A Roomful of Sound, Not Wires

WHEN Bradley Partridge bought a sleek flat-screen for the living room of his Atlanta home, he did not want the clutter of speakers hanging from the walls or the trouble of running wires around the room.

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The Yamaha YSP-4000 adjusts its 42 speakers itself.

So to get the surround sound he wanted, he installed a sound bar, a bank of speakers in a cabinet roughly 40 inches wide and 6 inches high and deep. It uses aural trickery to make sounds from the front of the room seem to come from the sides or the back.

“I could not believe how good the sound was from this little thing,” he said. “I was watching ‘The Perfect Storm,’ and the part when the boat goes up and down in the ocean? It really felt like you were in the boat.”

There are a number of systems that can supply a surround sound effect for people who cannot run wires through walls or who do not want to trip visitors with skeins of cable snaking across the floor.

A number of wireless systems can give listeners surround sound either by broadcasting radio signals to rear speakers or with sound processing trickery. Buyer beware, however; any kind of trickery is not going to be quite as good as true surround sound.

To call the speakers that broadcast signals “wireless” is a bit of a misnomer. Most rear speakers in such setups need to be plugged into a receiver and an amplifier, which in turn needs to be plugged into a power outlet. What the system lets you avoid is the wires that run from the amplifier to the back speakers, inevitably across a walkway. They also eliminate the need to cut into walls, floors or ceilings.

Signals travel from the front of the room to the back over the radio bands used by cordless phones, Wi-Fi or Bluetooth signals. Some systems transmit via infrared light, which is the signal most television remote controls use.

But professional installers say these systems have flaws. “They are all a compromise,” said Eric Lee, whose company, Integrated Control Experts Inc., in Chicago, installs home theater systems. Bandwidth is often too scant to carry full-fidelity sound; there can be problems synching the sound on the screen with the rear speakers; and the signals are prone to interference. An infrared signal, which is line of sight, can cut out if someone briefly blocks the beam. “Most of those wireless systems are terrible,” Mr. Lee said.

The professionals say the best solution, if wires cannot be run, is to use a sound bar, a low-profile bank of speakers meant to fit unobtrusively under a flat-screen TV. These faux surround systems count on “psychoacoustics,” which works because we interpret the direction of a sound based on slight differences in three bits of information: volume, frequency and the time difference in hearing a sound with the right and left ears. “Your brain learns to pick up tiny little signals that tell you where things are in three dimensions,” said Jack Buser of Dolby Labs, whose products make extensive use of psychoacoustics.

When we hear a sound from the right, it is slightly louder to the right ear. The delay in reaching the left is the time it takes sound to travel about four inches — thousandths of a second, but enough for us to place the sound.

The faux surround sound simulates that. Making a sound seem far to the front right means playing it slightly louder in the right speaker and giving it a slight delay and lower volume in the left speaker.

Part of the reason we perceive sounds as being behind us is that the external part of the ear filters out certain frequencies and lowers the volume from sounds that are from the rear. When sound processors remove the same frequencies and lower the volume a minuscule amount, our brains begin to perceive the sound as coming from behind. “It’s a combination of a lot of different techniques that allow the sound to trick the brain,” said Mr. Buser.

Yamaha, which marketed the first of the surround sound bars in 2004, adds a twist to the psychoacoustic principles. The YSP-4000 (listed at ,800) uses 42 speakers and complex processing to aim sound waves so they bounce off walls. A listener perceives the sound as coming from the point of the bounce.

The Yamaha system may have a slight advantage in rooms where watching TV isn’t the only activity. Its surround effect can be turned off, allowing sound to be sent in a concentrated beam to a single point. A night owl could watch TV in the bedroom without it seeming loud to the early riser next to him in bed. Systems that don’t need walls to bounce sound have an advantage in open rooms and loft spaces.

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