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Testing audiophile claims and myths

Discussion in 'Sound Science' started by prog rock man, May 3, 2010.
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  1. KeithEmo
    Yes.... here we go again.
    My original post was a simple answer to a simple question.

    Someone asked whether headphones burn-in.

    I pointed out that speakers do indeed show changes in their measured performance over time...
    Since headphone drivers are built exactly like little speaker drivers, it would only be reasonable to expect similar changes to occur in their performance over time.
    And, since headphone drivers vary widely in terms of construction and the materials used, I would expect this to also vary widely.

    It is close to a first principle of mechanical engineering that all flexible springy materials - like rubber and plastic - change their springiness after repeated flexing...
    (And, since the suspensions of speakers are made from this type of material, this applies to them.)
    I'm sure you can find the mechanical properties of the plastics used to make headphone diaphragms documented somewhere.

    To answer your actual questions (about speakers made by Emotiva):

    -
    During the development process we DO burn in both individual drivers and complete speakers before measuring or testing them.
    It is most common in the industry to leave low frequency filtered pink noise running overnight for this purpose - which is what we usually do.
    (Sometimes we simply ensure that someone has been listening to them for a few days before taking measurements.)
    Our speaker designers have found, from long experience, that the measured parameters on most speaker drivers do in fact change over the first few hours of use.
    (As far as I know, that change is always in the same direction; the suspension gets slightly softer and the free air resonance gets slightly lower; although some change a lot while other change very little.)
    We don't bother to take or keep measurements before the drivers are burned in - simply because we don't consider them to be representative of the speaker's typical performance.
    (We have no interest in plotting how rapidly the parameters change... all we're interested in is ensuring that the measurements we take will represent their performance through most of their usable life.)

    -
    We DO NOT burn in our production speakers before shipping them; and we DO NOT burn in the individual drivers before assembling them into speakers.
    We DO NOT recommend that anyone burn-in our speakers before listening to them, nor do we specify that they will change after burn in.
    However, when people specifically ask, we tell them that "they may notice a slight change in sound over the first few days of use".

    -
    All of the specifications and performance claims me make for our speakers should be considered to be "after a reasonable amount of burn-in".
    ("After a week or so of use at typical listening levels".)

    I have heard that, in the past, some manufacturers burned in individual drivers before initially testing them.
    The reason was claimed to be that, because of inconsistencies in manufacturing, different units or batches might change to different degrees.
    Therefore, individual units were first burned in, until they reached a stable operating characteristic, before being sorted, graded, and matched.
    I suspect that modern construction materials are consistent enough that there is no longer any justification for doing this.

    With a ported speaker, the cabinet is tuned to the free air resonance of the driver, among other things.
    When the spring constant changes, the tuning match between the driver and cabinet will also change, which can have a significant effect on both frequency response and damping.
    The degree to which this affects performance will depend on several different design parameters - which will be different for each speaker model.
    As a broad generalization, in a sealed enclosure, the driver will generally experience a single-order roll off, which will shift slightly as the resonance changes.
    This will generally result in a smaller and more benign difference if there is a slight mismatch.
    (And, as I mentioned above, we have never bothered to measure or record this, since we are really only interested in how the speaker performs once it is "operating normally".)

    As as aside, although we haven't tested it, I will state that I personally have never NOTICED an audible change during the burn in period with any of our speakers.

     
  2. KeithEmo
    Agreed.

    One article I read reasonably suggested an interesting alternative to the idea of significant driver burn-in.
    They noted that even slight differences in the fit of headphones can have a major effect on bass response.
    They suggested that the biggest change over time might be due to the ear pads settling into the shape of the listener's head and so providing a better seal.

    They noted one test showing a 10+ dB difference in bass response due to adding eyeglasses to their dummy head plus headphone setup.
    (The eyeglass frames compromise the quality of the seal between the listener's head and the headphones.)

    The fact is that the majority of mechanical systems with moving parts do experience some degree of burn in....
    And that is especially true for anything that includes flexible or springy plastic or rubber parts....
    Therefore, it seems logical to assume that the same would be true for headphones....

    I cannot imagine why this subject is even somewhat interesting.
    Once you've listened to your speakers or headphones for a few days they'll be "burned in"... if it matters.
    Or, if you're really concerned about it, then simply leave the music playing on your headphones or speakers overnight for a day or two.
    If they really change or benefit due to burn in then you will have achieved that change.
    And, if not, then no harm done, and no money spent. :deadhorse:
    It hardly seems worth worrying about either way.

