[Jakkal]

   
I also found the opposite regarding amp power. I own the 4 and the 64gb 5S but my 5S is noticeably more powerful. (about 2 clicks) Maybe it has something to do with the different headphones we are using. I tried mine with IE80's & M100.
I do agree with the output impedance though. Unfortunately there are clear signs of it with my IE80's. More bass, and less clear with less detail. With higher impedance cans that goes away and it sounds better than my 4. With the IE80's it would be a toss up between the 4 despite the improvements with the 5S simply because of the impedance issue. A high impedance iem would sound wicked with it I would expect.

 
Nope, iPhone 4 and 5S have 16 volume steps. Go 8 steps on both and compare, it it obvious, iPhone 5S has weaker amp than iPhone 4. Other than that it is just awesome phone. 

 

[_js_]

Nope, iPhone 4 and 5S have 16 volume steps. Go 8 steps on both and compare, it it obvious, iPhone 5S has weaker amp than iPhone 4. Other than that it is just awesome phone. 

Did you miss the bit about impedance of headphones affecting results? Not only will a 3-4 ohm output impedance mess with the FR curve of <32 ohm cans, it will lose efficiency as well. Power loss through a resistance goes as the SQUARE of the current times the resistance. Lower impedance cans take more current to drive, all other things being equal.

So . . . the 5s vs 4 comparison will depend on the impedance of the phones being driven, as well as max output current of both.

 

[vwinter]

Even a 3-4 ohm output impedance is within the recommendations for a 32ohm headphone. The PX100II doesn't drop below 32ohms if measurements are to be believed. It even rises up in the 100hz region indicating that there is likely more control in that region. I suspect there is just bad synergy for your tastes in that specific case.

With the 32ohm ASG-2 I hear a tighter sound bottom to top fwiw.

 

[GWagon]

   
That's a thought . . .
 
For now, I'm going to get my iPhone 4 back no matter what, but hold off on the decision to return my 5S.  I'm too emotional about all of this right now, both pro and con.  I'm sure it's destroying my objectivity (such as there is) regarding sound quality.  Now that my allergies are completely gone, I'll do some more A/B'ing with my Apogee Duet tonight as well as some relaxed listening, and see if that sheds any more light on the subject.
 
In any case, one question:
 
I see in a review of the Fiio E12 that it is supposedly not a good amp for a cell phone source because it will pick up EMI from the cell transmitter.  Is this true?  And if so, under what conditions will it happen?  Only when there is a call? All times except when in Airplane mode?  What's the story?  And what amp would NOT pick up interference from cordless phones and cell phones?  What about the O2, for example?

 
I found that my E12 had pretty bad EMI with my iPhone 5 strapped to it. I ended up moving to an IPC as I needed the extra space anyway and I preferred not having a brick attached to my phone. 

 

 

[_js_]

Even a 3-4 ohm output impedance is within the recommendations for a 32ohm headphone. The PX100II doesn't drop below 32ohms if measurements are to be believed. It even rises up in the 100hz region indicating that there is likely more control in that region. I suspect there is just bad synergy for your tastes in that specific case.

With the 32ohm ASG-2 I hear a tighter sound bottom to top fwiw.

 
It's not a PX-100 II.  It's a PX-100.  Do we have a impedance vs. frequency curve for that?  Because, seriously, it sounds REALLY different, especially in the bass--just as a high output impedance amp / low impedance headphone combo is described as sounding.  I searched for Z vs. Hz graphs of the PX-100's but didn't find any.  If it's true that it, like its successor doesn't drop below 32 ohms, well, then I'm at a loss!
 

   
I found that my E12 had pretty bad EMI with my iPhone 5 strapped to it. I ended up moving to an IPC as I needed the extra space anyway and I preferred not having a brick attached to my phone. 

 

 
Ah!  Thanks so much for this information.  What's an IPC?
 
So I've been A/B'ing my Grado SR-225's out of the 5S and Duet for the last 90 minutes, and well, there just isn't that big a difference, and I'm finding the music enjoyable out of the 5S.  BUT, not quite as good as I'm used to my 225's sounding out of either source, BECAUSE I just sent them back to Grado not too long ago to fix a rattle problem (i.e. "Grattle") and they replaced the drivers.  So the stupid things haven't been burned in yet.  I never put much stock in burn-in one way or another, but if my audio memory can be trusted (I don't really trust it longer than 5-10 seconds or so) then these do not actually sound as good as my drivers with years and years of listening on them.  And, in addition, maybe I'm wrong about having recovered from allergy issues, since I have to sit up to A/B, so maybe that's the difference.  I think I need to take the good advice posted earlier.  It's all good.  I'll figure it out, one way or another.
 
