（24-25高三下·重庆·阶段练习）It may someday be possible to listen to a favorite podcast or song without disturbing the people around you, even without wearing headphones. In a new development in audio engineering, a team of researchers led by professor Yun Jing, in the Penn State College of Engineering, has precisely narrowed where sound is heard by creating specific sound zones, called audible enclaves (声音飞地). In an enclave, a listener can hear sound, while others standing nearby cannot, even if the people are in an enclosed space, like a vehicle, or standing directly in front of the audio source.
In a study published today (March 17), the researchers explained how emitting two ultrasonic beams (超声波束) create audible enclaves, where sound can only be heard at the precise meeting point of two ultrasonic beams.
“We use two ultrasound devices combined with a special surface which emit self-bending beams that meet at a certain point,” said the main writer Jing. “The person standing at that point can hear sound, while anyone standing nearby would not. This creates a privacy barrier between people for private listening.”
By positioning the surfaces in front of the two ultrasound devices, the ultrasonic waves travel at two slightly different frequencies along a curved path until they meet, researchers explained.
Neither beam is audible on its own — it is the meeting of the beams together that create an interaction, which generates audible sound. The beams can bypass obstacles, such as human heads, to reach the meeting point.
Researchers tested the system in a common room with normal echoes, meaning the system could work in a variety of environments, such as classrooms, vehicles or even outdoors. “We essentially created a virtual headset,” Zhong said. “Someone within an audible enclave can hear something meant only for them — enabling sound and quiet zones.”
For now, researchers can remotely transfer sound about a meter away from the intended target and the sound volume is about 60 decibels, equal to speaking volume. However, the researchers said that distance and volume may be able to be increased if they increased the ultrasound intensity.
155．What is the main goal of the new sound technology?
A．To replace car radios.
B．To block all sounds in a room.
C．To make music louder for everyone.
D．To allow private listening without headphones.
156．How do the audible enclaves generate audible sound?
A．By adjusting frequencies.
B．By bypassing obstacles.
C．By reflecting sound waves off a curved surface.
D．By sending particular beams to their meeting point.
157．What is a current limitation of the technology?
A．It requires multiple ultrasound devices.
B．Its effective range is roughly one meter.
C．It cannot work in environments with normal echoes.
D．The sound volume is too low compared to headphones.
158．What can be inferred about the technology’s future development?
A．Reducing production costs is essential.
B．Beam paths need frequent adjustment.
C．Higher ultrasound intensity may extend range.
D．All public audio systems will be replaced.
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