[tmars78]

Quote:

Personally I believe that he doesn't want to alienate his customer base.

I agree with this statement. He is in the business of making money. And if you are happy with the way your amp has improved, of course he is going to agree with it. 

 

[BlackbeardBen]

Heidigger, are you actually postulating that because he claims he hears a difference, but he can't measure any changes, that there must be something changing in the amp that we can't measure?

This is hopeless...

 

[Mkubota1]

Quote:

aside from the small magnitude of the effects in solid state electronics a logical problem with physical theories of burn-in is why does it Always result in subjective sonic Improvement?
 

Because the grass is always greener- not browner?  The audiophile community (and any other higher-end fanatical hobby) has to accept the idea of different- not just better.  But that's often not enough when you're shelling out huge amounts of money or trying to appease egos.

 

[Prog Rock Man]

Quote:

Heidigger, are you actually postulating that because he claims he hears a difference, but he can't measure any changes, that there must be something changing in the amp that we can't measure?

This is hopeless...

Agreed, placebo etc is too easily dismissed.
 
Harman Int have found differences with blind and sighted testing, using the same source/amp and different speakers, so the eyes have caused the difference, not the equipment.
 

 
It is worth noting that blind testing produces smaller differences than sighted, which would go towards confirming the tendency of ABX tests to find smaller differences than those where people can see what is being changed. This test invloves speakers, where ABX testing finds the biggest difference. I am sure if we had a graph of four cables on test, we would have an ABX which is flat lined, but sighted testing by those who say cables cause differences all over the place.
 
Full report by Sean Olive here
 
http://seanolive.blogspot.com/2009/04/dishonesty-of-sighted-audio-product.html
 

 

[rroseperry]

It's pro forma for audio reviewers to mention that the amp under review has so many hours of burn in time. Very often the review proceeds to describe the sound of the amp before and after the burn in period. Why do so many people experience this phenomenon, or think they experience it? From where does the belief arise? The answer repeatedly given here: if you expect to hear a difference, you inevitably will hear a difference. People's ears are led astray by their eyes, and also by biases and expectations. The placebo effect and expectation bias are real phenomena; that can't be denied. Ethan mentions comb filtering. These are all plausible explanations, but they have not been proven to be the major causes.  A few posts back, Nick Charles asked Norbert Lehmann, the manufacturer of the respected and well reviewed Black Cube Linear Headphone Amplifier, about burn in. This was Lehmann's response:
 
[size=11pt]Dear Dr. Charles,[/size]
[size=11pt] [/size]
[size=11pt]thank you for contacting me in this matter. I experience sound improvements in several aspects over time, at least for some weeks.  To me it does not matter where the effects come from. What I guess to be  very important is the overall thermal stability of the circuit. There are, however, _no_ differences to be measured at least with my Audio Precision ATS2  which is a very nice unit for production tests but no real state of the art unit like the 2700 type. [/size]
[size=11pt] [/size]
[size=11pt]This is a rather unacademic approach for an engineer - but it helps. Sorry that I can't  supply a more satisfying answer. [/size]
[size=11pt] [/size]
[size=11pt]With kind regards from Germany[/size]
[size=11pt] [/size]
[size=11pt]Norbert Lehmann[/size]
 
What a surprising statement! This person who designs and produces amplifiers, who would have more experience with amps than probably all of us on this thread, confirms that he experiences "sound improvements in several aspects over time, at least for some weeks." The statement is extraordinary. I expect for the average person to be taken in by the sound of a given amp, but I find it more difficult to believe that the guy who has the most experience with this particular amp, confirms that he also experiences an improvement "in several  aspects" over a period of weeks. As a possible explanation, Lehmann guesses the "overall thermal stability of the circuit." He could not measure these improvements with the equipment on hand, though hastens to add that the equipment wasn't necessarily the best for the purpose. Placebo, expectation bias, comb filtering -- none of these sounds convincing in this case. The accusation is then made that the manufacturer is lying. Lehmann is keeping the myth of burn-in alive because it helps him sell more amps. I thought about -- and discarded -- that latter possibility. Just based on his note, I didn't get that impression. I believe it when he says that he's experiencing sound improvements. I keep going back to his statement about the overall thermal stability of the circuit. Can this stability vary or improve over time depending on how often the amp has been turned on or used, and why does it happen for only x number of hours before it reaches a certain stability? It basically has to do with how well it can conduct the signal?

 
 

I believe he means it too, in the absence of any other evidence. But note that he says (emphasis added):

To me it does not matter where the effects come from.

This says to me that engineer or no, he's as much in thrall to the mythologies of the audiophile community as any weekend hobbyist. His being an engineer and good at his work doesn't confer some special accuracy in respect to his personal experience of the equipment. The very fact that there's something that he hears but can't measure and has no idea how it comes about says that he's speaking as an audiophile, not as an engineer at that moment. It's not like it's not possible to build very good equipment and share the community's biases and beliefs

 

[BlackbeardBen]

Sean Olive's blog is great - I have to say he impresses me, although I certainly am not a fan of what Harman has done to the Infinity brand... 

 

[Prog Rock Man]

Indeed manufacturers do not agree on burn in. Here are the replies the Spanish site Matrix-hifi got when they asked speaker makers about burn in. I like Thiel's response of 'audiophiles says 30 hours'! Asking one hifi manufacturer about an issue and using their response to justify your position is poor evidence gathering. Here Matrix-hifi have gathered a lot of evidence.
 
