Beyerdynamic DT990 Pro - right driver distortion after the headphones 'warm up'

[Guetta]

Hello,
I have very strange issue with my headphones. I have bass distortion at a slightly louder volume on my right headphone driver. Strange thing is that lets say when in the morning I turn up my AMP and listen to the headphones, I can crank the volume all the way up and no distortion or anything on the part of the song where I usually hear the distortion.
After listening to music for a while, I go back to song I mentioned before and turn the volume slightly higher I can hear distortion on my right headphone driver. Left one is perfect and not limiting factor for higher volume. That is happening after the headphones warm up and there is no issue with the driver when they are not used for a while.
I am using them with JDS Labs Atom AMP and Khadas Tone Board DAC.
Can anyone explain to me what is happening here in my case? Why distortion only occurs after using headphones for a while?

 

[solderdude]

Given the power levels in a headphone it is unlikely it is warm-up as the temperature will not increase alarmingly. There is just a few mW.
Perhaps warmth from wearing the headphone is the culprit ?
Chances are the voicecoil is touching the magnet ?

Try a 10Hz test tone (don't play it too loud) and hear whether or not the faulty channel makes noises that should not be there.
Is it also happening on another source/amp?

 

[Guetta]

Given the power levels in a headphone it is unlikely it is warm-up as the temperature will not increase alarmingly. There is just a few mW.
Perhaps warmth from wearing the headphone is the culprit ?
Chances are the voicecoil is touching the magnet ?

Try a 10Hz test tone (don't play it too loud) and hear whether or not the faulty channel makes noises that should not be there.
Is it also happening on another source/amp?

I just tried 10Hz test tone, but I must turn my amp volume up to 3 o'clock to actually hear distortion. At 3 oclock I can hear it on right side but not on left... I never listen that loud but I want to know why left side is not distorting.

 

[Guetta]

I just tried 10Hz test tone, but I must turn my amp volume up to 3 o'clock to actually hear distortion. At 3 oclock I can hear it on right side but not on left... I never listen that loud but I want to know why left side is not distorting.

As I said before, that only appear after headphones are playing music for a while. No distortion lets say first 10 to 15 minutes

 

[solderdude]

It could be the driver, it could be a hair poking through the front and touching the driver.
You can remove the pads, lift the ring and remove the foam disc and listen if that changes things.

When distortion is time related one might also think about the amplifier being the culprit.
Swap L and R inputs on the Atom to check if it is coming from the DAC.

The drivers do not get warm at all. The power levels are too low for this.

When the DT990 is quite old it could also be caused by one of the reverse diodes across the driver. The older DT990's had that (12V zeners in anti-series).

 

[Guetta]

It could be the driver, it could be a hair poking through the front and touching the driver.
You can remove the pads, lift the ring and remove the foam disc and listen if that changes things.

When distortion is time related one might also think about the amplifier being the culprit.
Swap L and R inputs on the Atom to check if it is coming from the DAC.

The drivers do not get warm at all. The power levels are too low for this.

When the DT990 is quite old it could also be caused by one of the reverse diodes across the driver. The older DT990's had that (12V zeners in anti-series).

I bought the headphones 6 months ago and I did not use them very often, maybe 30 min a day. I swapped left and right side on Atom and I can hear distortion coming from same driver as before. With 10Hz tone test I can make them distort even after my components are just turned on, then reverting back to track where I know the distortion should occur and I can hear it... I think there is no anything on the driver because they are basically brand new. The foam white paper disc is so white and clean you can not look at it.

 

[Jimbob54]

I bought the headphones 6 months ago and I did not use them very often, maybe 30 min a day. I swapped left and right side on Atom and I can hear distortion coming from same driver as before. With 10Hz tone test I can make them distort even after my components are just turned on, then reverting back to track where I know the distortion should occur and I can hear it... I think there is no anything on the driver because they are basically brand new. The foam white paper disc is so white and clean you can not look at it.

I cant explain the time lag/ warm up but my 1990 got a right side rattle. Intense respiratory therapy combined with blunt force trauma treatment sorted the problem leading me to conclude it was a follicular intrusion . But then I do have a wiry and unkempt beard.

