Need "Ferrofluid" or equivalent for tweeter

[crooner]

Hi Guys,

I currently use a pair of B&W DM110i's with my high powered receivers. When I originally got these, one of the tweeters was not working. I disassembled it and discovered that one of the fine wires had disconnected right at the voice coil junction.

I managed to re-attach it with some heat from my soldering iron. However, it is now prone to overheating with moderate to high power levels. The other speaker does not have this problem.

When it overheats I have to take the tweeter out of the cabinet and repeat the soldering iron procedure.

This, needless to say, is a hassle. I was wondering if it would be a good idea to put some cooling substance or paste in the junction, like the ferrofluid used by some manufacturers.

Any suggestions? I wonder if "ferrofluid" can be bought at the Home Depot

I was also thinking about spark plug silicone grease. But I wonder if it's conductive. If so, it may not be such a good idea.

Thanks in advance,
crooner

 

[cincy]

Hi Crooner,
First, let me tell you I like your avatar, it brings back memories of seeing that movie
when it first came out.
Yes silicon sparkplug grease is electrically conductive. I use it for a lot of things like
RCA type connectors at the phono inputs etc. The brand I use is Permatex
dielectric tune-up grease. Good for almost all electrical connections. The tube
doesn't say how much temp it will take but I guess its a lot.
I do remember seeing ferrofluid in a catalog that were selling it in small amounts. When
it first came out like 25 years ago the price was $1000 per gallon.
1985 STEREO BUYERS GUIDE says that your speakers are crossed over at 3000hz so
that means your tweeter is working pretty hard. I would guess that the crossover is
allowing much more powerful low frequencies to go to the tweeter than it was
designed to handle. You may have to replace a capacitor or resistor in the crossover
or even a new tweeter would meet the same fate. My advice would be to check the
values of the crossover in your other speaker and make sure to make the other the
same. I would try to solder the tweeter as you did before.
The guide shows your speakers selling for $300 in 1985, power handling 10-75 watts
rms. B&W's top four speakers have a system they call APOC: Audio Powered Overload
Circuit. These systems sell for $7,500 pr to $1,790 pr. B&W says APOC prevents
driver damage at all power levels.
Hope this helps you.
cincy

 

[jwrags]

Webster's New Riverside Office Edition Dictionary

dielectric n. A nonconductor of electricity

I think spark plug silicone grease helps to keep the boots from welding to the ends of the plugs.

Best
John

 

[ilimzn]

What jwrags said!

Do NOT apply grase to the speaker VC as it will change it's internal damping quite dramatically and, what is worse, nonconsistently. Speaker VC can reach well into the 150C region, and if your solder is desoldering then even more in your case (*). Ferrofluid is a magnetically 'conductiove' but electrically non-conductive oily substance. It is usually ferromagnetic particles in an ester suspension. on of the biggest problems in producing a ferrofluid is keeping it's viscousness as well as suspendive qualities largely uncanged over a wide temperature range. The fact that ferroifluid is a magnetic material helps it keep inside the magnetic gap in the speaker, though even it will go splattering out on overdriven speakers. Still, the most common reason for ferrofluid 'failure' is the liquid part boiling off due to overheating.
In theory, you could use any temperature stable non-agressive oily substance (you don't want to chemically melt the VC wire enamel or bonding glue, or the bond between VC and membrane!), but keeping it in there will be the real problem.

(*) There are a number of thngs to check first.Are all the crossover components fully working? Is there any heat damage to the VC, or perhaps a shorted winding (this tends to heat up speakers quite considerably and of course, lowers efficiency)? Does the DC resistance of the speaker match a known good one? Are you sure one channel of your amp is not prone to oscillation? Etc...

Very important: VC connection wires in tweeters usually fail due to membrane overexcursion, and that is normally a result either of overdriving the speaker (by any of the many means) or a failed crossover component. You need to be sure you are curing the problem, and not just the symptoms.

 

[cincy]

Crooner,
John is correct about the definition of dielectric.
The tube of dielectric grease has these instructions for auto battery connectors and
terminals. 3. coat both parts of terminal contact with Dielectric Grease.
4. reassemble maintaining metal to metal contact.
There is no mention of silicon or silicone on the tube.
I've been using this product as we used to use petroleum jelly for auto batteries to
make good electrical contact (filling the voids on the surface).
Permatex has a web site www.permatex.com I will have to see if they can explain the
contradiction in terms i.e. why would you want to put a dielectric between to conductors.
cincy

 

[ilimzn]

You would want to put it there to prevent moisture, acid and similar things from coming in and eventually resulting in electrocorrosion. There is NO contact where the grease is (but there would not be anyway), only where the grease is displaced and there is metal to metal contact.

 

[crooner]

Thanks for your responses guys!

The speakers are the revised "i" version from late '86, early '87. I believe the specs are slightly different and they are fuse protected.

I assume the crossover network is in good shape, since both speakers sound the same when using FM interstation noise and the mode switch in the mono position.

The speaker that has the tweeter problem was probably abused by the previous owner (perhaps by dialing up the treble on the amp). I use them with flat tone controls always.

The voice coil wire is actually held together by varnish, not solder. So the soldering iron reheats the varnish and attaches the fine wire.

I was wondering if I could use just a tad, very little, contact cement on the junction. This is the same glue I routinely use to repair torn speaker cones.

And Cincy, yes, I love those classic movies. High Society is one of my favorites.

Best regards,
crooner

 

[brainsmasher]

I read somewhere that loctite has a andhesive that has copper flake in it which may be used to fix broken lead wires. I have yet to see or use it but if you are at the hardware store it may be worth a shot.

 

[hotgas]

I am not familiar with your tweeter construction. If you suspect heat is the cause of the detach of the wire I suggest you to do this experiment if you have a temperature recording machine or may be a meter:

1) Measure temperature on both tweeters at the same time while playing music. Notice the temp differences if any.

2) If overheat is indeed the cause you can use a good conductive silicone (GE TSE3281E or Dow 4420) on the junction. This type of silicone is great for high temp application but can get brittle if heat is too high (>150C). But I really doubt if the heat is too high for silicone application. Don't use the cheap silicone for home application as it is not made for high heat. I do not know the composition of contact cement but I don't think it can handle heat. Don't use Loctite as it is made from modified acrylic which is brittle like varnish thus can't handle viration well enough.

3) If heat is not the cause then it could be something else like other people already suggested, or maybe your tweeter is too loose, or whatever reason I don't know. But silicone still can help to keep the wire in place or even contact cement (its strength is questionable though).

Good luck,

 

[crooner]

Thanks hotgas and brainsmasher for your suggestions. Both are excellent, and I am debating which one to try first!

Best regards,
crooner

 

[NoTransistors]

You may want to try this

The horn tweeter on one of my Pioneer CS-99A boxes had the same problem. I managed to unwind an inch of wire from the voice coil, and the rest is history. Twenty years, and as much as 135 watts RMS later, it still works. Grab a beer, and give it a whirl. :beer:


Seth
Forever Analog