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Series Resistor Question

edited November 19 in DIY

Greetings from Oz

I'm trying to learn more about crossover design, although I'm not in a position to do it properly as I don't have measuring equipment and my copy of Speaker Building 201 got lost somewhere in the international mail.

I've seen a few forum posts where people say never to use a series resistor with a woofer as it will get hot and become a fire hazard.
However, I've seen at least two three-way designs which have a series resistor as the first component in the mid circuit. In one case, the mid was a Vifa TC-9, in the other, a Peerless 830656 mid. In each case, the second series component was a capacitor.

I'm not sure if it's appropriate to show the circuits as they're someone's intellectual property.

My question is: why isn't the series resistor in those circuits a fire hazard?

Thank you

Geoff

Comments

  • The filter on the mid limits the current the resistor will see so resistors used to pad mids and tweeters are not as big a risk of overheating. There's nothing that says they can't be fire hazards depending on how hard you party. In my younger days a pair of speakers I built were used by some young people who drove them with a 60 watt per channel amp with the volume at 10 for 8 hours. The metal housing on the L-pads were oxidized from the heat and some of the caps were toast.

    Ron

  • Thanks for such a quick reply Ron, that makes sense.

    Cheers

    Geoff

  • If you are using XSim, you can create a graph to show power dissipation of any resistor in your design. I'm not sure how accurate it is, but it seems to be close enough when I've used it. Don't forget to set the Watts to your max drive level for the driver(s) by double clicking on the Power Amp in the schematic.

  • @Tom_S said:
    If you are using XSim, you can create a graph to show power dissipation of any resistor in your design. I'm not sure how accurate it is, but it seems to be close enough when I've used it. Don't forget to set the Watts to your max drive level for the driver(s) by double clicking on the Power Amp in the schematic.

    Thanks Tom, I didn't know Xsim had that feature and I've been mucking around with it for about two years!

    What level or range of power dissipation would be OK using that feature, please?

    Thank you

    Geoff

  • It depends on what resistors you are using. The EE's in the crowd probably have a safe limit they try not to exceed. I would probably not push it above 75% of the rating of the resistor in question just to be safe.

  • Some parallel resistor legs can get hot too...

  • Thank you all, my question is answered!

    Geoff

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