[analogsurviver]

Quote:

If a product changes 20dB in 48 hrs, there are a few problems.  
 
1.  The material used in the headphones may be unstable. That much change in that short a time may indicate that the material hasn't reached its final state yet. If some aspect of response showed a 20dB change after 48 Hours of undefined "conditioning", it's possible they will continue to change significantly for a very long time. The problem is, nobody would purposely engineer a product that would change beyond normally accepted tolerance of say +/- 3dB...and even that's a whole lot..for the useful life of the product.  That's just poor engineering and materials selection.
 
2.  The conditioning signal may have over-stressed the materials beyond design limits.  You could for example condition your headphones in a way that would result in a 90dB change, but that would be damaging them with high power.  We could be into the edge of that damaging area.
 
3.  There are only two data points here: the starting condition and the ending condition.  Two data points are not even enough to define a trend, much less any useful rate of change information.   For a proper evaluation of the effects of conditioning, there should have been periodic tests a regular intervals.  
 
4.  There was, as I mentioned before, no "control" to the experiment.  No means of verifying that the test or measurement conditions didn't change.
 
5.  There was no mention made of a measurement made after a significant period of "rest" or "cool down" after the conditioning.  The entire effect could have been the result of deep heating, and that test would have shown that effect.  Perhaps the headphones revert after a period of time.
 
6.  There was mention made of 3Hz and 1Hz changes, which are way out of the design parameters for any headphones.  If that's the area where these huge change occurred, they could be indeed related to material fatigue, but a 20dB change at 3Hz is well into the areal if inaudibility.  
 
Just a few thoughts, not really meant to shoot down the test because we haven't seen the results yet.  But before I would place a whole lot of faith in the generalized concept of "conditioning", I personally would want to know a whole lot more.

All your considerations are valid. I would have liked to have permanent acces to measuring setup, to verify all your ( and mine as well ) doubts. Just for point 6 - area of change with 20 dB was (approx, give or take a Hz or two ) 30 Hz ( thirty hertz ), not 3 Hz, definitely audible and within design parameters and frequency response specification.
 
Point 5 is the most interesting to me. No they definitely do not revert back to starting condition - audible beyond any doubt. But I would like to know if they do, by how much and after how much time. That would require permanent acess to measuring setup - and that is $$$ beyond my means. Tyll can justify such ( or similar, he has basically Audio Precision setup, which gets calibrated - you guessed it - with Bruel & Kjaer equipment  ) expenditure; he sells headphones in one ( if not the one ) of the most lucrative markets on the planet. Slovenia has 2 million souls give or take a few - even if it had ten times the income of the USA, it would most probably not make economic sense, let alone at an income it has and the crisis it is in. 
 
Simple purpose of the whole thing is to squeeze maximum performance from the existing designs. How many headphones that have extended frequency response in bass with an acceptable distortion do you know ? If the diaphragm is too stiff ( almost all as manufactured are ) for the proper extension in bass, at - 20, -10 or - 6 dB say at 30 Hz it does not matter much - it is all too low and "inaudible". Listerners will usually report of a midbass hump in such cases. There are cases with bass response to be in + dB range relative to midrange, but that is rather rare, particularly in really low frequency range, say below 30 Hz. But they do exist. It would be wrong to burn these in any further, as it would compound the problem.
 
I remember my introduction to the equalizer - a friend had Phase Linear speakers with subwoofer. That speaker goes quite low. For the good relationship with neighbours, he set the 20 ( or was it 16 ) Hz at - 1 dB. At that setting, I thought the bass not to be significantly better than my incomparably more modest speakers. Set it for flat, that is to say to 0 dB or only 1 dB difference, produced a private earthquake. And neighbours banging at his doors.
 
If 1 dB  at 20 ( 16 ) Hz is that audible ( even if it was at such "lucky" point to make such huge perceived difference ) - imagine 3, 6, 10, 20 dB...
 
I would have liked headphones ( or anything else ) coming from the  manufacturer in a "finished" condition. But burn in in audio is unfortunate fact of life - visit any audio fair/exhibition, ask any distributor/importer, whether it was or not a good idea demonstrating a totally new "whatever" that they barely menaged to get from customs etc in time in order to be possible to demonstrate it at all. Most will, if honest, reply that it would have been better to have a totally new unit with zero play time on static display only. I do not believe in toooooo much burn in time  stories - but zero play time components just do not sound right. One can shoot oneself in foot by demonstrating zero playtime component - what good does it make to write later on the website that after say 100 hours it came to itself, when countless visitors to the show heard it waking up from zero ? Usually, second chance to present such a product in its proper light comes at the same show - next year  - you can bet that competition can and will in the meantime capitalize on such an error.

 

[Tyll Hertsens]

Quote:

 Tyll can justify such ... expenditure; he sells headphones in one ( if not the one ) of the most lucrative markets on the planet.

