
Headphone and Amp Impedance (2011) - pmoriarty
http://nwavguy.blogspot.com/2011/02/headphone-amp-impedance.html
======
thucydides
This guy also built and open-sourced a universally admired headphone amplifier
and DAC.

His O2 amp: [http://nwavguy.blogspot.bg/2011/07/o2-headphone-
amp.html](http://nwavguy.blogspot.bg/2011/07/o2-headphone-amp.html)

His O2 DAC: [http://nwavguy.blogspot.bg/2012/04/odac-
released.html](http://nwavguy.blogspot.bg/2012/04/odac-released.html)

JDS Labs and others sell them commercially for those who don't feel like
building them by hand.

~~~
jzelinskie
He/She has also inspired some other manufacturers to rethink their products.
IIRC Schiit was formed when some engineers thought they could improve the
O2/ODAC design on their own[0]. I own an original Schiit Stack (Magnus & Modi)
and would definitely recommend them.

[0]:
[https://news.ycombinator.com/item?id=8834176](https://news.ycombinator.com/item?id=8834176)

~~~
qb45
Not exactly, you may want to actually read the source you linked :)

The company existed before O2 and M/M were independent designs.

~~~
jzelinskie
Thanks. I had read that someplace else and went digging for the link and
simply assumed that was it.

------
lowmagnet
I wonder what nwavguy does for a living these days. He disappeared from the
Internet in that persona shortly after the release of his designs and dropping
some serious allegations at some manufacturers for a transient overvoltage
issue. He's a solid engineer and I hope he's just quietly improving the state
of audio somewhere.

------
teraflop
On a tangentially related topic:

When I used to listen to music on my previous phone (a Nexus 4) I would have
to constantly adjust the phone's volume: all the way to maximum when using an
aux cord in my car, and way back down when using headphones. Recently I
upgraded to a Nexus 5X, and noticed a surprising new feature. Somehow, the
phone detects which device it's plugged into, and remembers a separate,
previously-set volume level for each device.

Does anyone know how this works? It's really convenient, which makes it
surprising that I can't find it documented or even mentioned anywhere online.
I'm assuming the audio hardware is somehow sensing the impedance of whatever
it's connected to, but is that really a reliable indicator of headphones vs.
line-level inputs?

~~~
sdk77
In my opinion as an EE there would be some reasonably reliable ways to detect
either a line or headphone connection. Headphone impedances are typically
between 16 and 600 Ohms, and line impedance is typically in the 10's of kOhm
range. That's one way to differentiate. There has to be an output signal
(presumably audio) first, however. Another way is to apply a very small DC
current (that would certainly not damage headphones, so I would guess in the
micro-ampere range) and check if there is continuity or measure the DC
resistance of the load outright. For line inputs, as they're usually AC-
coupled, DC resistance would be infinite, and for (DC coupled) headphones it
is very low. It's an interesting subject and I wouldn't be surprised if there
are some patents involved.

~~~
jeff_marshall
Detecting AC vs. DC coupling would be obvious to a practicing EE, if presented
with the problem, yes? I'm just a software guy with an electronics hobby and I
think I could have figured that one out.

That said, DC vs. AC coupling detection could probably be granted a patent if
nobody had "disclosed" the idea prior to filing of such a patent, based on my
experience with software patents.

Sorry to vent, but patents on this sort of thing drive me crazy. I don't have
any gripe with you or your post.

~~~
sdk77
I did a quick search on google patents:
[https://www.google.com/patents/US9084035](https://www.google.com/patents/US9084035)
\- it uses a combination of AC and DC methods.

------
tacos
This guy is fantastic. Having spent a little time around professional audio,
it doesn't surprise me that he did amazing stuff for 18 months (anonymously)
then vanished from the web.

This piece on his site has lots of interesting insight into the audio
industry. It also relates to objective, critical thinking in general.

[http://nwavguy.blogspot.com/2011/05/subjective-vs-
objective-...](http://nwavguy.blogspot.com/2011/05/subjective-vs-objective-
debate.html)

~~~
calinet6
He had an interesting mind. Absolutely too objective, in my (subjective)
opinion. It was almost as if his entire purpose was to remove the validity of
all opinion from the discussion completely, and frankly, it was sad and
inhuman—despite his amazing technical contributions.

