[kwkarth]

Quote:

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.

I can't believe you can't see this.  I'm afraid you're the one who's missing the point here.  In our scenario here in this thread we're not interested in calculating xmax for a given driver diameter in a vented or sealed box in order to produce a given SPL at a given frequency.  We're not interested in output SPL in this exercise.  You are misappropriating or misapplying this tool, and apparently do not fully understand what's going on here.  If this missal doesn't get through to you, just forget it.I'm sure there are others who understand what I'm saying.
 
 

 

[kwkarth]

Quote:

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.

You have a point here.  Power outages...  I'll have to test that scenario and see what happens.  It's potentially different than flipping off the switch.
 
 

 

[nwavguy]

Quote:

I can't believe you can't see this.  I'm afraid you're the one who's missing the point here.  In our scenario here in this thread we're not interested in calculating xmax for a given driver diameter in a vented or sealed box in order to produce a given SPL at a given frequency.  We're not interested in output SPL in this exercise.  You are misappropriating or misapplying this tool, and apparently do not fully understand what's going on here.  If this missal doesn't get through to you, just forget it.I'm sure there are others who understand what I'm saying.
 
 

 
This really does matter a lot in how risky the Asgard is to headphones. So, if you would, please answer the following two questions:
 
Is your original statement that a slower power off transient is less risky to headphones than a faster one correct?
 
Is your original statement that the driver will move the same distance, for a given voltage, regardless of the duration of the transient also correct?
 
 
 

 

[kwkarth]

Quote:

This really does matter a lot in how risky the Asgard is to headphones. So, if you would, please answer the following two questions:
 
Is your original statement that a slower power off transient is less risky to headphones than a faster one correct?
 
Is your original statement that the driver will move the same distance, for a given voltage, regardless of the duration of the transient also correct?

I am not disputing that the turn off thump should be avoided when possible.  I don't have an issue with it because I unplug my headphones before I turn the amp off.
In this case of a 4Hz half cycle making the driver move farther or less far than an instant DC transient spike of exactly the same amplitude, yes, the DC spike could conceivably do more damage to the driver than the 4Hz half cycle because of potential driver overshoot due to its moving mass.  Its excursion could conceivably be farther and the voice coil former could potentially be damaged by physically bottoming out at a high velocity against the magnet pole piece back.  In both cases we're talking about the exact same signal amplitude.
 
 

 

[SpaceTimeMorph]

Just to add my two cents here... if the hypothetical power outage was due to a fault that caused auto-recloser actuation of the supply breakers feeding your part of the grid, then you could potentially have some superposition of whatever voltage was felt at the headphones (since I'm assuming it is an LVR-type load), which would exacerbate the problem greatly.

 

[kwkarth]

Quote:

Just to add my two cents here... if the hypothetical power outage was due to a fault that caused auto-recloser actuation of the supply breakers feeding your part of the grid, then you could potentially have some superposition of whatever voltage was felt at the headphones (since I'm assuming it is an LVR-type load), which would exacerbate the problem greatly.

right

 
 

 

[Joe Bloggs]

No headphones I know of has anything remotely resembling flat frequency response down the a few Hz, certainly not DC.  So no, this calculator wouldn't be very accurate.  Call it a worst case estimate?
 
Quote:

 
I'm not trying to confuse the masses. I'm trying to be clear about potentially misleading statements you have made:
 
 "The driver excursion travel would be the same distance, regardless of the period of the signal applied."
 
The above is simply not true. That's why I provided the information on excursion vs frequency. My "little demo link" is valid and applicable. With a reasonably flat frequency response a constant input power gives a constant output power regardless of frequency. So SPL is directly proportional to voltage in that calculation.
 
And this generalization of yours is also misleading:
 
"100mW of power for less than 0.25 seconds.  That's not enough energy to harm any full size headphone I know."
 
It's not the energy in terms of thermal heating that's the problem here. It's how much voltage does it take to reach the driver's safe excursion limits (technically known as Xmech). And that's going to be very headphone specific so it's rather impossible to say it's not enough to cause harm across a wide range of headphones.
 

