[xnor]

kwkarth, the problem here is the mechanical clipping. If that would happen during normal operation you'd hear very nasty noises coming from the drivers - for a good reason, the diaphragm is not supposed to travel that far into one direction. Whether damage is done to the drivers or not, well, we can only guess but it is something which is very valid to be concerned about.

 

[kwkarth]

 
Quote:

kwkarth, the problem here is the mechanical clipping. If that would happen during normal operation you'd hear very nasty noises coming from the drivers - for a good reason, the diaphragm is not supposed to travel that far into one direction. Whether damage is done to the drivers or not, well, we can only guess but it is something which is very valid to be concerned about.

I understand what you're saying.  I don't believe, in the case of the AKG K701, that any damage occurs to the headphone.  Virtually every headphone I have has been plugged into the Asgard.  By habit, I reduce volume to min and unplug the headphone from the jack before I turn the amp on or off.  Most high performance equipment has required this sort of treatment, so I just do it as a matter of course.
 
I'm beginning to realize, however, that we have a new generation of audiophiles coming on the scene now, that expect ipod simplicity from their audio systems. 
 
As far as mechanical clipping goes,  I do not think x max was reached in the case of the k701.
 

 

[Shike]

Once again, whether the mechanical clipping was or was not reached is up for debate.  However, the fact that AKG said not to use the headphones with even a fourth the transient is a clear answer that the headphones shouldn't be exposed to it regardless if it can be helped.
 
How one goes about that is up to the individual.

 

[kwkarth]

Quote:

Once again, whether the mechanical clipping was or was not reached is up for debate.  However, the fact that AKG said not to use the headphones with even a fourth the transient is a clear answer that the headphones shouldn't be exposed to it regardless if it can be helped.
 
How one goes about that is up to the individual.

Just to remind you and hopefully put your mind somewhat at ease, the "transient" that the K701 was subjected to was not really a "transient" in the classical sense.  It was a DC offset drift which occurred as a soft ramp up and then down.  Had it been a true transient, it might possibly have damaged the headphones.
 
 

 

[nwavguy]

 
Quote:

Just to remind you and hopefully put your mind somewhat at ease, the "transient" that the K701 was subjected to was not really a "transient" in the classical sense.  It was a DC offset drift which occurred as a soft ramp up and then down.  Had it been a true transient, it might possibly have damaged the headphones.

 
The above is very misleading. DC is dangerous to headphones. Period. AKG has told Shike even about a tenth as much as you measured could be dangerous. The issue is the driver excursion and just because the transient (or whatever you would like to call it) happens slowly and "softly" doesn't mean it's safe for the driver. Sufficiently fast and quick (say 1 mS) would be much safer.
 
I can slowly ramp up a DC voltage to any headphone and kill it. Stop trying to sugar coat the truth here when people's headphone are at stake.
 
Jason from Schiit has responded in a way that's about as good as can reasonably be expected. And that's great. But everyone should take this issue seriously and not try and sweep it under the rug.
 

 

[maverickronin]

Quote:

I'm beginning to realize, however, that we have a new generation of audiophiles coming on the scene now, that expect ipod simplicity from their audio systems. 

Or maybe they expect basic safety precautions?  Even if you remember to do that sort of thing every time it won't do you any good if the power goes out.
 
So far I'm withholding judgement on this particular example but if a piece of equipment like this can't safely work with nearly any pair of electrodynamic headphones then it should at least come with some rather stern warnings and recommendations.

 

[kwkarth]

Quote:

 
The above is very misleading. DC is dangerous to headphones. Period. AKG has told Shike even about a tenth as much as you measured could be dangerous. The issue is the driver excursion and just because the transient (or whatever you would like to call it) happens slowly and "softly" doesn't mean it's safe for the driver. Sufficiently fast and quick (say 1 mS) would be much safer.
 
I can slowly ramp up a DC voltage to any headphone and kill it. Stop trying to sugar coat the truth here when people's headphone are at stake.
 
Jason from Schiit has responded in a way that's about as good as can reasonably be expected. And that's great. But everyone should take this issue seriously and not try and sweep it under the rug.

As far as I know, no one is trying to sweep this under the rug.  Please stop trying to obfuscate the facts of this matter by inciting riot.  Get your scope out and measure the phenomena for yourself and report on what the period of this sine wave is.  It's period is about 0.25sec.  So it should be one half cycle at around 4Hz
 
 

 

[nwavguy]

Quote:

As far as I know, no one is trying to sweep this under the rug.  Please stop trying to obfuscate the facts of this matter by inciting riot.  Get your scope out and measure the phenomena for yourself and report on what the period of this sine wave is.  It's period is about 0.25sec.  So it should be one half cycle at around 4Hz
 

I'm only trying to keep this factual. You're the one who keeps making statements that are just flat wrong which is the real obfuscation going on.
 