    The fact is that the majority of mechanical systems with moving parts do experience some degree of burn in....
    And that is especially true for anything that includes flexible or springy plastic or rubber parts....
    Therefore, it seems logical to assume that the same would be true for headphones and speakers....
    However, testing it for different models and types of headphones would be a lot of work, and it hardly seems worth the bother.
    (It's something that may or may not serve a purpose, only happens once for a given pair of headphones, and doesn't cost anything to do.)

     
  3. bfreedma

    So many words. All utterly absent of evidence of claimed AUDIBLE burn in/break in.

    I’ll try just one more time Keith- can you produce hard evidence of audible changes due to headphone break in. Or speakers. A link to an appropriate article(s) or measurements would be sufficient - no novella necessary.
     
  4. castleofargh Contributor
    that IMO is a defective test method. if even that doesn't make you feel a difference, you've at least got your own answer to the question "should I bother with burn in?". but measured variations from pair to pair are often too big to assume that they're accurate copies of each others. also how do we switch from headphone to headphone in the delays suggested for noticing small differences in listening tests? IDK.

    I'm tempted to assume that the one and only legit purpose of burn-in is to get beyond the time period where mechanical failures have the highest statistical chances of occurring. but I'm guessing that many manufacturers already do that themselves if only to minimize RMA and similar fun like having many people crying online that the product is crap and broke after a day.


    the other name for this is superstition.

    evidence of a given effect is what should always matter, when getting that effect was the reason why we did something in the first place. if you do something to reassure yourself and you do get reassured, then I guess you're right to keep doing it as you've achieved the desired effect. but if you honestly burn in gears so that they sound their best when you first use them, then I do not understand how you can be satisfied with "no harm done" as a reason to keep doing it.




    my views on the all burn-in concept are that it's yet another trick that audiophiles came up with to avoid having to look in a mirror.
    it goes along with banning blind test from most forums and pushing an aggressive anti measurement movement for decades.
    all those things keep proving how imperfect and full of crap we humans are. so let's get rid of them and enjoy dreaming that we're perfect and consistent spectrum analyzers. and dreaming that our feelings were indeed plain objective reality about the gear all along.
    I do not know how much change can occur to some specific headphone driver, but I do know that if we go take the last 20 people who claimed that their headphone "burned-in" significantly, none of them will have any evidence for their claim. and most, if not all of those who didn't make it all up in their mind thanks to flawed memory, will in fact have noticed a change due to placement, pad wear, or simply a change in listening level as they most likely were listening louder than usual when they did their first "critical listening". even if something is going on with the driver, I believe we have enough data to say that those other causes of change will almost always be of higher magnitude and more noticeable as they impact our impressions of the frequency response.
    so let's drop the act and simply admit that the all burn in thing is a façade for people who can't let go of the illusion of their own consistency over time. it's a lie to make people feel better about themselves by blaming everything on the gears.
     
    Last edited: Jan 4, 2019
  5. Phronesis
    Physically, it's plausible that some properties of drivers would change with use, and that could generate a measurable difference in sound. And I've seen some measurement data to that effect. So there shouldn't be any controversy there.

    Where it gets silly is when audiophiles talk about 50 or 100 or 300+ hours of burn-in, with that burn-in changing the sound from having some noticeable problems to being sublimely good, with all the problems fixed. If the drivers were really changing that much, I'd say they were poorly designed and/or poorly built, and I'd worry about the sound eventually degrading due to things getting too 'loose'. A much more plausible explanation IMO is that the perception of listeners changes over time such that their ears/brains adjust what's perceived so that it sounds more 'correct', based on a model of correct sound built over time from prior listening experiences. Changes in pads, etc. could also be a factor, but I wouldn't expect that to consistently change the sound in the direction of improving it.

    BTW, as evidence of my being a double agent, I got locked out of the Z1R thread for a week due to my comments about burn-in, cables, perception, etc. I don't blame the mods for that, it's what they had to do in response to outcry from people in the thread with an aversion to 'science' and Z1R owners who couldn't bear to have the image of the Z1R maligned. This stuff can really be worse than politics and religion. I'm not a proper Sound Science card holder, but I feel a lot more comfortable talking with you guys than people in the rest of head-fi. Regardless of what we agree on or don't, at least we can have real discussions and debates here.
     
    Last edited: Jan 3, 2019
  6. Phronesis
    The burn-in period is also a good way to have people keep the product past the return period: "I'm not quite happy with the sound, but they say it needs 50-100 hours of burn-in, the return period is about to end, and I've only done 25 hours. I'll guess I'll keep it and wait for it to sound as good as everyone says it will." (Keep hope alive!)
     
    bfreedma likes this.
  7. CactusPete23
    Changing Directions here a bit with a question.

    Are there any Good Mid-Fi Single Ended Portable DAP's out there? Or Do they need to be balanced to sound better? i.e. Is this myth or reality?

