Can speakers sound worse during break-in period?

I purchased a NOS pr of speakers ( I’m not disclosing their name. Not interested in hearing from their haters) and was really liking them before I started to seriously break them in. It seems like after 24 hours they seem to have changed and sound worse, or not as good as they did. Are they just going through changes with some drivers opening up faster than the others? I know there are many components involved in this process and some might be a head of the others. I’m assuming that’s the case and when everything comes together they will sing.
You answered your own question. Speakers will go thru different sonic changes during breakin. They may sound too bright with no bass extension for awhile, then change to booming bass the next day.

The manufacturer or dealer can tell you approximately how many hours breakin may take.

Don't panic.  Speakers are different in this regard and, yes, some go through what you are experiencing. It may take several hundred hours of music before things settle in
Always the contrarian.Go measure your fictitious speakers, or get some new hearing
My personal experience is that capacitors can do this more than drivers.

Usually drivers (woofers) get better bass over time, they all go in the same direction.  They don't get worse, and then better, but caps do all sorts of funky things. If you are hearing imaging or harshness issues, that's your answer, but 4 days of playing music is more than enough.
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NOS would suggest that your speakers are older (vintage) but never used. Do you mean to say never used speakers that were made in the last few years?
There not Vintage one generation back. They’re a pr the company never sold and offered them to a dealer at a special discount. 
It's been my experience different brands break in at different rates - simply depending on the materials involved. Revel says no break in time required, Buchardt at least 100 hours.
My Thiels probably took 2-3 months to break in, and it was quite noticeable when they did. Bass isn't something you imagine. The midrange also lost some forwardness/harshness, and people who'd heard early then later concurred. However my Maggies sounded great from the start and changed very little other than a bit more slam. Think ribbons are good to go out of the box.

I'd imagine different drivers are going to go through changes at different rates, so yes I can believe it could sound worse for a bit until they all get in sync. What I plan to do when I get my next set is simply put on the Stereophile test CD, and run it 24/7, louder when I leave the house.
"break in cant be measured its not real"
This statement is a load of crap.  I've been breaking in 4  - 15 inch woofers for about a week.  During that week,  FS has dropped around 3hz, QTS has dropped about .5 which is sizable. Not sure why someone would make such a statement, many other changes,  but break in is clearly measurable and over this time drivers,  all size drivers will make very noticeable changes. Normally the biggest change comes at around 4 hours of running them at decent levels,  it changes little by little until you hear real differences again at around 50 hours and still change on most drivers through 100 hours and I've seen a few speaker take even more. 
Some things you can’t measure: sweetness, presence, fullness, soundstage dimensionality, brittleness of high frequencies, boomy-ness, thinness, air, wetness, slam, rhythm, wimpy-ness and realism.
I would argue that many,  if not most of those things mentioned also change during break in. Of course,  that may or may not be the intent of your post. 
The answer to your question is YES.  Depending on the speaker they can go through a number of changes during the break in period.
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To find the right position for the speakers and the listening place in your room, to get accustomed to the speakers, to eq the speakers where necessary, that could take a couple of weeks. I guess you can call it break-in period. But if you don't like or have hope for the speakers from the beginning I would say leave them.
timlub1,745 posts03-25-2020 9:04pm@geoffkait
I would argue that many, if not most of those things mentioned also change during break in. Of course, that may or may not be the intent of your post.