~~~
chroma
I think his viewpoint is spot-on. The goal of most audio systems should be to
accurately reproduce the original waveform. If you want to add "warmth" or
"color" or whatever to the sound, it's better to quantify what that means,
then purposefully distort the audio in a dedicated device (or in software).

Think about what life would be like if displays were built and reviewed like
audio tech. Imagine companies like NuForce and Schiit sold screens that didn't
accurately reproduce colors. Owners of these displays would praise them for
their "warmth" or talk about how much green colors "pop" or whatever. It would
be absurd.

We can actually measure contrast ratio, color accuracy, viewing angles, etc.
That's how we evaluate displays. People who prefer a different gamma or white
point change it in software. They don't buy defective monitors. But switch the
topic to audio and people forget all that. It's bizarre.

~~~
ubercow13
I greatly respect NwAvGuy and agree with almost everything he says, but I
think in practical terms that's a slightly over-simplified perspective. Look
how inaccurate even these headphones are [1], arguably the best or one of the
best ever made.

Getting the inaccuracies to be the _right_ inaccuracies is quite subtle and
very important in my opinion. See for example this review of his [2] and in
particular the paragraph near the end:

>AN EQ EXPERIMENT: I tried using highly configurable parametric EQ to tweak my
Denon D2000s to be similarly forgiving and I failed. When I filter out
equivalent amounts of sibilance and harshness with the Denons, more of the
music is gone and the result sounds veiled and artificial. The HD 650, to my
ears, somehow works more like polarized sunglasses. They largely remove what I
don’t want while revealing more of what’s left. It’s not just a simple
frequency response difference. My objective side wants to pin down what’s
going on but I don’t have a full explanation besides the HD 650’s lack of
distortion.

[1]
[http://www.innerfidelity.com/images/StaxSR009.pdf](http://www.innerfidelity.com/images/StaxSR009.pdf)
[2] [http://nwavguy.blogspot.co.uk/2011/06/sennheiser-
hd-650.html](http://nwavguy.blogspot.co.uk/2011/06/sennheiser-hd-650.html)

~~~
chroma
I was mostly talking about DACs and amplifiers, not headphones. Headphones
have to deal with more trade-offs: comfort, size, isolation, and the fact that
it's really hard to get them to accurately reproduce sound. Still, so what if
current headphones suck at reproducing sounds? That doesn't mean we should
ignore quantitative measurements. If the "right" inaccuracies are so subtle-
yet-crucial, it's important to quantify them! Then we can evaluate headphones
based on how accurately they create those inaccuracies.

And I think you're missing the point of the EQ experiment. NwAvGuy wanted to
see if there was more to quantifying headphone quality than a frequency
response curve. He was right. That just means that objective evaluations of
headphone quality will need to include more measurements. That doesn't mean we
should disregard measurements and go with subjective impressions. Otherwise,
something as mundane as a warm drink can skew the reviewer's opinion.[1]

1\.
[http://news.bbc.co.uk/2/hi/health/7688315.stm](http://news.bbc.co.uk/2/hi/health/7688315.stm)

------
amelius
Circuit theory becomes much more elegant if you start to use complex numbers
(conceptually, the Laplace transform [1]). But for an introductory lesson,
this page seems nice, though perhaps a bit long.

[1]
[https://en.wikibooks.org/wiki/Circuit_Theory/Laplace_Transfo...](https://en.wikibooks.org/wiki/Circuit_Theory/Laplace_Transform)

(If you grasp this reference, then you understand, I'd say, about 25% of what
electrical engineering is about)

~~~
sprash
But only if you use linear components (meaning L,C,R). Introduce just one
diode and the system of diff equations needs to be solved numerically. In
which case you have switch to simulations like spice anyways. Therefore there
is no reason to even bother with Laplace transforms nowadays. For hobbyists
(and the vast majority of professionals) I would consider it completely
useless knowledge.

~~~
raverbashing
> Introduce just one diode and the system of diff equations needs to be solved
> numerically

Not really. Maybe that's why nobody invented anything with a diode in the
signal path before computers were commonplace right? Like radio and guitar
distortion pedals

> Therefore there is no reason to even bother with Laplace transforms nowadays

Sure, let's forget the math and make engineers totally dependent on numerical
simulation without knowing the basics, I'm sure that'll work just fine

> For hobbyists (and the vast majority of professionals) I would consider it
> completely useless knowledge.

LOL

Sure, in the same way that sorting algorithms don't are useless for computer
science students, right? Just call .sort() and you're done!

