Water damage... causes

[Chris Davis]

Re: Water damage... causes

Recently I discovered that the HF section of a three way cabinet I have (out of four) was out to lunch. Some testing quickly revealed it was neither the amp nor the cabling. So, we cracked open the box to find some significant water damage. About 1/3 of the back of the mid driver (magnet structure) was covered in rust (it worked properly though) and there was corrosion on the crossover bi-amp/tri-amp switch. This area is nearly sealed from the one that holds the HF driver and horn (which mounts from the front) though there are vents on the sides. After pulling the grille off and extracting the HF horn/driver assembly and subsequent dis-assembly, I found the following:


The weird thing is, the diaphragm looked nearly 100% brand new - no obvious signs of damage. However, it measured open circuit. This is not a cheap driver, and I am not a rich man, so therefore I am very saddened by this turn of events. I can barely stomach opening the other boxes.

My question is this: is this something that could be caused by condensation? All of our equipment is kept in an unheated space as we are a pretty small operation these days. We do know that these have seen some rain and wet weather, but I've never seen anything like this. I have other speakers that have been in way way worse conditions and never had any issues. Since this horn was sealed off from the rear compartment I fail to see how both could have been damaged so badly by water. I can see how the horn could have collected water if tilted up (though it never has been) but that wouldn't explain how the water got into the rear compartment. The reverse is true too. The cabinet has a rear door (bolted on with gasket) and I could see how some water could have gotten in there in a strong downpour BUT how did it make it's way into the sealed off area with the horn mouth and HF driver? The other strange thing is that the LF driver is as clean as a whistle. Cone is firm, no signs of dry rot, magnet is clean, no corrosion - it looks brand spanking new. These boxes are about 7-8 years old of which we've owned them for 6-7 years.

This is why I fear condensation...

Okay, I finally found my password and figured out how to log back in (I think the major upgrade a while back changed the name of the login screen or something like that).

Is the rear chamber of the mid mostly sealed off then? (someone thought you might have KF650's) If so, I might suspect that at one point in time moisture did get in...and a lot of it. Since you said your woofer is unchanged, that would make sense to me since the ports would air it out as soon as the atmosphere outside changed. On the other hand, I could see the (mostly) sealed midrange rusting like that if moisture got trapped in there over a long period of time. The wood on the inside is probably holding moisture too, maybe contributing to the overall issue. Have a look at the other boxes too. I don't have a good feeling about them. I can't believe this hasn't happened to other people before.

 

[Phil Graham]

Re: Water damage... causes

I am sure I am thinking in general terms while Phil is probably thinking of a specific process such as galvanic corrosion based on dissimilar metals, but to my knowledge oxygen remains the most common oxidizer (most favorable thermodynamically) in naturally occuring water samples.

Jay,

A few (chemistry filled) thoughts:

1. There are dissimilar metals in this case, as the soft iron core of the driver magnetics system is protected from corrosion by a surface coating of unknown composition. The coating will most likely also offer some measure of passivation and/or cathodic protection.
2. If the local galvanic couple is such that the sacrificial anode is depleted, or the passivation porous, then we enter the zone where O2 potentially matters.
3. Once we are in the zone where O2 matters, the Ksp of O2 in the system has overall little relevance on the corrosion, as there are multiple points of flux for oxygen bearing species, and the local chemical potentials can be far from equilibrium. O2 flows in to the system from the air, and out of the system as a corrosion product.
4. Often, diffusion of O2 through an oxide product layer is the rate limiting step of corrosion process. This is essence of much passivation behavior.
5. For iron or steel, magnetite (FeO*Fe2O3) forms a stable passivation layer in the absence of dissolved oxygen. Dissolved oxygen attacks that layer.
6. Concentrations of ions and neutral chemical species can vary wildly inside localized electrolyte regions on the surface.
7. Differential amounts of aeration of the liquid produce an electrochemical cell between a metal that nominally has the same electrochemical potential everywhere. On the aerated side of the cell, the cathodic reduction reaction is: O2 + 2H2O + 4e- <--> 4OH-
8. The electrochemical potential of this differential aeration cell will drive corrosion of both the new cathode and anode. Over time the chemical reaction in #7 raises the pH and passivates the cathode, resulting in the de-aerated anode corroding faster with time. Again, the base metal is nominally the same everywhere.

