23. The groove
When a steel pan note is vibrating, some of its vibrational energy is transmitted into the air and to the rest of the pan, but the main part is reflected back and conserved in the note. The acoustic purpose of the groove seems to be to provide this conserving mechanism. Tuner Denzil Fernandez says: "The purpose of the grooving is to create boundaries where-by a transverse wave can be generated and trapped within the region of each boundary." This notion seems to be in accordance with acoustic theory.
The groove presumably introduces a local difference in what is called the acoustic impedance of the metal. The acoustic impedance is a property of the metal that describes how difficult it is for sound waves to travel through it. The harder the material, the faster and easier the sound waves travel, and the less the impedance. The grooving "breaks" the crystal structure of the metal and makes it soft, forming a "joint" that acts as an acoustic impedance barrier. When the vibrational impulses in the note reach the barrier they are reflected back into the note.
Harder grooving will presumably result in an increased difference in the acoustic impedance. This will result in a more effective reflection, which means that less acoustic energy will leave the vibrating note. The less the amount of energy that is lost to the surroundings, the longer and weaker the tone will be.
The bore pan, presented in the section about developments, presents a way to study the effect of the groove joint: If the holes are made closer to each other the border will be softer. Denzil Fernandez' experiments show that this makes the tone longer and weaker, which proves that the energy is conserved better in the note.
It is fully clear that no one can make a steel pan without grooving it, but the needed amount of grooving impact is still to be revealed. My studies show that it seems to be enough to make a light groove, whose mark is barely visible in the metal of the finished pan. Presumably, this disturbs the crystal structure enough to create a sufficient acoustic impedance barrier. Future experiments with controlled mechanical grooving may reveal the effect of the groove hardness.
The width of the groove presumably doesn't have any acoustical significance. But it should not be wide enough to generate any internal resonances by reflection of sound waves, i.e., the width should be less than 10-15 mm.