AEON, MrSpeakers' New Closed Back Planar Magnetic Headphone
Aug 21, 2018 at 3:02 AM

That table doesn't mention impedance though. So when looking at amp specs, they usually specify mW at either 16 ohms or 32 ohms (some 8 ohms).

So are you looking for 60mW at 16 ohms? Or what impedance?

Cheers!

Sorry, just to link my reply back to your question a bit better: if the only spec the manufacturer gives is power into a single impedance, they're not really telling the whole story. They're giving you the data for *a single point* on a power vs. impedance graph; you can't 100% reliably extrapolate the rest of the graph from that.

edit: I'm actually really not sure of the rest of the story from there, so I'm gonna delete that bit of this reply =) Basically, try and find a spec or measurement for the *right* impedance. If you can't, I dunno if there's a way you can reliably tell for sure whether the device can output the correct amount of power for *your* headphones, based on the spec for a different impedance. Maybe someone else does know.

edit 2: I should probably just point you down to the relevant bit of the "more power?" post here: it starts at "CONNECTING THE DOTS". Just search for that text and read, it tells you your options Seems that if you can find the spec for a *lower* impedance, you can figure it out reliably; if you can only find the spec for a *higher* impedance, you can't.

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Aug 21, 2018 at 3:34 AM
Sorry, just to link my reply back to your question a bit better: if the only spec the manufacturer gives is power into a single impedance, they're not really telling the whole story. They're giving you the data for *a single point* on a power vs. impedance graph; you can't 100% reliably extrapolate the rest of the graph from that.

edit: I'm actually really not sure of the rest of the story from there, so I'm gonna delete that bit of this reply =) Basically, try and find a spec or measurement for the *right* impedance. If you can't, I dunno if there's a way you can reliably tell for sure whether the device can output the correct amount of power for *your* headphones, based on the spec for a different impedance. Maybe someone else does know.

edit 2: I should probably just point you down to the relevant bit of the "more power?" post here: it starts at "CONNECTING THE DOTS". Just search for that text and read, it tells you your options

Yeh as mentioned not many amp specs will specific their 8 ohm power output, for example. Often the closest you can find is a 16 ohm power output.

Does that mean it's incompatible with the ~13 ohm (nominal) AEON closed? Maybe, maybe not.

I guess the connecting the dots approach is great if you can't get any more info at all.

But the first thing to try might be to ask the manufacturer?

Aug 21, 2018 at 3:37 AM
fwiw, 16 and 13 are sufficiently close that I'd just use the number with a bit of padding...so long as the spec says it outputs a bit more power than you need at 16ohm you're almost certainly gonna be fine . edit: sorry for all the edits, it's late and I was misremembering / mixing up some things :/

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Aug 21, 2018 at 3:40 AM
fwiw, 16 and 13 are sufficiently close that I'd just use the number with a bit of padding...so long as the spec says it outputs a bit more power than you need at 16ohm you're almost certainly gonna be fine

Nice. It probably helps that the impedance curve is pretty flat too, I'm guessing?

So not only close to 16 ohm (if that's the only amp power spec given) but close across the entire audioband?

https://www.innerfidelity.com/images/MrSpeakersAeonBook.pdf

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Aug 21, 2018 at 3:52 AM
Well, it makes things simpler If you're dealing with headphones where it's *not* flat, I think - per nwavguy again - the conservative thing to do is base your calculations off the *highest* measured impedance. So e.g. for a pair of HD800s, you'd wanna base your calculations off the peak measured impedance which, per innerfidelity, seems to be about 630 ohms. There's an interesting question and answer in the comments on the "more power" post:

https://nwavguy.blogspot.com/2011/0...omment=1319471547806&m=1#c1261856411748130361

"If you want to be conservative, and know the maximum impedance, you can use that value for calculating required power." But he unfortunately didn't answer one bit of the question that I also am curious about: the consequences of trying to drive a pair of headphones with an impedance curve at a volume which the amp can manage into the *lower* impedance in the range, but not the *higher* impedance. So, say you've got a pair of HD800s - minimum measured impedance about 330 ohm (at about 2kHz), peak measured impedance about 630ohm (at about 100Hz), sensitivity 102dB/mW. Say we want to drive it at 110 dB SPL peak; per the formula we need 6.31mW to do this. What if we have an amp that can put out 7mW into 330 ohms but only 4mW into 630 ohms, or whatever? Will we get a distorted frequency response with weak bass, or what? Anyhoo! Getting off topic there I'm off to bed, night!