Yes, the transient is around 4 hz. And at 4 hz the driver will have massively greater excursion, for the exact same input voltage, as it would at say 1000 hz.
 
This means a fast transient is actually much less likely to be harmful, not the other way around as your previous post implies. I'm happy to provide all the math to prove this beyond any doubt if you'd like? But I'm trying keep this as simple as possible.
 
 

 

[kwkarth]

Quote:

I'm only trying to keep this factual. You're the one who keeps making statements that are just flat wrong which is the real obfuscation going on.
 
Yes, the transient is around 4 hz. And at 4 hz the driver will have massively greater excursion, for the exact same input voltage, as it would at say 1000 hz.
 
This means a fast transient is actually much less likely to be harmful, not the other way around as your previous post implies. I'm happy to provide all the math to prove this beyond any doubt if you'd like? But I'm trying keep this as simple as possible.

If you will refer to your link again, you may notice that xmax is more predicated upon the acoustic coupling of the driver(s) to the air to produce a given SPL.  In our case here, SPL has NOTHING to do with our conversation.  In our case xmax limiting for a given frequency is determined by driver mass and hysteresis and has nothing to do with maintaining any given SPL.
 
 

 

[nwavguy]

Quote:

If you will refer to your link again, you may notice that xmax is more predicated upon the acoustic coupling of the driver(s) to the air to produce a given SPL.  In our case here, SPL has NOTHING to do with our conversation.  In our case xmax limiting for a given frequency is determined by driver mass and hysteresis and has nothing to do with maintaining any given SPL.
 
 

Your wrong. If you look at the math below the calculator box in the link I provided you'll see driver displacement (excursion, travel, Xmax, etc.) is a function of FREQUENCY. For a constant input (voltage), as you lower the frequency, the driver excursion will increase until you reach the limits of the driver. That's just fact and very applicable to this issue.
 
Put as simply as possible: A 1 mS 2 volt transient will move the driver a much smaller distance than a 250 mS 2 volt transient. If you don't believe that I'm sorry.
 
 

 

[Steve Eddy]

Quote:

Originally Posted by nwavguy /img/forum/go_quote.gif
 
For a constant input (voltage), as you lower the frequency, the driver excursion will increase until you reach the limits of the driver. That's just fact and very applicable to this issue.
 

 

Um, if that's the case, then ANY DC voltage (can't get any lower in frequency than DC) should cause the cone to excurse to its limits.
 
I've never known that to be the case. A varying DC voltage causes the cone to excurse a varying amount depending on level.
 
se
 
 
 

 
 

 

[nwavguy]

Quote:

Um, if that's the case, then ANY DC voltage (can't get any lower in frequency than DC) should cause the cone to excurse to its limits.
 
I've never known that to be the case. A varying DC voltage causes the cone to excurse a varying amount depending on level.
 
se
 

Steve, you make a good point and I'm over simplifying. The excursion is actually influenced by the stiffness of the suspension, the mass of the diaphragm, and the acoustic loading on the diaphragm. At different parts of the frequency spectrum different things dominate the excursion calculation and limits. These days speaker design software does all the hard math and just pops out plots of excursion versus frequency. And it's a sharply falling plot.
 
I believe, as a rough guide, below about 3 times the resonance frequency it's roughly an exponential relationship (frequency squared) until the stiffness of the suspension starts to dominate at very low frequencies and at DC it's entirely (obviously) the stiffness of the suspension. For example, the driver moves 4 times as far at 50 hz as it does at 100 hz with same input voltage.
 
Regardless of the complex math, you can put a driver in your hand, sweep it with a signal generator, and you'll see exactly what I'm talking about. And, more to the point, if I set up a half cycle 1000 hz burst on my arbitrary waveform generator, compared to a half cycle 4 hz burst at the same voltage, the difference in driver excursion is huge. I'm sure the drivers in headphones behave somewhat differently but the same basic principals should still apply.
 
The bottom line is the more brief the transient is, for a given voltage, the less risk to the headphones.

 

[Steve Eddy]

 
Well I think for all intents and purposes here it can be looked at as DC.
 
se
 
 

 

[nwavguy]

Quote:

 
Well I think for all intents and purposes here it can be looked at as DC.
 
se
 
 

For the Asgard yes, I agree. And DC is the most dangerous. It's the combination of the level (around 2 volts) and the long duration (around 250 mS) that makes the Asgard a concern. The typical power on/off transient from other headphone amps (which are usually more of a brief "click" around 1 mS), even if they're the same voltage, are much less dangerous.
 

 

[Clayton SF]

Heck. I don't what's going on and don't understand any of this tech talk. All I know is that I bought the Asgard the week it was released. I have used my K701 exclusively with the Asgard. Until I saw the video of the K702 dome inhaling and exhaling my only worry was what my next headphone purchase would be. Since I don't want to keep plugging and unplugging my headphones when turning the Asgard on and off I am going to return it.