Driver 'break-in' period

[Vikash]

To my knowledge the measured T/S parameters a greatly dependant on the current used when measuring the parameters. This means that you absolutely must use the same test conditions as the manufacturer in order to me able to compare results.

The measured T/S params for the XLS10 are very similar to that provided by Peerless. I'm guessing that our test conditions are quite different.

I can’t seem to find any information about the conditions where the T/S parameters are measured, but it’s it certain that the driver would need a long time to cool off, as the temperature increase during “burn in” in both electrical and mechanical parts need to be eliminated before measuring the parameters.

Measurements are taken in a warm home offiice. I left at least 2 hours between break-in and measuring.

Now that the air con unit is here, perhaps it would be interesting to test one of those drivers at the most extreme temps I can to see the effects...

 

[JensRasmussen]

Time to wait after the”burn in process” depends on the thermal time constants of the driver. Have you any measurements of the DC resistance? A change in DC resistance, from the new driver, would indicate to me that the driver has not been cooled for a long enough period. 2 hours seems a bit short, comparing to the 12 – 16 hours I used on a 6½" driver when I did my thesis on thermal speaker models. Anyway some numbers would be great, since they would tell quite clearly if the driver has been probably cooled.

Qoute:
“The measured T/S params for the XLS10 are very similar to that provided by Peerless. I'm guessing that our test conditions are quite different.”

Drivers of that size have longer linear displacement capabilities, and maybe therefore it’s less sensitive to different measurement currents. What sort of constant current amplifier are you using?

\Jens

 

[Vikash]

Time to wait after the”burn in process” depends on the thermal time constants of the driver. Have you any measurements of the DC resistance? A change in DC resistance, from the new driver, would indicate to me that the driver has not been cooled for a long enough period. 2 hours seems a bit short, comparing to the 12 – 16 hours I used on a 6½" driver when I did my thesis on thermal speaker models. Anyway some numbers would be great, since they would tell quite clearly if the driver has been probably cooled.

Qoute:
“The measured T/S params for the XLS10 are very similar to that provided by Peerless. I'm guessing that our test conditions are quite different.”

Drivers of that size have longer linear displacement capabilities, and maybe therefore it’s less sensitive to different measurement currents. What sort of constant current amplifier are you using?

\Jens

DC resistance remained constant the few times I measured it (AP100Z0), which was once at 0 hours and then again after the first break-in + rest. Since there was no change I assumed that it didn't require measuring again.

But, I do remember a change in DC resistance on the XLS10 but discarded it as an error on my part for not accounting the DMM's resistance. This could actually have been insufficient cooling time then...

I did not use an amplifier for T/S measurements. I find that my SC outputs to a sufficient level. Some details of measurement setup here:
http://www.vikash.info/audio/sw_jig/measurements.asp

 

[Vikash]

Anyway some numbers would be great, since they would tell quite clearly if the driver has been probably cooled.

I've found the log I kept with details on measurements and times they were taken. It may be of some use.

 

[greyhorse]

Ok, I got one for all of you in the break-in doesn't exist camp. What you're all saying is that break-in is just the mind getting used to the new speakers, and that what we're hearing are the relative differences between the old and new speakers right?

Then why is it, that everytime I supposedly upgrade to a new set of speakers, I get bass that's either thin and restrained or indistinct, and I always perceive less of it? Are you telling me that every time I upgrade, I'm getting consecutively less and less bass? I might as well buy the cheapest drivers in the world to get the best sound then huh? Who'd a thunk it? That's what we're all doing wrong!

But hey, the same thing can be said across pretty much the whole frequency spectrum. Every set of speakers I bought, save the last set, which makes 7 pairs in all, have had very indistinct midrange and treble performace to begin with. Just out of coincidence, every set of speakers I bought have all been downgrades too I guess. Now I'm really sorry I threw out those Sony SS-A5Ss...

 

[Ron E]

Ok, I got one for all of you in the break-in doesn't exist camp. What you're all saying is that break-in is just the mind getting used to the new speakers......Then why is it, that everytime I supposedly upgrade to a new set of speakers, I get bass that's either thin and restrained or indistinct, and I always perceive less of it?

Interestingly enough, the bass usually changes very little if at all due to the loosening of the suspension. The changes are complementary and the resulting changes in frequency response are very often less than 0.5 dB over a small bandwidth, like 1/3 to 1/6 octave - although it depends on the alignment. I bet the difference between a Q of 0.7 and 0.68 just stands out like a sore thumb.....

But hey, the same thing can be said across pretty much the whole frequency spectrum. Every set of speakers I bought, save the last set, which makes 7 pairs in all, have had very indistinct midrange and treble performace to begin with.

