ZMF x Vibro Cups waiting for the burn treatment!

ZMF x Vibro Cups waiting for the burn treatment!


Before we get crazy into talking about whether burn-in exists or not, let’s define it, at least in a general way.


(From Wikipedia) the process by which components of a system are exercised prior to being placed in service.


Is to detect those particular components that would fail as a result of the initial burn in time.

Now…this isn’t exactly the same idea as what we “audiophiles” have come to think of burn in as.  So let’s assume we have the product and it will not fail.  For an audiophile with headphones, burn in, at least to me is:

The process of exercising a headphone using various volumes, tones, and music, to increase the coherency of the headphones audible output.

Now, what the hell does this mean?  Simply, that a headphone will sound better after being exercised for X amount of time in various ways.  Have I experienced this?  Yes.  Do I believe what I hear as “burn-in” is totally founded on factual data? No.

The question I am most often asked through email is one that wants a description of how my headphones sound.  I personally do believe that our brains get burned in, or used to a type of sound that we’ve heard over and over again. 

For example, if one has been listening to a super bright headphone, and hears for example, Diana Krall’s voice on that headphone 500 times, that (to this listener) is how her voice is supposed to sound.  Then they get a new headphone, it’s not as bright, maybe it has more bass or mid-presence, and all of the sudden, that headphone is uncomfortable to them because Diana Krall’s voice doesn’t sound “right” anymore.  After an initial listen they leave the headphone playing and go do some internet research. They go on a forum that exclaims their new headphone doesn’t sound muffled or dark to many people, but has actually been called neutral more often than not, and the previous headphone is described as being sibilant to many.  Does that mean that said user is hearing things incorrectly, or that their brain is improperly burned in?  Then, because of this social data, the headphone listener instead of sending the headphones back, listens more, maybe an hour or two and finds that although Krall’s voice doesn’t sound the same, or as bright, they actually prefer the sound of the new, “darker” sounding headphone.  What happened here?

Did the headphone burn in?  Did the user’s brain give the new sound a chance because of social media? Did the user’s brain adjust because of more extended time with the headphone?  In my opinion, probably some combination of the 3, but what we must realize, is that we, as users are the variable most of the time with headphones.  Most manufacturers have decently high tolerances, one model will most likely sound similar throughout its production.  What will always change though is the user’s ear.  And in the end, it’s the headphone user’s responsibility to understand how much burn in their brain needs to get use to a type of sound, and how much they are affected by social media.  I do believe though, that if a headphone doesn’t sound “right” to the manufacturer until it is burned in a certain amount of time, the manufacturer does have the responsibility of either burning that headphone in to their required amount, OR being very upfront with the user about this.  I have read that Sennheiser says their headphones don’t need burn in when received by the user.  I wonder if their playing them in factory or if they just don’t believe in the phenomenon?

As for ZMF’s, I have typically noticed that the t50rp driver “calms” down after 10-15 hours, with most changes happening during that period.  Because of this I let every pair burn in for at least 10 hours before being shipped out, and I tune all pairs to accommodate for that adjustment.  There are many sets that get tuned and don’t sound “quite right” even though they measure correctly, then after 10-15 hours they sound how they are supposed to to my ear.  This has increasingly been the case with the ZMF x Vibro’s.  I don’t know if it’s the wood breaking in or my brain, but I certainly notice a difference.  After about 100 hours I don’t hear any more “burning in” with the ZMF x Vibro’s, and with the ZMF in original Fostex enclosures it’s about 50 hours.

 The ZMF burn station.

The ZMF burn station.


What do I notice when the ZMF’s burn in?

1.       Smoother “connection” between all frequencies. 

a.       With unplayed – “burned” headphones each frequency seems to be working separately, where the sound can be forced and have a lack of cohesiveness.  Once burned in the range is smoother, more connected, and pleasant.

2.       Less sibilance, smoothed upper mids, more enjoyable and meatier mids.

a.       The high treble and sibilant areas can be somewhat forward before burn in.  After 10 hours they are smoothed out, and after 25-50 hours they really settle.  This causes the mids to sound a little fuller, more forward and engaging, as the highs don’t take away anything from the focal point of most music.

3.       More lifelike decay.

a.       Attack and Decay is of the utmost importance for any music to sound natural.  I’ve always tuned for naturality and organic timbre in my headphones.  After burn in, instruments and voices feel more life-like because of more proper decay.  Before, bass can be a little boomier, and instruments can feel slightly “plasticky” or forced.

4.       Improved Imaging

a.       When the ZMF x Vibro was first finished I was astonished at how well using wood cups added imaging capabilities to all genres.  After burn in accuracy is even greater, as instruments can be pin-pointed slightly more easily. 

How did I adjust the ZMF’s because of Burn In Effect?

To be honest, I didn’t adjust the originally housed ZMF’s at all because of Burn-In as I have noticed the plastic cups don’t go through as many changes as the wood cups.  I believe the reason for this is that the baffle of the woof cups is screwed directly into wood “joints” within the cup.  Wood, being more “alive” than plastic, needs to get used to the vibration the drivers are bringing to it.  Also the wood posts are much thicker than the plastic posts used in the original design, spreading the energy much wider throughout each cup.

1.       The initial tuning is off the bat brighter and a little harsher than I’d like.  I burn in every set 10-15 hours before final tests and adjustments, and eventual shipping.  It adds time to every set’s final tuning, but allows me to measure after the initial burn in where most changes seem to take place.

2.       I find myself using fiber-glass on the ear side of the driver more to adjust the treble area.  More fiberglass = less 5-10K area treble.  I now include a couple squares of fiberglass with every set should the end user want to bring down treble more.

3.       Go through two stages of tuning and measurements before calling a set “good.” Before and after burning the headphones in.

4.       More alteration of internal damping (from set to set) material to meet the target frequency range.

Okay – so at this point, you’re probably thinking, DANG – that all seems like a ton of change for something as simple as just letting a headphone play for a few hours.   Well, all of it, is subtle, and at least some of it can be attributed to mental factors, as I do not have scientific data to back up the above statements, just experience through making a bunch of headphones.  ZMF’s are all measured, but the before burn-in and after graphs have not been compiled and measured in summary.  So at the end of the day – it’s up to you, the listener to decide if you need to burn in your ZMF’s as soon as you get them, or, just listen and enjoy.

Great "Burn In" resources:

1.  Inner Fidelity "Evidence of Burn In"

2. Wired: "Please stop burning in your headphones."

3.  Head-fi:  "Burn in - real or placebo?"

 Wood "burns" easier than plastic.

Wood "burns" easier than plastic.

Zach Mehrbach