See Principles and Prevention of Corrosion, 2nd Ed by Jones
Section 6.5, starting on pp. 191
Section 11.1, starting on pp. 357

 

[Jay Barracato]

Re: Water damage... causes

Phil,

The basic difference (I believe) in our two points of view is that I think you are referring to the case where an external potential is present to do work on the system. For my thought problem I was working on "corrision" as being the spontaneous reaction. In a completely anoxic environment, dissimilar metals alone is not enough to cause the reaction, with the exception of an extremely slow process where hydrogen is the reduced material.

I believe that the reduction of O2 to water has a greater E value than the reduction of O2 to hydroxide. Therefore with no external current present the reaction with O2 to produce H2O will take place until the O2 is depleted. If an external current is present, than the reaction with the lower E (H2O to OH-) will take place. As you pointed out, once the oxygen is depleted the rate of reaction drops by several orders of magnitude as the source of the material to be reduced becomes a surface chemistry problem.

In 1982? a guy I knew, knew his boat was sinking, killed all the power before being picked up by a nearby boat. A couple of months after being submerged in the ocean, the electronics came up basically unharmed. On the other hand it is not uncommon to have a couple of volts through the water in a salt water marina. Sinking in the slip would be far more damaging.

Your point about the replenishment of the oxygen is probably more on track for the thin layer of moisture that was probably a cause in the OP's problem.

 

[Ryan Lantzy]

Re: Water damage... causes

What a bummer, Ryan. I don't know if those are our drivers but if so let me know if you have any problem getting replacements. I would be surprised if you couldn't just clean the gap and insert a new diaphragm, but of course the back cover must still fit properly... I could ask engineering what they think, as well. If that's what I think it is the diaphragms are much less than the whole driver!

Thanks for the kind offers Bennett.

No problem getting one (other than $$$) but the OEM "version" is ferrofluid cooled while the B&C stock version is not, which possibly explains the increased power handling of the OEM part. I don't know if there would be any audible difference, but based on price it wasn't worth quibbling over in the end so OEM it was.

As for salvaging it... honestly I think it would be difficult to clean it out well enough to guarantee there'd be no rubbing, definitely not worth destroying another $200 diaphragm over.

 

[Ryan Lantzy]

Re: Water damage... causes

Ryan, I am not sure what boxes you have, KF650z? What is the material that the horn is made out of? Is it possible that with your humidity up there that the magnet structure there is acting as a zinc and is therefore corroding while it is actually (unintentionally in this case) protecting the horn from corrosion due to it being a dis-similar metal? It really wouldn't take a whole lot of moisture to make the more corrosive metal start to deteriate if it is in contact with another metal.

The horn piece is a composite/plastic material - no metal. Though there is an aluminum mounting plate.

 

[Ryan Lantzy]

Re: Water damage... causes

Is the rear chamber of the mid mostly sealed off then? (someone thought you might have KF650's) If so, I might suspect that at one point in time moisture did get in...and a lot of it. Since you said your woofer is unchanged, that would make sense to me since the ports would air it out as soon as the atmosphere outside changed. On the other hand, I could see the (mostly) sealed midrange rusting like that if moisture got trapped in there over a long period of time. The wood on the inside is probably holding moisture too, maybe contributing to the overall issue. Have a look at the other boxes too. I don't have a good feeling about them. I can't believe this hasn't happened to other people before.

