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Just caught my speaker on fire!

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  • MSaturn
    replied
    Re: Just caught my speaker on fire!

    Badass.

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  • LouC
    replied
    Re: Just caught my speaker on fire!

    This kind of failure probably required a "perfect storm" with Freddie Mercury at the eye! ;)

    I had a similar experience with an intermediate version of a 3 way crossover (melted the hot glue off the board and blistered my finger). I reported it here and was told that I must be mistaken and must have miswired the crossover.

    Now I double check my boards outside the boxes at high volumes for an hour or so. Any resistor that even gets warm is doubled. The only times I've found issues:
    • Padding mid ranges in 3 ways - particularly when padding closer to the amp
    • L-Pad shunt resistors on midrange drivers


    It makes sense though. A shunt resistor's job is to dump power before it gets to the driver. Mid drivers are usually getting more power. Unless there's a component ahead of it that dumps/blocks some of it, padding resistors could take a lot of watts. If I use padding resistors, I often put them in lead wires (rather than on the board). Easier to change later, and better heat dissipation.

    I've never found any problems on tweeter circuits. I've never used any kind of padding or direct shunt on a woofer. (Bad JuJu)

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  • davepellegrene
    replied
    Re: Just caught my speaker on fire!

    Originally posted by danklugherz View Post
    Wow Dave, that had to put the scare into you! Have you checked the other XO? I can't recall ever hearing of this happening before. Maybe you should mount a fire extinguisher to your speaker cabs. :D
    My wife keeps walking by me shacking her head. What can I say sometimes I like lots of beer and loud music. At least I'm not on the road crashing into stuff. She also said the same thing. You should have pulled the other one apart to make sure you weren't going to burn down the house, but in a some what sarcastic voice.

    Dave

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  • davepellegrene
    replied
    Re: Just caught my speaker on fire!

    I will say again I don't think this was a flaw in the design as much as a noob building a poorly ventilated crossover. Yes there was hot glue on them. As Curt said it was the resistor in the shunt circuit. It was tight against the board and also had foam over top of it. The resistor doesn't appear damaged on the outside but I assume it gave out. I am thinking the driver my daughter and I heard bottom out may have been the mid. Being the noob I am I'm going to take a stab at saying this would be the resistor to attenuate the mid and when it went out it wasn't attenuating the mid any longer so they were getting full power.

    When I pulled the driver the board started to glow when it got air so it may have ignited eventually had we not pulled it. I do have smoke detectors on all levels and fire extinguishers threw out the house. I may have to start keeping one next to me when I want to jam to my Queen DVD from now on. I am assuming it was a combination of the foam against the resistor and resistor against the board with to much hot glue on them.

    I will probably order the resistors Ben and Curt suggested. They will only cost $12 to replace. I am going to pull all the furniture foam out of them and go with the stiff fiberglass like I have been putting in my later builds. I can tell a difference in sound so now would be a good time to do this. I am going to pull all the other boards and raise the resistors and make sure they get plenty of air around them.

    I may go ahead and double up the ones on the other boards as well. I am assuming this could happen on the tweeter and woofer circuits too? Am I correct in saying this happened in the shunt circuit because it was sending the power away from the driver instead of though it? So any resistors in series with the tweeter mid should be fine?

    I can say the Mini's will crank and sound very clean doing so. As a matter of fact I probably could have kept on playing them til they caught fire. :D:eek: As far as I could tell last night all the drivers were still playing fine when I lowered the volume and listened to each one separately.

    Now everybody in my family can stop saying were are you going to put those after there built. Now I know. They will be back ups if I need them while my other speakers are getting worked on.

    Dave

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  • danklugherz
    replied
    Re: Just caught my speaker on fire!

    Wow Dave, that had to put the scare into you! Have you checked the other XO? I can't recall ever hearing of this happening before. Maybe you should mount a fire extinguisher to your speaker cabs. :D

    Leave a comment:


  • markk
    replied
    Re: Just caught my speaker on fire!

    It does bring up a good point. Usually only a modest effort is put into power handling. Usually we think that our speakers are limited by excursion. But that's not always the case. I took a quick look at the schematic and it does look like the 4 ohm shunt resistor is going to dissapate the bulk of power in that midrange circuit. The shunt resistor/driver combo has more than half the voltage drop, and the shunt resistor valus is less than the impedance of the 1337. It's a bit hard to guess, but it's not unreasonable to think the bulk of the power is going to the mid circuit.

    Not a problem normally, but definitely a problem under a high output scenario. Using 2 or 4 series, or parallel or both to distribute the power load is a good idea.

    Just makes you want to go completely active....:eek:

    Leave a comment:


  • Jim Holtz
    replied
    Re: Just caught my speaker on fire!

