- Center Channel: The most important (and underrated) speaker in a surround system is the one that talks to you, delivering a sports announcer play-by-play monologue or a movie character’s dialogue. The center channel speaker also strengthens the soundfield by filling stereo’s “hole in the middle” and delivering the leading edge of sound effects. Most center-channel designs are horizontal though fully identical front speakers will provide a more seamless soundstage.
- Surround Channels: Placed at the sides (and sometimes the back) of the room, the surround speakers expand stereo’s frontal soundstage into a surround soundfield that envelops listeners and pulls them deeper into the game or movie. The subwoofer is the “.1″ in 5.1-, 6.1-, and 7.1-channel systems.
- Subwoofer (sub): In addition to conveying low-frequency sounds (e.g. the gut-punching impact of exploding cars in a movie), most subs also have an internal amplifier to prevent low sounds from drawing power away from the rest of the speakers. That’ll prevent the soundstage from collapsing under high-decibel beatings.
What Are All Those Dolbys?
- Dolby Digital: Delivers five discrete channels of surround sound plus a subwoofer channel in digital broadcasts and DVDs. No channel is derived from any other channel.
- Dolby Pro Logic: Derives 5.1 channels of surround from two-channel sources such as analog broadcasts and videocassettes. The center and surround channels are derived from the front left/right with a trick called matrixing.
- Dolby Pro Logic II: With its separate movie and music modes, this is the most up-to-date and best-sounding version of Pro Logic. The music mode can adapt CDs and even LPs to 5.1 channels—and it sounds great!
- Dolby Pro Logic IIx: Adapts sources with anywhere from 2 to 5.1 channels to 6.1- or 7.1-channel surround.
More Dolby for Movie Fans
- Dolby EX: A cinema-oriented extension of Dolby Digital that adds back-of-room surround channels to the usual side-surrounds. It uses matrixing to derive one or two fake back channel(s) from the side left/right. Also known as THX Surround EX (because THX co-developed it with Dolby Labs). Of possible interest to movie buffs but not to sports fans (there are no EX broadcasts as such).
- DTS: Dolby’s arch-competitor offers DTS 5.1 (a 5.1-channel surround encoding format that allegedly sounds better than Dolby Digital) and DTS Neo-6 (a 6.1-channel stereo-to-surround expansion format that competes with Dolby Pro Logic, DPLII, and DPLIIx), among other things. DTS 5.1 decoding is standard equipment in surround receivers and DVD players. Of considerable interest to movie buffs, though televised sporting events, like other broadcast programming, do not use DTS.
- THX: A certification program designed uphold high-end performance standards in home theater—allowing the audience to hear precisely what the mixing engineer intended. Latest version is THX Ultra2.
Surround Sound Shopping Tips
- Match Your Drivers: For a seamless soundfield, make sure tweeters (high-frequency drivers) are all of the same size and materials. Matching woofers (for midrange and lower frequencies) is helpful but not as crucial.
- Sensitivity and Efficiency: Sensitivity specifies how loud, in decibels (dB), a speaker will play with a one-watt tone measured from one meter away in a non-echoing test chamber—regardless of the speaker’s size. Efficiency is measured in an average room, not a test chamber, and is 2-3dB higher because it gets a boost from the walls. Consider 86dB the minimum for sensitivity, and 89dB for efficiency; add a few decibels when asking a budget receiver to fill a larger room.
- Power Ratings: Most receiver and amplifier specs are a pack of lies. Manufacturers fiddle with the number of channels driven, frequency response, impedance, and other parameters to get that all-important 100-watt-per-channel number. Most “100 watt” receivers deliver less than 35. Read magazine test reports—or better yet, take our advice about sensitivity and efficiency.
- Impedance: Measured in ohms, this spec reveals how much a speaker resists current. An eight-ohm speaker will usually work well with a receiver, six ohms is more problematic, and four or less is suitable only for a muscular outboard amplifier (not a receiver).
source: cnet.com