Jez Corbett wrote:Can drivers that small really deliver deep bass?
[edit -- Sam got there first!] Yes, but only if the earpieces fit with a good seal in the ear canal, so on generic in-ears / earbuds selecting and fitting the right size of removable grommet to suit your own ears is absolutely critical to the performance -- as is fitting them into the ear correctly. Moulded in-ears should fit perfectly by definition, of course...
Although some in-ears manage to use a 'traditional' moving-coil driver like a miniature headphone system (like the Sennheiser IE800s, for example) the vast majority of ear-buds/in-ears use 'balanced-armature' drivers.
However, it's difficult to make these with a very wide and uniform operating bandwidth, so for high performance applications most manufacturer combine two, three, or even four, balanced-armatures of different sizes in each earpiece optimised to cover different parts of the spectrum -- much like a multi-way speaker system.
But yes, the performance of a good in-ear system well-fitted is just as good as a decent external headphone.