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Author Topic: Can a driver that sat on shelf too long be saved?  (Read 487 times)

Mark Wilkinson

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Can a driver that sat on shelf too long be saved?
« on: August 10, 2022, 11:40:32 AM »

Remembered i had a pair of Meyer 15" (ST-815) in storage, that i bought maybe 15 years ago as spares.
Not sure how many years my dumbass let them sit unboxed, flat with cones facing down.
Decided recently to give them a try in some single 18" ported sub boxes i have laying around. Just made some adapter plates .

Got a whacky measurement, so i immediately checked impedance.
The left plot below is that trace.

Realized cone sag/stiff suspension was probably the problem. Been running 20Hz sine waves with about 6mm one-way excursion for long periods through them.

The middle plot is after running in the sun for 6hours yesterday.  Looks pretty good I think.

Right plot is today, where it looks like the suspension has returned towards stiff.


I've tried the 20Hz break-in with cone up, cone down, regular orientation etc.
Impedance peaks get a little higher with each successive break-in run.  This is measuring right after the run.
A measurement the next day also shows successive runs getting a little better, but with less apparent progress than compared to measuring right after a run.

In your guys experience, will these thing ever get fully right, ever loosen up ?  Or are they a lesson learned ?

Any better signal to use? Or technique?  Thx.  Mark


« Last Edit: August 10, 2022, 11:43:07 AM by Mark Wilkinson »
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Mike Caldwell

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Re: Can a driver that sat on shelf too long be saved?
« Reply #1 on: August 10, 2022, 11:01:13 PM »

How far had the cones sagged down?
Were they touching the shelf that they were face down on?

Art Welter

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Re: Can a driver that sat on shelf too long be saved?
« Reply #2 on: August 11, 2022, 04:52:47 PM »


Impedance peaks get a little higher with each successive break-in run.  This is measuring right after the run.
A measurement the next day also shows successive runs getting a little better, but with less apparent progress than compared to measuring right after a run.

In your guys experience, will these thing ever get fully right, ever loosen up ?  Or are they a lesson learned ?

Any better signal to use? Or technique?  Thx.  Mark
Mark,

Too tight, "fully right", loosened up, worn out, the continuum...

"Factory" TS specifications for pro woofers are done after break in, on warmed up drivers.

I'd expect you would find different impedance curve results the next day on a "cold" driver compared to measuring right after a run- suspension changes are dynamic.

Are you finding any frequency response or sensitivity changes when measured at normal use levels between "cold" vs after a run?

Art
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Douglas R. Allen

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Re: Can a driver that sat on shelf too long be saved?
« Reply #3 on: August 11, 2022, 06:41:15 PM »

  As Art mentioned. Heat of course effects the voice coil impedance. I'd chart the coil temp right after shutting off the signal and again 1 hour later and the next day. Do this for a few days to see if your really getting a change in the driver.

Douglas R. Allen
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Mark Wilkinson

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Re: Can a driver that sat on shelf too long be saved?
« Reply #4 on: August 12, 2022, 08:58:41 AM »

  As Art mentioned. Heat of course effects the voice coil impedance. I'd chart the coil temp right after shutting off the signal and again 1 hour later and the next day. Do this for a few days to see if your really getting a change in the driver.

Douglas R. Allen

Thx guys,

@ Mike,
I meant to say drivers were in unopened boxes. So I couldn't see any sag.
It's funny, visibly,  they haven't ever looked like there is any sag.
I've been wondering if the suspension hardened in a way to make an asymmetric load on excursion.

On the DIY forum, I asked about these and there Art suggested I check with Meyer to make sure there is no ferrofluid in them....been side tracked, and plan to do that today.

@ Art,
There has been enough change in the sound, cold vs a long break-in run, that I haven't run transfers yet.
I've been thinking this is a relatively minor problem that will just go away with extended break-in...and really, I guess i haven't done the proper homework yet.

@ Douglas,
I've been doing exactly as you suggest.  Measure cold before break-in run, measure right after break-in run, and then measure cold after full cool down.
I've done this 3-4 times indoors, and 3 times outdoors in direct sun.

There has always been a huge difference between the hot and cold impedance curves, far more so than on any other subs I've measured.
But so far, both hot traces and cold traces continue to gradually move higher with each successive break-in run.

That is why i've thought progress is being made, but the progress is so slow that I posted here to see if others have experienced something similar, and if there is a better way to go about this.

(I'll give Meyer a call, and run some hot and cold transfers to gain more info...)


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ProSoundWeb Community

Re: Can a driver that sat on shelf too long be saved?
« Reply #4 on: August 12, 2022, 08:58:41 AM »


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