There is not really such a thing as break in. Sorry to dispel all these myths that writers who get paid by the word have put in your head; but let's examine the parameters one by one.

After studying what I call "audio anthropology" for 55+ years, here's my take on break-in, especially as it applies to speakers.

The few other valid and measurable effects are the "forming" of electrolytic capacitors, and changes to batteries, which because of their continuing and changing chemical action are more organic than anything else, and therefore exhibit all sorts of subtle and not so subtle operational changes. We all know batteries drain, and therefore their entire mode of operation is continually changing - their voltage for example. That's easy.

OK, then there are tubes. Since the thermionic emission of tubes means that electrons are boiling off the cathode, as time goes by the cathode gets depleted, and various other subtleties take place, and so yes, you might say that tubes 'change'. You could theoretically consider this 'break-in' if you were to also say that the reference point would not be reached until the tubes were operating for 100 hours. What if your reference point were at zero hours? Then from that point on, the circuitry would get "worse".

But for essentially everything else, the effect is more human than a phenomena of physics.

The psychoacoustic truth is that nearly anything will sound correct if you listen to it long enough; it becomes the new baseline (pun almost intended) of your reference, and then "other" things will then sound wrong, or at least different.

When you listen to a new unknown for awhile, its physical characteristics fill slots in your auditory mental library that may or may not line up with your auditory notions, pre-conceived notions, or expectations. For instance, if you play one brand of piano for a long time, when you play a different one it seems "wrong" for a "certain amount of time". As you become more adjusted to it it might not seem so "wrong" but it will still seem "different". The entire mechanism of your hearing, including the vagueness of your auditory memory "learn" the complex frequency and phase characteristics of the overall sound and stamp that impression onto your admittedly soggy notions. Very few people can listen to a Steinway, then a Bosendorfer, then a Yamaha, then a Young Chang and come back 6 weeks later and pick them out again. Of course YOU may think you are in the minority and are able to do this. That's what being an audiophile is all about. (!)

If you go back and forth between driving an 18-wheeler, a sports car, and a squishy sedan, each seems like a "wrong fit" for a little while until the new proprioception reference points settle in, then eventually the vehicle you are in becomes the "norm". In essence your nervous system and its inherent feedback loops are micro-phaselocking to all the physical and spatial reference points, and there is a "fit" between your body-mind loop and its operating environment. While you are IN the truck you may long for the tight feel of the sports car, but the truck is still your current reference set, and then the NEXT vehicle you are in, no matter what it is, is referenced back to your last reference point, the truck. This is the same phenomena as with speakers. You notice it because speakers are mostly so different from each other.

Besides, all speakers are of course designed and tested "new" --- with new parts. No one designs and tests speakers with used drivers, with the surrounds loose and worn out, etc.

Yes, sure everything has a downward curve. Speakers, like people, start getting worn out from the moment they're born. So you might say that speakers never get better, they only get worse over time; the surrounds get looser and less able to mechanically snap back to their original center position; the magnets get weaker, although only a tiny fraction.. and so on. Of course the phrase "over time" may typically mean MANY, MANY years, just like people. There is no technical change over a few hours or days... but as a human you might have a perceptual change over a few minutes, few hours or few days.

Yes, there are also the issues of temperature and humidity, but for these purposes we will assume a moderately stable "living room" set of measurements.

The new(er) driver technologies such as those used (and often invented) by such companies as JL Audio are light years ahead of the stuff that so many of us might have enjoyed in "college". From the early 70's on many manufacturers used the worst if not the cheapest drivers available to both (a) make a buck and (b) ensure that with a reasonable amount of smog and a reasonable amount of frat house partying, the most owners of these subs would "use up" the drivers and therefore they would require reconing or replacement. Under the thinly veiled guise of "better sound" the manufacturers used the worst and therefore most absorbent paper cones; the worst and therefore most smog/pollution-sensitive 'foam' surrounds, (often called "foam rubber", but not rubber at all, actually a urethane) and so on. The resistance to humidity, ultraviolet, temperature cycling, pollutants, thermal effects of the coil and magnet, and so on was somewhere between non-existent and minimal.

