[ev13wt]

You only need an amp if:

Output impedance is too high for the headphones (Shure IEMs some to mind), changing the frequency response.
Headphones distort because the amp is under powered.

 

[pinnahertz]

You only need an amp if:

Output impedance is too high for the headphones (Shure IEMs some to mind), changing the frequency response.

Actually the impedance issue is not simply that headphones might have a lower impedance, it's the impedance vs frequency that causes the FR problem. Several of the Shure IEMs have impedance curves that start at 30 ohms, dip to 15, the swing up to 60. But before you look at impedance graphs and try to conclude what effect that may have on response, consider that these guys do know how to design excellent transducers, and do know the kind of source impedance the driving amp is likely to have. That impedance swing may affect FR, but that may also be intentional!

If an impedance curve if relatively flat across the audio spectrum, but the headphones are lower in total impedance, there's no FR issue when driving from a relatively high output impedance amp.

On the other hand, you'd have to define "high output impedance" as something like 20 or 30 ohms. Decades ago we used to put 100 ohm built-out resistors on speaker amps and then connect 8 ohm headphones. The power loss was intentional and necessary, the FR wobbles we just accepted. Those days should be pretty much gone by now. No decent amp should have output Z so high that there's an issue.

Headphones distort because the amp is under powered.

If you check what power is required for your headphones to reach 90dB SPL, you'll find that the requirements are typically pretty light. The Shure IEMs, for example, require only a few milliwatts. Any amp, I mean ANY amp, can drive them to ear-damaging volume without clipping. Under-powered amps really aren't the problem.

There are a few full size cans that do like a bit of power, but the real issue is output voltage swing. Higher impedance cans often need higher voltage to get the required power into them. That's why some amps have a gain switch. And in that case, it may be possible for a lower output voltage amp to be driven to clipping, but it's a lack of voltage, not power, that causes the problem.

Most popular headphones don't need anything special, though. And therefore don't benefit from an amp.

Post specifics, we can have a look.

 

[Niouke]

interresting subject.

I used to own sony XBA-3 and XBA-40 IEM's and now own sony XBA-300's along with Westone UMP PRO 30's.
I used the XBA-3's and 40's a long time on my smartphone (Sony Z1 and Z5) and was quite happy with the SQ. I then tried them with a portable amp in the middle during a visit in Japan and it was a revelation to me as the music seemed much more dynamic, lively etc etc to the point I had to buy an amp on the spot (a sound blaster E1 replaced by FiiO E11K later)

my subjective experience tells me these four BA iem's need amps to perform best, and the impedance curves seem to hint in that direction, but was it all illusions?

 

[pinnahertz]

interresting subject.

I used to own sony XBA-3 and XBA-40 IEM's and now own sony XBA-300's along with Westone UMP PRO 30's.
I used the XBA-3's and 40's a long time on my smartphone (Sony Z1 and Z5) and was quite happy with the SQ. I then tried them with a portable amp in the middle during a visit in Japan and it was a revelation to me as the music seemed much more dynamic, lively etc etc to the point I had to buy an amp on the spot (a sound blaster E1 replaced by FiiO E11K later)

my subjective experience tells me these four BA iem's need amps to perform best, and the impedance curves seem to hint in that direction, but was it all illusions?

Probably. I had the reverse experience where I got a highly reputed amp, and heard no difference because I expected not to. I verified that with ABX testing, though.

 

[bigshot]

ditto

 

[castleofargh]

interresting subject.

I used to own sony XBA-3 and XBA-40 IEM's and now own sony XBA-300's along with Westone UMP PRO 30's.
I used the XBA-3's and 40's a long time on my smartphone (Sony Z1 and Z5) and was quite happy with the SQ. I then tried them with a portable amp in the middle during a visit in Japan and it was a revelation to me as the music seemed much more dynamic, lively etc etc to the point I had to buy an amp on the spot (a sound blaster E1 replaced by FiiO E11K later)

my subjective experience tells me these four BA iem's need amps to perform best, and the impedance curves seem to hint in that direction, but was it all illusions?

I'll take a different stand on this, my buddies might not be familiar with those IEMs or most IEMs in general.
the impedance curves alone are more than enough to explain some audible differences from different sources. if you had the bad luck of going from some high impedance output on one source to one around 1ohm or less on another, it wasn't in your head. nobody would have dared to say they sounded the same after trying them. I only played with the xba3 and 4 at the time but they were such a perfect case study of what not to do if you seek something stable.

those IEMs went as low as 10ohm if I remember correctly, so while not dangerously low yet, when a device writes from 16 to 300ohm in the specs, they could put that 16ohm value because everybody did. or because their design was really not good with lower impedance loads. there was a fairly famous case of a samsung phone supposed to have good audio stuff, low impedance etc, some time back where the phone would start distorting like mad into several low impedance IEMs when the user was pushing the volume level a little. the IEMs were simply outside of the usable range and samsung failed to consider the situation of crazy low impedance IEMs.