 

 

[Joe Bloggs]

And to take the same point further, a a 4Hz half cycle would move the driver further than a 1kHz half cycle for the same voltage, yes?
 
The calculator nwavguy posted can be used accurately if you take into account the frequency response of the phones.  Say you know that the response of the phones would be 50dB down from 1kHz at 4Hz--for the default parameters you still get Xmax = 1.5mm@4Hz, 70dB vs Xmax = 0.007mm@1kHz, 100dB.
 
Quote:

I am not disputing that the turn off thump should be avoided when possible.  I don't have an issue with it because I unplug my headphones before I turn the amp off.
In this case of a 4Hz half cycle making the driver move farther or less far than an instant DC transient spike of exactly the same amplitude, yes, the DC spike could conceivably do more damage to the driver than the 4Hz half cycle because of potential driver overshoot due to its moving mass.  Its excursion could conceivably be farther and the voice coil former could potentially be damaged by physically bottoming out at a high velocity against the magnet pole piece back.  In both cases we're talking about the exact same signal amplitude.
 
 

 

 

[kwkarth]

Quote:

No headphones I know of has anything remotely resembling flat frequency response down the a few Hz, certainly not DC.  So no, this calculator wouldn't be very accurate.  Call it a worst case estimate?

 
This calculator is a complete non-sequitur.

 

[kwkarth]

Quote:

And to take the same point further, a a 4Hz half cycle would move the driver further than a 1kHz half cycle for the same voltage, yes?
 
The calculator nwavguy posted can be used accurately if you take into account the frequency response of the phones.  Say you know that the response of the phones would be 50dB down from 1kHz at 4Hz--for the default parameters you still get Xmax = 1.5mm@4Hz, 70dB vs Xmax = 0.007mm@1kHz, 100dB.

No, it cannot be used to determine driver excursion based upon frequency alone.  Its purpose is to determine required driver size/number of drivers needed for a vented or sealed box subwoofer enclosure while maintaining a given SPL at a given frequency.  It has nothing to do with the issues we're discussing in this thread.  Even when using it for building a subwoofer, it does not take into account the acoustic volume of the room one is designing it for.
 

 

[Joe Bloggs]

 
Quote:

No, it cannot be used to determine driver excursion based upon frequency alone.  Its purpose is to determine required driver size/number of drivers needed for a vented or sealed box subwoofer enclosure while maintaining a given SPL at a given frequency.  It has nothing to do with the issues we're discussing in this thread.  Even when using it for building a subwoofer, it does not take into account the acoustic volume of the room one is designing it for.
 

The calculator is supposedly accurate for sealed-box / infinite baffle arrangements, ie, no augmentation to the FR from the enclosure--could be translated to open headphones?
Not taking into account of the room acoustics--isn't that good for our purposes, since there's no room to take account of with open headphones?
 
Anyway, regardless of the accuracy of the calculator, do you agree that driver excursion generally goes up for the same voltage as the frequency goes down?

 

[kwkarth]

Quote:

 


The calculator is supposedly accurate for sealed-box / infinite baffle arrangements, ie, no augmentation to the FR from the enclosure--could be translated to open headphones?
Not taking into account of the room acoustics--isn't that good for our purposes, since there's no room to take account of with open headphones?
 
Anyway, regardless of the accuracy of the calculator, do you agree that driver excursion generally goes up for the same voltage as the frequency goes down?

No, not if the following conditions are met;
 

• We're talking about standard 20-20kHz spectrum
• It's a well designed, low mass headphone driver
• SPL output capability has nothing to do with our considerations.
• Power level is kept constant, regardless of frequency.

 
You see, the misapplication of that calculator has everything to do with the fact that SPL output is an important part of their design criteria, and has no bearing on our situation.  In our scenario, we are very much concerned with how much power or energy we're putting into the driver.  In the subwoofer calculator, it's not even a considered criteria.  Reason is that the primary purpose for the calculator is to help a designer choose the right driver/drivers for a sub system based upon the constraints of driver size and x-max capability while meeting specified SPL output criteria.
 
