Speaker break-in is not an unusual question to see on any audio forum. Generally someone's bought speakers and they're trying to figure out if those speakers are really for them. There's a lot of issues that come into play here: positioning, calibration, effects of the room. Often the person who posted the question is somewhat inexperienced and hasn't done the best job of placing the speakers. Or perhaps they've just bought the wrong speakers (but they sounded good in the store!) for the room that they're going in. The purpose of this post though, is not to deal with those issues, deserving as they may be of an in-depth discussion.
This is about the issue of speaker break-in. Scientifically, the topic of speaker break-in has been studied rather extensively using techniques such as laser interferometry, measurements of speaker parameters, and controlled listening tests.
David Clark, an AES Fellow presented "Precision Measurement of Loudspeaker Parameters", which was published in the March, 1997. Abstracting from that paper is the following quote:
"A break-in process is recommended. Drive-unit storage may cause the diaphragm suspension to drift away from its normal or in-use position. Break-in, with the drive-unit axis in the in-use orientation (usually horizontal), restores the normal diaphragm position. The recommended procedure pneumatically stretches the suspension to one excursion extreme, then the other and continues to alternate, decreasing the excursion each time until x is at zero. This process can be completed in less than 1 min."
Mr. Clark also indicated that drivers which had been stored face-up or face-down sometime need 1 minute of pink noise to restore the original center position. This could also be accomplished by a few strokes of the suspension which many manufacturers do routinely when the speaker is at the end of the assembly line. This suggests that most speakers, are in fact broken in when you get them.
Further work has been performed by Tom Nousaine who has measured speaker parameters pre and post break-in as well as having conducted controlled listening tests. He has found that the Fs of the speaker falls however that is offset by a rise in Vas. Both these parameters were related to the changes in compliance that occurred. During the playing or exercising if you will of the speaker both the spider and the surround become more compliant (they move easier if you will). Additional measurements on samples of identical drivers indicated that the changes that occurred pre and post breakin on a single driver were smaller than the variations within a particular lot of drivers. Since there are manufacturing tolerances for drivers this indicates that whatever changes are that occur are smaller than those of manufacturing tolerances. This further indicates that the net effect of speaker breakin is nada, nothing, zilch, forget about it, etc.
In one experiment, Nousaine used a driver that was said to need 48 hours of break-in. Placing the driver in a 1.5 cubic foot box, he found the system resonance to be 53 Hz before break in. After 48 hours the resonance was 49 Hz. After a few minutes rest, the resonance had gone back to 51 Hz. The following morning it was back to 53 Hz. This indicates that whatever small changes that occur in a driver's characteristics during playback comeback to their original state after rest.
These experiments have been performed with other drivers such as from Dynaudio with similar results. Overall this indicated that whatever changes do occur, they do not change the sound quality.
Moreover, Richard Pierce, a well known consultant and speaker designer who has examined the parameters and behavior of thousands, if not tens of thousands of drivers. His findings also concur with Clark's and Nousaine's with regards to how drivers behave in the real world.
Ten years ago, he wrote the following in Usenet.
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 is 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 loosens 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 time 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 a 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 elastomer has recovered from its 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 needed to reach the Curie points of the typical magnetic materials found in loudspeakers).
What I really think is at play in all this is the adaptive signal >processing abilities of the brain. It is not the speakers which get broken in, rather it is ones 'ears'.
When this has been suggested, despite the fact there's about a century of research backing it, it is more often than not greeted with jeers and cries. See, you can't sell special "break-in" CD's if the speakers aren't broken in.
So if the sound quality does not change in any significant way, what then does occur? Well listening adaptation would then have to be looked upon as a very strong reason for the perception of speaker break-in. Anyone who has spent time listening to audio systems or components knows their opinions with regards to the nature of the sound changes with time. In the case of speakers, when one buys them and brings them home, you become used to the sound of that particular speaker. That sound may grow upon you or you may find there's something that you don't like about it. Nonetheless, however they sound in your particular home, it'll be different from the way they sounded either in someone elses home or the stores where you heard them.
Now I've had a few emails that I've sent to various speaker manufacturers over the years and these are some of the replies on this subject of break-in.
We've found (as have our dealers and customers) that the most significant changes occur within the first 75-150 hours, with smaller incremental changes occurring up to a few hundred hours. After that point, you shouldn't notice much change at all, as the speakers would be broken in thoroughly. This time is the same for each model and is best accomplished by just playing music through them.
Thank you for your interest in Revel.
Sent: Tuesday, July 30, 2002 8:37 AM
Subject: speaker breakin
Thank you for your enquiry into Krix Loudspeakers. Most speakers will benefit from a 'run in' time and our speakers are no different. We suggest running speakers at moderate listening levels for between 20 - 50 hours. After this time you should hear some differences as the components of the speakers start to 'free up',
I hope this information has helped, should you have any further queries please feel free to reply to this email.
National Consumer Sales
With all mechanical parts they do require a running in period, this ideally should be about 36 hours, what I suggest you do is listen to your speakers at a moderate level when you can over this period. Following this procedure will help prolong the life of your speakers.
Customer Specialist Support
Tel: +01236 420199
Thanks for your recent email to Definitive Technology.
In order to break-in your BP10Bs, we recommend playing them at a moderately loud volume for about 40 hours. (After this period, the suspensions on the speaker cones loosen up a bit.) Generally, you'll hear a smoother high frequency response as well as a greater openness or transparency.)
If you need any other information, please email me at firstname.lastname@example.org
Now if studies have indicated there is no significant change during pre and post breakin and that whatever changes in driver parameters that do occur, are restored to their original values over time, one must ask the question, if the speaker companies are aware of this, and larger companies, that have access to such data as I've presented here do, what is the purpose for specifying breakin that amounts to around 40 hours, give or take? To my mind, the reasons would have to do with ensuring that the customer keeps the speakers in their home for a couple of weeks to hopefully either get used to them or to convince themselves, rightly or wrongly, that they do like the speakers. During this process of listening, the customer, as can be seen on some of the posts on this forum, is actively seeking out other users opinion, corroborations, justifications, positive/negative opinions. So myself, I would recommend that anyone purchasing speakers listen to them in their homes and if during that time, which should be well before the RETURN PERIOD, they don't like them to take them back where they bought them and rethink the choice they made. Any salesman who says you need this CD or this procedure to break-in is doing so for either a couple of reasons...they're ignorant, or they're hoping you need a little more time for the speakers to grow on you so you don't return them and he/she doesn't blow the sale and commission.
As to why Thiel, and for that matter others like Anthony Gallo, subscribe to significant loudspeaker break-in, I don't know. Yet the late John Dunlavy thought it was much ado about nothing. Arnie Nudell didn't bother addressing it Neither did Kantor or Barton. I just don't know. Maybe it's a marketing position that they've taken. Maybe they say different things to different people. Maybe they're not aware of the research that's been done and that might not be so surprising considering that their focus is more pragmatic based. Other than resorting to the oft stated, "That's what I hear.", I don't think they've done any work in this area. At least none that's been shared in anything approaching a rigorous fashion. Nor do I don't think anyone's pinned them down after a couple of pitchers of beer and a few margaritas. That might be interesting.
As for my position, it seems that the work has been done to answer this question but it just hasn't been widely disseminated to the general public in a fashion that's easy to comprehend. Further, one should never break-in the speakers for so long that their ability to return them if unsatisfied is compromised.