How inductive is a inductive wire wound?

[digital desire]

In this crossover net 2 R2041:

Image not available

I have from the BOM a 15 ohm metal film resistor. When I turn up concert DVD's, it gets hot enough to melt the high temp hot-melt glue, and make a smell my wife "notices". The crossover is not in the cabinet due to other issues.
So I was going to switch it out with a pair of 30 ohm wirewound 10 watt resistors, but have found out they are not non-inductive. Are they inductive enough in this application to matter? The gentleman I bought them from insists that he has been making crossover's for years, and this is not issue.
Anyone?
Thanks.

[JonP]

Well, hard to be 100% without actual measurement, but I'd agree with him in that it's very likely that there will be insignificant inductance.

I've measured several types of low ohm resistors (like we speakerbuilders use) on a lab quality LCR meter, and the inductance is on the order of one to a few microhenries. I can't imagine that your 15 ohm would be more than a few tens of microhenries. Which is .010 - .020 millihenry... vanishingly small to a speaker crossover.

The "non-inductive" wound resistors only seem to matter when you get into the many hundred or thousands of ohms values, with a large number of turns of wire inside.

So, get those pair of double values, paralell them up for more wattage capability, and listen away! I might suggest spacing them up on small supports of some kind of heat resistant material, and apart from each other, to allow airflow around more of the surface area. You'ld add better cooling to the higher wattage capability...

[Eric S]

Two issues come to mind for me, neither of which have to do with inductance. First, the wattage rating of your resistors may not be high enough. I usually use 12 watt Mills wire wound resistors for my crossovers. Most metal film resistors are rated at only 1/2 to 1 watt. It could simply be an issue of pushing too much power through too small a resistor. In extreme cases, parallel two resistors like Jon indicated.

Second, you mentioned that the resistor is melting the glue that you used to hold it in place. I am not sure how you created your crossovers, but since the resistors are likely to absorb a fair amount of power, they need to be able to cool off. This is best accomplished by arranging your resistor so that it has some free space all around it. Placing a large blob of hot glue on it and sticking it to a board will prevent the necessary air circulation to allow the resistor to cool on its own. Can you re-arrange the crossover so that the resistor is held up off of the board with the leads such that there is free air all around it?

Eric

[cjd]

Yeah, I'm also curious what kind of resistor you're using!

C

[digital desire]

These are the resistors I just bought:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=9703865959&ru=http%3A%2F%2Fsearch.ebay.com%3A80%2Fsearch%2Fsearch.dll%3Ffrom%3DR40%26satitle%3D%2B9703865959%2509%26fvi%3D1

If that link does not work, it would be item number 9703865959 on there.



The seller assured me that they are inductive, but that I would have to get up into the Mhz to start to see any effects.

This is the resistor that is in there now:

http://www.madisound.com/cgi-bin/index.cgi?cart_id=1539839.2138&pid=248

Not sure why this particular resistor made it into the BOM, maybe only because it was the only 15 ohm found there? Anyway, it is in the bom, when the rest of the resistors are the Dayton 10 watt wirewound, more or less look identical to the fleabay ones.

[cjd]

Those Eagles should be fine...

[Eric S]

Yep, those new sand-cast ones look fine :T I would put two in parallel, so you'll end up with 15 ohms and able to dissipate 20w. Be sure to give them some breathing room to cool and you should be fine.

Since those eagles are rated at 10w, I suspect it was the glue that caused your problem...

Eric

[digital desire]

Nope, not the glue. When I get cranking on that speaker, (I like my concert DVD's to sound, well, almost as loud as the original!) that resistor gets hot enough to burn my finger.
My plan was of course to do double up 30 ohms, just wanted to make sure the "inductive" resistors were not that inductive to cause me any weird problems.
Thanks everyone! :T