[mantis toboggan]

I'm thinking of buying the shure se215 because of their apparently wonderful sound cancellation.  This might sound like an idiotic question but does sound cancellation depend on the eartips or the actual headphones?  Because I'm looking for something a little less expensive than the se215's

 

[ZARIM]

I think it's depend on both because some IEMs design to stay in outer ear like UEF10Pro, Sennheiser IE8, JVC FX700 and they isolate less than IEMs stay deep in inner ear like ER4P/S, HF series. The tips also are same like foam tips created more isolation from surrounding than silicon tips and three flange are even better. Shure SE215 can insert fairly deep and they isolate better than many other dynamic IEMs.

 

[soundstige]

It only depends on how much density and mass is put in your ears, period. Now, this could mean a metal housing will isolate better than a plastic one, or a vented housing will isolate poorer than a closed one, or a tighter seal is achieved with expanding foam tips compared to thin rubber ones, or that an IEM will isolate more when inserted deeper into your ear than normal, or that an IEM with a larger driver will isolate more than one with a small driver; and so on.