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.
1 The âspot priceâ (the current market price) of silver is for 1 troy ounce of pure silver. 2  One regular ounce is equal to 0.911458333 troy ounces. 3  Sterling silver is only 92.5% pure silver (at least technically, but in practice it's less due to after melt weight loss and assay at .9 and not .925).0 1-oz sterling silver teaspoons on a postal scale for example would be worth $307 from a 85% recycler and $271 from a 75% recycler at the spot price of $43 per troy oz for pure silver.