xtroria
100+ Head-Fier
- Joined
- Nov 19, 2013
- Posts
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- 14
My reference IEM is the Sony XBA-4 & AKG K3003 both are @ 8 Ohms.
http://store.sony.com/4-driver-in-ear-headphones-zid27-XBA4/cat-27-catid-EOL-Headphones-Earbuds
This is a tricky IEM for a lot of solid state amplifiers to drive effectively. I see that most SS headphone amps if not all are rated to be used with hps between 16-600 Ohms. Besides the negative effects of high output impedance on an amp when using this IEM (must be 1 Ohm or below), how come amps can't drive this load or not designed to drive it?
I'm not an expert at this topic, so there might be some mistakes in my explaination.
Basically, output impedance acts like a resistor, connected in series to your transducer (iem / headphone / speaker). Now when resistor is connected in series, the bigger resistance will take up more voltage.
So if for example you have a 3 ohm output impedance connected to the SE846 which has 5 ohm resistance @ 4khz, the output impedance will take 37.5% of the voltage supplied by the amp.
Compare this to having 0.5 ohm output impedance connected to the same thing. (0.5 ohm IMO is the highest output impedance any dedicated DAP should have) The output impedance will only take 9% of the voltage supplied from the amp.
A pretty big difference, isnt it? Low impedance headphone / iem is known to be "current hungry", as opposed to the high impedance headphones that has "voltage hungry" trait
Oh for additional note, BA driver iems are notorious for their impedance swings. For example, SE846 is rated at 8 ohm, but its lowest impedance is 5 ohm. So, objectively speaking you want the highest output impedance to be 1:10 ratio, based on tyll's statement in his pono review