[xnor]

"Data lines, including digital audio, are also frequently balanced, normally using AES/EBU (AES3) with XLR connectors for pro audio."
 
Read the link I posted above.
 
And note how it mentions "pro audio" and "recording" over and over again - so, as far as I can tell, you won't need any of this stuff.

 

[ccbass]

This is going to sound ridiculous, but what a very general impedance where amp'ing is necessary? 
 
Obviously sensitivity is going to vary, but lets say an average of 100db.   What # of ohms is going to provide too much resistance for the average ipod or laptop to drive a headphone?
 
50?  100?  150?

 

[xnor]

Quote:

This is going to sound ridiculous, but what a very general impedance where amp'ing is necessary? 
 
Obviously sensitivity is going to vary, but lets say an average of 100db.   What # of ohms is going to provide too much resistance for the average ipod or laptop to drive a headphone?
 
50?  100?  150?

a) Anything below a few thousand ohms.
b) You mean too little? Some devices struggle with 16 ohm IEMs... (roll-off, crosstalk etc. are the effects)

 

[ccbass]

Quote:

a) Anything below a few thousand ohms.
b) You mean too little? Some devices struggle with 16 ohm IEMs... (roll-off, crosstalk etc. are the effects)

Wait what?
 
Wouldn't higher impedance phones require amps for more voltage input?
 

 

[Sumflow]

  Xnor is there some kind of general rule about this?
Quote:

xnor /img/forum/go_quote.gif  I would set the speakers volume control a bit higher than what you think is your normal listening level, and control the rest from your computer. 

When you have multiple pots like that, what effect will it have on clipping, to run some open and some restricted?

 

[xnor]

Quote:

Wait what?
 
Wouldn't higher impedance phones require amps for more voltage input? [into the headphones]

Sure, but that's not the problem. You said sensitivity of 100 dB at 1 mW, for a 600 ohm headphone that makes 0.77 V. Where you'll need huge voltages is if you want to destroy your headphones, i.e. approach the power rating. Try to put 200 mW into such headphones and you'll see what I mean. That's what higher impedance cans were made for in the first place, ruggedness for studio applications, the ability to plug them into almost any device and use in parallel.

 
Quote:

When you have multiple pots like that, what effect will it have on clipping, to run some open and some restricted?

I don't understand where you're heading but I don't think that there's a general rule. Purists will argue the digital volume control, bit-perfectness etc. but I cannot be bothered to touch the knob every time I want to do volume adjustments, which I do quite often. If you don't just adjust the knob once and you're set.
As for clipping, many recordings touch 0 dBFS regularly so clipping or distortion might occur, depending on your DAC (though, audibility is questionable). Check out the gamma2 DAC anti-clipping mode, which attenuates the digital signal by 2 dB.

 

[ccbass]

I think I'm getting lost in the whole high impedance/high voltage/low current vs. low impedance/low voltage/high current.
 
I just need to think things through.  And my mistake, I think I was thinking about low sensitivity/high impedance phones.
 
 
Even if you can drive headphones without an amp, why do you?  Let's assume the DAC does not come into play here.  Like why do you amp headphones with an iPod even if the iPod can provide enough power? 
 
Quote:

Sure, but that's not the problem. You said sensitivity of 100 dB at 1 mW, for a 600 ohm headphone that makes 0.77 V. Where you'll need huge voltages is if you want to destroy your headphones, i.e. approach the power rating. Try to put 200 mW into such headphones and you'll see what I mean. That's what higher impedance cans were made for in the first place, ruggedness for studio applications, the ability to plug them into almost any device and use in parallel.

 

[xnor]

Quote:

 
Even if you can drive headphones without an amp, why do you?  Let's assume the DAC does not come into play here.  Like why do you amp headphones with an iPod even if the iPod can provide enough power? 

 
A portable device might not have the current drive capabilities your headphones need or provide enough volume. Early iPod models had a quite strong bass roll-off, varying output impedance and generally problems with low impedance head/in-ear phones.
 
When you say "without an amp" you mean without a dedicated/additional amp, because every device with a headphone jack has an amp integrated.
 
Some people swear by expensive iPod modifications, using some kind of line-out combined with an extra portable amp but, imo it's not worth it. If you measure both configurations you probably will get a bit better results on the paper and enough power for eardrum-piercing levels, but I'd rather save the money for better headphones.
 

 

[Ypoknons]

The thing is, if it was down to only power, we'd all be using stepped down speaker jacks or something like that by now. Dampening aside, there's also matter of power supply considerations (Tangent Audio and AMB comment and much on this matter, it's beyond me to judge the accuracy of the opinions), what else is there to consider? 

 

[xnor]

With portable audio the only choice is batteries anyway, so I don't think it matters much. Also, I've yet to see device measurements that indicate problems with the power supply.

 

[ccbass]

Let's say you have the option of two headphones in low and high impedance, such as 50ohms and 600ohms.  Lets also assume that you have an amp that can provide enough voltage and enough current for either phone.  Why would you choose one over the other.
 
From what I can tell, the 600ohm phone is better because the voice coil would respond better with higher voltages.

 

[jcx]

Quote:

if the manufacturer wants they can use the same total weight of copper and with thinner or thicker wire (and a compensating more or fewer turns) give you different impedance - exactly equivalent to designing in an ideal transformer
 
if they go this route then the electro-acoustic response should be exactly the same - same sensitivity in dB re mW, same low frequency resonance and Q - it should sound the same except for the "built in" transformer ratio changing the I,V ratio required from the amp - of course any amplifier output impedance gives different damping ratio unless you can also switch the series output R
 

 

[xnor]

^ This.
 
My choice would depend on a number of things like price, (in)efficiency, player/source you want to use them with etc. With beyerdynamic cans you even have a third (the default) choice: 250 ohms.
 
Beyerdynamic says that their 32 ohm models are made primarily for (weak) portable, battery-operated devices and the 600 ohm models for mains-operated devices for use at home/studio, the 250 models can be used universally. They also say that all models sound the same, which they actually don't, and that the higher impedance models have a better impulse response due to lower mass.
 
However, this can not be generalized. From a technical point of view there are many variables involved that define the impedance, freq. and impulse response. Higher impedance doesn't automatically mean better sound-quality (or lower sensitivity, or harder to drive, or ..). It depends on the construction.

 

[Ypoknons]

Indeed. Going from the specs to the actual sound requires interpretation and assumptions - an interpretation may be wrong or relevant factors can be missed. Despite all the problems with pure subjective listening tests, placebo and bias, I would think it's good practice to at least try and listen to see if the results bear out the technical and theoretical. 

 

[ccbass]

So what you're all saying is that the length of the copper voice coil, the thickness of the driver, the build, etc, all affect how a headphone is going to sound.
 
Wonderful.  I need to get myself to a HF meet.