But I surely would like to know if anyone else has tried the PX-100's (not 100 II's) with the 5S and what their take is.  Because I can't imagine anyone liking the sound!  I have two pairs of PX-100's.  One which I've used for 2.5 years, and my reserve, like-new backup pair.  Both pairs sound quite bad out of the 5S.  And both pairs sounded great out of the 4.  Or such is / was my subjective take (to state the obvious).

 

[GWagon]

Oh sorry, IPC = iPod Classic

 

[shotgunshane]

Impedance for a px100 seems to be around 40ohm. You can check it out at headphone.com's learning center.

 

[Jakkal]

Did you miss the bit about impedance of headphones affecting results? Not only will a 3-4 ohm output impedance mess with the FR curve of <32 ohm cans, it will lose efficiency as well. Power loss through a resistance goes as the SQUARE of the current times the resistance. Lower impedance cans take more current to drive, all other things being equal.

So . . . the 5s vs 4 comparison will depend on the impedance of the phones being driven, as well as max output current of both.

 
Ok I have tested with Brainwavz HM5 which are rated 64ohms and the result is the same, iPhone 4 has more power than 5S.

 

[Dumbleroar]

Why have Apple started to make their phones with a higher output impedance? Surely they must realise people's listento their music via their phone and a lot of iem owners have earphones with a low output impedance? Or do they want you to go out and buy the iPod touch?

 

[elfary]

Why have Apple started to make their phones with a higher output impedance? Surely they must realise people's listento their music via their phone and a lot of iem owners have earphones with a low output impedance? Or do they want you to go out and buy the iPod touch?I thi

 
Since Steve passed away it seems that iPhone headphone out is worse than that of the iPads and iPods. It seems that for second year in a row the iPhone amplifier is weaker than that built in the iPhone 4 and iPhone 4S (Which is has even more output power than the one inside the iPhone 4).
 
iPhone sound took a little step back under Cook tenure. It seems odd taking into account how stunning is the headphone out of the iPad Mini and the Touch 5. It sure is still great but not the greatest as it was the case with iPhone 4/4S

 

[Achmedisdead]

I'm so glad I can't use IEMs and therefore am exempt from all these worries about output impedance.

 

[3ntropy]

So I've just been listening to my 5S with TF10s, which apparently had issues with output impedance on the 5, and to my untrained ears they are perfectly fine. Did a little A/Bing with my HTC One (unfortunately couldn't do the 4S as I have sold it), and they are very comparable, I want to say the 5S is very slightly more clear and forward, which being better would be a matter of preference. I think I prefer the 5S.
 
I also tried Amperiors, which are listed as having 18 ohm impedance, and they were also 100% fine. In terms of volume both phones got louder than I care to listen at. So far on the 5S I have listened to SE215s, TF10s, UE200s and 220s, and Amperiors, and it has been fine on all of them.
 
Edit: Also in terms of the headphone out on the iPad Mini, I know it is the same chipset as the iPad 2, does it have the same codec as well? Because I definitely prefer the iPhone to the iPad 2. 

 

[shotgunshane]

I think all the concern over ~3ohm output is overblown. My iPhone 5 sounds great to me, especially on iOS7. Having had the 4, 4S and 5 side by side for testing, one would be hard pressed to tell the difference in unsighted tests. And having experimented with varying degrees of output impedance with multiple iems, there's not much to be concerned about until you get over 10ohm. Even then it can be very difficult to pick out changes on many iems (TF10 not withstanding). In fact, many iem see an improvement in technical ability with added impedance, if getting closer to a neutral reference is an improvement in one's book. All that being said, less than 1ohm is certainly preferred.

 

[customNuts]

   
Nope, iPhone 4 and 5S have 16 volume steps. Go 8 steps on both and compare, it it obvious, iPhone 5S has weaker amp than iPhone 4. Other than that it is just awesome phone. 

 
No one is denying your findings so it probably best to not through around blanket statements such as "Nope, iphone 4 has more power than iphone 5S, it's obvious" cause that has proven to be not the complete truth of the matter at all by several members. As mentioned, impendance issues could be causing it - I don't know. Since you seem to be the only one with these findings, maybe your 5S has a glitch or a fault. Again, I don't know but peoples findings are not up to you to deny. 
At the end of the day, I agree it's an awesome phone & I'm getting great results with higher z phones & thats all that really matters to me.
Peace.

 

[customNuts]

Also I try to never underestimate the power of synergy in audio.