One key variable is its interplay with your pickup. The closer you bring the EBow to a magnetic pickup that is on, the louder and brighter the sound. This only happens very close to the pickup. This is called the playing area. You can vibrate the string anywhere along its length from the nut to the bridge, but the dramatic volume change occurs only very near a pickup that is on. Staying in this small playing area gives you lots of control over the tone and volume dynamics.