 

 

[kwkarth]

Life isn't always like this;
 

 
Just because you have a shiny new hammer, not every problem happens to be a nail.

 

[Joe Bloggs]

But if you don't know anything about the driver design and only know the voltage applied, you won't know the driver excursion either.
 
My reasoning was thus:
1. a driver with flat frequency response would give the same dB SPL at the same volatage no matter what frequency it is applied at and the driver excursion would be as given in the calculator if the enclosure assumptions are met (no mention of the "subwoofer" on the page, I agree it's a speaker-centric page, however open headphones should be effectively equivalent to infinite baffle)
2. when a frequency response chart if measured like this

It is done my driving the headphones with tones of different frequencies of the "same voltage"
http://www.headphone.com/learning-center/about-headphone-measurements.php
 
3. Therefore, when you drive the K701 with a tone at 1kHz and another tone at 10Hz and you reach, say, 30dB SPL with the 1kHz tone and 20dB SPL (less 10dB) with the 10Hz tone, you know that you have driven them with equal voltage although you don't know what that voltage is--because 10dB is the difference between 1kHz and 10Hz on the graph.  (not strictly accurate because this graph is measured through a dummy head;  if the graph were measured through a simple acoustic coupling this should be accurate)
 
Knowing the frequency response you can convert from dB SPL to voltage and vice versa while solving for the driver excursion relative to different frequencies;  without the frequency response you wouldn't be able to solve for the driver excursion no matter whether you start with dB or volts.
 
As for your four conditions
"

• We're talking about standard 20-20kHz spectrum
• It's a well designed, low mass headphone driver
• SPL output capability has nothing to do with our considerations.
• Power level is kept constant, regardless of frequency."

 
1st 3 criteria should be met with the Asgard / K702 problem.  But for the 4th I really think you mean "voltage" is kept constant?  For the same voltage power will be different at different frequencies unless the impedance curve of the drivers is one flat line?

 

[nwavguy]

Quote:

No, not if the following conditions are met;
 

• We're talking about standard 20-20kHz spectrum
• It's a well designed, low mass headphone driver
• SPL output capability has nothing to do with our considerations.
• Power level is kept constant, regardless of frequency.

 
You see, the misapplication of that calculator has everything to do with the fact that SPL output is an important part of their design criteria, and has no bearing on our situation.  In our scenario, we are very much concerned with how much power or energy we're putting into the driver.  In the subwoofer calculator, it's not even a considered criteria.  Reason is that the primary purpose for the calculator is to help a designer choose the right driver/drivers for a sub system based upon the constraints of driver size and x-max capability while meeting specified SPL output criteria.
 
 

 
The only reason any of this is matters is you were trying to convince people they didn't have to worry about the Asgard transient as it was long and slow. And I still maintain that's not true. A brief fast transient will result in less driver excursion (and also less thermal dissipation).
 
As I said I can take my bench power supply and ever so slowly and gently ramp up DC into any headphone until they're damaged. The driver will still bottom out despite the gentle ramp. But I can probably apply that same "lethal voltage" to the same headphones for 1 mS and they'll easily survive.
 
Next time I'm at one of the shows with the headphone vendors I will make it a point ask them about turn on/off transients and what sort of damage they've seen, etc. We already have an answer from AKG that even a few tenths of a volt can be dangerous.
 
The issue with the calculator that Joe and I have been trying to get across is SPL is proportional the the voltage applied. So just because SPL is involved doesn't render the whole thing irrelevant as you keep suggesting. I was only offering it as evidence excursion decreases with increasing frequency. The calculator is assuming flat frequency response. So 1 volt at 5000 hz is 105 dB SPL and 1 volt at 50 hz is still 105 dB SPL. But the 50 hz example will result in far more excursion for the same voltage than 5000 hz. I wasn't suggesting trying to use the calculator to provide the exact mm of excursion.