Today, these design improvements are incorporated into most hollow body, steel-string guitar. The second solution added metal resonator plates to the top of the guitar to take advantage of the "twangy" acoustic properties of metal. The twang not only made guitars louder, but the change in tone helped them stand out move when played along with other instruments. With these modifications and added features, guitars could be heard more easily, but they still could not fill a large building with sound. Here is where advances in electronic play a role. One possibility, of course, is to put a microphone in front of the guitar. In theory, this works well enough. In practice, it can create several problems. The microphone limits a player 's movements, and it often picks up other sounds, amplifying them along with the sound of the guitar. Even when everything works perfectly the core problem remains: the guitar itself is not any louder.