Aug 21, 2018 at 6:26 AM
The Flows have low impedance but also low sensitivity/efficiency - which is really just a fancy way of saying they need power There's a handy post here which helps you calculate how much power headphones actually need:

https://nwavguy.blogspot.com/2011/09/more-power.html

the AFC and AFO both have nominal 13 ohm impedance, the AFC's efficiency is 92dB/mW, the AFO is 94dB/mW. From the table we can see the AFCs are going to need somewhere around 60mW power to drive them to 110dB peak SPL (which is a very high level, but nwavguy recommends it as a good guide for various reasons, e.g. recordings with high dynamic range where the average volume may be 30dB below the peak). That's not crazy high, but it is higher than IEMs and headphones specifically intended for portable use.

Looking at the AK70's specs, it looks like it ought to be able to do that, though: https://avprogear.com/astellkern-ak70-mk-ii-portable-premium-dap/

There's another handy resource here - https://www.owenduffy.net/calc/voltcnv.htm - which lets you convert between all kinds of different ways of specifying power. The lowest specified power for the AK70 (mark 1, unbalanced) is 2.0Vrms. If you put 13 ohms and 2.0Vrms into the calculator, it'll show 307mW, which is more than enough, in theory. However, that output spec was measured with no load, which is a kinda flattering way of doing it. Amps can't always manage the same amount of output power into different input impedances. Fortunately, the reference-audio-analyzer folks measured the AK70 for us, so we can find out:

https://reference-audio-analyzer.pro/en/report/amp/astell-kern-ak70-unbalance.php

there's a whole buncha scary numbers there, but if you ignore most of 'em and go to the "Maximum voltage output level vs load" table, it gets interesting. Look at the "Optimal or equal class AB" Vrms column (the whole 'class' thing is a bit complicated, see https://reference-audio-analyzer.pro/en/test-amp-class-power.php#ab , but it sorta-kinda means "max power before the audio quality may possibly be measurably compromised"), and we see it can only manage 0.17 Vrms into 16 ohm (close enough to 13 for rough figuring). Hell, even under "Max, before clipping" - which is 'absolutely max power it'll put out, regardless of whether the signal gets a bit noisy' - we can see it can only manage an absolute max of 0.27 Vrms into 16 ohm. It *can* manage 2.0Vrms - AK aren't lying - but it can only really do it into 763ohms, or no load at all.

So, let's go back to the calculator and try plugging in 0.17 Vrms and 13 ohm...and we only get 2.22mW. Even 0.27 Vrms (the 'max, before clipping' number) is only 5.6mW. To put it another way, if we scroll down a bit to the 'math part' of the post, nwavguy gives us this calculation to figure out exactly how loud a given source can drive a given pair of headphones:

dBSPL = Sensitivity in dB/mW + 10 * LOG ( Pmax in mW)

I *think* that's meant to read Sensitivity in dB/mW + (10 * LOG Pmax in mW) , otherwise the calculations come out weird. So if we plug in the numbers there we get 92 + 10 * LOG 5.6 , which if I didn't mess up the ordering, is 99.48dB - the absolute loudest the measured AK70 could make a pair of AFCs play (in fact it may be slightly lower, since the measurement was for 16 ohm not 13 ohm, presumably the real measurement at 13 ohm would be slightly lower). That'd be the *peak* volume on a track; the average volume would be lower (though for highly compressed music, not much lower).

