[Make Smile]

I've just bought an etymotic er4s IEM on amazon, but it sound different than an old er4s of a my friend. So what is the reason, because the driver has changed or new er4s need to burn-in.

 

[tomb]

The quality of sound is greatly dependent on the ear plugs and the seal of the fit in your ear canal. Did your friend have different tips? Maybe yours are not making the same seal. Or, perhaps he had smaller tips that allowed you to insert the IEMs further into your ear.

Like many, I think the best fit/seal is through using the Comply foam tips. You should get great detail and reasonable bass using those.

 

[alpha421]

Check if it needs new filters, assuming you bought second hand.

 

[Make Smile]

I used the same tips for both.
Sound of my er4s isn't as good as old er4s.
I think if driver has changed because my er4s has seri about 34xxxx, while of my friend has seri 22xxxx, very old.