Speakers and Pole Position: Monopole, Bipole, Dipole, Omnipole
The speakers in a home theater system may have multiple sets of speaker drivers that face in different directions (positions). Bipole and dipole speakers are designed to help contribute to your surround-sound field. Monopole speakers are commonly used in a home theater system, and omnipole speakers are used primarily outdoors.
Here’s a closer look at speakers and poles:
Monopole: These speakers have all the drivers on one face of the enclosure and are known as direct radiating speakers. These can be used anywhere in your home theater. You’ll get the best and most precise surround-sound performance when all of your speakers (front, center, and surround) are direct radiators.
Bipole: These speakers have drivers on two faces, opposite each other. They are designed for side/rear surround speaker applications. Bipole speakers fire their cones to the front and rear at the same time and in phase. In other words, the cones go out or in together, in the same direction (both out or both in) and at the same time.
Dipole: These speakers also have drivers on two faces, opposite each other. They are designed for side/rear surround speaker applications. Dipole speakers are out of phase with each other. When one side’s drivers are pushing out, the other side’s drivers are pulling in.
Omnipole: These speakers radiate their sound in all directions, in a 360-degree fashion, and are popular for outdoor applications.
Although the electrical phase in bipoles and dipoles is different, the basic construction of bipoles and dipoles is similar. Look for speakers that are both bipoles and dipoles. Most of these speakers have a switch that lets you switch the mode they operate in. Some people prefer music played back through bipoles and movies through dipoles, and these speakers let you make that choice on-the-fly.
Bipoles and dipoles (and omnipole speakers for that matter) all provide a more diffuse surround-sound experience. There’s nothing wrong with this, and in some cases it can enhance your experience, but today’s surround-sound soundtracks are recorded and mastered using direct radiating speakers and the discrete surround-sound channels with Dolby Digital or DTS (or their higher-resolution counterparts such as Dolby TrueHD and DTS-HD Master Audio).