Originally Posted by analogsurviver
Correct for HA-S500 - it has seen measurements well after "everything" - and obviously survived , as did other hps subject to the same method.
The main objective was to find if circumaural HA-S770 with carbon nanotube driver has good characteristics to begin with ( does not, FR is off by miles ),
to show that burn in is real, what was not planned was failure of one driver due to too short output wire(s). It was first measured for everything with less than 5 hour "easy" programe listening, where I specifically wanted to exclude any loud or bassy programme that would require large diaphragm excursion and thus this pair first measured was in next to out of box condition. Second measurement followed after 48 hour burn in of the surviving driver - and think one day of total rest - these measurements were made so to speak in overtime.
Due to failure of one HA-S770 driver, I diverted much of the measurements agreed upon initially for 770 to 500 - because it is much more accurate to begin with and responded to burn in in normal way. I would love to have that mesuring setup available, to measure out of box, with such and such burn in signal after every so and so much time, etc - sorry, finances do not allow it. Ha-S500 proved to have such low distortion that using Panasonic WM61A mic capsule could prove to be the limiting factor - after Linkwitz mod ( required because of distortion at higher SPL ) one can never be certain if the distortion specs are still OK or not, again requiring calibration with B & K, which again costs money - FAR more than capsule(s) itself.
So, let me see if I have the data correct.
The HA-S770 was measured >5 hrs use, "out of the box".
The HA-S770 was next measured at 48 hrs of burn in of surviving driver, plus one day of "rest".
The data posted from the precision B&K test set up:
"After 48 hour burn in, it could follow 1 ( in a word : one ) Hz signal ."
"But the curve "before" and "after" is clear as a bell - there is reduced hump in the midbass around 100-150 Hz and extension in the low bass - at approx 30 Hz, there is "only" about 20 dB ( ! ) difference in level"
"THD+N measurements of HA-S500 are very good, the only exception is distortion below say 100 Hz at 100 dB SPL, which is to be expected from 40 mm driver. At 90 dB SPL they are low even in bass."
"I went to the trouble of having made these measurements by no less than Bruel & Kjaer because I really had it with people who do not believe in burn in and insist on precise measurements to verify it."
Followed immediately by this:
"But I will describe how this change can be heard..."
"Every other hp to date behaved in similar fashion - to a lesser or greater degree. It can be heard, I did not do measurements, as it is that audible The region most affected is bass, say from 200 Hz all the way down."
"If you ask HOW do I know HA-S 500 is still superb - because it has very good channel matching, generally within 3 dB across the meaaured range, of 20 Hz to 25 kHz, THD+N peaks at its resonance at approx 4.5 kHz and it does nor exceed 0.4 % even there - from 1 kHz up, it has less than 0.2% THD+N except for the peak mentioned - at 90 and 100 dB SPL." (no comment as to if the measurements quoted were yours or someone else's, or just specs.
As to the lack of THD data:
Originally Posted by analogsurviver
Ha-S500 proved to have such low distortion that using Panasonic WM61A mic capsule could prove to be the limiting factor - after Linkwitz mod ( required because of distortion at higher SPL ) one can never be certain if the distortion specs are still OK or not, again requiring calibration with B & K, which again costs money - FAR more than capsule(s) itself.
Beg to differ, these only need to be differential tests, not absolute to prove burn-in. If you don't like the nearly free Panasonic, how about the Behringer ECM8000 for about $60? Again, making good measurements to confirm burn-in doesn't have to cost a lot. From what you've indicated so far, the cost of the tests may have exceeded the cost of a good DIY setup by several times already. But that's not the point. We'd all be much happier with data...any data.
I've been through the posts looking for data, and I might have missed a statement or two, but the above quotes are all I could find. I did find a lot of opinion about why and how it happens, and the different issues with drivers and headphones, but I'm not finding data.
I did find this, though: "I have print outs for frequency response before and after burn in for 20 Hz to 25 khz range and from 20 Hz to 1 kHz range..."
Do you have or know someone that has a digital camera, scanner or camera phone? Simple photos of these would qualify as at least some actual data. You could label them in pencil as to which they were. No translation required, we can all read numbers in most languages.
I'm sure you realize that what's been advanced so far is opinion. There seems to be concern that measurements would be challenged unless they were done with expensive test equipment from B&K, but frankly, any tests would be challenged without data, and most even with it. Data points 20dB outside the general trend (measurements by others) will ALWAYS be questioned.
The next step is posting actual test results, there's really no point in describing them or the so-called burn in effect any further.