Surround sound does the job at the movie theater and in many family rooms and finished basements.
Why not in the classroom?
The Baltimore County school board has set aside $400,000 in its proposed budget to install and test "sound enhancement" systems - wireless microphones and speakers designed to distribute a teacher's voice evenly around the room. At least seven schools in the Baltimore area are already using it, and others in Maryland and across the country are investing in the equipment.
Proponents say the technology can help children hear lessons over the shuffle of papers and other classroom noises. They say it can also ease the strain on teachers' voices.
"It's the only way to be able to have the children in the back row hear the same as children in the front row," said Suzanne DeMallie, a Towson mother who lobbied the school board to consider the devices.
Generations have gone through school in classrooms without sound systems. And the State Department of Education and other agencies recommend trying to minimize background noise first, before installing the new technology.
But even as educators differ on the best way to improve classroom acoustics, most agree that the issue is an important one.
"Seventy percent of the time spent in a classroom is spent listening. That's how our educational systems are set up," said Pamela A. Mason, director of audiology professional practices at the American Speech-Language-Hearing Association.
She said the sound field amplification systems, as they are also known, were first developed for hearing-impaired children but that those with normal hearing benefit also.
Noises all around
A typical classroom is awash in sounds: the hum of overhead projectors, computers or ventilation systems; the kickball game outside; the roar of an airplane overhead. Hard surfaces such as tile flooring and painted walls reflect noise, as well as words, creating interference. It can be even worse in "open" classrooms without walls.
And children's hearing is not the same as adults'. Voices must be at least 15 decibels higher than the ambient noise for children to understand speech properly, said Paul J. McCarty, an adjunct professor of environmental psychology at Brigham Young University.
Adults require a much smaller difference because they can use context and other information to figure out what they've missed.
"Children haven't acquired enough life experiences to fill in the blanks, so to speak," McCarty said. It's especially important for children learning language to be able to hear similar-sounding consonants clearly.
On a recent morning at Sparks Elementary School, teachers and interns from Villa Julie College hooked the microphone headsets behind their ears or let them rest on their shoulders while they taught. One clipped a microphone to her collar.
A box mounted on the ceiling projected sounds to the rest of the classroom. Villa Julie intern Sara Saffell held the mike for third-grader Tanner Baldwin while he read a passage to the class. "You can move around the room and everyone can hear you," said her mentor, third-grade teacher Susan Schmelz.
Like the school in Sparks, schools in Anne Arundel and Harford counties have used some of their discretionary funds to buy amplification systems. The Prince George's County school system is testing the equipment in three elementary schools, a spokesman said. Districts in Florida, Ohio and other states are installing the systems in new buildings.
The State Department of Education and other agencies recognize that sound field amplification technology can help in existing buildings where attempts to improve acoustics have failed, according to a state classroom acoustics manual that will be published this year.
However, the guidelines do "not support widespread use of these systems in new construction." Instead, the manual states that the best approach is to design schools according to established acoustic standards.
Though the teachers' voices may be louder, the speech can be harder to comprehend in a classroom with lots of hard surfaces and a sound field system, Lou Sutherland, a fellow of the Acoustical Society of America, wrote in an e-mail.
Increased volume doesn't necessarily make announcements in train stations and arenas more intelligible, said Lois L. Thibault, coordinator of research at the U.S. Access Board, a federal agency that creates guidelines to reduce barriers for people with disabilities.
Thibault said that introducing the system in a bad listening environment would create a "cocktail party" effect, where everyone is forced to speak louder.
Teachers and students could hear one another better if schools laid down carpet, installed sound-absorbing ceiling tiles or used other means to minimize noise from such sources as heating and ventilation systems, Thibault said. The practice of putting old tennis balls on chair feet helps reduce noise as well.