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Cellphones and pagers that vibrate warn users of an incoming call without
disturbing anyone else, but the vibrating unit adds weight and bulk to the
phone. So Matsushita of Japan has developed the Vibsounder, a miniature
loudspeaker that can vibrate as well. The trick is to add a cone to the
loudspeaker that resonates at very low frequency, creating a vibration strong
enough to be felt through clothing.