Why Copper?
A heavier 32 oz. copper bowl has a greater physical mass than does a 24 oz. bowl, which tends to create a weaker coupling making it more resistant to movement from the energy of the displaced internal air mass. This lengthens the decay time of the vibrating head because the energy from the displacement of the trapped air is not as readily lost as mechanical energy through the vibrating bowl walls, frame and external parts; consequently, this energy can be used to influence the vibrations of the head potentially generating more volume and sustain (see Fleisher & Fastl).
The actual aural differences between drums with 32 oz. bowls and those with 24 oz. bowls to someone in the audience is debatable, but many professional timpanists report that the most noticeable differences in sound happen during the attack portion of the envelope (attack transients), and when the instruments are being played at sustained high dB levels. During the attack, drums with 24 oz. copper bowls are purported to have more of an immediate response to the sound (more attack transients). This is because the mechanical energy loss through the bowl walls has the potential to add more collateral color (percussive attack transients) to the sound than drums with 32 oz. bowls. However, at sustained higher dB levels e.g., a loud roll, drums with 24 oz. copper bowls are purported to distort the sound to some degree, and the drums are said to “bark” more than those with 32 oz. bowls. This occurs because the excessive amount mechanical energy being used by the attack transients takes away energy from the vibrating head. Consequently, the vibrating head does not have the mechanical energy needed to support the necessary volume, and the drum is often said to be “over played.” Needless to say that in the hands of a master, either will sound fine.
Which should I buy? 24 oz. or 32 oz. hand-hammered copper bowls?
32 oz. copper bowls have more physical mass and better thermal mass than do 24 oz. copper bowls.
1) The greater physical mass tends to tends to lengthen the decay time (sustain) of the head because not as much energy is lost via transmission through the bowl walls; this conserved energy can therefore be used by the head to produce sound.
2) The better thermal mass (transfer/conduction and retention of heat) allows the bowl to retain a more consistent air volume, and reach and maintain thermal equilibrium more efficiently, which keeps the internal and external air masses more in balance. The air inside and outside of the bowl work together as a single process to fine tune the partials of the vibrating head.
Timpani Timbre: Why do all timpani not sound the same?
(Coming Soon)