Other than the subwoofer, all of the speakers in a surround sound setup (front left, center, front right plus all of the surround speakers and height speakers) are typically powered with amplifiers already built into the home theater receiver.
For short cable runs inside the room, it is difficult for an amplified signal to pick up outside interference so regular, unshielded speaker cable will do. We recommend 14 gauge cable because, in our experience, it is difficult to notice a performance improvement with anything thicker.
When running cable behind a wall or in the ceiling, most building codes will require that you use UL rated CL-3 cable which has a higher fire retardancy than typical clear jacket cable. And because cables run behind ceilings and walls tend to be longer and potentially closer to electrical cables, we add a layer of shielding to this type of cable.
Because low-frequency subwoofers require significantly more power than other other speakers, manufacturers do not build an amplifier into the home theater receiver for the subwoofer. Instead, subwoofers are typically sold along with an amplifier, hence the name "powered" subwoofer.
On the home theater receiver, the audio output for the subwoofer channel (typically labeled as LFE for Low Frequency Effects), is a single analog RCA style connector. Becasue the signal is non-powered, it is susceptible to outside noise interference. For this reason, a good, shielded RCA-type cable is needed to connect the LFE output to the subwoofer amplifier's input.
Many manufacturers build the amplifier for the subwoofer directly into the same cabinet that houses the woofer. This design, while cheaper to manufacture, can produce unwanted vibration noises and also takes up valuable air volume inside the cabinet. The amplifier then either takes away from volume needed by the woofer to produce the lowest frequencies, or the cabinet is built larger than it needs to be. This design also requires that the subwoofer be placed near an electrical outlet to supply power to the built-in amplifier. Another downside to this design is that the cable between the home theater receiver and the powered subwoofer often needs to be lengthy, and a quality shielded cable can be expensive.
In contrast, many years ago HTD followed the lead of high-end speaker manufacturers and began designing our subwoofers with a separate enclosure for the amplfier. Our subwoofer amplifiers can be placed near your home theater receiver where A) you likely already have an electrical outlet, and B) your shielded cable can be short - we offer one (sold separately) that is just 3 feet long. With this design, you can run regular speaker cable to the subwoofer's location, just as you do for your other surround speakers. And, you don't have to worry about locating the subwoofer near an electrical outlet.
Don't worry if you or your contractor has already prepared your room with a long shielded cable assuming the amplifier is built into the subwoofer. Our Level TWO and Level THREE subwoofer cabinets are cleverly "notched" along the bottom to discreetly hide the amplifier underneath should you need to connect this way.