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Old 9th February 2013, 07:54 PM   #11
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The +8 dB is real... it should be plainly audible in an A/B test.
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Old 9th February 2013, 10:14 PM   #12
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Quote:
Originally Posted by AudioLapDance View Post
I thought the light tone of the thread was apparent?
We are inundated with technically inaccurate assertions here all day, every day, having them presented in a lighthearted manner doesn't make them any more palatable.

So let's look at this...

Quote:
Originally Posted by AudioLapDance View Post

1) Not a problem as stated because what I'm driving is:
909 + lowest dip (120 ohm) = ~1k
And the volume is fine--this is an 'attenuator'!
You're not driving 909 + 120 ohms.

You're still driving 120 ohms, you've just increased the driving (source) impedance by 909 ohms.

Lighthearted huh? LMFAO.
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Old 9th February 2013, 10:46 PM   #13
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Quote:
Originally Posted by counter culture View Post
...
You're not driving 909 + 120 ohms.
You're still driving 120 ohms, you've just increased the driving (source) impedance by 909 ohms ...
I know that and my idea wasn't phrased right. The point I was trying to make is that I'm not in danger of my source resistance eating up all my voltage swing and not getting enough volume. This was the reasoning behind point 1. In my case I'm trying to do that--it's an attenuator.

Quote:
Originally Posted by counter culture View Post
...
We are inundated with technically inaccurate assertions here all day, every day, having them presented in a lighthearted manner doesn't make them any more palatable ...
I didn't realize I was coming across that way.

Quote:
Originally Posted by counter culture View Post
...
LMFAO ...
?

Last edited by AudioLapDance; 9th February 2013 at 10:49 PM.
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Old 9th February 2013, 11:32 PM   #14
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Sure it's attenuating, but ideally the output impedance is close to zero regardless of volume control position.
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Old 9th February 2013, 11:38 PM   #15
Blues is offline Blues  United States
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Quote:
Originally Posted by counter culture View Post
Interesting. The .pdf author credits nwavguy but ignores his recommendations...
Like I mentioned... "...their website and blogs that helped me have a better perspective of what I was trying to accomplish." It does not necessarily mean I agree to all their findings.

The solution is kinda counter-culture, isn't it? Established culture being to add another gain stage, with an input stage that cannot take the full source output voltage, adding a pot to attenuate the input signal so as to not clip the output, an output stage that might not have enough juice to supply a low Z load, cure all that ails it with feedback, and so on...

It's easy enough to give Jeff's suggestions here a try which I encourage all to diy and find out.

Like Jeff said, we have enough output voltage from modern sources we can even afford to lose some by attenuation...
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Old 10th February 2013, 02:22 AM   #16
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I want to stress that the WarpSpeedIER is different in that it has a low value shunt resistance across the headphones which ... changes things. I would like to save that for later or maybe even a different thread.

And yes Blues, the cheesy pictures of the bad hack job circuit were
intended to get people to try ... it can't be worse than mine!

1 ( 8th inch jack.jpg
anywhichway youcan.jpg

See!

Surely you have some old, cut-up RCAs around somewhere and surely you have a 1/8" or 1/4" jack around and surely some 1k resistors and surely some way to crimp/clip/twist/ ... solder even! them together and ... stop calling me Shirley. Hmmm, that joke works better when spoken ...

Try it and see how it sounds! Maybe we could get some real measurements posted ...


We have enough voltage swing with the standard 2Vrms and ... well possibly enough current to drive ~1k ... depends on the particular output stage. I want to focus on points 2 (freq resp) and 3 (lack of damping, distortion).


Anyway to continue with this technically incorrect circuit ...

I just plugged my IERs in! These are one of the inexpensive ones Linkwitz looked at: Sony MDR-EX71SL

Brutal 16 ohms (like a mini speaker?!?) and 100dB/mW

So that's DAC output impedance (~100 ohm), 909 ohm and the nominal 16 ohm IER. My DAC's seeing 925 ohm and so far ... sounds ok?!?

With IERs the case is different, here's an impedance chart of the Sony MDR-EX51:

Sony%252520MDR-EX51%252520impedance%25255B5%25255D.jpg

NwAvGuy: Headphone Impedance Explained
The graph is a bit deceptive, note the scale! As NwAvGuy points out:

WHAT ABOUT TYPICAL EARBUDS? The vast majority of reasonably priced dynamic (not balanced armature) earbuds headphones have a 16 or 32 ohm nominal impedance that might vary by just 1 or 2 ohms. Here's the popular Sony MDR-EX51 which is mostly 17 ohms and rises to 18 ohms at its 5 khz resonance:

So here point 2 falls away because I don't have a wildly swinging impedance to screw up the freq resp.

