Well, some components that get sold and the new owners do not like, the dealer, or makers claim it takes a long time to break in.
So long in fact that the ability to return the item passes!
When a product sucks.. You should give it a few days.. then just get rid of it.
I do have to say I had a Kimber Hero balanced cable I bought new, seven meters long, which was really awful when i first connected it. (And I thought 'This Sucks") but I gave it a few days of 24/7 running and it got better enough to not just return it.
But some other items just never did get any better (actually was no better than a $200 (used) item, so the $2,000. item went back to the dealer.
Only a fool IMO, would have accepted: "it needs to break in blah blah.. "
So this all is just a warning about 'break in' used to 'trick' folks into keeping stuff that should just be returned.
On the otheer hand break in is real, and can take some time.
So it is a two edged sword.
My take is if it sucks right off, and does not get better soon... take it back.
So I use a three day test.
If it is no good after running for three days, Time to reconsider.
Break in seems to make good sounding equipment get even better. Like icing on a good cake.
And NOT turning a pig's ear into a silk purse.
So for deciding whether it is good enough to keep three days is it.
For final subtle improvements beyond that.. can go on a long time.
And it is not by type, more like by specific items..
"Break-In" could just be the length of time it takes your ears to become accustomed to the sound of new equipment added to your system.
Once an item reaches its thermal stabilized operating temperature there should be little change as long as new factors have not been introduced.
Try reading the many ,many threads already addressing this topic. The search function works quite well.
The recommended break in period for my speakers exceeds my life expectancy. I was not told this when I purchased them.
It really depends on the item. When I got my new original Dynaudio C1's I was told they need about 350 hrs to sound their best. I had never run into anything like that before. Anyhow out of the box they sounded great. BUT between 100 - 150 hrs they really sounded horrible. Highs were rolled off - bass was rolled off - mids got very shouty and I just wanted to cry. Magically just after 150 hrs they started to sound good again. At about 200 hrs they really sounded great and at 350 hrs finally settled down and sounded fantastic.
Now the only other things I have found to take a longer time to break in were new power cords and new vacuum tubes. Typically around 200 hrs. On the other hand my cdp only took about 25 hrs.
That has been my personal experience
I found only speakers really had noticeable breakin.
Pretty much no matter the component or wire I'll give it 10 straight days of it being on constantly and/or having some kind of music or signal being sent through it. Then I'll give it a critical listen. If it doesn't sound good after all that I'm selling it or returning it.
I came up with this from a lot of stuff I've read. Be it reviews on the net or the actual instructions that came with the item. Pretty much everything I've come across requires 150 to 200 hours of break in so I figure why bother with trying anything different. Just give it over 150 hours then give it a critical listen. When I had a short time to audition or return I'll do something along what Elizabeth said about giving it 3 days.
Everything in the I can ever remember buying usually sounded good enough when I brought it home from a dealer, to know I was happy. Any changes I heard were mostly subtle.
In other words, I knew whether I could keep it or not, at the beginning, or in a few days.
Equipment I've bought without hearing, still gave me an idea what I had to deal with, at the beginning. If it was too questionable, I usually let it go. When I heard that same equipment somewhere else, years later (well broken in), I recognized those same characteristics I didn't like years earlier.
I'm not saying it doesn't need broken in, just be careful if it bothers you that much. A few days should give you a good idea, and time for you (nerves and excitement), and the equipment to settle in. It may not be a keeper, if it still is questionable.
Speakers do need a break in, often you need to play white noise for at least 100 hours to get it started. When dealers talk about break in, turn it back on them with the 'dealer' doing the break in for you before the sale is final.
I did an informal comparison between some new components and broken in ones to see if there was any difference. You can read about it in my article at Dagogo.com entitled, "Doug Schroeder's Audiophile Law #6: Do Not Overemphasize Burn In"
To find it you need to go to the main page, select "The Columns", and "Commentaries" from the drop down menu. I have several Audiophile Law articles there.
(I would put a link to the article here but often when I have the post has disappeared)
If the component utilizes capacitors in it's circuitry; the better the dielectric material(ie: Teflon/polypropylene/polystyrene), the longer the piece will take to, "break-in." Cables also act, to a degree, as capacitors, with regards to the dielectric/"break-in" ratio. This isn't the only dynamic at work, but has a lot to do with the sound of components changing, over time.
I agree with Buconero. You can run pink noise through the speakers for 24 hours, but if it takes more time than that, let the dealer do the work. Tell them you need a little break in time before spending your money. There's no guarantee you'll like the sound even after (getting used to it) break in time. By then, it may be too late to return them.
Buconero117 and Polk432 make an excellent point. For stuff needing a long break in, tell the dealer to do it, then you will be able to make a reasonable judgement in a reasonable time.
IF the dealer really believes in the long break in.. they should be willing to do it. If it is just Bs to get you to keep stuff you do not like.. then you know to pass on it.
Put the onus on the dealer.
it depends upon the manufacturer of the product.
i have been told by two manufacturers that there is no need to break-in a component.
if it has tubes, one hour is sufficient.
there is no definitive answer.
there is an easy way to determine when a component has broken in.
listen to your stereo system. if you hear changes, break-in has not yet completed. after a while, you will notice that your stereo system sounds pretty much the same from day to day. of course there are normal variations from day to day, as a consequence of several factors.
before placing the "new" component into your stereo system, listen to your stereo system for several days in a row, to appreciate the subtle variation in sound, if there is any. then introduce the new component.
my experience is that one week of a signal is the minimum break-in period, but sometimes it is longer than that.
i was reviewing the cable and i thought it broken in. one day i was listening and i realized that i was wrong. the cable was continuing to break in and its sound changed after i had submitted the review. i believe the cable had 300 hours of a signal passing through it before i evaluated the cable.