>>>>>Actually I was responding to the statement that any parameter of sound can be measured. I do agree sound characteristics changes during break-in, whether or not these characteristics of the sound can really be measured is a different question.
Time to enjoy the roller coaster ride - play them as much as you can over the next few weeks after which point you'll either love them or hate them.
it took hundreds of hours for my von Schweikerts to settle in....when I first listened I was alarmed but stayed the course. 
So perhaps Woofer compliance is the area of most effect ?
That being said, small difference around 30-40 Hz ? 
Audible... doubt it. How does one design, manufacture, sell, something with the promise of perfection upon burn/break in, and at what time table.
And is there planned obsolescence built in as well ?
Perhaps then the answer is to buy certified second hand. Benefit being if you can.., hear something at it's best or worst. Voila' pay half the grossly exaggerated value at new. 
Eat better, buy an exotic car, travel or stay home listening to music sounding the way you like without all the B.S.   
I understand Zu "burn" their drivers in for 400 hours prior to installing them in the cabinet and I believe they still exhibit minor tonal changes after using them in the home.
Whether that is due to the amp or further "burning in" is beyond me.
Do I need to 'burn-in' my Harbeths?No: the only component part of a Harbeth loudspeaker that can change as a result of 'burning-in', is the resin-doped cloth suspension that centres the neck of the cone in the magnetic field - sometimes called the 'spider'. Under the microscope, once the resin-cloth has been worked backwards and forwards, it crazes into millions of small interconnected islands. This process is irreversible and takes only a few hours with bass heavy music played a little louder than normal. After that point, the drive unit can be considered fully stabilised with the resonant frequency settled to its final value. The ferrofluid used in Harbeth tweeters becomes appropriately viscous after a few minutes operation. Neither the coils, resistors, capacitors, cables nor any other part of a Harbeth speaker has any short-term ageing mechanism.
If you check with the manufacturer, you will get the answer to your question.  Typically, Magnepan tells customers that there will be a period of adjustment as the mylar does experience come changes from new.

Why is this an issue I can't understand as every manufactured physical and electronic item in the world changes with use and time.  I know the wonderful 327 in my C2, which is 53 years old, is not performing identically to its first day on the road.  For this, I am thankful, by the way.

Your manufacturer will be pleased to discuss this with you, I am sure.

I noticed that sound changed over initial period with speakers and earphones. Not with other things. Real or my imagination is another issue but it happened every time that I can remember.
Here's a variant on this discussion...*s*

There's a definite 'break-in' for my DIY Walsh' cones, new adhesives, all that....

But...when one opts to a 'different array', new or used....

Are 'they' being 'broken-in'....or is it You?

Home, from the purchase, the delivery, the 'hook-up'....everything lit up...

'New", out of the carton, is one thing....but 'new', as to you, in your space, your 'stuff'....

....just being the devils' advocate....;)  No need to get feisty, now...*g*

It took many days of my Revel Studio 2 speakers to break in.  I had a dealer demo a broken in pair in my home and I loved them so I bought a pair.  I set up the new pair with the help of my dealer and they sounded horrible- not at all what I had heard days before with the broken in pair.  After about a day of constant playing they started to sound a little more like they did before but it took over a week of constant play for them to fully break in.
 I set up the new pair with the help of my dealer and they sounded horrible
Theres no way they could sound horrible as a result of not being broken in. Its more likely they remained sounding horrible but you just learned to live with it. When are you going to upgrade them if you haven't already?
Huge yes, I heard a huge difference from the first 10 hours until 200 hours, and 300 hours.

 They are much more punchy now, deep, midrange is flawless,  
    Amps, speakers, preamps, CD players, all get better after a couple hundred hours.
capacitors warmed up, I always turn my stereo on the night before, and let everything warm up before critical listening

Here’s a progress report on my speakers break-in process. I’m happy to report after 100hrs ( XLO burn in disc track 9 ) things have improved. They’re starting to open up, driver integration is better and sounding much fuller. They still need more hrs on them but things are starting sound very good.
Kenjit, Can you explain why a mechanical object breaking in cannot be measured. A woofer gets better excursion over time. It levels out at a point, but definitely changes. Since the driver is just a motor moving air to make sound the more efficient the motor becomes the more nuanced sound it can create. This is most notable at low volumes after the break in period. The same thing happens to a car engine. It actually gets better gas mileage after 5000 miles than it did at mile 100. If I am wrong please explain your comment so I can be educated. 
Break-in is  not only hoax , is some type vendor trick.If any customer
paid for example speakers he did not satisfy and planning to return The vendor say---wait, wait , after 100 hours break in sound will be much more better, and after  time, the guy  used to live and say, Speakers is not bad, sound much better, 
@hshifi.    better excursion over time and similar statement is the legend.   hoax