So: yeah, it's not too surprising your AK70 is kinda maxed out driving the AFCs, based on those measurements at least; if you have a different model from the one they measured, or you're using the balanced output, the numbers would be different, but probably not crazy different.

The AK70's output impedance was measured at 3.40 ohm; that's not *very* high, and probably isn't causing a problem, but it is kinda borderline. I think the general guideline is that the output impedance should be max 1/4 of the input impedance, and 13/4 is 3.25, so yeah, right on the line. (edit: seems nwavguy recommends 1/8, so this *could* be a problem. There's more info on the actual problems caused by using an amp with a higher output impedance and headphones with lower input impedance at https://nwavguy.blogspot.com/2011/02/headphone-amp-impedance.html?m=1 . For Aeons the second point - "Headphone impedance changes with frequency" - doesn't matter, as for planars the impedance does *not* in fact change with frequency, but the other two points may be relevant.)

I mean, you say it's loud enough for you at 130/150, so is this *really* a problem? Do you sometimes need to play it louder? Just the fact that you're at a high number doesn't necessarily mean it's a problem. You're likely in the range where the measured THD+noise is kinda above the ideal level (the difference between 'class AB' and 'Max, before clipping' from earlier), but if you're not *hearing* any obvious issues, is there really a problem?

If you are worried, though, yes, you *could* get more power with an amp or a different DAP: look for one that can manage at least 0.9Vrms into 16 ohms, and ideally has <1ohm output impedance just for safety. There are plenty like that. (FWIW I'm currently hanging onto an Opus #1s and an iBasso DX200 and trying to pick which one to keep, both of those can power AFCs easily, but there are many other options too).

Oh wow this was a lot to read! Am still trying to get my head around it all but from the gists that I am able to get, it would seem that yes, while the AK70 seems to be able to drive the AFCs, it can only do so at a much higher volume than I am accustomed to using it at - it's at the 95-105 mark when I listen with the Momentum 2.0s, but I'm not sure if that's a reliable comparison. I've had the chance to use my AK70 with the AFCs for a few hours today, and something definitely feels a bit. Off? Like, the music is at an acceptable volume to my ears, similar to the Momentums and 6XXs that I am used to, but the sound is.. Thin? Distant? The bass felt muddy. Listening to The Blue Nile's "Tinseltown in the Rain", I couldn't even hear the chord changes during the chorus, of which I had no problem doing when playing the AFCs and 6XXs from my Schiit stack.

I still would very much like to keep my AK70 - it's nearly two years old and selling audio equipment that can't be bought with pocket change gets completely ignored here in my country. It's still a great source when I'm driving in my car. But for office use, maybe something like the micro iDSD BL would be ideal between the AFCs and my laptop? If Dan from MrSpeakers himself is using it, it must be good.

Not many hi-fi audio equipment choices here where I'm from - everything I own was bought online, so I always take the time to deliberate on my purchases before making the plunge. How awesome it would be to live somewhere where after a week of trying the product you can either return it for a full refund or sell it to another interested person with little to no struggle like you guys in the US and all.

Aug 21, 2018 at 9:44 AM
fwiw, 16 and 13 are sufficiently close that I'd just use the number with a bit of padding...so long as the spec says it outputs a bit more power than you need at 16ohm you're almost certainly gonna be fine

You won't, though. The Fulla 2 is specced at 550mW at 16 ohms, but it can't drive the AFC.

Aug 21, 2018 at 10:09 AM
That is a matter of opinion. I use the fulla 2 with my AFC all the time. Yes, it sounds better off my LAu, which is to be expected. but the fulla 2 can still drive them...

Aug 21, 2018 at 11:03 AM
That is a matter of opinion. I use the fulla 2 with my AFC all the time. Yes, it sounds better off my LAu, which is to be expected. but the fulla 2 can still drive them...

I mean, if you don't mind bursts of static at dynamic peaks, sure...

Aug 21, 2018 at 1:15 PM
I mean, if you don't mind bursts of static at dynamic peaks, sure...
I have not had that issue...