Also don't forget Digital Signal Processing, that also relies on that "useless
knowledge"

~~~
sprash
> Not really. Maybe that's why nobody invented anything with a diode in the
> signal path before computers were commonplace right? Like radio and guitar
> distortion pedals

No, those problems were solved via ultra simplified models. E.g. The current
through a diode is described as I = I_0 \Theta(U - 0.7 V). And the rest was
done via try and error.

> Sure, let's forget the math and make engineers totally dependent on
> numerical simulation without knowing the basics, I'm sure that'll work just
> fine

How about, lets learn how to solve every differential equation you will ever
come across in electronics using e.g. Runge-Kutta.

> Just call .sort() and you're done!

If you want to get shit done you do exactly that. This is a great problem of
many fresh CS graduates. Instead of doing the actual work they would rather
first implement their own sort function. In 99.9% of the cases it is a
complete waste of time.

> Also don't forget Digital Signal Processing, that also relies on that
> "useless knowledge"

In Digital Signal Processing you mainly need to Fourier transform and know the
properties of the sin(x)/x function, Nyquist, Shannon etc... Learning how to
solve a very special case of systems of differential equations using the
Laplace transform won't help you there at all.

~~~
srean
>Instead of doing the actual work they would rather first implement their own
sort function.

Strawman much. On the otherhand I regularly come across people who call
library functions without understanding their runtime consequences, well those
are the good ones, the bad ones 'get shit done" by calling sort just to find
the maximum. Yeah they do get exactly that done, that is, shit.

------
steejk
I could have done with reading this article a week earlier.

I just built a converter to allow earphones to be used in aircraft audio panel
outputs which are typically 150-350 Ohms. Another bizarre thing I learnt is
that 1/2" and 1/4" stereo jacks are wired opposite ways.

~~~
MrBuddyCasino
Not sure if we are talking about the same thing, but on a flight with a Boing
777, I found the throw-away headphones that they hand out upon boarding with
the very strange connector (dual mono jacks) to be so bad as to be nearly
useless.

I tried to cut the cable, remove the isolation and connect my Apple earbuds,
which worked somehow but not very well because the (very thin) wires were
individually isolated. Did you come up with a solution?

~~~
legulere
There are adapters you can buy for like 3$.

------
gchokov
Nice, good and cheap amp ($19) mentioned at the bottom of the article, in case
you need immediate boost over stock audio from your phone -
[http://nwavguy.blogspot.bg/2011/03/fiio-e5-headphone-
amp.htm...](http://nwavguy.blogspot.bg/2011/03/fiio-e5-headphone-amp.html)

~~~
ju-st
Or when you are annoyed by a shitty soundcard in your business notebook, get a
Behringer external DAC/soundcard for $29 (
[http://nwavguy.blogspot.de/2011/02/behringer-
uca202-review.h...](http://nwavguy.blogspot.de/2011/02/behringer-
uca202-review.html) )

~~~
stordoff
I have a UCA202 (and a UFO202 - AFAIK it is identical but with a phono stage
on the line ins) to use with my Surface (the build-in card is very noisy) and
it is a noticeable improvement over the built-in card. Definitely recommended
if you need a USB DAC without spending a fortune.

~~~
te
I use an Acer C720 Chromebook running Linux to drive my virtual piano
software. I had no complaints with it's on-board audio performance, but after
reading multiple exhortations on the internet about how much better external
soundcards are, I bought a $5 USB soundcard widely available from multiple
vendors on ebay. OK, I can just barely hear an improvement over the on-board.
It's better in the sense of "significant" (ie definitely there), but it just
isn't a material difference to me.

If I'm that deaf to the differences between these two sources, I'm curious if
people think the UCA202 will change my life?

~~~
nitrogen
The noise floor is the main issue with most cheap sound hardware. It's often
loud, and not spectrally flat. You'll be able to hear more of your music at
lower volumes if you get a high quality DAC with a low noise floor.

The other big issue is distortion/nonlinearity. This is much less of an issue
than the noise floor, but can still be noticeable on cheap DACs.

It's likely that you can do a lot better than a $5 DAC on both of these
factors.

