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.
The spot price for silver is $17.90 on 4/7/2010. If you are referring to troy weight, a a troy ounce is about 10% heavier than a standard ounce with the number .999 referring â¦ to the purity of the metal, about 99.9% pure.Update: The price of silver as of 21 June 2012 is $26.88/ounce.he spot price for silver is $17.90 on 4/7/2010. If you are referring to troy weight, a a troy ounce is about 10% heavier than a standard ounce with the number .999 referring â¦ to the purity of the metal, about 99.9% pure. Update: The price of silver as of 21 June 2012 is $26.88/ounce. 1 person found this useful.