I am in 100% agreement with Dick Pierce on driver "break-in" or driver "burn-in".
My question is two fold: why would speakers need breaking in ? Is anyone aware of any measurements and tests having being done of before and after performance that has shown a measurable difference?
Dick Pierce replied:
"I am aware of at least one person who has done extensive measurements of this type: me. I have a database of several thousand drivers that I have measured.
Well, there are, indeed, several mechanism that are, indeed, at work that cause the operating parameters of drivers to change through use. However, the notion that once one gets a speaker home it requires "breaking in" suffers from several problems.
First, as a driver comes off the line, it's actual performance if fairly far from it's intended performance target. Reasons for this include the fact that the centering spider, typically manufactured from a varnish- impregnated linen, is far stiffer than needed. Working the driver back and forth lossens the spider considerably.
Now, one might say: there's objective proof of the need to "break in" a loudspeaker! Not so fast. The break-in period for the spider is on the order of several seconds, and if it takes you several seconds or minutes or whatever once you get the speakers home to loosen the centering spdier, it's not proof of the need to break them in, it's proof that the speaker you just bought HAS NEVER BEEN TESTED!
But, on to other points.
When I measure a driver, I can see a significant change in a variety of operating parameters as the speaker is driven. Usually, in woofer, the resonant frequency drops as the speaker is used, often by as much as 10-20%. This is due, as you suggest, to a relaxing of the elastomers used in the suspension.
However. If I turn the stimulus off, within a few minutes most, if not all, of the change has completely recovered, and we're back to go again. The elstomer has recovered from it's stresses (this is especially true of certain polybutadene-styrene surround
formulations).
There are plenty of other, real, physical changes. For example, one can see a reduction of the electrical Q with time under heavy use, simply because of the positive temperature coefficient of the resistance of the voice coil. Allow the speaker to cool down, and it's completely recoverable.
Get it hot enough, and you might permanently loose some flux density in the magnet. But you have to get REAL hot to do that. Hotter than most of the compounds used in making a speaker can endure without catastrophic failure (damned few glues, varnishes, cones and
insulating materials can withstand the temperatures neede to reach the Curie points of the typical magnetic materials found in loudspeakers).
When this has been suggested, despite the fact there's about a century of research backing it, it is more often than not greated with jears and cires. See, you can't sell special "break-in" CD's if the speakers aren't broken in.
Well, there will be loads of opinions. However, actual data on several thousand drivers don't seem to give two shits about opinions, the +usual claims of "mysterious unmeasurable quantities" notwithstanding."
"Playing a low frequency sine wave has the singular advantage that IF you know the frequency of maximum excursion, you simply place the frequency of the sine wave there and get the maximum excursion for the minimum input power. With sealed box enclosures, it's easy to find, but with vented and other higher-order systems there are several maxima and which is suitable is dependent upon the system alignment.
However, in the work that Ihave done, I have found that while it is true that large excursions DO loosen up the suspension considerably, within 1 minute of cessation of the excercising signal, about 95% of what you have gained in compliance recovers, and almost all the remainder disappears within about 5 minutes. The only time I have seen permanent increase in suspension compliance and other such effects is as the drivers themselves came off the production line in initial QC test. If a speaker HAS to be "broken in" at home, it's a good indicator that the speaker manufacturer simply has not tested your speakers.
Otherwise, there is no evidence of any "magic" break-in that "magic" CD's and the like can effect at home that cannot and has not already been done at the factory. You'll find FAR higher variations in peformance due to daily changes in relative humidity, for example, then you will with break-in procedures which, as I said, are mostly temporary in their effect.
Simply playing loud music through a speaker for a protracted length of time WILL change the performance of the speaker substantially, but not by "breaking" it in: Simply the rise in temperature of the voice
coil/magnet structure will have the effect of raising the Q of the system somewhat, leading to s alsight but possibly noticeably change in low frequency performance. Raising the temperature will also drive water out of the system, which might change the physical parameters of the system.
However, as soon as the system is left alone, both temperature and moisture content will ronce again reach equilibrium with the surrounding environment, and you're back to go again.
There does exist, however, interesting data to suggest that the listener has a significant "break-in" period, a phenomenon that may be important in and of itself, one which should not necessarily be
ignored."
