Headphones let a single user listen to an audio source privately, in contrast to a loudspeaker, which emits sound into the open air for anyone nearby to hear. Headphones are also known as earspeakers, earphones or, colloquially, cans. Circumaural and supra-aural headphones use a band over the top of the head to hold the speakers in place. The other type, known as earbuds or earpieces consist of individual units that plug into the user's ear canal. In the context of telecommunication, a headset is a combination of headphone and microphone.
Osmium is usually sold as a minimum 99.9% pure powder. Like other precious metals, it is measured by troy weight and by grams. Its price in 2012 was about $400 per troy ounce (or about $13,000 per kilogram), depending on the quantity and its supplier.
From 1986 to 1988, the monthly average New York dealers price of rhodium ranged from $1,150 to $1,300 per ounce. In early 1989, the announcement of problems at South Africaâs Rustenburg Platinum precious metals refinery caused the price to jump to more than $2,000 per ounce. To convert to dollars per kilogram, multiply by 32.1507. Note: 1911-29, New York price of refined metal, in Hill, J.M., 1922, The marketing of platinum: Engineering & Mining Journal-Press, p. 718. 1930-66, Producer price at New York of 99.9%-pure palladium, in Engineering & Mining Journal, Mineral and Metal Markets.