For the same reason you have to get used to a new cellphone or any other sound reproducer - because it is different, not because it is worse.....remember that crappy reentrant PA horn on your last boat tour? By the end of the tour, you could almost understand what the guide was saying....

If everything was "indistinct", it is "amazing" that you thought the speakers were an "upgrade" to begin with

 

[RHosch]

Of course there is a driver break-in period -- and althou it may level off, it continues until the driver dies... it is a physical device subject to mechanical stress...

I have heard many a time, same speaker, same driver lot, unbroken in speaker, next to broken in speaker. Clearly not the same. And a large enuff sample set that it wasn't a fluke.

It's like a pr of blue jeans. Stiff when you get them, needing some wear & washes to get them comfy.

dave

Materials stressed past their yield point (or something similar to it, depending on material model used) will indeed change with mechanical stress. But I must ask you... does the coil spring on your car lose stiffness with age? Why not? And why do you assume that speaker surrounds and spiders are more like leather baseball mits than car suspension coil springs?

More importantly, what driver designer in their right mind would use materials that more closely followed the behavior of a leather mit than a car coil spring?

There is an age old fallacy regarding break-in that can be summarized as "all mechanical devices subjected to repeated stress break in." Well... wrong. There are plenty of materials that below a certain stress limit and strain limit will exhibit indefinite fatigue life, and show no change in modulus at all with cyclic aging. There are plenty more that exhibit a change in strength, but not stiffness. There are precious few that show strong strain/modulus relationships... natural rubber being one of them.

 

[Ron E]

ANother argument against break-in, and for accomodation - assuming for a moment that break-in occurs and there are real changes in the frequency response that are not predicted by T/S parameter shifts...

Why are the changes _always_ to the better? Something to think about.....

I have _never_ heard anyone say something like, "yeah it sounded great until it broke in and then it was pure rubbish....."

 

[Vikash]

Why are the changes _always_ to the better? Something to think about.....

absolutely

 

[greyhorse]

By that logic, any time we listen to a system widely different from what we're used to listening to, we should hear it as sounding bad. And yet this isn't case with a number of systems I've had the chance to listen to, and I'm sure you've heard systems like this yourself.

How is it that "mental adjustment time" is needed -every time- I buy/build something new, but isn't needed when listening to an already burned-in system? I personally hate this burn-in thing, and would like to avoid it if I could. I'm having to endure it right now, and it's agonising.

I'm not sure how relavent this is, but Sony used to take the time to break-in thier premium speakers for several days before shipping them, so customers wouldn't have to hear the speakers at thier worst. This was in Japan, and back when Sony used to make serious speakers. My father was in charge of production for some of the cheaper Sony speakers at the time, and was friends with a lot of the design engineers there.

 

[greyhorse]

More importantly, what driver designer in their right mind would use materials that more closely followed the behavior of a leather mit than a car coil spring?

A lot of foams used for speaker surrounds disintegrate when exposed to UV, but designers use it anyway. While it would be great if speakers lasted forever, I'm sure the choice of using a given material has more to with its acoustic properties.

There are plenty of materials that below a certain stress limit and strain limit will exhibit indefinite fatigue life, and show no change in modulus at all with cyclic aging.

Are these materials commonly used in building speakers? I'm kind of curious actually, rather than defensive, if these materials are used, and in what brands.

 

[RHosch]

A lot of foams used for speaker surrounds disintegrate when exposed to UV, but designers use it anyway. While it would be great if speakers lasted forever, I'm sure the choice of using a given material has more to with its acoustic properties.

The point is that if the design goal is to build a predictably linear suspension (spider and surround), which is a reasonable design goal by any standard, the design engineer would choose materials that best accomplish that goal. Non-linear materials or materials having high cyclic strain elasticity effects (like dryed leather, for example) would be avoided like the plague. Surrounds are chosen for their ability to operate in the purely elastic region... if they are also very long lived, that is a plus.

Are these materials commonly used in building speakers? I'm kind of curious actually, rather than defensive, if these materials are used, and in what brands.

Of course they are. Practically any synthetic polymer operated in its elastic region will exhibit a very, very weak correlation between cyclic strain and modulus drift. So weak as to be a non-factor as far as break-in is concerned. The one exception in common speakers is varnished spiders, which can have excess varnish in the folds that yields (effectively changing the fold/joint stiffness) quickly during driver motion. This yielding should take in the dozens to hundreds of cycles. Even a bass driver playing the lowest frequencies should be fully "broken-in" in a few seconds... a minute at the extreme.