In fact many headphones don't: you can check at
Learning Center - Build a Headphone Graph | HeadRoom Audio

Here's a bunch
graphCompare.php.png


So with my smooth, 16 ohm impedance IERs plugged in, that leaves NwAvGuy's point 3)

As output impedance increases electrical damping is reduced. The bass performance of the headphones, as designed by the manufacture, may be audibly compromised if there’s insufficient damping. 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.

Reduction of electrical damping leading to:

A) bass "boomy", less controlled
B) worse transient response
c) higher LF rolloff

Two things come to mind:

I need to understand the properties of the headphone element--Qm, Qe and Qt

How pronounced will A, B, and C be under actual conditions?



What do you guys think?

Cheers,
Jeff

Last edited by AudioLapDance; 10th February 2013 at 02:33 AM.
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Old 10th February 2013, 03:44 AM   #17
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Quote:
Originally Posted by AudioLapDance View Post
No Headphone Amp really is best!
No, it's not. You can run some phones in the manner you describe, but in many instances the results will be less than optimum. A lot less than optimum in some instances. You have chosen to highlight a case where the disadvantages are minimized, but this is far from typical.

Quote:
Originally Posted by AudioLapDance View Post
So here point 2 falls away because I don't have a wildly swinging impedance to screw up the freq resp.
No, YOU don't.

Quote:
Originally Posted by AudioLapDance View Post
In fact many headphones don't.
But many do. Which is the whole point.

Quote:
Originally Posted by AudioLapDance View Post
How pronounced will A, B, and C be under actual conditions?
Pronounced enough to be worthy of note, otherwise he wouldn't have bothered mentioning them.

So why don't you tell people, 'You can run your headphones straight off a DAC, but the results may not be good.' - which is the simple truth, which you seem determined to avoid acknowledging, presumably because it would show up this thread for the nonsense it is.

It's not good advice for most people, particularly people with limited technical knowledge. Which is what makes it reprehensible for you to continue to promote it as unequivocally beneficial when you have been explicitly advised that there are circumstances in which, for sound technical reasons, the results may not be good.
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Old 10th February 2013, 04:20 AM   #18
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Dear people, you can run your headphones straight off a DAC, but the results may not be good.

This thread is an attempt to explore why my headphones don't sound as bad as I thought they should when hooked up in this wrong manner.

I'm trying to walk through slowly and address specific points in my particular situation. I'm purposely trying to keep things simple so people with less technical knowledge can see where and why this circuit does and doesn't work in my case.

***Please don't generalize any of my very specific, unmeasured and hastily drawn conclusions to your own headphones or output stages***

There are circumstances in which, for sound technical reasons, the results may not be good.

Perhaps if we technically analyze, listen to, measure and generally explore these circumstances we can make the results less not be good.

If you want you could build this simple Do It Yourself circuit and see ... or hear! Ha! ... what these frequency response variations, undamping, and distortions sound like. You could use this hands-on knowledge to evaluate future projects!


With really bad puns like:

No Headphone Amp really is best! :-)

That don't even make grammatical sense and leave themselves open to wide interpretation and circuits held together with clips and crimps and no measurements this thread may end up being nonsense ! Heck maybe it already is!

But maybe I can learn something. So, any thoughts about impedance, damping and the mechanical and electrical Qs of headphone drivers? In particular, smoother impedance IEMs and more peaky 120 ohm over-the-ear headphones.

Cheers,
Jeff

Last edited by AudioLapDance; 10th February 2013 at 04:45 AM.
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Old 10th February 2013, 04:39 AM   #19
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There's two issues here that tend to get confused, on purpose I believe by some headphone makers, and by Wikipedia.

One is the source impedance expected by the headphones, the other is the load impedance expected by the source.

If headphones with significant variation in impedance with frequency are driven with a source impedance other than what the headphones were tested with, then the frequency response will change with respect to the published data. Some Sennheisers' bass can be emphasised, for example, with a low-impedance source. AKGs, OTOH, appear almost exactly as a pure resistance, so don't care much. The relationship between frequency response and fidelity is a tricky issue for headphones, and I feel the best policy would be to use whatever source impedance the manufacturer used for testing during design.

If the source sees a load much lower than it was designed for, it's output may be distorted...sometimes very badly. Opamps are often not capable of driving headphones directly for example. I guess the "standard" 120 ohm series resistor originated partly for this reason, and partly for safety.
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Old 10th February 2013, 05:20 AM   #20
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Quote:
Originally Posted by PlasticIsGood View Post
.. The relationship between frequency response and fidelity is a tricky issue for headphones, and I feel the best policy would be to use whatever source impedance the manufacturer used for testing during design...
Do you know where to get such info?

Are there any general principles to follow for phones that don't have testing data like old: Sony MDR-EX71SL IEM, AKG311 'ear buds' or really old over-the-ear AKG K301s?

Thanks,
Jeff

Last edited by AudioLapDance; 10th February 2013 at 05:26 AM.
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