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Science behind burn in

post #1 of 58
9/25/08 at 7:13pm
Thread Starter 
Coming from a very technical background I was fascinated by the concept that electronic equiptment would experience burn in. Does anyone know any definitive science behind this, which components (caps, inductors, transistors) are responsible for the supposed burnin in of amps. I am also a little fascinated that headphones burn in. Anyone have any scientific basis on this.
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post #2 of 58
9/25/08 at 8:45pm
Hello,

About burning in speakers, all that I have are these measurments, that show a significant change in measurable characteristics over 72 hours of burn-in :

Burn in - Hydrogenaudio Forums

However, someone argued that after several days of rest, the characteristics should go back to their initial values.

And a survey made by Matrix-hifi among speakers manufacturers :

Matrix-Hifi
(Go to "El Rincon", 09/02/2006: Rodaje de altavoces: Lo que opinan los fabricantes )

We can see that among 21 speaker manufacturers, one third has no opinion (they often say that "according to their customers" etc) , one third say that speaker burn-in is made nearly instantly (it takes no more than several seconds), and one third say that it takes more than one day.
...and one who said that burn-in was a bad thing because it shortens the lifespan of the speaker (JBL).

I don't know of any evidence of burn-in regarding sonic performances of hifi electronics (except listening accounts).

The case of CPU burn-in used by overclockers is sometimes cited as a proof that semiconductors have a burn-in period. Actually, CPU burn-in is a urban legend. Measurments show that burning in processors actually decrease their overclocking ability, not the opposite (see for example AnandTech ).
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post #3 of 58
9/26/08 at 12:31am
Thanks Pio2001, very interesting links.
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post #4 of 58
10/7/08 at 3:46pm
I think, personally, that burn in is hokum.

It makes sense if you consider that a speaker or headphone driver has a mechanical element that moves and could possibly get worn in, but over a circuit? I'm not an electronics guy, but I am dubious.

However, there was a time when I had a pair of headphones warrantied (they basically worked, they had a tendency to rattle at low frequencies, but for the sake of argument, they could work normally and I was just being OCD getting them warrantied) and still had the old ones in my possession when the new ones came. I didn't exactly abx them, but I listened to the old ones (around 50 - 100 hours of use by that time) and the new ones back to back and couldn't discern a real difference. Even in the case of a moving coil or diaphragm wearing in, I'm doubtful there is much of a change. At least with that model of headphone.
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post #5 of 58
10/7/08 at 4:35pm
it makes sense that there is a SOME amount from a materials engineering / conductor / chemistry point of view: with electrons flowing over little bumps on imperfect surfaces, how electrons flow, etc.
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post #6 of 58
10/8/08 at 1:38am
Thread Starter 

Burn in

Alright, I will give you this, in theory it is possible that if the components get hot enough the conductors would be annealed which removes defects and would increase sound performance. However, this is very unlikely, the temperatures required for most metals are hundreds of degrees. Typically when you have local defects in a structure (mechanical or electrical), further use will cause further degradation until failure.
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post #7 of 58
10/8/08 at 8:01am
i believe in Headphones burning in.

but Amps? and IEMs?
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post #8 of 58
10/9/08 at 1:10am
I'm of the belief that it's true to an extent - but mostly an urban legend. I'm happy to accept that mechanical parts reach an equilibrium after some use. Also happy to accept that electrolytic capacitors need a little bit of time to achieve equilibrium.

But when people start talking about 50 hour burn ins... and how the sound improves... Well, if they show me some capacitor measurements before and after 50 hours, then I might be convinced. Can't seem to find any on the net.

Not to sound cynical, but if the manufacturer says this product requires 50 hours burn in - you take it home and it sounds crap - they can fall back on the, "oh wait for it to burn in" line.

Enjoyment of sound is very subjective. So, of the billions of dacs, sound cards, cd players etc sold in all the world, not a single person has liked the sound of the dac pre-burn in compared to post-burn in (assuming that the sound has indeed changed)? I find that a bit odd.

What's most likely, is that the person has adjusted to the sound of the dac rather than the sound changing.
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post #9 of 58
10/9/08 at 2:21am
Wow, Supernerd pretty much hit it on the head for me as well.

Headphones: yes, I think they break in, but I think the actual physical break in period is much less than people claim...I think brains just take longer to accept a sound signature and for it to "burn in" their skulls.

Components: Sure, somewhat...Caps and the like definitely balance out, and soundstage and imaging open up. Some caps do this much faster than others...no timeline on this as fara s I'm concerned. Claims of 300 hours seem a bit dubious. With that length of time, how can you ever remember what it sounded like initially?

Cables: Not in any measureable amount, because I think cables burn in as soon as a current is run through them. I've never heard any difference in interconnects, power cables, etc.

