the acoustic bass. Many EUBs have wooden or metal bars to brace the instrument against the musician's body, to act as the upper bouts of a wooden double bass. The wooden or metal brace bars help the EUB to rest against the player's body in a position roughly similar to the way a double bass rests against the body. The most complete example of this is the Yamaha 'silent bass' which has a removable frame designed to match the outline of right hand side and left upper bout of an upright bass allowing for easy transference of double bass techniques. Most EUBs are fretless, but a small number are fretted, to facilitate their use by players of fretted electric bass. Some fretless EUBs have some fret markings as a visual aid, particularly for higher pitches. Amplification Solid bodied EUBs produce very little sound without electronic amplification. Hollow-bodied EUBs produce a quiet tone that is loud enough for individual practice. However, since hollow-bodied EUBs do not have a large resonant cavity like a double bass, they cannot reproduce the lowest notes of the instrument without an amplifier. To amplify the EUB, the string vibrations are sensed with a pickup. Early EUBs used magnetic pickups similar to those in electric guitars, or percussive magnetic diaphragm pickups (e.g., the Ampeg Baby Bass). Many modern EUBs use piezoelectric pickups located in the bridge or a combination of pickup types. The signal from the pickup is usually preamplified and equalized with a preamplifier and then sent to a bass amplifier or a PA system. For practice in a hotel room or apartment, an EUB can also be connected to headphones. Some EUBs have a hollow resonant chamber, such as the Eminence EUB, and some AlterEgo, Aria and Azola models. While these small resonant chambers are usually not large enough to provide much acoustic amplification, they do change the tone and response of the instrument. Condenser microphones can be used to amplify EUBs with hollow bodies, often in combination with other types of pickups. EUB players who use the bow need to use the appropriate pickup, microphone, and preamplifier/equalizer combination to avoid the tendency for the amplified tone to be scratchy and high-sounding. To obtain a more natural arco sound, some performers use a condenser microphone for arco passages. Most bass pickups are designed to capture the pizzicato sounds of a double bass rather than the