Have you tried the "moonbaby's-ex-wife-audio-testing" routine (aka "the loud 'n' ugly" test)?
This is where you run some sort of program material through the phones at a reasonable volume level, being careful to not overdrive the amp section. Is the sound clean and tight on bass notes? Or does it get "farty" and blurry (like the ex!). Chances are that if DC hit the transducers for any extended length of time, you'd have a set of dead 'phones...

fsx wrote: Hello everyone,

I have recently bought a pair of Beyerdynamic DT 770 PRO 80 Ohm, but I noticed that the jack on the audiocard has some DC, and sometimes while keeping the volume high the sound distorted.
Then I plugged my headphones into the mixer to avoid the DC problem, but how can I know if I damaged them already even if the exposition to DC has been just for some days?

Thanks in advance.

I think I said in a reply in your other thread that your symptoms indicated the likely presence of d.c. on the sound card output. Did you verify this? The phones won't have been damaged by that amount of d.c. even if exposed indefinitely. I've used moving-coil headphone earpieces as d.c. servo positioners for exactly the reason that they can work in this way. On the other hand, distorted sound is what you get from cheap soundcards running at high volumes.

I was surprised that the OP used the phrase "I noticed" when commenting on the discovery of the d.c. issue.

Especially after having just read where this point was addressed by you Boswell.

Boswell wrote: [quote=fsx]Hello everyone,

I have recently bought a pair of Beyerdynamic DT 770 PRO 80 Ohm, but I noticed that the jack on the audiocard has some DC, and sometimes while keeping the volume high the sound distorted.
Then I plugged my headphones into the mixer to avoid the DC problem, but how can I know if I damaged them already even if the exposition to DC has been just for some days?

Thanks in advance.

I think I said in a reply in your other thread that your symptoms indicated the likely presence of d.c. on the sound card output. Did you verify this? The phones won't have been damaged by that amount of d.c. even if exposed indefinitely. I've used moving-coil headphone earpieces as d.c. servo positioners for exactly the reason that they can work in this way. On the other hand, distorted sound is what you get from cheap soundcards running at high volumes.

Sorry for having written "I noticed" but it was just to cut it short to the point as I wrote in a hurry, in effect it has been you (Boswell) that suggested that, so I should have credited you, but if you want to look at another point of view, it has been my ears that noticed the distortion and you suggested that the symptom might be DC (but I'm just kidding here :)). I have rerouted the audio card to the mixer as written in the other post and the problem vanished, plugging the headphones jack to the mixer's phone output. Anyway I think you're right about DC because in other devices it didn't pop at all, I'll measure it as soon as I will have a multimeter.

Sorry again Boswell if I offended you with such omission. And thanks to Space for letting me acknowledge my mistake.

There was no question of offence - it was merely amusement. I was worried that you were getting hung up on whether you had done permanent damage to your headphones. They will happily sit passing that amount of d.c. for as long as you can afford to pay your electricity bill.

thank you very much :), is it the same for the dreaded "turn-off bump", while there is a loud bump when turning off something like a computer or an amplifier? I mean, can this damage the headphones or speakers?

That bump can and probably will.
(When coupled with DC offset it's more dangerous because the speaker is already off-centre, meaning it's more easy to push it too far)

Codemonkey wrote: That bump can and probably will.
(When coupled with DC offset it's more dangerous because the speaker is already off-centre, meaning it's more easy to push it too far)

uhm ok, now I'm paranoid... if it happened just one time can this have damaged already the speaker? should I be able to check for damages with a simple sweep? or am I nervous for nothing? :shock:

It won't so much get damaged over a period of time, it's more likely to one day, go entirely, if you keep having spikes through it. You could turn down the signal, unplug them and then power off...
(or power off the speakers/amp separately if possible).

Imagine you're strapped in a chair, at some sort of theme park. It's static, then suddenly it flies forward 20 feet towards a brick wall with great intensity, then backwards 40 feet, then forwards 30 feet before slowly going back to it's original position. That's what the speaker cone does.

fsx wrote: thank you very much :), is it the same for the dreaded "turn-off bump", while there is a loud bump when turning off something like a computer or an amplifier? I mean, can this damage the headphones or speakers?

The thump is a totally different animal, and in an extreme form is quite capable of blowing out loudspeaker cones or headphone diaphragms. Again, a rule of thumb is that if you can tolerate the noise when wearing the phones or listening to the speaker, it's probably not damaging the transducer. And again, it's not a cumulative effect, so many thumps of a medium amplitude are not going to add up to one damaging big thump.