 

Manufacturer	Simplified Reply	First Reply	Second Reply	Factory Burnt In?
New Form Research	+ 100 hours	3 or 4 hrs during 4 weeks		NO
Thiel	Iinvalid reply	Audiophiles says 30 hours		NO
Apex	Iinvalid reply	Use it for a while		No reply
ScanSpeak	Almost immediately	5 minutes with signal tone	1 month using music	NO
ATC	Almost immediately	Unnecessary, speaker’s ready when leaves the factory		NO
Vifa	Invalid reply			NO
Beyma	Almost immediately	30 minutes with signal tone	About a week with music	NO
Visatón	Almost immediately	Pushing membrane a few times at the most		No reply
Manger	24 hours	Our speakers are burnt in at the factory during 24 hrs, we cannot find any difference after this period.		YES
Madisound	+ 100 hours	5 to 6 days at the speaker’s resonance frec.		NO
Meniscus Audio Group	Iinvalid reply			No reply
Acoustic Elegante	Almost immediately	Burnt in in the first minutes of use		NO
JBL Pro	Almost immediately	Short, if any, burn in period		NO
Eminence Speaker	+ 1.000 hours	Speaker will burn in forever		NO
Audiothechnology	+ 1.000 hours	Depending on the cone material and its compliance		NO
HiVi - Swan Speaker Systems	24 hours	18 to 24 hrs		NO
Jordan	Iinvalid reply			No reply
Adire Audio	Almost immediately	About one minute		NO
Orca Design	+ 1.000 hours	Depending on the cone material: - Paper cones 1 min - Treated paper or plastic 1 week - Silk Dome Tweeters 2 weeks - Metal domes several monthes - Ribbon tweeters a few minutes - Plastic tweeters about 1 week	1 minute 1 watt, then 1 minute to max AES power	NO
Morel USA	+ 100 hours	Most of the cones 2-3 weeks, some needs hours and others 2 to 3 monthes		NO
HIQUPHON	Almost immediately	No need for burn in		NO

  
Of course, we do not know how audible burn in is from the above.

 

[maxflinn]

hey idc prog rock man

, i've found ya..
 
wow, just had a quick look through this thread and i can see you've really put some time and effort into it, fair play to you for that.
 
i'll have a good read over the coming days and see what i can learn, i may even have something to add

 

[Prog Rock Man]

Hi Max, glad you found us.
 
The original version of this thread was put onto the What Hifi forum, but deleted, as we know they do to any thread which asks too many difficult questions, let alone those that attempt to provide some reasoned answers, with lots of lovely evidence!

 

[CEE TEE]

Wow, Sean Olive's blog had a great continuing discussion and I went through the links and found free downloadable video courses from Infinity:
 
http://www.infinitysystems.com/home/technology/technology_academy.aspx?test=1&Language=ENG&Region=USA&Country=US
 
I haven't watched them yet but the last one is on testing...thanks, Prog Rock Man for the link to Sean Olive!
 
UPDATE:  The infinity videos are 90% sales pieces.  

 

[EthanWiner]

Quote:

Ethan mentions comb filtering. These are all plausible explanations, but they have not been proven to be the major causes.

 
I proved with hard data that the frequency response changes drastically over distances as small as four inches. If that isn't acceptable proof to you, then I give up. Again.

 
Quote:

This was Lehmann's response:
[size=11pt]"To me it does not matter where the effects come from."[/size]
[size=11pt]This is a rather unacademic approach for an engineer[/size]

 
[size=11pt]"Unacedemic" is an understatement. Any design engineer who doesn't care why the sound of his circuits changes over time is incompetent and a fool.[/size]
 
[size=11pt]--Ethan[/size]

 

[Heidegger]

Quote:

Heidigger, are you actually postulating that because he claims he hears a difference, but he can't measure any changes, that there must be something changing in the amp that we can't measure?

This is hopeless...

The only thing I'm postulating is that the guy with the most experience with headphone amps of anybody here confirms that he experiences burn in.
 
Raise your hand if you have more experience with headphone amplifiers than Norbert Lehmann does.
 

 

[Heidegger]

 
Quote:

 
I proved with hard data that the frequency response changes drastically over distances as small as four inches. If that isn't acceptable proof to you, then I give up. Again.

 
Quote:

This was Lehmann's response:
[size=11pt]"To me it does not matter where the effects come from."[/size]
[size=11pt]This is a rather unacademic approach for an engineer[/size]

 
[size=11pt]"Unacedemic" is an understatement. Any design engineer who doesn't care why the sound of his circuits changes over time is incompetent and a fool.[/size]
 
[size=11pt]--Ethan[/size]

Comb filtering plays a role, but, as you know, we're talking headphones here. I don't believe Lehmann is incompetent. I believe he experiences burn in regularly, just can't explain why. Not everything in life has been explained yet. 
 

 
 

 

[b0ck3n]

 

Comb filtering plays a role, but, as you know, we're talking headphones here. I don't believe Lehmann is incompetent. I believe he experiences burn in regularly, just can't explain why. Not everything in life has been explained yet. 
 

 
 

You're sounding like a broken record. Nothing has changed since your first post regarding amplifier burn-in. If indeed burn-in is real, and it somehow eludes present measurement process, a blind test would be able to identify it.

 

[Heidegger]

Let the record show that nobody has raised their hand. Experience counts for something indeed it does.