earphone desgin and quality research

Hi all, im new to the forum so apologies if this is in the wrong place.

im doing a little bit of research on what needs to be considered when making a high quality earphone (wireless) set. ill be working with a manufacturer off of alibaba so i need to know im not getting a low quality product. what do i need to take into account regarding the "anatomy" of a speaker, for instance what materials will produce the best sound. any advice is greatly appreciated.

kind regards
Cole