The cabinet in question is indeed a KF650z. The LF is rear loaded in this box with the cone open to the inner "chamber" There are ports on either side of the HF horn that vent said chamber. The back of the mid driver is inside this chamber as well. What I was getting at before was that given the amount of corrosion on the back of the mid I would have expected that there was a good amount of water inside the cabinet (or very very humid air). That being the case, it's surprising that the cone of the LF showed absolutely no signs of wear. None, it looks brand new, as does it's reverse (which is exposed to open air). It is also surprising that corrosion happened both inside this chamber, and in the HF driver as it is sealed in its own separate chamber with no air flow between them (other than exchanges of air through the cabinet vents and the HF horn mouth).

 

[gordon mcgregor]

Re: Water damage... causes

Chris is probably right about the woofer venting out and drying off quicker than the other more sealed in drivers, if you can I would check the other boxes if there is any other signs of damage then use a dehumidifier in you truck, if you can't use a dehumidifier then try and increase the amount of air flowing through the load area, I think it was Gene Pink who fitted solar powered fans and some floor vents to his trucks see f you can search his post on the old old LAB. Boat chandlers or RV suppliers have these little solar fans which are designed to keep air moving in Rvs and boats in storage it is quite amazing how much air they move over a 24 hour period.G

 

[gordon mcgregor]

Re: Water damage... causes

I have had this happen when I kept my speakers in an old concrete shed at the back of my house at the time and now when I think about it the woofers didn't look as bad as the high drivers. has any of you other gear shown signs of corrosion ie flight case catches and the like? G

 

[Phil Graham]

Re: Water damage... causes

Phil,

The basic difference (I believe) in our two points of view is that I think you are referring to the case where an external potential is present to do work on the system. For my thought problem I was working on "corrision" as being the spontaneous reaction. In a completely anoxic environment, dissimilar metals alone is not enough to cause the reaction, with the exception of an extremely slow process where hydrogen is the reduced material.

At some level it comes down to semantics. There is galvanic corrosion, hot corrosion, and a million other terms. You are of course correct than an environment with no ready exchange reaction path (i.e. electrolyte) for mass transport of ions, then then the potential difference between the metals produces no perceivable reaction on normal time scales. The driving force is still there, but it is kinetically limited.

I believe that the reduction of O2 to water has a greater E value than the reduction of O2 to hydroxide. Therefore with no external current present the reaction with O2 to produce H2O will take place until the O2 is depleted. If an external current is present, than the reaction with the lower E (H2O to OH-) will take place. As you pointed out, once the oxygen is depleted the rate of reaction drops by several orders of magnitude as the source of the material to be reduced becomes a surface chemistry problem.

These reaction systems are always about surface chemistry. You can have a very rapid reversible exchange current reaction (Exchange current density - Wikipedia, the free encyclopedia) at the surface, which is the case with dissolved oxygen and iron, but little or no net corrosive reaction. As for the assertion that one of the reactions occurs to completion before the other one kicks in, the reality is both reactions will occur simultaneously with different driving forces and settle on a system wide thermochemical equilibrium. Then, in the real world, kinetics will influence the time domain response of this transition to the equilibrium state.

In 1982? a guy I knew, knew his boat was sinking, killed all the power before being picked up by a nearby boat. A couple of months after being submerged in the ocean, the electronics came up basically unharmed. On the other hand it is not uncommon to have a couple of volts through the water in a salt water marina. Sinking in the slip would be far more damaging.

A circuit board from 1982 would have most likely have ceramic (SiC) packaging for the ICs and possibly an overall varnish, it surprises me little that it was fine.

Your point about the replenishment of the oxygen is probably more on track for the thin layer of moisture that was probably a cause in the OP's problem.

Over the long term, differential aeration tends to drive these reactions on the base metal, with replenishment from the air. Some sort of failed passivation, or sacrificial anode expenditure, probably preceded the differential aeration effects.

