arco sounds. Some pickup manufacturers produce piezoelectric pickups that purportedly provide a natural reproduction of arco sound. Preamplifiers and equalizers for acoustic instruments or double basses can also be used to "roll off" the treble frequencies or "notch out" the "scratchy-sounding" frequencies. An external parametric equalizer could also be used to remove unwanted "scratchy" sounds. Types There are many varieties of EUBs available at present. Some EUBs cannot be used with a bow because of the large radius of the fingerboard and the flatness of the bridge. These types are therefore solely used for pizzicato playing. Other EUBs have a curved bridge which permits a bow to be used. While EUBs are often four-stringed, 5, 6, 7, and 8-string models are available. As well, solid, hollow and 'floating top' configurations are made. While hollow and 'floating top' models produce a more resonant tone, they are also more prone to feedback; as such, solid-body EUBs may be the best choice for bassists who play in loud styles, such as jam bands or metal fusion groups. Playing techniques The EUB is played in a similar manner to the double bass. All EUBs can be played pizzicato style. However, only those with a suitable fingerboard and arched bridge radius can be bowed. Some EUBs are designed with integral stands, freeing the player from the need to brace/support the instrument. More rarely, EUBs may be designed to be strapped on the body using guitar straps. The use of stands may make bowing much easier, especially for the beginner, because then the instrument does not have to be stabilized with the knee and thighs. Like a double bass, the instrument may be played either standing or sitting on a tall stool. The optimum height for most players will be when the (index) finger in the first position (i.e., second fret on a fretted instrument) is at the same level as the player's eye. If the bass is higher than this, discomfort in the muscles of the neck may be experienced after playing long passages in the first position. If the bass is too low, the player may need to bend or stretch when attempting to play notes at the higher end of the fingerboard. The strings are generally plucked with the sides of the top joints of the index and middle fingers, although sometimes the tips are used to produce a mellower tone or to