------
ericzawo
I currently use a Schitt ([http://schiit.com/](http://schiit.com/)) Modi and
Magni stack with my Beyerdynamic DT880 600 ohm headphones. When I tell you
that music is a completely different experience at home with these cans,
believe it. I'm a DJ and honestly prefer staying in and listening to mixes
than going to my mate's parties to hear what they're spinning because they
absolutely obliterate any live system (and I've been to some of the best
venues in North America.) I know it's a poor comparison of course, but I'm
never going back to monitor speakers for personal use again. If you're looking
for a decent AMP/DAC combo, I highly recommend Schiit.

~~~
chroma
NwAvGuy has some not-very-nice things to say about Schiit. Basically, that
they don't know how to design audio gear. He discovered that one of their amps
could damage your headphones. For this warning, he was banned from the Head-Fi
forums: [http://nwavguy.blogspot.com/2011/07/banned-at-head-
fi.html](http://nwavguy.blogspot.com/2011/07/banned-at-head-fi.html)

~~~
cthalupa
NwAvGuy has his side of the story, Schiit has theirs.

[http://www.head-fi.org/t/701900/schiit-happened-the-story-
of...](http://www.head-fi.org/t/701900/schiit-happened-the-story-of-the-
worlds-most-improbable-start-up/765#post_10463052)

Personally, I'm extremely satisfied with the variety of Schiit gear I own,
from my work Modi/Vali setup to my home Ragnarok/Yggdrasil

~~~
chroma
I have some issues with Schiit's accounting.

First, that much DC is simply unacceptable, even when removing power from an
amp. Amps don't just lose power because they're deliberately turned off.
Sometimes people trip over a cord. Sometimes, a circuit breaker trips.
Sometimes, the power goes out. Sometimes, batteries die. None of this
circumstances should endanger downstream equipment.

Second, the fix is _extremely_ simple. As Schiit admitted, it took less than a
day to develop and ship boards without this issue. There is only one reason
why a company would sell a device with this problem: incompetence. If they'd
cop to screwing up, I'd respect them. Instead, they dissemble and equivocate.

Third, so _what_ if their own experiment didn't manage to _destroy_ a pair of
expensive headphones? "I can't reproduce this failure." doesn't mean, "This
failure can never happen." The headphones only survived because they were
designed with extremely robust safety factors. Even then, it's quite likely
that Schiit's amp damaged the headphones. 1-2V of DC is _way_ out of spec and
has –in some cases– damaged and destroyed equipment. There is video of
Schiit's amp distorting headphone drivers. That's crazy. No equipment should
be doing that.

Fourth, "other audiophile gear also does it" is not a valid excuse. As NwAvGuy
has shown, Sturgeon's law[1] applies to this stuff. Just because there's lots
of terrible gear out there, that doesn't mean it's OK to produce more terrible
gear.

After reading Schiit's accounting, I'm certain they lack the engineering
knowledge to build safe, effective audio equipment. I think their intentions
are good, but there's simply no excusing such a glaring oversight. In my book,
Schiit is an anti-brand.

1\.
[https://en.wikipedia.org/wiki/Sturgeon%27s_law](https://en.wikipedia.org/wiki/Sturgeon%27s_law)

------
jhallenworld
On the one hand, any loudspeaker amplifier with feedback is going to have very
low output impedance (minimum acceptable damping factor of 20 with an 8 ohm
load or .4 ohms max). So for at home, AC powered use just hook your headphones
to the speaker outputs.

On the other, things do get interesting with low power / battery powered
amplifiers, for example where they use a low power OP-amp for headphone
drivers. For this case, the article is very relevant.

Heh, or get headphones with nearly flat impedance, for example Sony MDR-v600:
[http://www.cliftonlaboratories.com/headphone_impedance.htm](http://www.cliftonlaboratories.com/headphone_impedance.htm)

------
kazinator
Good grief, headphones do not need electrical damping. This is relevant to
large speakers, and only at around their resonant frequency (as mounted in the
cabinet). If you're getting some funny resonance in your headphones,
electrical damping isn't going to do anything; it's a mechanical issue.

------
basicplus2
one further point to keep in mind is the rule for the inductive reactance of a
device (either an amplifiers output or a speakers input) is stated for 1000Hz
which is an old rule for the mid range of audio for the clear hearing of
intelligible speech, and of course the most efficient transfer of energy is
when the output of an amp matches the input of the device it is driving.

To understand a given amp and speaker you also need to know the inductive
reactance for the full range of frequencies you want to use.. so amp and
speaker maybe matched at the rated impedance is at 1000hz but way off at 15khz