    Originally posted by davepellegrene View Post
    Wow! I was playing my Queen Live in Montreal DVD tonight on my Mini Statements. I was playing at pretty high volume and kept bumping up the volume, but really being careful to stay below distortion levels. About a half hour into the DVD my daughter worked her way front row. I'm kind of smiling getting a kick out of it right behind her. We hear what sounded like the woofer bottom out. Kind of surprised me because it wasn't bass heavy. We look at each other so I turn it down a couple notches. My wife is out on the deck watching through the slider and comes running in and says there is smoke coming out of your speaker. I look at her like yeah right. So I walk up to the speaker to see what she is talking about and sure enough I smell smoke from the ribbon. Everything is still playing. I backed the volume way down and all the drivers sound fine. After about 10 minutes I put my hand on the back of the speaker and its warm. This can't be good. So I pull one of the woofers out. Unbelievable there was no sign of distortion at all. I can't believe I could get something that hot and not even know it.
    Hi Dave,

    WOW! That is amazing! I've never heard of a crossover getting that hot before. Curt, as always, came to the rescue with excellent advice. I'll have to think about this for future builds. Considering the low cost of resistors, paralleling might be a very good idea as a standard design upgrade for systems that will be cranked very hard.

    I'm glad that the Mini's didn't suffer any other damage.

    Jim

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  • Face
    replied
    Re: Just caught my speaker on fire!

    Were the resistors covered in hot glue?

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  • dano
    replied
    Go

    Whats the proper way to calculate the power dispensation of resisters in crossovers? Also are fuses or light bubs a good Idea for speakers designed for high power.
    ________
    SUZUKI RGV250 SPECIFICATIONS
    Last edited by dano; 04-28-2011, 06:38 PM.

    Leave a comment:


  • tomzarbo
    replied
    Re: Just caught my speaker on fire!

    I'm curious...

    What would have happened if neither you, nor your wife saw the smoke?
    Could there have been an actual fire?, or would there have been a disconnect on that part of the circuit which would have been obviously audiable?

    Was the ribbon driver okay?

    Also, I must say... that's pretty cool!

    TomZ

    Leave a comment:


  • arlis_1957@yahoo.com
    replied
    Re: Just caught my speaker on fire!

    would just elavating off the board be enough? in what situation should they be of higher wattage? do they make tiny onboard extinguisher systems for queen lovers?
    his guitar player wasn't half bad either.

    Leave a comment:


  • Wolf
    replied
    Re: Just caught my speaker on fire!

    Originally posted by curt_c View Post
    C
    Yah- I likey!!! I've used them quite a bit.
    Wolf

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  • curt_c
    replied
    Re: Just caught my speaker on fire!

    Another option would be using higher wattage Arcol or Vishay/Dale non-inductive resistors. They can be purchased at Mouser Electronics.

    I agree, Freddie was a great singer/songwriter, and Queen's music was meant to be heard LOUD...

    C

    Leave a comment:


  • davepellegrene
    replied
    Re: Just caught my speaker on fire!

    I should also ad what a geek my daughter is. As I'm pulling out smoking parts she's snapping pictures so I can post them on techtalk.

    Dave

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  • davepellegrene
    replied
    Re: Just caught my speaker on fire!

    Originally posted by curt_c View Post
    From what it looks like Dave, it was the 4 ohm shunt resistor in the mid network that failed, and the good news is, it is unlikely that it did any other damage when it went. The cable ties on the 1 ohm series resistor look a little discolored as well, but maybe this was just from being adjacent to the shunt resistor, I can't tell from here.

    This is the first MiniStatement network failure that I am aware of. You can tell your wife and daughter that it was the designer's fault (me) and not yours, as I didn't anticipate them being played at such high SPL's. -Or maybe it was because I never auditioned that particular Queen CD on them...

    In any case, I'm glad the damage was limited to the resistor and board, and I apologize for the scare it must have given you and your family.

    I would suggest you rebuild both mid networks with the following modification:

    Replace the 4 ohm resistor with two 8 ohm resistors in parallel. This will double the power dissipation to 20 watts. If the 1 ohm looks like it has been overheating, replace it also with two 2 ohm resistors in parallel. None of the other resistors in the design should need to be replaced or modified, but if you see any other indication of overheating, please let me know, so we can address it.

    When installing them, make sure the resistors are mounted so they are not flush to the board. This allows airflow on all sides. In addition, insure the crossovers are not covered with foam or stuffing. They need airflow to provide their rated power dissipation.

    If I can be of any further assistance please let me know either here, or by email.

    C
    You are right it is the shunt resistor. By no means was this your fault or a design flaw. I was pushing them very hard with my QSC GX3. I believe is rated at 450 watts per channel at 4 ohms.
    I was thinking the same thing paralleling the resistors. I am just happy I didn't do anything to the ribbons. That was my biggest concern. There is also some melted foam so that probably had something to do with it also.

    I guess it should tell you something about the volume when my wife was sitting outside watching the DVD through the sliding glass doors.

    It is also a really rocken DVD. I was trying to hold back a few notches for the end when Freddy comes out in his white shorts. :o Anyway what an amazing voice he had.
    Dave

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