The Vibration Speaker from Thumbs Up transmits vibrations to surfaces -- such as the packaging for the speaker itself -- to create sound.

Courtesy Thumbs Up Ltd.

Few developments in musical history stand apart from all others: The first musical instrument, the development of recording technology and the day Bob Dylan switched to electric guitars are among them. Perhaps the most important change in the last few decades is the shift to mobile devices as music delivery systems.

Smartphones, MP3 players, tablets and other gadgets make music more accessible. But this shift to mobile music brings along a challenge. Listening to a device using headphones can be great. But most mobile devices don't have internal speakers strong enough to provide a really satisfying experience if you want to share music with other people.

One solution to the problem is to use portable speakers. But many portable speakers lack oomph. The sound might be tinny or thin. You may only be able to coax a relatively low volume from them. Another approach is to use vibration speakers, sometimes called vibration transducers.

These gadgets turn surfaces into speakers. Mount one on a window or set it on a table and suddenly you get a rich, full sound. The effect can be astonishing, particularly since these speakers can be relatively small. So how can such a tiny device create full sounds?

To really understand how a vibration speaker works, we first need to take a closer look at the world of sound and how we perceive it.