In recent years, plastic gears are frequently used for office instruments and precision machinery by the advantage of lightweight and low noise etc. But for improvement of working environment, more noise reduction of machines is needed. There are many noise data on metal gears but are few on plastic gears.
Noise level and frequency characteristics of plastics spur gears, which are made by injection molding and cutting method, are measured. The influences on noise of the helix deviation, the direction of draft and the distance between two gears were measured. It was found that the important factors on noise of plastic spur gears are helix deviations of cutting gears, and drafts of injection molded gears.
Gamelan is the traditional ensemble music which has mainly progressed in Indonesia and Malaysia. Bali in Indonesia is known as an island of entertainments with gods. For Balinese people, Gamelan is a part of life and is indispensable to soundscape for daily life. There are various Gamelan and instruments on rites and dances in Bali of Indonesia. The keyboard instruments for most of Balinese Gamelan are tuned to get the interference beats emitted by beating a pair of instruments. However, it is not defined how the interference beats are emitted. Gamelan Gong Kebyar is a new Gamelan that created in early 20th century and is the most popular Gamelan in Bali now. In this paper, the beat frequency calculated from fundamental frequency for the keyboard instruments of Gamelan Gong Kebyar is compared with the beat time calculated from their wave-form. The beat frequencies for the keyboard instruments of seven sets of Gamelan Gong Kebyar retuned by several tuners are also compared and considered.