The vibraphone is an percussion instrument. It looks like a xylophone but the bars are made of aluminium instead of wood. Like the xylophone, the bars are arranged in a similar way to a piano keyboard so that tunes can be played. An alternate form is the 6-plus-6-system, where each row has the bars in a whole-tone distance and both rows are in a half-tone distance. The player uses mallets (beaters), either one or two in each hand. There are tubes underneath each bar. These are called "resonators". They make the sound louder. There is also an electric motor which can be switched on by a pedal. This makes fans go round and round in the ventilators and makes a very strong, vibrating sound. This is why the instrument has its name. Sometimes people call a vibraphone vibes.