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Old 09-26-07, 08:57 PM   #1
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Driver Break in - Fact or Fiction?


I have notice a debate about speaker break in on this and other forums. As someone that has been around this for many years, particularly at the factory level, I would like to offer my observations and some facts to clear the air.

Quote:
I think where the myth of break-in occurs is at a factory production level.

Most speaker drivers are tested to verify their T-S parameters and frequency response before assembly. This requires some testing at the factory. Plus, once a speaker is built, there is usually a test period to verify the crossover and drivers are all working as planned. Granted, this is not a full 40 hour burn in, but the drivers have at least seen some use before going to the consumer.
It is true that the drivers do see some testing prior to final pack out, but it is not really accurate to say that this breaks them in.

Generally, a driver will get a sweep test a couple of times during it’s life and nowadays, a response check as well. Sweep voltage depends on the customer or manufacturer’s preference, but you would find a lot of drivers swept at about 4 to 5 volts from their target resonance to a bit higher up to around 5K. Tweeters a little different, but again, a reasonable range; mainly looking for loose particles or a RVC condition (voice coil rub). This sweep will typically be over in 3 or 4 seconds max- that is it. You would again have this sweep test as the driver is installed into the system and again at the system level. The amount of change you see in the suspension is minimal- there are just not enough cycles or at a high enough power level to really impact the stiffness of the damper or the compliance of the surround.

Testing – for instance a MLS or other stimulus – response test is also at a very low level and is completed in a few seconds- again, you just do not have the power or duration there to impact the compliance of the driver. When it comes to testing tweeters, you will often see differences as well- often due to dispersion of the ferrofluid in the gap. I have done a very extensive study on this as a QA – manufacturing project for a high end and very well known OEM who we supply automation equipment to and the ferrofluid balance was the biggest factor for changes in the tweeter over the first few hours of it’s life. (FYI- When I proposed this concept before the study was done- I even thought it to be an absurd notion but the facts were that it was actually the thing that caused a lot of problems at the manufacturing level.) For drivers that do actually get a parameter test run on them before shipment (very uncommon except among more expensive subwoofer drivers), the signal level is very small and the timeframe is very short. There are a couple of platforms out there that will do rapid T/S parameter testing using a fixed Mmd based calculation. MLSSA, Clio QC and I believe Sound Check will do that sort of testing. You can use a Klippel to do high level testing, but this takes quite a while and is certainly not a production level test for any driver that I know of.

For those that do not believe in the break in time for a driver, here is a way to prove it to yourself once and for all…

Break in is very real and anyone with basic testing skills and equipment can verify that it does happen. How? First of all, you can look at the driver Fo – right out of the box. Measure this about 10 times and then average the number. Now put a signal through it at moderate levels for about an hour. Let the speaker cool down for one hour. Measure the Fo again, get the average and compare. Want more proof? Go for the full Monte T/S parameter testing using a similar routine… Multiple tests, average the numbers and then run a signal on the driver for an hour or so. Cool down time, re-test, re-average and compare. Still not convinced? Set up the driver in an anechoic environment, lather, rinse, repeat as before and observe the differences in the response, particularly near resonance.

What breaks in?? Mostly the damper, but to some degree, the surround as well. In general, the surround has a far smaller impact on the mechanical model of the speaker, but it is there a little bit. Mostly look at the damper and how much it changes over the first few hundred cycles at or near Xmech and resonance. There may be other factors as well, but they are going to be minor in comparison to the damper compliance change and the overall changes in the mechanical model of the speaker as related to that. Obviously, in a design that does not have a damper, the changes you observe will be different. Tweeters and other single suspension devices typically operate at very low excursion, higher frequencies where the mass and shape are the bigger factors.

Electrical break in- I have also looked at electrical break in of drivers and I will say that it ranged from minimal to a non-issue on a typical driver. There are slight changes in the coil after heating and the magnets can loose some of their zip if overheated; especially cheap-o and low Y factor stuff (it is my experience that is true anyhow…). This is mainly a factor in the cheaper stuff that most of you would not have any desire to fool with, but is all over the word, particularly in LCD / Plasma TV sets and other consumer goods where the heat generated by the driver is not the big issue- the device that the driver is located in is the overriding factor. You would also see differences in the planar drivers such as the Neo 3, but I would expect them to be absolutely minimal at the electrical level unless the driver was abused or overheated.

Others here may have done studies related to the electrical changes in coil drive devices (drivers and tweeters) and they may have different experiences or comments. Particularly in a case like a large, high power sub with a multi-layer coil and enough Bl to bend space a little bit. I have not had the opportunity to delve into that sort of driver on a study like this, but it would be interesting to hear from some that have. Manville from JL is probably the most likely candidate that I know of on here- they (JL) have a lot of really heavy duty drivers and I believe that JL actually puts a lot of brain power into their products. It would be interesting to hear from them on this topic.

Edited note - Damper = Spider


Last edited by phaseshift; 09-27-07 at 02:11 AM..

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Old 09-26-07, 09:56 PM   #2
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Re: Driver Break in - Fact or Fiction?


Yeah, I've seen before and after measurements of LF drivers showing changes in Fs, Cms and Vas. I've seen measurements for the TC-3000 here and I saw measurements for a Peerless woofer on another site.

The only thing that gets me is breaking in cables.


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Old 09-26-07, 11:11 PM   #3
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Re: Driver Break in - Fact or Fiction?


