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Author Topic: Cleaning compression drivers help please!  (Read 6939 times)

Alan Singfield

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Cleaning compression drivers help please!
« on: March 06, 2014, 07:01:30 am »

Hi,

I have some JBL 2445's, which look like they have been left somewhere damp.

Basically there is heavy oxidisation and what looks like rust around the edges of the driver.

Since all the diaphragms have failed on these, I'm looking for any tips on how to clean them.

I've attached a picture of the offending articles.

Abrasives are out presumably, as they will scratch the surface of the aluminium.

Any advice welcome. Thanks in advance,
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Alan Singfield
Sound Engineer/Director
Black Box Professional Audio
Glasgow, UK
www.blackboxproaudio.com

Jim McKeveny

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Re: Cleaning compression drivers help please!
« Reply #1 on: March 06, 2014, 07:55:08 am »

I hope someone can post otherwise, but there really isn't any reasonable cost method to bring those gaps into a usable spec, in my experience. There is an impulse to dig in there with aluminum oxide paper, but the results would never be square enough for critical use.

Last time I saw drivers in this condition they had come out of bar room wedges. A horn is just a backwards funnel!
« Last Edit: March 06, 2014, 07:59:41 am by Jim McKeveny »
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Steve M Smith

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Re: Cleaning compression drivers help please!
« Reply #2 on: March 06, 2014, 08:07:15 am »

I have nothing of value to add but it's nice to see the words oxidisation and aluminium spelled correctly!

You certainly have nothing to lose trying to clean them up.  Perhaps some white vinegar could remove some of the oxidisation (there - I did have something to add after all!).


Steve.
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Nick Enright

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Re: Cleaning compression drivers help please!
« Reply #3 on: March 06, 2014, 08:29:17 am »

I hope someone can post otherwise, but there really isn't any reasonable cost method to bring those gaps into a usable spec, in my experience. There is an impulse to dig in there with aluminum oxide paper, but the results would never be square enough for critical use.

Last time I saw drivers in this condition they had come out of bar room wedges. A horn is just a backwards funnel!

yep, to everything. If it's not critical, try cleaning with caig deoxit and a brass brush at first. 1000grit is what I've used to remove oxidation from various parts of compression drivers.

if the gap is really bad you can sorta save it with cardstock and 1000grit wet/dry paper. wrap the cardstock in the paper, this provides a stiff enough surface to support the paper. slide it into the gap, it'll cut the oxide into very fine slurry with the caig.

Clean very very well with masking tape and cardstock.

Even when I'm cleaning non-rusted compression drivers I'll slide a piece of 1000grit through the gap to eliminate any rough spots from the arcing that almost inevitably occurs when the coil cooks.

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Nick Enright
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Jim McKeveny

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Re: Cleaning compression drivers help please!
« Reply #4 on: March 06, 2014, 08:42:59 am »

[quote

You certainly have nothing to lose trying to clean them up.
[/quote]

Except the fresh diaphragms!
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Jerome Malsack

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Re: Cleaning compression drivers help please!
« Reply #5 on: March 06, 2014, 08:50:13 am »

When the clean up with the white vinegar is done and a wipe with mineral free water? 
denatured water,  alcohol wipe to remove some of the vinegar (acid) to reduce the active.

Isopropal  alcohol 90 percent. 

When clean and fairly smooth I feel there should be no reason to be concerned.  If the corrosion continues.  When some of the corrosion flakes off will it find its way to the gap and create a problem?  Will the vinegar/water/alcohol stop the corrosion and prevent the problem ?
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paul bell

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Re: Cleaning compression drivers help please!
« Reply #6 on: March 06, 2014, 08:56:11 am »

Nick beat me to it, use a brass brush. It's soft enough to not gouge the gap and isn't magnetic so it won't keep getting stuck in the gap and broken bristles won't get sucked in.

I've recently discovered Purple Power cleaner, available at Pep Boys and Auto Zone. Very good cleaner that dissolves even the gunkiest gunk.
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Jim McKeveny

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Re: Cleaning compression drivers help please!
« Reply #7 on: March 06, 2014, 09:11:31 am »

This corrosion evidenced isn't from a hyper-pure water or condensation, but from fluids that include unknown salts and other corrosives. These liquids did not migrate though the back cover, but were dumped into the driver exit, probably while the circuit was energized.The metallic surfaces within the gap have swelled in response, and are unlikely to return to spec with simple solvents and abrasive brushing.

I would not be willing to drop a $150+ factory diaphragm into a questionable gap when finer - used, but blown - 2445's are available at reasonable cost online.
« Last Edit: March 06, 2014, 09:18:08 am by Jim McKeveny »
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paul bell

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Re: Cleaning compression drivers help please!
« Reply #8 on: March 06, 2014, 09:26:30 am »

I've brought back to life quite a few drivers that suffered the "they dumped a drink and/or drinks into the monitors" fate. After a good cleaning, these drivers go on to perform again. Any corrosion that might've "grown" in the gap will be taken out by the brush, it's surface crud, not new metal.
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Alan Singfield

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Re: Cleaning compression drivers help please!
« Reply #9 on: March 06, 2014, 09:58:24 am »

Thanks, some useful replies there.

The oxidisation has likely been caused by careless band members throwing drinks around. They came out of a club which primarily does metal bands, so they treat them like children's toys, i.e it's fine to stand on them and generally abuse them.

However, I think they may also have been left somewhere damp, or stored while damp. They were purchased second-hand from a dealer, and it has turned out that the 10 wedges are not loaded with identical parts.... This only became apparent once we had to start repairing them, but also may help to explain the loss of some 15's, as they seem to have been taken from a lucky dip. Makes limiter settings rather difficult to calculate....

The brass brush method makes sense. I was hoping for a lazy man's option of some sort of chemical bath they could be soaked in and then polished up with a cloth. However, i'll be getting my hands dirty this afternoon.

Thanks everyone for your help.
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Alan Singfield
Sound Engineer/Director
Black Box Professional Audio
Glasgow, UK
www.blackboxproaudio.com
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