 
FYI, I no longer work or have any interest in HeadRoom's operation.

 

[xnor]

Quote:

Unfortunately not. After one driver of HA-S770 failed, I reverted the remaining measurements to HA-S500.

That's why I hoped for THD+N measurements. Maybe there was some damage done to the S500 driver as well, not a complete failure of course, but maybe the suspension or the diaphragm was stressed too much during burn-in.
 
From the gr-research site posted before, Dan Wiggins responds:
"The biggest reason there is a break-in period for drivers is the spider. The spider - for those who don't know - is a piece of cloth, permanent pressed, and dipped in epoxy. When you break in a driver, you introduce micro-cracks throughout the epoxy, which will make the spider softer."
 
Afaik there is no spider in a headphone driver. The surround is responsible for both keeping the diaphragm centered and providing the suspension. And for many headphone drivers I'd argue that the suspension is not made for large diaphragm movement.
If you play test tones (especially sine waves are tough) too long and too loud the driver could fail, the diaphragm could lose its stiffness (AKG driver vs Asgard DC spike video anyone?), the surround could get damaged ...
 
If no damage occurred it makes no sense that we'd see huge (20 dB as you said) differences. If it makes sense to you please explain how and why.

 

[jaddie]

Quote:

All your considerations are valid. I would have liked to have permanent acces to measuring setup, to verify all your ( and mine as well ) doubts. Just for point 6 - area of change with 20 dB was (approx, give or take a Hz or two ) 30 Hz ( thirty hertz ), not 3 Hz, definitely audible and within design parameters and frequency response specification.

Your observations are unique.  Others show much less change:
http://www.innerfidelity.com/content/evidence-headphone-break
 
Quote:

Point 5 is the most interesting to me. No they definitely do not revert back to starting condition - audible beyond any doubt. But I would like to know if they do, by how much and after how much time. That would require permanent acess to measuring setup - and that is $$$ beyond my means. Tyll can justify such ( or similar, he has basically Audio Precision setup, which gets calibrated - you guessed it - with Bruel & Kjaer equipment  ) expenditure; he sells headphones in one ( if not the one ) of the most lucrative markets on the planet. Slovenia has 2 million souls give or take a few - even if it had ten times the income of the USA, it would most probably not make economic sense, let alone at an income it has and the crisis it is in. 

 
You don't need to invest much at all accomplish differential measurements.  You don't need an exotic test system, a decent sound card and free software would be fine.  A test mic with at least some low frequency response is required, but those can be had very cheaply, Panasonic electret capsules are under $5.  REQWiz is free.  If you pick out the right hardware there are existing calibration curves that make the system quite accurate in the absolute, but that's not required at all for differential testing.  
 
You don't even need a simulated ear.  Just a way to reliably and repeatably position a headphone over a mic and get the pad to seal around it.  You're looking for a difference, not an absolute measurement.  No need for AP or B&K.  
 
The important part of testing like this is good scientific method, and lots of data.  That's an investment in time, not money.  There's already been enough information in this forum for anyone to design a thorough and scientific test regimen at almost no cost for the analysis system.  The cost is in the headphones themselves, and the time it takes to run the tests and analyze the data.

 

[jaddie]

Quote:

If you play test tones (especially sine waves are tough) too long and too loud the driver could fail, the diaphragm could lose its stiffness (AKG driver vs Asgard DC spike video anyone?), the surround could get damaged ...
 
If no damage occurred it makes no sense that we'd see huge (20 dB as you said) differences. If it makes sense to you please explain how and why.

I would hypothesize that damage of this nature is cumulative, and the degree of damage (or conditioning) would follow the usual exponential decay curve where 66% of the damage occurs in a relatively short time, the balance much more gradually.  The total time length of the curve would be related to specific power delivered to the driver, following the inverse curve to the point where above a certain point the damage happens very quickly and extends to destruction.  
 
Oh well, just a hypothesis, I'm not going to try to prove it on any of MY headphones! 

 

[xnor]

I don't think so. If the voice coil is the weak part and it overheats then of course it will fail fairly quickly. But if the excursion limit is just reached all that might happen is that the stiffness of the diaphragm deteriorates. Remember the focal spirit one post at IF with the crinkled diaphragm? The headphone still basically worked but the THD+N measurement results went crazy.

 

[jaddie]

Yes, true.  It gets down to getting more and better test data.

 

[analogsurviver]

 @ everybody : Will translate and publish ASAP - some recordings in the pipeline that have priority.
 
I agree one can use Panasonic WM61A mic/soundcard approach etc - and will go that route in the future. Based on the THD+N measurement of HA-S500 after LOTS of everything, I definitely do not think driver has developed more distortion - it is crazy low in absolute terms, not just for this price range.
The only exception is region below 100 Hz at 100 dB SPL, but that is normal with 40 mm driver.
 