    When I look at getting a better sounding Portable DAP, It looks like most manufacturers today quickly jump to Separate DAC's and Amps to get balanced output. It is like there is an expectation that "balanced" makes a player better automatically. And when I look for a mid-fi or better DAP, I can't seem to find a many good ones that are just single ended. Somehow, I think that a single ended DAP with just one DAC and Amp, but using good components and design, could sound better (And be lower cost, lower power usage, ligher weight) than lots of the Balanced DAP's out there? (Looking for something to drive Efficient Headphones and IEMs for portable use. )

    So, is it a reality that a mid to high fi Portable DAP must be balanced? Or can a good single ended DAP provide better sound quality that many Balanced DAP's ?

    And then IF a really good single ended DAP is being made. who makes them? (Or is this a design/marketing opportunity !)


    Thanks!

    PS: I am not sure if this question fits this thread. So please point me in the right direction if the experts in the thread think I'm in the wrong place. Thanks ! Tried searching the forums, but could not find this specific topic being discussed...
     
  8. KeithEmo
    Let's make this simple...

    No, I have no intent of producing evidence that burn-in produces audible effects in any particular product.
    Do you plan to introduce any evidence that, in a specific headphone or speaker, burn in does NOT produce an audible change?
    Or are we both just stating our opinions on the subject?

    I'm not personally interested in having a debate on the subject.
    And neither am I especially interested in convincing anyone either way.

     
  9. KeithEmo
    That is an excellent point - and one to keep in mind...
    (And perhaps a good reason to make sure that you apply the recommended burn-in before the return period expires.)

    And there is also another slightly less sinister possibility...
    We humans tend to grow to prefer things we are familiar with...
    Perhaps they're just making an excuse for you to keep it long enough to become familiar with it and decide you like it...
    (And, by suggesting that you listen for differences, they are providing even more incentive for you to focus on how it sounds.)

    In all fairness, if you've been listening to something for weeks, and still haven't decided that you like it...
    Then you probably don't like it enough to buy it.

     
    Phronesis likes this.
  10. KeithEmo
    I absolutely agree.

    If there are going to be audible changes due to mechanical "break in"......
    I would expect them to be most significant after the first few hours ......
    If you haven't noticed a significant change, in the right direction, by then... then I wouldn't be hoping for it to come along later.

    What we're talking about here is mostly an initial stiffness in flexible or elastic products....
    Like leather or plastic shoes or leather gloves that get softer after being worn for a few days....
    And the time scale should be something similar....

    Likewise, as you suggest, it also provides time for our brains to normalize and start considering the sound of that particular product as "normal and right".
    However, if they're going to occur, both of these effects typically occur over the first few days or hours...


     
    Phronesis likes this.
  11. bfreedma

    Stop playing games.
    You made a specific claim - the burden of proof is entirely yours. Asking me to provide anything is simply deflection.
    If you had simply stated you had an opinion in your initial post on the topic, I wouldn’t have responded.
     
  12. Phronesis
    FWIW, I didn't read Keith's comments as intending to support the audiophile belief that extended burn-in can make a substantial difference.

    Also, I've seen some measurement data showing some differences in speakers due to burn-in, but the differences were relatively small, and if audible at all, likely to be insignificant. Please don't ask me to track down the links, I'm still feeling lazy after the holidays!
     
  13. castleofargh Contributor
    sadly you will probably never find the measurements relevant for that. to start with the elephant in the room, "balanced" for amateur audio gear can mean almost anything so long as you end up with more than 3 pins for both drivers. so from the get go, different "balanced" DAPs may not even be offering the same designs and specs. it's just another one of those oversimplified stuff that we audiophiles love to draw false conclusions upon because it makes things look easy and clear. the trend for expensive balanced DAPs is exactly that IMO. it's yet another occasion to have something special requiring special cables, so of course it has that elite smell we all want.
    with that said, I would expect some differences between single ended and balanced on a same device, mostly depending on the headphone/IEM used. probably the balanced output will have higher impedance and that can make a pretty obvious change in signature for some IEMs with chaotic impedance curves reaching super low values. higher impedance output on DAPs is nowadays supposed to be to audiophiles what the sun is to vampires, but now the trend is to go balanced so we all pretend like low impedance output isn't important anymore. I remember seeing the exact same thing with A&K and their crap first DAP at ludicrous price. everything was wrong the impedance output was stupidly high, but magically the impedance output stopped being relevant for a while because the expensive stuff didn't do it right. if it's expensive, someone will say that it sounds amazing. that's ultimately the law around here. actual performances rarely dictate what the FOTM will be.

