Break-in. Best Practice or BS?

[moldyoldy]

I'm interested in some intelligent discussion regarding cone driver "break-in". My current reasoning tells me that a cone driver's suspension has the proper (intended) compliance upon assembly, and that this same compliance should continue for the life of the driver. However, many claim that cone drivers must be "broken in" by continuous long excursions before they will perform as designed. I contend that if a driver's compliance can be altered substantially in a few hours use, that such change would continue with further use, and soon render the driver useless. Do any manufacturers recommend break-in?

[Earl K]

Here,

- See the text that's circled and underlined .

- Obvously ( from the gif. ) extreme mechanical movement does alter the compliance . I doubt that every woofer shipped by JBL goes through such a maximum power test .
- I've broken in many foamed compliances. Each woofer type and compliance type will have a uniquely identifiable shift ( within a limited range ) of its Fs ( effected by compliance ) . This will shift the ts parameters around .
- I guess if a person isn't measuring Fs, then they'll be unaware of this shifting.
- The compliance ( therefore the Fs ) does stabilize at a set figure. But eventually, with continous maximum input wattage ( constant hard usage ), these figures will eventually go down as the hinges ( the spider & the compliance ) wear out .

[Don Mascali]

It is customary to "Break in" a new VLF or LF driver before testing T/S parameters. They change significantly in the first couple of hours of operation.

On the other hand, I always considered the suggestion to listen to new systems for a while before making a judgement as allowing time for your ears to become atuned to the new sound and forget the last system. Ears seem to have a very short memory span.

[Zilch]

There's a measurable, indeed, significant, shift in Fs (and other parameters) with break-in.

JBL specs incude it as part of the test procedure; two hours, as I recall. I just run new drivers overnight at more modest levels than JBL's power test.

My understanding is that it is required for the new materials to establish their flexural "seat," and while the process does continue, it's asymptotic.

Presumably, both spiders and surrounds are involved at low frequencies, but it's easily envisaged that preferred flexural patterns would also develop within the cone and dust dome at higher frequencies.

Interestingly, I did not detect a significant change in Fs when breaking in butyl-surround LE14H-3 drivers; it may be they were run-in at the factory, tho....

[Tom Brennan]

"After several hundered hours use the micro-dynamics became more coherant and the soundstage both broadened and deepened"

And all that bullshit.

[Don McRitchie]

There's a measurable, indeed, significant, shift in Fs with break-in.

JBL specs include it as part of the test procedure; two hours, as I recall.

I believe that this is just done to simulate operating conditions. Documentation that I have encountered on this subject indicated that if you then allow the driver to rest for some period of time and test it again with no power conditioning, it will usually measure back at its original pre break-in numbers.

I remember John Dunlavy posting on this subject on Usenet a few years ago. Back at the time that he was running Dunlavy Audio Labs, he was reliant on third party drivers for his systems. As a result, he did extensive testing on break-in and other factors in selecting his drivers. In most cases, while there were measurable changes after power testing, they usually returned to their pre power test state after a period of rest. In other words, most "break-in" phenomenon he discovered were just temporary dynamic changes and not a permanent physical change.

[Zilch]

Yet in the example Earl cited above (2242H), JBL publishes the post-power-test value (35 Hz) as the T/S Fs.

:dont-know

If the change is not permanent, then woofer testing for box design is a wank? I'm always looking for measured Fs to closely match published T/S....

[Don Mascali]

The average DIY hobbiest probably uses the published T/S data and can hit the mark on tuning. If you were to use the initial data you could miss it by quite a bit.

The speakers would only sound good when you came back from vacation and would creep away from optimum tuning after a little regular listening.

[4313B]

such change would continue with further use

It does, it's a mechanical object. It will wear out. That's why we recone them. Recones aren't just for cones and domes little kids decide to kick in. JBL has new designs that reduce excessive suspension wear.

I also fully agree with your designer's standpoint issues, but most of us aren't on that end of the food chain. Remember, this is in General Audio, not DIY..

Good clarification.

I'm seeking the best answer for the masses

That would be "plug and play". Can't think of much else to say except maybe .

I suspect that drivers are being damaged by inappropriate methods used by the uninformed.

I neither suspect it nor care. In fact, I don't give any thought to what anyone else is doing to their drivers at all. I'm busy with my own crop of drivers.

woofer testing for box design is a wank?

No. You do what you need to do to implement your specific intended application.

So, my box tuning varies significantly depending upon how long it's been idle?

Box tuning is largely independent of what transducer is mounted in it. If you want to get picky, a box tuning might measure slightly different with a 2235H in it instead of a D130 if only because of specific drivers loses (e.g. center dome and surround porosity) and potential volume displacement differences. Environmental factors can also affect box tuning due to changes in the density of air.

If you use eBay at all you will know that none of this matters anyway. If the surrounds are rotted out of your drivers, the domes are kicked in, and the spiders are shot to hell it will not affect the sound.

*****

Here's some old data on a fresh LE14H-1 recone:

I don't have a problem with pulling the driver from it's box tonight and measuring it again. It's been in a 240Ti box for quite some time now.