I should point out that some of these materials can display a frequency dependant modulus (visco-elastic material model), and others can change modulus over time as the chemical structure changes due to age (drying caused by chemicals leeching into the air). Neither of those is related to "break-in" as popurlarly described however.

 

[roddyama]

...
I should point out that some of these materials can display a frequency dependant modulus (visco-elastic material model), and others can change modulus over time as the chemical structure changes due to age (drying caused by chemicals leeching into the air). Neither of those is related to "break-in" as popurlarly described however.

You also have to take into account the affects of curing. All of these polymers and chemicals will go through a curing process for days and weeks after being formed. Not to say this is the Holy Grail, but physical changes will occur during this process. The excitation of operation along with temperature variation will increase or delay this process.

 

[Ken L]

.... the design engineer would choose materials that best accomplish that goal.......

Hi RHosch

Good to see you around - hope all is well with you _grin_

In a theoretical and perfect world - the design goals would be accomplished perfectly -

However, the designer is limited to those material that _best_ accomplish his goals within the limitations imposed by various factors.

Since he is not working in a _perfect_ environment with perfect materials it is not unreasonable that the finished product has limitations that would result in "Break-in".

As to theory vs practical - Planet10, the moderator of this forum has a _lot_ of practical experience with certain drivers and he readily believes in "break in" because of his observations -

I'll put my money on _experience_ before theory _big grin_

Regards

Ken L

 

[RHosch]

You also have to take into account the affects of curing. All of these polymers and chemicals will go through a curing process for days and weeks after being formed.

Which will take place long before the speaker ever makes it to the OEM's integration facility, and loong before the finished product ever arrives on your doorstep.

 

[RHosch]

However, the designer is limited to those material that _best_ accomplish his goals within the limitations imposed by various factors.

Since he is not working in a _perfect_ environment with perfect materials it is not unreasonable that the finished product has limitations that would result in "Break-in".

You are imagining a limitation where none exists. Materials which continue to operate in a linear elastic manner independent of applied cyclic or non-cyclic stresses below a certain threshold are plentiful. Many of these can be found in various speakers. For all practical purposes, these materials behave "perfectly" for their given lifespan, in the context of elasticity and "break-in" at least.

What you are saying is what Planet10 essentially said... that being "all materials wear out." Well, in the context of practical uses, that just isn't true. A steel spring that doesn't corrode will behave the same now as it does billions of cycles from now. Many materials behave in this linear elastic manner.

As to theory vs practical - Planet10, the moderator of this forum has a _lot_ of practical experience with certain drivers and he readily believes in "break in" because of his observations -

I value experience as well... especially when it is gained without the influence of bias. Unfortunately bias is difficult to remove in everyday living, so much of Planet10's experience has to be viewed in that light. I'd be particularly interested in any experience he has under controlled conditions however.

 

[Ken L]

You are imagining a limitation where none exists.

We have perfect materials today?

Designers don't work under limitations imposed by price and manufacturing processes,etc.?

Regards

Ken L

 

[phase_accurate]

Non-linear materials or materials having high cyclic strain elasticity effects (like dryed leather, for example) would be avoided like the plague.

No they are in fact used !!! Some drivers exhibit a progressively nonlinear restoring force in order to protect them from overexcursion.

A steel spring that doesn't corrode will behave the same now as it does billions of cycles from now. Many materials behave in this linear elastic manner.

I dont' expect Hooke's law and the related theory of material properties to be more accurate than Ohm's law for instance (in fact I believe the contrary). And the latter one is also a simplification !!!!

I recently had a pair of drivers broken in using a sweep generator and an excursion between +- 5 mm and +- 10 mm. And yes I have the feeling that the LF reproduction improved. But I may also ask the one who built them about his experiences regarding this subject.

Regards

Charles

 

[Vikash]

No they are in fact used !!! Some drivers exhibit a progressively nonlinear restoring force in order to protect them from overexcursion.

If you're talking about the suspension, then perhaps its more to do with the arrangement allowing for progressive restoring force rather than the material. Hence, once the force is removed, it springs back to its starting form.

 

[roddyama]

You also have to take into account the affects of curing. All of these polymers and chemicals will go through a curing process for days and weeks after being formed. Not to say this is the Holy Grail, but physical changes will occur during this process. The excitation of operation along with temperature variation will increase or delay this process.

Which will take place long before the speaker ever makes it to the OEM's integration facility, and loong before the finished product ever arrives on your doorstep.

This is not necessarily true. Case in point, the US-EPA requires measurement of the off-gassing of curing polymers used in vehicles long after the vehicles have been assembled and left the factory.