Quote:
Geoff St. Germain wrote: View Post
The only thing that gets me is breaking in cables.
Only if they're properly isolated from the floor and made of pure silver whose molecules have all been oriented in the same direction lol!!

Great read phaseshift. Thanks!


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Old 09-27-07, 12:40 AM   #4
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Re: Driver Break in - Fact or Fiction?


Thanks for the detailed explanation Gui... I've made this a sticky here and copied it to the Home Audio Speakers forum as well.



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Old 09-30-07, 04:53 AM   #5
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Re: Driver Break in - Fact or Fiction?


As someone who has always believed in speaker break in only because every moving object wears at some level thus changing its characteristics not because of testing and various study results. I have often wondered just how much impact the break-in has on sonics of a speaker system. Is it really audiable? I haven't had the pleasure of owning a set of speakers from new, just drivers for my own homebuilt projects, yet haven't heard anything to write home about after a few hours/days of use.

Now I know my ears aren't that bad, I manage to score all the difficult audio engineering jobs like multi sophited churches with bucket loads of big brick pillars, or engineering the local charity concert in a stage theatre from a room 99% detached from the auditorium . although I am no professional, I never seem to detect enough of change in sonics to warrant the worry about it.

What are other peoples thoughts on the perceptability of this?


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Old 10-01-07, 08:23 PM   #6
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Re: Driver Break in - Fact or Fiction?


Quote:
drf wrote: View Post
As someone who has always believed in speaker break in only because every moving object wears at some level thus changing its characteristics not because of testing and various study results. I have often wondered just how much impact the break-in has on sonics of a speaker system. Is it really audiable? I haven't had the pleasure of owning a set of speakers from new, just drivers for my own homebuilt projects, yet haven't heard anything to write home about after a few hours/days of use.

Now I know my ears aren't that bad, I manage to score all the difficult audio engineering jobs like multi sophited churches with bucket loads of big brick pillars, or engineering the local charity concert in a stage theatre from a room 99% detached from the auditorium . although I am no professional, I never seem to detect enough of change in sonics to warrant the worry about it.

What are other peoples thoughts on the perceptability of this?
The point I am getting at here is not to say what a person can or can not hear… That is up to the individual listener. My point is that there are mechanical changes in a speaker that can be measured and that do have some impact on the performance, including the response.

I would say that from a listening only point of view, it would likely be a lot tougher to distinguish differences in a speaker system in a PA application as opposed to a listening room or other hi-fi application. In the typical PA application, you have a lot of reflection and acoustic issues from the room + multiple source points, multiple path lengths and in a lot of cases, you are not able to use common speaker sets to fill the venue. My experience tells me that distinguishing a difference in that sort of environment would be just about impossible unless you were starting from scratch with all new gear and you have a pretty “clean” environment (less reflections than your typical auditorium).

From a DIY point of view, I would say that this is the best opportunity to see the changes since you can measure, poke and prod the speakers and see the changes before you put them into the system. Just as importantly, you can see how closely the drivers match as a new set and how much they change and finally, how close they are after they have been in use for a few days.

As a side note-
My wife saw me typing on this topic and said “why don’t you mention how simply pressing on a (new) driver far enough to get near bottoming will make the Fo drop a bit or how massaging the tweeter dome will sometimes fix the problems with the response?”. Well, she is right; the simple act of just running a driver through it’s suspension limits one or two times will give you changes on the mechanical side of the equation.


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Old 10-01-07, 09:46 PM   #7
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Re: Driver Break in - Fact or Fiction?


I just spent over an hour talking to a friend who just happens to work at one of my favorite high end audio stores here. National Audio and befor that Premier Audio (he has worked these stores for over 15 years so he knows his stuff). He said without a doubt there is a break in period for speakers. Some are very noticeable and others not.
This is even more evident in subs because of the excursion that the speaker has to do. The speaker surrounds soften up and the coil will change as it heats up and the copper expands and fits into place. This will take weeks of use sometimes before all has settled into place.


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Old 10-01-07, 09:51 PM   #8
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Re: Driver Break in - Fact or Fiction?


Quote:
tonyvdb wrote: View Post
I just spent over an hour talking to a friend who just happens to work at one of my favorite high end audio stores here. National Audio and Premier Audio(he has worked these stores for over 15 years so he knows his stuff). He said without a doubt there is a break in period for speakers. Some are very noticeable and others not.
Yet another anecdotal report. Old news.


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Old 10-02-07, 12:26 AM   #9
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Re: Driver Break in - Fact or Fiction?


Thanks for the response, but I am not questioning the fact that there is a break-in in drivers. As I said before simply the fact that it is a mechanical device suggests there has to be some sort of change in its structural integrity over use. The reference to P.A and re-enforcement drivers was merely a clarification of my hearing abilities*, I did not mean for it to sound like I was referencing p.a gear as a means of judging whether or not break in occurs.

I was/am, however, interested to know how many people believe they have perceived an audiable change in drivers after a break-in has occured?

I think your wife is right too, although I would still question how perceivable the change is after a cone was massaged or brovcken in in such a manner.

*on a side note; I have noticed that even the cheapest hi-fi drivers/enclosures are leaps and bounds above top end Pro-audio gear as far as clarity and depth are concerened.


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Old 10-02-07, 06:23 AM   #10
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Re: Driver Break in - Fact or Fiction?


Quote:
Kal Rubinson wrote: View Post
Yet another anecdotal report. Old news.
Yes it is, for those who are familiar with the subject. But it's "new" news for someone who is just learning.


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