Acoustics
Traditionally, it is the first of the instruments to be made. A highly skilled gong-smith will smelt and cast, then supervises the hammering process, but will be solely responsible for the final fine tuning of the gong ageng pitch- the rest of the ensemble is tuned (and named) according to the qualities of the gong ageng. It is the single most costly and lengthy item to fabricate- and often requires multiple re-castings due to stress-cracks created in the beating process of forming it and undesired tonal or timbre qualities. The pitch desired is very deep, distinctly pitched rumble that sound like thunder or the "rolling waves of the sea". Slight differences in the opposite halves of a gong create a desired "beating" in the sound. It is named according to subjective poetic descriptive images for different speeds of beats, comparing slow beats with waves of water and faster beats with Bima’s laughter (Bima is one of the Pandawa brothers in the Mahabharata epic).
The gong is fabricated to resonate at the lowest thresholds of human hearing (20 Hz to 20,000 Hz). Actual pitch will vary, but a fine gong ageng of example of the Nusantara Museum of Delft was measured to have a fundamental tone of 44.5 Hz. The Gong Ageng has about a dozen prominent exponentially decaying partials, with some component frequency ratios that closely correspond to harmonics and others that are enharmonic. Many of the partials have a slow amplitude and frequency modulation of a few Hertz, and a faster modulation around 20 Hz. The instruments of the gamelan are then fabricated on the fundamental tone of the gong ageng pitch is basis of the slendro pitch "6" (enam, or nem) of It is typically pitched to match the 6 of the gamelan.
Read more about this topic: Gong Ageng