable and thus impossible to tune. Unfortunately, there is no way to redo the tempering if the pan is burned too long. The existence and the acoustical significance of these two processes have to be investigated further by analysing the metal before and after the heating.
The next vague point of the tempering is the cooling of the pan. Some tuners use water, some use oil, but nowadays most tuners don't seem use anything at all. They just let the pan cool by itself in the air.
People that are knowledgeable about metals tell me that it is impossible to temper without using any cooling liquid. This would only result in an anneal. But the tuner doing the practical work knows that the pan feels harder after the heating. This is a contradiction that needs to be investigated further in cooperation with metallurgists.
Future solutions to the present problems would be: First, an investigation of what happens in the metal during the tempering. Second, measurements of a properly done tempering. Third, development of a controlled tempering method, such as the use of an oven.