For those of you who are interested, this works by using a mathematically calculated exponential horn. This is the most efficient shape for a amplifying horn, which produces an amplified sound due to the resonance of the column of air (so no batteries required). By adding such a horn to the standard iPod speaker, it actually makes the way in which the energy from the speaker is converted into moving airwaves more efficient.

Exponential horn technology that was originally put into wind up gramophones manufactured by by HMV (c. 1928) in the days when all the power came from a spring. Also the same technology used today in Bose speakers.

http://www.gramophones.info/gramhmv163.html

How well this works will depend on how well they've manufactured the maths!