but I would strongly advise against taking that experience with sony IEMs or any multidriver IEM reaching very low impedance somewhere, and use it to think that it shows the need for a portable amp in general. it really doesn't. to make a point, the irony at the time was that sony DAPs were around 3 to 5ohm(lame), and the PHA1 was something like 8 or 10ohm I think. we even came to a point where some gears got a list of suggested pairing and half the sony models weren't in the list made by sony ^_^. it was like they had made those IEMs and amp to troll themselves.
a simple rule of thumb for stability and low encounters of troubles: avoid gears with weird specs! too low impedance, crazy impedance curve, crazy high sensitivity, any extreme is a chance for trouble with at least some sources. that said most TOTL IEMs are such troublemakers. stuff with a gazillion drivers and 80crossovers with super extreme sensitivity and impedance reaching very low. so my rule of thumb would be to avoid all of those like a plague, which can seem like a strange advice to audiophiles but I stand by it ^_^. stability and versatility are unlikely to be found in the most extreme specs.(applies to politic! viewed on TV!).

I like to use my sony DAP( A15) with crappy amp section, because it's small and I enjoy the UI, but with it I use a limited list of IEMs. with my pair of RE400 (about flat impedance at close to 35ohm), I can really use about any source I like and they sound very fine and pretty much the same to me. even with my se215(around 18ohm but still flat impedance), everything is fine on all my sources and I can hardly tell them apart.
but I have a few IEMs where I can basically tell you which of the sources I own is being used by ear. they will create or exacerbate differences. when it's audible background noise or distortions so bad into a low impedance load that it's audible, the better source is a simple matter. you need one with lower noise floor or one that doesn't piss it's electric pants when the current flow gets a little high. but when the result is simply a signature change, the notion of better source can be a matter of personal taste. it's not really that one is better contrary to all you'll read in the reviews, but that with a given source, the guy likes the signature more and that's most likely all there is to it. maybe you would agree, maybe not. and the low impedance amp that measures so good might not be your favorite pairing. many people really loved their sony PHA1.
some IEMs/headphones will invite stability. others won't. I tend to think that stability is a sign of a product well done, but elitists just love it when something needs special care. to each their own.

 

[bigshot]

I tend to think that stability is a sign of a product well done, but elitists just love it when something needs special care. to each their own.

And then they don't take that special care and get funky results and claim that every amp sounds different. I really don't know why people make things hard on themselves. If you're going to spend a lot of money on something, at least get something that is compatible.

 

[Niouke]

All multi balanced armature IEM's seem to be problematic to drive, mine are far from being TOTL but are still very source dependant it seems

For my defense I bought my first expensive IEMs, the XBA-3, after testing dozens of them on my then xperia Z1. They just sounded the best to me, I had no idea of what balanced armature were The trouble started when I changed my smartphone to a Z5 and was underwhelmed with the SQ...

 

[castleofargh]

All multi balanced armature IEM's seem to be problematic to drive, mine are far from being TOTL but are still very source dependant it seems

For my defense I bought my first expensive IEMs, the XBA-3, after testing dozens of them on my then xperia Z1. They just sounded the best to me, I had no idea of what balanced armature were The trouble started when I changed my smartphone to a Z5 and was underwhelmed with the SQ...

what annoys me the most with impedance changing the signature, aside from having the bad surprise to possibly dislike the sound on the new source, is how easily it leads people to false conclusions. that's really detrimental as a whole to the hobby:
I have an IEM, I try it on source A I like the sound, then I try it on source B and the sounds sucks. I conclude that source B sucks and A is better in general. instead of the prudent and probably more realistic claim that it sucked for that specific pairing. it also leads to all those arguments about a DAP or amplifier being warm, or cold, or rolled off in the subs, when they will usually measure fairly flat and fine into a stable and high enough load. IMO any DAP or amp review made entirely using 1 multidriver IEMs with massive impedance swings for subjective impressions, should be deleted. I'm confident it would be a real benefit to the consumer.

 

[Niouke]

The more I learn here, the more I realize most "reviews" are garbage (don't start me about tellementnomade).Having studied the basics of electronics I always was skeptical about certain topics, like sound coloring cables.

 

[pinnahertz]

The more I learn here, the more I realize most "reviews" are garbage (don't start me about tellementnomade).Having studied the basics of electronics I always was skeptical about certain topics, like sound coloring cables.

...And so it goes in Audio. I know of no other branch of technology quite as saturated in myth an misinformation, though there is some in almost every technological segment.

 

[ev13wt]

And then they don't take that special care and get funky results and claim that every amp sounds different. I really don't know why people make things hard on themselves. If you're going to spend a lot of money on something, at least get something that is compatible.

But for that, a person must want to educate themselves.