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[Jim McKeveny]

Measuring the impedance some new out-of-box 18s, I was reminded of how much difference there can be in the early life of a cone v. the preponderance of its life cycle. The factory spec was 34hz, the measurements on new cones was 46+hz. That is pretty significant difference as a percentage.

B&C does note on their spec sheets that a high power level of 20hz is applied for a period of time to break-in suspension before measurements taken. I'm sure other mfrs. do similar.

Question: Wouldn't this difference impact the early performance of speaker cabinets closely aligned() with a particular Fs +/- ? Lower order tunings perhaps not so much, but horn, tapped horn, and bandpass boxes? And should we not measure/judge LF performance on any minutes-old system? Anybody? Ivan?

[Art Welter]

Question: Wouldn't this difference impact the early performance of speaker cabinets closely aligned() with a particular Fs +/- ? Lower order tunings perhaps not so much, but horn, tapped horn, and bandpass boxes? And should we not measure/judge LF performance on any minutes-old system? Anybody? Ivan?

Fb of a bass reflex, or Fc in a horn system is unaffected by raising driver Fs,  a higher driver Fs would generally affect higher order tunings more.
At the low power levels (milliwatts) that a speaker is often measured at, a suspension not "broken in" might read 10 Hz high, but at the actual levels in use (a few watts to hundreds) will still respond pretty normally.
It could take months for a driver to "break in" to a factory specification if it's suspension is never pushed near Xmax for at least a few minutes. If a high powered driver is going to be auditioned at very low power, it needs to have been "broken in" prior to the audition. 

[Luke Geis]

I am not sold on the whole breaking in of drivers idea. There should be no instance where you take a set of speakers out of the box at an event and run it. You will almost certainly take them out at the shop and orientate yourself with the new speakers a little. And I would venture a pretty good bet that even if you did take them to an event, after your day of setup and tuning them and then doing your own show and tell session, the drivers will likely be pretty much ready to go. If there is a 10% variance out of the box from the " broken-in " spec, I would not be too worried. Most resistors in any given piece of gear has up to a 10% tolerance. I would also bet that the quality control at the upper echelon of equipment supplied by Martin, L'Acoustics, D&B, et all, has a much smaller allowable tolerance for any given piece of gear, where even if it was off by a little out of the box, after a show or two it would be on par.

[Ivan Beaver]

To be honest, I have only performed one "break in test".

It was with a B&C woofer.  I placed a new driver in a tapped horn, and measured it.  Then subjected it to some various "break in" signals for a significant period of time.  Sine wave, pink noise etc.  NO, I did not use any fancy "hi-fi" break in signals.

I made sure the post break in temp was very close to the original measurement and the humidity had not changed (not enough to matter anyway)

Also making sure the cabinet and mic positions did not change.  This was done inside the warehouse, so lots of open area, and also making sure nothing have moved (ie reflections) to affect the signal

The result was less than 0.1dB variance at the most.  Over most of the range (no highpass or low pass filters were used), the post break in was exactly the same as the original.

So yes, there was a change.  Did it matter?  If I go pee in a lake, does the lake level change? YES.  Does it matter, NO.

Would other drivers act the same way?  To be honest, I have not measured them, but I would still say, not enough to matter.

[Steve-White]

Not to sound "Jerkoffish" but Luke nailed it.  While loudspeaker "Break-In" is something that can be measured and "quantified" without a doubt.  IMO it's more of a "Run-in" than a break in.

An engine goes through a "Break-In" and should in fact.  In some cases must go through proper break-in to ensure maximum performance and lifespan.  Per instructions I did an initial "Break-in" procedure on a new air compressor to seat the rings on the pump pistons, on the milling machine to run-in the spindle bearings, on the lathe for the gear boxes & spindle bearings.  The Quincy compressor has a rated pump life of 50,000 hours (Yeah, seems a bit much but still it's designed to take a beating) and at 31 hours of run time, barely has any oil mist (smoke) coming out of the crankcase breather as it's still "Breaking-In" and will probably be seated at ~100 hours.

Taking a new cone driver and measuring it, then run it 100 hours and measure it again at the extreme low end region near the Fs and it will read differently.

Does it matter?  No.  Do they need any type of run-in?  No.  Take 'em out an pound 'em.

Driver break-in is for Audiophiles that run magic power cables that enhance signal performance and are audibly "different".  Perfect example of the placebo effect - spending more money must matter. 

[Riley Casey]

Why do I feel like I'm reading a thread from the hifi nut forums?

[Chris Grimshaw]

To be honest, I have only performed one "break in test".

FWIW, I've watched Fs drop by about 10Hz after some hammering, but the online consensus is that the T/S parameters will shift in complementary ways. ie, while the numbers may shift around, the sum remains roughly the same.

When it comes to subwoofer drivers etc, I'll always hit them with some high-power VLF signals in free air, to make sure the only sound is air rushing around the voicecoil. Just a quick QC check to make sure the driver is performing as intended.

Side note: the new 18" super-subs can move some serious air.


Chris

[Helge A Bentsen]

I have a pair of dipole subs in my living room. After some days use I noticed a slight increase in the low end of the sub (below 40hz). Enough that I had to pull out a few dB's of low end boost to balance them out again. These subs have a pretty hefty low end boost as a part of their DSP design.
Talked to a transducer engineer, he told me that this was not unusual in dipole designs due to slight drift in T/S parameters. He also said that it's pretty rare to hear a difference in sealed/ported boxes due to the T/S parameters balancing each other out against the box.

[Jim McKeveny]

I have a pair of dipole subs in my living room. After some days use I noticed a slight increase in the low end of the sub (below 40hz). Enough that I had to pull out a few dB's of low end boost to balance them out again. These subs have a pretty hefty low end boost as a part of their DSP design.
Talked to a transducer engineer, he told me that this was not unusual in dipole designs due to slight drift in T/S parameters. He also said that it's pretty rare to hear a difference in sealed/ported boxes due to the T/S parameters balancing each other out against the box.

Thanks for all the replies. The essential of my question was: How meaningful is this measurement?

[Art Welter]

Thanks for all the replies. The essential of my question was: How meaningful is this measurement?

Jim,

What measurement, and at what drive level is "this measurement" taken at, and what pre-conditioning prior to test?

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