 

[Jay Barracato]

Re: Water damage... causes

I was thinking all along of the extreme case, and as most of my research work was in the marine environment. You might be surprised at just how anoxic water can get and how little exchange is really occuring. Since you mentioned it, I would say that the kinetics also determines the competitive equilibria. I think if you were to compare the thermodynamic Keq of the two possible products while it is fair to say SOME of the less favorable product is formed, it will also be at an insignificantly small amount due to the difference in stability.

And as for defining conditions (as I was indulging in a Fermi estimation) I would say the presence or lack of an external voltage is fairly critical to defining the situation.

By the way, in the sunken boat example, all the metal that was brought to the surface was basically unreacted; steel, brass, aluminum. Much of it looked better than the same stuff sitting out in the atmosphere would have looked after 2 months.

 

[Bennett Prescott]

Re: Water damage... causes

No problem getting one (other than $$$) but the OEM "version" is ferrofluid cooled while the B&C stock version is not, which possibly explains the increased power handling of the OEM part. I don't know if there would be any audible difference, but based on price it wasn't worth quibbling over in the end so OEM it was.

Ahh, bummer. As far as I know we don't have anything with ferrofluid, at least not in the drivers we have that you wouldn't want to get hit on the head with, which is most of them. I believe that era is past.

 

[Phil Graham]

Re: Water damage... causes

I was thinking all along of the extreme case, and as most of my research work was in the marine environment. You might be surprised at just how anoxic water can get and how little exchange is really occuring. Since you mentioned it, I would say that the kinetics also determines the competitive equilibria. I think if you were to compare the thermodynamic Keq of the two possible products while it is fair to say SOME of the less favorable product is formed, it will also be at an insignificantly small amount due to the difference in stability.

Kinetics, by the very definition of the word, does not have any place in a Keq calculation. The core of thermodynamics is our ability to calculate changes in state inifinitesimally for the reversible case, and then use it to say something useful about the theoretical equilibrium of the real, irreversible system.Of course in real systems, kinetic considerations are often dominant, and the thermodynamic equations of equilibrium stability not predictive of the actual concentrations. Those real values, however, are not equilibria. Not that anyone here is going to conflate the two approaches Also, especially in the gas phase, those insignificant product amounts really can matter greatly. There are many important "insignificant" reaction in gas phase chemistry, such as the water gas shift reaction.

And as for defining conditions (as I was indulging in a Fermi estimation) I would say the presence or lack of an external voltage is fairly critical to defining the situation.

Certainly a voltage influences the situation, as calculated by the Nerst equation for equilibrium. My point is that your assumption that galvanic couples requires dissimilar metals is not necessarily the case. Two coupons of the same metal in contact with solutions of different ionic makeup, including the case where dissolved oxygen modifies the ionic content, can produce a galvanic couple when shorted together, assuming a suitable ion bridge between the coupon solutions. The net reaction current can be estimated from mixed potential theory.

 

[Ryan Lantzy]

Re: Water damage... causes

I have had this happen when I kept my speakers in an old concrete shed at the back of my house at the time and now when I think about it the woofers didn't look as bad as the high drivers. has any of you other gear shown signs of corrosion ie flight case catches and the like? G

Some of our flight cases have surface rust and other forms of oxidation/corrosion, but these get pulled through the snow/salt/ash on their way out to the truck so that isn't surprising and I think it's largely unrelated to this.

 

[Jay Barracato]

Re: Water damage... causes

You are pulling in excessive detail that is not fully applicable. There is no way in a natural setting that you are going to have enough of a concentration difference to have a concentration cell. I was doing a thought problem based on a piece of metal placed in fairly anoxic water that does have significant ion concentration.

And I would say that kinetics does apply to equilibrium as one of the basic definitions of equilibrium is where the rates of the forward and reverse reactions are equal and that Keq can be calculated (estimated) from the rate constansts, k. At best most thermodynamic Keq are order of magnitude estimations.

I will tell you what, I will drop a piece of iron in a beaker of unagitated sea water, and we can come back in a couple of months to see what corrosion is on it.