Properly designed and made drivers, with stable materials, still look the same in measurements before and after they are "exercised". We can take a driver at room temp, check its parameters, then exercise it by driving it right to its xmax limits for hours, then measure it again, and the amount of change is small, and mostly due to coil temperature. More stable materials are just that -- more stable. As soon as the coil temperature goes back to ambient, the measurements are the same.

And besides, the most difficult thing to do in all of speaker manufacturing (besides getting it right in the first place, the subject for at least one long book) is consistency! We want a finished speaker (that means speaker cone, speaker driver, and finished product in a box, including amplifier, crossover, and adjustments) made today to sound the same - within incredibly tight limits - as one made last week, or last year -- or next year! And we also want 6 of them made today to sound the same, and to measure to within a hair of a reference manufacturing standard.

To dispel any myths about manufacturing tolerances, everything has a tolerance. If you machine 2 pieces of metal which then have to fit together, they each have a + or - mechanical tolerance. So here's the surprise: if you purchase 6 tweeters (or mid range drivers, etc.) from a manufacturer and connect them up to a rotary switch and feed them white noise, you will hear 6 different sounds as you rotate the switch. That's a sad fact of life. Amazing! There is simply almost no such thing as "the same" ! They are all close perhaps, but all somewhat different. Your ears may be able to discern that difference... or maybe not. Here's why:

To touch on specs and frequency response for a moment, many if not most mfgs spec response as + or - so many dB, i.e. ±3dB. Therefore you can have 2 drivers sitting on the test bench connected to the aforementioned rotary switch, and one driver might have a bump of 2.5 dB batween 2k-4k and the other might have a dip of 2.5 dB between the same frequencies and they are both "within spec" yet to a human, switching back and forth between the two, they sound rather different. Perhaps very different. (they are 5 dB "apart") But the overall point of this article is not manufacturing tolerances, but "change(s)" in parameters.

Of course over a VERY long period (15-25 years) some parts can degrade, especially capacitors. If the wrong solder is used it can craze and the connection can get bad and turn into a noisy rectifying junction. Carbon resistors can change a % or so here and there... well you get the idea. Those changes are subtle and occur over time.

You might say that the magnet [in the speaker] weakens MICROSCOPICALLY over time, perhaps a few percent in many years. Some magnetic materials - and much about magnetism still borders on alchemy and magic - change their strength and other properties permanently when exposed to temperature abnormalities.

There is the phenomena of "driver compression" which changes with temperature, and an issue with temperature in general. For example, if you start out with a subwoofer in a cold room and the coil heats up until it is "hot" then the sound from that driver will be a little 'different'. But at the same time, your own hearing and perception will be different than when you started because since you have been exposed to these loud sounds your thresholds will change, therefore you cannot base your perception on a fixed point because your perception of your perception is continually changing!

Do not confuse "break-in" with "burn-in". Burn-in is a factory procedure when after a unit is built it gets connected and operated (often into a rated load, for example a power amp connected to a load resistor) to determine if anything will fail - an infant mortality test for all the components if you will. This has nothing to do with running the equipment so it gets "better" and therefore the manufacturer has "saved" you some "time and effort", although sadly, some manufacturers or after-market snake oil vendors will try and sell you on this idea.

And last but hardly least, the absurd myth about 'break-in' with wire and cable (ahem... 'interconnects') During my time at a private laboratory division of Hughes Aircraft I had many opportunities to witness and partake in various discussions about various devices being tested in the most amazing ways: everything from electron microscope examinations of hard and floppy disc surfaces to cloud chambers where transistor junctions were being tested to determine the extent of cosmic ray bombardment, to changes in different alloys undergoing thermal changes (from nearly liquid state to near absolute zero) and scientifically, no one has ever been able to determine anything happening technically that would change the sound of an RCA cable the first few hours, weeks, or months you play it. The rest of this discussion about the manufacture of wire is the next huge topic: stay tuned.

So there you have it.

Bottom line: enjoy your speakers. If you need a laundry list of things to worry about (besides "break-in") I can supply that for you.