For a speaker to be effective, the 3 main qualities are - having a balanced sound quality, having powerful drivers, and sufficient volume. When your system has a balanced sound quality, it means that the bass will not overpower the high ends, and the high frequencies will not sound screechy. You will have a smooth, clear listening experience. Strong, powerful drivers allow your speakers to project the sound effectively. Lastly, your speaker must be able to deliver sound at a sufficiently high volume, without having to depend on amplifiers.