Yes, in headphones there is no spider and all the movement is governed by the corrugated "surround" that is still one piece with the rest of the diaphragm - and it is in this corrugated  section most ( all ? ) the changes must happen. If one blows gently to the diaphragm of a new out of the box hp driver, there usually will be no displacement. Merest breath on burnt in driver will usually result in displacement - compliance of that surround must have changed to a much higher value - allowing greater extension in the bass.
 
The signal used is high - but not enough to cause thermal demage. It is the frequency that is made as low as it can get to generate as high excursion as it can get that does the trick - 1 Hz ( one hertz ) square wave at 2.5 V peak to peak amplitude WITH NO VISIBLE SAGGING as seen on the DC input of an oscilloscope - with no DC component, as measured directly on the drivers/hp input cable. If you feel that square wave does not contain enough high frequencies for burning in, you can superimpose some pink or white noise of lower intensity upon the basic square wave.
 
If you try it, you will find out this 1 Hz square wave is still relatively loud - closing the hps in a drawer/closet etc helps.

 

[xnor]

Quote:

 @ everybody : Will translate and publish ASAP - some recordings in the pipeline that have priority.
 
I agree one can use Panasonic WM61A mic/soundcard approach etc - and will go that route in the future. Based on the THD+N measurement of HA-S500 after LOTS of everything, I definitely do not think driver has developed more distortion - it is crazy low in absolute terms, not just for this price range.
The only exception is region below 100 Hz at 100 dB SPL, but that is normal with 40 mm driver.
 
Yes, in headphones there is no spider and all the movement is governed by the corrugated "surround" that is still one piece with the rest of the diaphragm - and it is in this corrugated  section most ( all ? ) the changes must happen. If one blows gently to the diaphragm of a new out of the box hp driver, there usually will be no displacement. Merest breath on burnt in driver will usually result in displacement - compliance of that surround must have changed to a much higher value - allowing greater extension in the bass.
 
The signal used is high - but not enough to cause thermal demage. It is the frequency that is made as low as it can get to generate as high excursion as it can get that does the trick - 1 Hz ( one hertz ) square wave at 2.5 V peak to peak amplitude WITH NO VISIBLE SAGGING as seen on the DC input of an oscilloscope - with no DC component, as measured directly on the drivers/hp input cable. If you feel that square wave does not contain enough high frequencies for burning in, you can superimpose some pink or white noise of lower intensity upon the basic square wave.
 
If you try it, you will find out this 1 Hz square wave is still relatively loud - closing the hps in a drawer/closet etc helps.

Are kidding, trolling or just ignorant?

 

[analogsurviver]

Quote:

Are kidding, trolling or just ignorant?

None of the above - at least not intentionally.

 

[xnor]

In the "Asgard crinkles AKG driver" thread someone asked AKG about what short-time offset is safe and AKG responded that even 0.25 volts of DC during power down might damage their headphones. That is a single, short DC current during shutdown of a headphone amp.
You're sending +/- 1.25 V DC for half a second over and over again through 36 ohm, 104 dB/mW headphone drivers... No wonder the S770 driver failed (32 ohm, 113 dB/mW).
 
I'm speechless...

 

[LeDave]

My JVC HARX900 has better sound overall than my Audio-Technica ATH-M50 for some reason and the price difference is double in favor of the Audio-Technica. However the JVC has double the usage of the Audio-Technica, could this be a burn-in thing? I know that I have at least 65 hours of usage on my Audio-Technica.

 

[LeDave]

Delete, double post.

 

[kramer5150]

I don't really place much value in the whole burn-in concept / debate, unless theres a blind A/B comparison and a brand new + well used headphone to go with it.  6 or so years ago I met with another member, who swore he could hear the difference between his 3-4 year old, ~9000 S/N K701 and a brand new ~11000 S/N he was borrowing.  So we did a blind A/B comparison and sure enough he could pick out the new and old cans every time on his rig.  I gave it a whirl on the millet rig I had at the time and honestly had a very difficult time hearing any sonic differences.  I simply could not consistently pick out which can I was listening to.  Plugged it into his rig.. same thing.  no dice for me.  I think the cans owner knew EXACTLY what to listen for, to hear the differences.  He would mentally tune out other sounds and artifacts and zone in on the types of sounds needed to present the sonic differences.  Even after he told me what the differences were, and what to listen for... frankly I had a hard time with it.
 
it was a fun exercise... good learning experience for me.  It taught me I really liked the K701 as a complimentary can to my Grados and HD580.
 

 

[kramer5150]

Quote:

My JVC HARX900 has better sound overall than my Audio-Technica ATH-M50 for some reason and the price difference is double in favor of the Audio-Technica. However the JVC has double the usage of the Audio-Technica, could this be a burn-in thing? I know that I have at least 65 hours of usage on my Audio-Technica.

Could be... more likely its just a preference for the bassier X900.