Aug 21, 2018 at 1:39 PM
You won't, though. The Fulla 2 is specced at 550mW at 16 ohms, but it can't drive the AFC.
That sounds pretty crazy, if it somehow dropped off that much in power between 16 and 13 ohms - as we figured out the AFCs need way less than 550mW...since bearFNF isn't having the same problem maybe you just got a bad unit or something? I dunno.

Aug 21, 2018 at 1:48 PM
Oh wow this was a lot to read! Am still trying to get my head around it all but from the gists that I am able to get, it would seem that yes, while the AK70 seems to be able to drive the AFCs, it can only do so at a much higher volume than I am accustomed to using it at - it's at the 95-105 mark when I listen with the Momentum 2.0s, but I'm not sure if that's a reliable comparison.

Basically, yes, but it's worth bearing in mind that this *alone* isn't a problem. Some headphones need more juice than others. If your amp can provide enough juice to make them play as loud as you like, without audible problems, it really doesn't matter what number or dial position the volume control is at. It's just a number =) The Momentum 2.0s just need less juice than the AFCs, that'd be the same with any amp. Whatever the amp, you're gonna have the volume dial a bit further to the left with the Momentum 2.0s.

I've had the chance to use my AK70 with the AFCs for a few hours today, and something definitely feels a bit. Off? Like, the music is at an acceptable volume to my ears, similar to the Momentums and 6XXs that I am used to, but the sound is.. Thin? Distant? The bass felt muddy. Listening to The Blue Nile's "Tinseltown in the Rain", I couldn't even hear the chord changes during the chorus, of which I had no problem doing when playing the AFCs and 6XXs from my Schiit stack.

I guess that could possibly be the damping problem described in https://nwavguy.blogspot.com/2011/02/headphone-amp-impedance.html?m=1 : "The bass might become more “boomy” and less controlled. The transient response becomes worse and the deep bass performance is compromised (the headphones will roll off sooner at low frequencies). A few, such as those who like a very warm “tube like” sound, might enjoy this sort of under damped bass. But it’s almost always less accurate compared to using a low impedance source." Does that sound like what you're hearing? Otherwise it could just be a symptom of the AK70's output not being very 'clean' when it's pushing close to its maximum power.

I still would very much like to keep my AK70 - it's nearly two years old and selling audio equipment that can't be bought with pocket change gets completely ignored here in my country. It's still a great source when I'm driving in my car. But for office use, maybe something like the micro iDSD BL would be ideal between the AFCs and my laptop? If Dan from MrSpeakers himself is using it, it must be good.

Absolutely, it's hard to go wrong with what the guy who made the headphones is using It's specced for 200mW at 15 ohm and output impedance of less than 1 ohm, so it certainly looks compatible in terms of numbers.

Aug 21, 2018 at 1:48 PM
That sounds pretty crazy, if it somehow dropped off that much in power between 16 and 13 ohms - as we figured out the AFCs need way less than 550mW...since bearFNF isn't having the same problem maybe you just got a bad unit or something? I dunno.

Search the thread. Many people have problems with it, and Jason Stoddard has confirmed that Fulla doesn't have the current it needs to properly drive these headphones.

Aug 21, 2018 at 1:50 PM
Search the thread. Many people have problems with it, and Jason Stoddard has confirmed that Fulla doesn't have the current it needs to properly drive these headphones.
Huh, crazy. Has anyone measured it to see how much power it can actually put out at 16 and 13 ohms? It just seems like such a massive dropoff. (Note there's a measurement-based review of the Fulla 2 on a site which is...not exactly popular around here which makes it look like the Fulla 2 has a hard time putting out very clean output at almost any power level, but let's not go too far into that as I don't want to get into trouble =) let's just say I probably wouldn't buy that amp for anything myself, haha.)

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Aug 22, 2018 at 1:26 AM
Has anyone tried pairing AFC with RME's ADI-2 dac? I've been very interested in that dac recently and wonder if its headphone output can drive the AFC properly.