 

[John Roberts]

Re: Water damage... causes

Not to change the subject back to Ryan's speakers, but humid air getting inside the speakers during the gig, and cause condensation on the metal parts later while sitting in the cold trailer.

Is there anyway to stick a dehumidifier into the trailer and maybe run it for a day or two after gigs?

Another possibility is packing desiccant packs into the cases with the speakers. It seems these desiccant packs can be cooked and reused over and over.

JR

 

[Phil Graham]

Re: Water damage... causes

You are pulling in excessive detail that is not fully applicable. There is no way in a natural setting that you are going to have enough of a concentration difference to have a concentration cell. I was doing a thought problem based on a piece of metal placed in fairly anoxic water that does have significant ion concentration.

The literature, case studies, and engineering consultancies are full of all kinds of examples of these types of concentration differences being real, and causing corrosion issues. Every textbook on corrosion has a section on pitting corrosion, and pitting corrosion results from these local concentrations effects.

I'm not making this stuff up. I have engineering friends working on this type of corrosion activity daily, and at one point interviewed to work on this type of corrosion with an engineering consultancy. There are ASTM standards that describe the nature of different types of pitting corrosion due to local concentration effects attacking the passivating oxide.

And I would say that kinetics does apply to equilibrium as one of the basic definitions of equilibrium is where the rates of the forward and reverse reactions are equal and that Keq can be calculated (estimated) from the rate constansts, k. At best most thermodynamic Keq are order of magnitude estimations.

At no point in the pedagogy of classical thermodynamics, Gibbs style, does the forward and backward reaction rate come into play. Gibbs determines the equilibrium state from equations of state and chemical potentials. Guldberg's work on the law of mass action is contemporary with Gibbs' work, but it approaches the idea from a different place. Take the two, add in Arrhenius' work on activation energy, and the more modern considerations of statistical thermodynamics, and everything melds together of course. But when you use HSC, chemSAGE, solgasmix, or any of the other chemical equilibrium calculation means, they are calculating activities based on Gibbs' approach.

I will tell you what, I will drop a piece of iron in a beaker of unagitated sea water, and we can come back in a couple of months to see what corrosion is on it.

Be my guest, but I struggle to see how that relates to the corrosion processes of the original poster. All of the effects I have discusses are practical potential methods that could have lead to the onset and ongoing corrosion of Ryan's compression driver.

 

[John Roberts]

Re: Water damage... causes

I will tell you what, I will drop a piece of iron in a beaker of unagitated sea water, and we can come back in a couple of months to see what corrosion is on it.

You may want to check what color it comes back too... if green it is reacting with chloride (from salt in sea water).

but again what does this have to do with the price of tea in China?

JR

 

[Jay Barracato]

Iron in distilled 11.6895 g initial
Iron in 33 ppt artificial seawater 13.4845 g
Iron in 33 ppt artificial seawater 11.5939 g coupled with copper 13.6386 g
Copper in 33 ppt artificial artificial seawater 13.7496 g.

 

[Jay Barracato]

Re: Water damage... causes

Not a lot, I think Phil and I were just exercising some braincells.

Just an updated version of a fermi problem.

 

[Art Welter]

Re: Water damage... causes

As for salvaging it... honestly I think it would be difficult to clean it out well enough to guarantee there'd be no rubbing, definitely not worth destroying another $200 diaphragm over.

Ryan,

We had instances of "beer in the funnel" syndrome with stage monitors, the combination of beer, titanium, aluminum and iron caused some incredible science fair crystalline growth, as well as rust worse than what your drivers show.

They cleaned up fine, and had no problems with new diaphragms. Some diaphragms were able to be carefully pulled out of the encrusted gaps and cleaned up and reinstalled.

Was not aware of a product called "Corrosion X" back then, but it works wonders in preventing and cleaning up corrosion problems.


Art