The first step in selecting speakers is to pick out the format. There are many different formats to chose from such as bookshelf speakers, wall mounting speakers, floor standing (or tower) speakers, in wall/ceiling speakers, and more. Of course, this choice will be dependent on whether the speaker is located at the front channel (left and right speakers), center channel speakers, or surround speakers.
Your speaker format choice will be dependent on the environment the speakers are placed in. The wall locations, the size of the room, the size of the speakers, where the speakers will be located, and the all important Wife Acceptance Factor (WAF) will play significant parts in choosing your speaker format.
Bipole and Dipole Speakers
Direct radiating speakers are the most common type of speakers, but there are other technologies out there such as bipolar and dipole.
Direct radiating speakers produce a very localized (i.e. know where it is coming from) sound as the sound waves are emitted from the front of the speaker. In contrast, bipolar speakers have two sets of drivers, usually one in the font, and one in the back of the speaker. The two drivers are in phase with one another, which means that both sides push air at the same time. The sound coming out of the back side of the speaker is reflected against the walls, which makes the sound waves a split second behind the sound being produced by the front driver. The result is a less localized sound and more of a natural sound.
Dipole speakers are similar to bipole in that they both have multiple drivers, but are different by having the two set of drivers out–of–phase. Two drivers out–of–phase will have one driver pushing air (i.e. making sounds) with the other driver pulling in air. This causes a null point or a dead zone of sound usually at the 90 degree axis of the speaker (see illustration above). The null point is a great effect for surround sound speakers because it makes the speakers very difficult to locate. The sound from the speakers can have a great “where did that come from?” feel.
For music lovers, a desired trait for speakers is the ability to pinpoint instruments. Therefore, if you plan on using speakers for mostly music, then bipole or dipole speakers are not recommended, and you should stick with direct radiating speakers. However, if you are using the speakers primarily for home theater purposes, then bipole and dipole speakers can be great at producing more natural sounds. Keep in mind that the speaker locations are extremely important in producing the proper effects.
In–wall / Ceiling Speakers
In–wall / ceiling speakers are great at “hiding” the speaker and can be aesthetically pleasing. Most in–wall speakers use the wall cavity as the speaker enclosure. This usually results in lower sound quality since drywall is not as solid as a typical speaker housing. However, in–wall / ceiling speakers can be great for distributed audio systems, and also for surround sound speakers when there is no room for regular speakers.