The human brain: absolutely...
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post #10 of 58
10/9/08 at 10:34am
some notes on the psychology/physiology of burn-in: (the one taking place between your ears)

the psychological burn-in is
1. helpful: if you're used to dark-sounding headphones, neutral ones may sound bright at first until you get used to the new sound
2. nothing to be ashamed about
3. just as real as objectively measurable changes in sound - for the individual undergoing the adaption. note: "real" not as objectively measurable reality, but meaning "i perceive it differently because my perception has changed". real to me, inside.

flexible calibration is an important aspect of how our senses work. light seems brighter after darkness, sound rings louder after silence. muffled is the new clear after having your ears washed.

interestingly, psychological burn-in (and its necessity) is a well-established consensus on head-fi and the larger audiophile world when it comes to iems which you have to get used to, but largely ignored when it comes to headphones, speakers and sounded components.
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post #11 of 58
10/9/08 at 11:00am
I definitely believe there is some degree of burn-in for a speaker since mechanical parts are involved. If a speaker cone is made out of cardboard or some material I have no problem believing that hours of flexing that material will make it slightly easier to flex.

In electronics I am much more skeptical of burn-in.

It is true that electricity flowing through a conductor causes an electro-magnetic field. As we all know like magnetic fields repel and opposite magnetic fields attract. If these fields are in close enough proximity to other magnetic fields they could have an impact on each other. To some extent this could cause them to vibrate on a micro-electrical level (human undetectable).

I concede that with all of the circuits, parts, and wires in close proximity in a piece of electronics there might be to some (albeit small) degree of interaction with each other magnetically speaking. If this interaction after time effects the sound I have not yet personally experienced nor found data to support.

I firmly do not believe in cable burn-in. There can be EMI changes on the signal based on the physical position of the cable, how the cable is constructed, or its proximity. However, I would love for someone to prove how a cable can actually "change" just by passing free electrons through it.
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post #12 of 58
10/10/08 at 1:11pm
flashnolan, about the cables, I am a believer but have no real evidence or proof that they change in any way. Other than how they sound--- Every cable I've deliberately burnt in changed for the better; try it.
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post #13 of 58
10/11/08 at 10:45pm
Quote:
Originally Posted by supernerd View Post
But when people start talking about 50 hour burn ins... and how the sound improves... Well, if they show me some capacitor measurements before and after 50 hours, then I might be convinced. Can't seem to find any on the net.

I've seen this on a lot of capacitor data sheets, this one especially...
Quote:
After 2000 hours' application of rated voltage
at 85°C, capacitors meet the characteristic
requirements listed at right.
Quoted from this Nichicon VX data sheet.

Maybe it's just this one capacitor from this one company, or maybe after 2000hrs it's just like it specs out just like it did initially.
Maybe Nichicon is "pro-burnin."
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post #14 of 58
10/11/08 at 11:12pm
Burn in of electronic devices is IME simply voodoo, parts that do not peform optimal after maximum a couple of minutes must be defective. I do not know how the sum of them, in a given circuit, should be treated any differently...Once you reach the working temperature in the circuit, there should be no more changes...(there are a few exceptions, as for example the tubes, that require more time to get warm and work their best)

Caps are ready to go in seconds, and also mostly all parts deteriorate overtime, so IMO you will rather get wrost performance, than an optimal one overtime with the use...

What does happen, IMO, is that while you get a new equipment, that probably you are not familiar with, you need time to get used to it, your brain and ears needs time to adjust to the new presentation, that is the time that is considered in most cases as "burn in"...

Just take two identical amps, one new and one used, and compare them, the differecnes, if any, will be just due to the tolerances in parts, but nothing else...

I would like to see those really golden ears that most of the times are behind this theory in a really double blind test trying two identical amps, to determined which is the burned in, and the one new...

OTOH mechanical, and electromechanical devices, are a completelly different case...
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post #15 of 58
10/13/08 at 6:50pm
Quote:
Originally Posted by Sovkiller View Post
OTOH mechanical, and electromechanical devices, are a completelly different case...
where is this line really drawn?

Some would say that a transformer is a purely electrical device, but it clearly exhibits mechanical properties when it "sings" along with the signal... transformer humming and hearing the music from a transformer are both effects of this.

Capacitors could easily be put in the electromechanical category. When you consider that they are occasionally vulnerable to microphonics which is a physical effect there is certainly room to doubt how well the plates are held in the electrolytic. after this, it is reasonable to assume that the plates not only move with external motion, but in response to the signal too...

Is it really a black and white answer?

Brand-new electrolytic caps can sound VERY VERY different from well used ones. The fact that the amp is "new" does not mean that the manufacturer did not run it for a week before he shipped it. IME, 170 hours (about 1 week) will get you past the worst parts of any cap, while occasionally leaving some room for continued improvements.
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