 

[Objectivist01]

I cant explain the time lag/ warm up but my 1990 got a right side rattle. Intense respiratory therapy combined with blunt force trauma treatment sorted the problem leading me to conclude it was a follicular intrusion . But then I do have a wiry and unkempt beard.

It could be your right ear getting fatigue after some time?

 

[Jimbob54]

It could be your right ear getting fatigue after some time?

Nah, loose hair

 

[Vini darko]

Hi. Try pulling the pads and foam off. Get a very bright light (phones usually have one). Carefully inspect the driver and its grill looking for any debris or lose coil wires. Also see if the glue on the coil looks good if its visible.

 

[Vini darko]

@solderdude any work done by a electronic circuit or mechanical system generates waste heat. So the coil will be expanding. If there's any tolerance issues in the coil gap (burnt glue, burrs, debris for eg) this will cause unpleasantness.

 

[JohnYang1997]

Are you sure it's the headphone itself instead of the right channel of the amp? Have you tried other amps/dacs?
At least you can swap left right of dac to amp cable to rule out the dac. Then you need to find a way to check your amp. Try leaving the amp on overnight without 990pro connected.

 

[solderdude]

@solderdude any work done by a electronic circuit or mechanical system generates waste heat. So the coil will be expanding. If there's any tolerance issues in the coil gap (burnt glue, burrs, debris for eg) this will cause unpleasantness.

We are talking mW here... so a temp rise of 1 degree... perhaps. This is not a woofer voicecoil which can get very hot as is has to dissipate many watts.

I think the driver will warm up substantially more from radiated heat on the head then the mW.

I bought the headphones 6 months ago and I did not use them very often, maybe 30 min a day. I swapped left and right side on Atom and I can hear distortion coming from same driver as before. With 10Hz tone test I can make them distort even after my components are just turned on, then reverting back to track where I know the distortion should occur and I can hear it... I think there is no anything on the driver because they are basically brand new. The foam white paper disc is so white and clean you can not look at it.

Looks like a production flaw in that case. It should still have warranty. Return it with a a clear fault description and ask for a replacement.

 

[Objectivist01]

We are talking mW here... so a temp rise of 1 degree... perhaps. This is not a woofer voicecoil which can get very hot as is has to dissipate many watts.

I think the driver will warm up substantially more from radiated heat on the head then the mW.



Looks like a production flaw in that case. It should still have warranty. Return it with a a clear fault description and ask for a replacement.

In that case how is the sound returning to normal at a cold start again?

 

[Jimbob54]

In that case how is the sound returning to normal at a cold start again?

We dont know what the sound is so we cant explain anything yet. As JohnYang1997 says , rule out the amp, rule out a hair or other foreign object in the driver.

What you're left with is unexplained issue somewhere in the cup. Even if its mechanical and heat related (which is doubtful), its still a fault- return and replace

 

[F1308]

I have no idea about guarantee being affected, but have a try placing the headset in the fridge, allow it to cool and
then play again to check if as temperature rises you hear the distortion again. No need to measure temperature every three minutes, just see if the distortion comes back after those ten minutes or after half an hour...
It has previously been done hereabouts with a loudspeaker that was tested at different ambient temperatures to show how the sound improved as temperature rised...

https://www.audiosciencereview.com/...eumann-kh80-dsp-monitor-measurements-3.14637/

 

[Guetta]

It happens only on really loud volume, driver is rattling at bass part.

Yesterday I disassembled the driver and it is perfectly clean, no dust or anything. I almost broke it completely during disassembly process. Won’t ever do it again.

 

[F1308]

It happens only on really loud volume, driver is rattling at bass part.

Yesterday I disassembled the driver and it is perfectly clean, no dust or anything. I almost broke it completely during disassembly process. Won’t ever do it again.

Next try is keeping things as they are and hear the very same tracks but placing the left can on your right ear and the right hand one on your left ear. Let's hope it is not your timpani ringing, given the LOUD volumes you are talking about.
It once happened to me on both ears while checking Tchaikovsky's music on my then new gear.

 

[solderdude]

I would simply have returned it when it was still under warranty when all other things were ruled out.
There can always be poor drivers slipping through quality control.

I would assemble it again and see if it still happens. Maybe that is enough to get rid of this problem ?

 

[F1308]

Let us know, please...!!!!