Whether it can be measured is not the issue. The question is how significant is it if its audible? There are many more problems that can ruin the sound of a speaker and people that focus on things like cables and break in of drivers dont realize that. How about custom tuning the speakers with a bit of equalization? How about retuning the crossover? I tend to agree with what Harbeth wrote.

If you dont like what youre hearing its very unlikely that break in has anything to do with it. Has the OP bothered to retune the crossover to see how that sounds? If not, why not?
To have a guy that is clueless and argues almost every point under gods creation is one thing,  but to have a guy chime in that calls himself a manufacture that apparently has never taken the time to measure drivers at several points of break in is beyond my comprehension.  FS, QMS, QTS and even LE and RE all change as the motor and suspension break in.  It is threads like this that makes me back off of posting. 
I am most fond of posters who argue one thing one day, and then within the same thread argue exactly the opposite. That kind of gymnastics will always be pretty amazing to watch.
Maybe we are coming at this in different directions. I still believe in what I said, but if I am understanding this is that the speakers should always sound good and get better. Just like my car analogy. If it sounds bad then something else is wrong. The only thing I can think is if you break in with a limited amount of frequencies you may run into some issues. If you play 1khz for a hundred hours then the woofer did not move due to the crossovers.  If break in on a speaker is not real then why do most manufacturers recommend this and tell the dealers to do this? Is there a representative from a speaker manufacturer that can weigh in on this? Maybe the OPs crossover is messed or he had some interference from other things. 
I suspect surrounds on midrange cones and woofers become more supple as they are used. Though that could vary widely depending on the surround material. Usually showing gains in lower frequency response and probably dynamics too. I was also told by a very prominent speaker designer that the caps in the crossover will "sweeten up" with several hundred hours of use. I guess he means the caps become more linear over time and thus differences could be audible and measurable. I would agree that if the speaker in question were to sound bad right out of the box, other problems might exist.
a very prominent speaker designer that the caps in the crossover will "sweeten up" with several hundred hours of use. I guess he means the caps become more linear over time and thus differences could be audible ,  

This is very interesting , may be the caps is coming more dry or more juice 

Yes, capacitor break in means.... "more juice"

Actually, a capacitor consists of two or more conductive plates which are not connected or touching each other, they electrically separated either by air or by some form of a good insulating material such as waxed paper, mica, ceramic, plastic or some form of a liquid gel as used in electrolytic capacitors. This insulating layer between a capacitors plates is known as the Dielectric.
The dielectric material can interact with current flow. As the cap is used and voltage is passed, the plates can heat up, which very much affects how the skin affect of different dielectrics and resistance (Z) ESR/ESL of the cap. The signal, like water, will take the path of least resistance. It can even create a temporary magnetic field. Different Dielectrics do react with a hysteresis effect differently to all of this in caps. That why an electrolytic, mylar, polyprop, polycarb, teflon, paper in oil etc, all have a unique sound signature. As all of this stabilizes, the caps do settle in and YES, you hear them settle down as they break in. Another common word for this is the caps are FORMING.
To all the naysayers I must say I’m sorry your mind is made up and if it can’t be measured on paper it doesn’t exist. I let my ears tell me what the truth is not a set of numbers that try to explain why it’s impossible to hear something if it can’t be measured. I started this post asking a basic question and have now answered that question: yes speakers do go through changes during a break-in process and do sound worse before they get better and better. I’ve now put close to 125 hrs on them and it’s a night and day difference from the first 25 hrs. They have come alive in a way that gives no regret or cause to wish I never bought them. They are the best speakers I’ve ever owned!!!!