    it's also possible that when using a crazy low impedance IEM with very average amp sections, the crosstalk levels may rise up to the point of being noticeable. in such a case a balanced output might just offer the extra separation that makes a subjective difference? I'm really just guessing here but under the wrong conditions that seems perfectly possible.
    in my mind there is no doubt that a proper single ended design can do just as well if not better than balanced. but when forced to design something within a given size, using a given power source(again because of the size and weight restrictions), it's most certainly a bad idea to estimate the expected sound fidelity based on the output plug or some chipset's name. actual measurements into various loads should set the hierarchy for fidelity. but we seldom find such measurements into the loads relevant to modern TOTL IEMs. so beside trying and hoping to get lucky, I really don't know what to do.
    the one brand I can think of, where the balance output trend may really be a blessing, is Sony. because they have decided to stick with their own weirdo class D system that has been great for battery life, but not so great for everything else. and for years, SONY has struggled to get a DAP that could get above 0.5Vrms and they still had poor output impedance anyway. most really didn't measure best at full output. so for Sony, an easy trick to double the output voltage may really have been the difference between passable output and pretty good output. personally I loved Sony when the expensive stuff were the tiniest revolutionary ones. not so much now when the expensive stuff has some bulky machine casing to "show" why it's expensive. but that's just me whining about my personal preferences ^_^.

    all in all I hate special plugs because of all the extra expenses to ensure cable compatibility. and I don't like how balanced stuff cost more because they're balanced so balanced must be better because it costs more because it's balanced because...
    but a good design will be good no matter if it's balanced or SE. if I was on the market for a new DAP now, I wouldn't let something like balanced vs SE decide things for me. there are enough criteria and personal desires to filter out DAPs until only a handful remains to chose from. buttons, functions, size, battery life, etc.
     
    ruthieandjohn likes this.
  14. CactusPete23
    @castleofargh
    Thanks for the good ideas and thoughts. The current myth sure does seem to be that new higher end DAPs need to have balanced out.
    I'll keep looking for now. Wish I understood the issues in Amplifier Design at a fundamental level, rather than just the superficial knowledge I have. But I'm probably too old a dog to learn that much today.
    Still have a gut feeling that a great single ended DAP could be designed; and could get higher market share... (Though the major market may be going to music from phones going to wireless earphones. Even today LDAC is pretty good. Plenty good for mass market audio. )

    May take a look at the current Sony lineup... Battery life is definitely nice. Thanks again
     
  15. Steve999
    Some random thoughts. @CactusPete23, I am no expert but I don’t think you need balanced cables for home hifi. I think they are good for long runs in live settings and in pro audio settings as a way of keeping some types of noise down. Anyone may correct me.

    @Phronesis good to have you here. The Sound Science section of head-fi is really odd when you think about it. But you keep changing your picture. It’s nearly every day now. Don’t think I don’t notice. You had some singer from an incarnation of the Lincoln Center big band the other day, with pink glasses, I think.

    @bfreedma I was a big fan of the burden of proof concept but as I think of it and play around with it perhaps it’s better left for the courts than for science. It’s too easy to stand it on its head and in the end there is no one axiom from which which we can prove all things. It’s tough conceptually. It causes us to reach very bad conclusions at times. Better to say, perhaps, show me one shred, just one scintilla, of evidence in support of the claim made, other than a subjective impression, and then we can have an intelligent discussion. Courts get things wrong all of the time because of the formal structure of the burden of proof, the factually guilty are found not guilty, the negligent are found not negligent, the innocent are thrown in prison, and most of today’s still-extant evidentiary premises of law are centuries old and have not held up to recent scrutiny in psychological and social studies or DNA tests for that matter. Perhaps the burden of proof belongs in the trash can. And thanks for helping me choose a new receiver and the help with the subwoofer concepts—it’s all wonderful.

    @Phronesis I remember reading years ago a letter from a manufacturer to a head-fi poster saying burn-in of drivers took place in less than a second and was part of the manufacturing process. I’m no expert, in a way that’s a freedom, I can just recount what I think I read.

    @castleofargh i am still working on my chess game. I was kicking around the idea of a game of chess960 so I might stand more of a chance. Also I want the white pieces.

    I am listening to the symphonies-where to start playlist on Spotify, at 320 kbps Ogg Vorbis, baby!!

    Now I have an actual question. Let’s say I’m listening to something in 320 kbps Ogg Vorbis (which I am). I don’t know—is that less than 16 bits worth of dynamic range? I really don’t have my arms around these concepts. Does lossy compression lift the noise floor and reduce dynamic range? Please note that I have no doubt that 320 kbps Ogg Vorbis or 256 kbps Apple AAC is audibly transparent for me. I’ve done the foobar ABX thing. I’m just trying to get my arms around the concepts.
     
    Phronesis likes this.
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