[brucew268]

It seems that impedance is an indicator of how difficult headphones are to drive. But are 150 Ohm IEMs as difficult to drive as 150 Ohm full size cans?
 
For instance, the Geek out recommends the 450mW for <100 Ohm cans and the 750mW for 100 - 300 Ohm cans. I use HiFiMan IEMs (RE-262) @ 150 Ohm and can attest that they sound much better with a Fiio E11 (high volt setting) than straight out of my Sony E475 or Galaxy S4.
 
(Volume is not the issue but presentation, which opens up and blossoms with the E11. I would imagine it could show a lot more with even better amplification. Plus the E11 is not practical out of my laptop since the laptop only offers headphone out not line out, and it cannot play while charging. So I need a combo USB DAC/Amp.)
 
Recommendations for DAC/Amping 150 Ohm IEMs?

 

[Bobby S]

Impedance can be a bit misleading.
In absolute terms a low impedance driver would present most difficulty to an amplifier, as it is with speakers.
Low impedance demands more current from an amp. For speakers that can be an issue, as the current demands can be very high indeed (in the order of tens of amps).
 
With high impedance drivers, the current demands are low, but the voltage demands are higher. So a high impedance driver needs more voltage to reach a certain amount of volume. Voltage is typically easier to provide by amplifiers, so in absolute terms higher impedance tends to mean easier loads.
 
Now... when it comes to headphones, the absolute terms don't apply that well.
For headphones efficiency is often times more important than impedance.
For example... a low efficiency, low impedance headphone would be hell to any amplifier, as it will demand both high current and high voltage.
A low efficiency, high impedance headphone would be tough to drive too, but the demands will be mostly voltage oriented.
 
With high efficiency headphones, the demands on both (current and voltage) aren't that great, so it doesn't matter that much what the impedance is.
 
As far as IEMs go, having a higher impedance model usually means you'll just need more voltage from your amp than your typical 32 ohm IEM. For most portable sources that can be a problem.
On the other hand very low impedance IEMs can become a nightmare if the source you're using has a high impedance output and will struggle to drive the headphones correctly (due to insufficient damping factor and the inherent distortions introduced in the sound).
 
Sorry for the long rant, hope it's not too difficult to follow (just got off from work)

 

[ProtegeManiac]

 
Sorry for the long rant, hope it's not too difficult to follow (just got off from work)

 
Not a long rant, it's a "detailed response." 

 

[brucew268]

Thank you for setting this in context. I guess I shouldn't forget all I knew about driving speakers from my days installing amps and speakers in my car. That's what happens when it is late into the evening and I allow the language of reviewers and manufacturers to set the reality that frames my thinking, instead of what I know about basic audio electronics.
 
So if my current amp drives the IEM's well at 300mW/16 Ohm with S/N 98 dB, then an amp should be more than sufficient which produces 450mW/16 Ohm with S/N 115 dB.

 

[cel4145]

Thank you for setting this in context. I guess I shouldn't forget all I knew about driving speakers from my days installing amps and speakers in my car. That's what happens when it is late into the evening and I allow the language of reviewers and manufacturers to set the reality that frames my thinking, instead of what I know about basic audio electronics.

So if my current amp drives the IEM's well at 300mW/16 Ohm with S/N 98 dB, then an amp should be more than sufficient which produces 450mW/16 Ohm with S/N 115 dB.

Yes. But know that 300mW to 450mw is only about 1.5db more volume output. You have to double the wattage to get 3db more volume, and a 10db increase is generally considered a perceived double in volume. So don't count on that new amp to have any appreciable difference in volume.

 

[ProtegeManiac]

Yes. But know that 300mW to 450mw is only about 1.5db more volume output. You have to double the wattage to get 3db more volume, and a 10db increase is generally considered a perceived double in volume. So don't count on that new amp to have any appreciable difference in volume.

 
Just to add to this, on most IEMs which have 100db++ at 1mW sensitivity, you might not need to get 3db more. Even my smartphone can blow my eardrums driving my ASG-1 - what better amps or sources like the iFiio X3 and X5 can do better in amplifying them is slightly better control of the drivers (damping factor on top of SNR) that tightens up the bass at my listening levels, and can go louder before they distort (but again, I don't even get there).

 

[cel4145]

Just to add to this, on most IEMs which have 100db++ at 1mW sensitivity, you might not need to get 3db more. Even my smartphone can blow my eardrums driving my ASG-1 - what better amps or sources like the iFiio X3 and X5 can do better in amplifying them is slightly better control of the drivers (damping factor on top of SNR) that tightens up the bass at my listening levels, and can go louder before they distort (but again, I don't even get there).

And to add on to this, I just realized that your original post refers to some Kickstarter amp project. There are plenty of proven amps regularly recommended on Head-Fi--and plenty that have been proven not to be that great. My advice is to stay away from Kickstarter project audio equipment until it's been produced, sold, and reviewed.

Look into the FiiO E18, JDS Labs C4D, and the Leckerton Audio UHA-4.