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Surround Speakers

What are the different types of surround speakers available and what are the differences?

There are three "common" types of surround speakers available today plus some unique types created by different speaker manufacturers.

"Monopole" speakers consist of a speaker or group of speakers all firing on the same plane in the same direction. This includes the vast majority of all speakers made. What people think of as "normal speakers" are termed Monopole. With regard to current surround sound formats, monopole speakers are the least desirable because they are the least effective in creating an "enveloping sound field" (ambience). They are good at localization, but that alone is not enough to produce the desired surround effect.

If you take a monopole speaker and add another speaker placed 180 degrees opposite of it (i.e. back to back) firing in the same phase, you have a "bipole" speaker. Firing in phase means all drivers on both sides are at the same excursion point at the same time. This creates the exact same sounds coming from both sides of the speaker at the same time. By design, Bipole speakers send no sound directly toward the listener. A bipole speaker will produce good "ambience" as all the sound is reflected off the walls of the room, but is not effective in producing "localized" sounds.

If you take the basic design of a bipole speaker with the rear facing drivers firing exactly opposite of the front, you have a "dipole" speaker. Dipole speakers produce a very diffuse sound, which is good for ambience, but, like bipoles, are not very effective at localization. Dipole design further reduces direct sound to the listening position.

Both bipole and dipole speakers should be mounted on the sides of the listening position and use reflected sound off of the walls to produce their effects. So if monopoles can offer localization but not enveloping ambience, and bi-pole/dipole speakers deliver ambience without localization, what can provide both important characteristics at the same time?

Can I use the same speakers for the rear as for the front or do I have to use surrounds?

Rear speakers are used for, basically, two different types of sounds. Although music applications may have some "localized" sounds (sounds coming distinctly from one of the rear speakers), the majority of the rear speaker's use is to "surround" the listener in sound by simulating, for example, the sound of a large audience in the background and/or reflected music from the rear walls of a concert hall.

Home Theater (movie) sound uses a more even combination of both ambient and localized sounds. The main or front left and right speakers in a system are most often, monopole speakers, which radiate high and midrange frequencies in a directional pattern, thus making them less able to create good ambience when used as surround speakers.

When choosing surround speakers, it is important to use similar mid/high frequency drivers as are in the front, usually staying with the same brand of speakers that are used as mains. The other advantage with using specially designed surround speakers is that their smaller size and mounting capability allow them to be placed in the correct space at the correct height for maximum effect. This is a controversial aspect of home audio as some people advocate use of identical speakers front and rear.

Brass & Granite Audio

www.Oregondv.com
Salem, OR 97303

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