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Old 15th March 2003, 02:01 AM   #1
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Default Crossovers - Exposed solder joints a fire hazard?

Hi. This weekend I am assembling my project Definitive/Seas MTM. With the help of my grandfather I soldered together the crossovers, and it then occured to me that the convoluted acoustic foam (egg-crate foam) is very similar to the stuff that was probably on the the back wall of that Rhode Island night club that caught fire. So my question is, should I be concerned about arcing between two exposed solder joints that are about 1 cm away from each other? And if I use electrical tape to cover each solder joint, will that work to insulate them from each other? I don't know if arcing is generally an issue in a crossover network.
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Old 15th March 2003, 03:24 AM   #2
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At the voltage levels experienced in even the most high-powered crossovers, 1cm is more than enough spacing to ensure no arcing will ever occur. Just make sure that the components are physically mounted well so they can't shift around, and 1cm is plenty.

I can't remember how many volts are required to jump 1cm of air at the moment, but I know it's in the kilovolt range.
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Old 15th March 2003, 07:04 AM   #3
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Kilovolt?? Wow.

1000 volts * 1000 volts / 8 ohms = 125000 watts = ONE DEAD SPEAKER.

Yeah, I don't think you need to worry about arcing.

I would still put some heat-shrink tubing over exposed joints, or perhaps some kind of glue. Make sure you're not going to make a lot of heat through the jounts though. Remember: <b>a good solder joint is really just a good solid joint with solder so it never comes undone.</b>

*feels a tangent coming on*

EVERYONE RUN! I'M GOING OFF ON A TANGENT!! AAAAUGH!

*runs away*
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Old 15th March 2003, 09:11 AM   #4
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Quote:
Originally posted by Nappylady
EVERYONE RUN! I'M GOING OFF ON A TANGENT!! AAAAUGH!
Sounds like she flew out of the spin drier full of nappies at right angles to the radius.
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Old 15th March 2003, 09:22 AM   #5
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Default Re: Crossovers - Exposed solder joints a fire hazard?

Quote:
Originally posted by BAM
it then occured to me that the convoluted acoustic foam (egg-crate foam) is very similar to the stuff that was probably on the the back wall of that Rhode Island night club that caught fire.
If you want to cover all eventualities, have the crossover inductor placed so that it is not touching that foam stuff. If it ever happens to run really hot then it won't likely set anything other than itself alight. Not that that is a common occurence, but if it is easy to do then why not. After all, these new speakers of yours _are_ going to "set the world on fire", are they not?

Good project, BAM. Don't forget to post some pics in this here Worldwide Boast Book.
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Old 15th March 2003, 12:34 PM   #6
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One final question:

On a Linkwitz-Riley Second-Order crossover, does the tweeter need to be wired out of phase with the woofers?
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Old 16th March 2003, 12:46 AM   #7
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Default Re: Crossovers - Exposed solder joints a fire hazard?

Quote:
Originally posted by BAM
the convoluted acoustic foam (egg-crate foam) is very similar to the stuff that was probably on the the back wall of that Rhode Island night club that caught fire.
I don't think you have to worry about arcing between solder joints, but you do have to worry about hot, overdriven, components catching the foam on fire. I have actually been witness to this once. John grrenback was over from England and we were demoing his RS-4s (vented/Audax 8"). We were driving it with a Bryston 4B. John kept having us turn it up. Pop and the room was filled with the acrid smoke pouring out from the square vent -- we had gotten one of the padding Rs hot enuff to start the foam damping on fire. Since a speaker -- even a vented one -- is not real conducive to maintaining combustion, it was mostly smoke. It was an impressive enuff show thou that i still hear the story related some 25 years later

dave
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Old 16th March 2003, 04:23 AM   #8
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Default Yikes !.

Hi Dave,
Your story is good advice.

This reminds me of a story that I was told 20 years ago regarding a 'Sansewage' speaker.
The owner was out in the backyard doing some gardening, so he turned his system up to loud.
The voice coils and formers got hot enough to cause a particular glue to decompose and evolve some kind of gas that combusted and set light to the cones, which then set the room curtains on fire, and extensively damaged his house.
This event became the subject of forensic testing, and the glue used was deemed to be the cause.
I expect that this glue is no longer used.

Eric.
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Old 16th March 2003, 05:13 AM   #9
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Interesting.

I was testing a homemade voice coil a few weeks ago and decided that because I'd used 8 ohm's worth of 30-guage speaker wire (this wire is WAY too big for use in commercial voice coils; it makes them too heavy to be more than ~70 dB efficient) it would be able to handle 100 watts no problem, and I was right! Unfortunately, I had forgotten that I'd used a rather un-suitable voice coil former--a section of M&M's Mini's tubing! I wasn't watching the voice coil, but I know by the time I reached >10 watts, the whole thing was turned from pink to brown!

The best part was scraping away the charred plastic to reveal that the actual voice coil was completely unharmed--makes me wonder if maybe I could use such a voice coil and a very heavy (perhaps glass?) cone structure along with a disgustingly high-powered amp for some esoteric subwoofer purpose...
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Old 16th March 2003, 05:48 AM   #10
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Default Crossover

Quote:
Originally posted by BAM
One final question:

On a Linkwitz-Riley Second-Order crossover, does the tweeter need to be wired out of phase with the woofers?
On a 2 way second order crossover, the tweeter is connected out of phase with the woofer.

On a 3 way second order crossover, it's the midrange that is connected out of phase with the woofer and the tweeter. The woofer and tweeter are connected in phase with each other.

Even though they are out of phase electrically, they will be in phase acoustically.

Hope this helps; Doug
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