[Kunlun]

Just thinking about the Etymotic er-4B versus er-4p, I went out and bought a 30-ohm impedance adaptor for a few bucks and a laugh.
 
What should I expect in terms of sound changes, if any for:
 
1. iems with a single dynamic driver?
 
2. iems with a single BA (like the er-4)?
 
3. iems with multiple BAs or BA-dynamic hybrids?
 
 
Thanks!

 

[xnor]

The biggest difference will be in the frequency response.
 
Take a look at the SE535 impedance curve. It starts out flat, rises until about 1.5 kHz, drops to a low point at 6 kHz and rises again.
 
If you add resistance, or your amps has high output impedance to begin with, the frequency response will be changed accordingly. It should be about +2 dB at 1.5 kHz and -5 dB at 6 kHz..
 
If all of that is cryptic to you: with the SE535, the mids will be a bit louder, and upper mids/lower treble will be quite a bit quieter.