Announcement

Collapse
No announcement yet.

Just caught my speaker on fire!

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

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

    Dave How close was the foam on top of the XO to the resistor? I'm wondering if the heat built up there and caused the foam to start to melt and possibly drip on to the resistor.

    Take it easy
    Jay

    Leave a comment:


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

    Just to clarify for a few that are not sure. I had the peg board OX mounted with a 1/4" space between the board and the MDF cabinet side. The resistor was mounted tight to the board with two zip ties. Hot glue was applied over the zip ties covering about half of the resistor. Then two inches of foam was applied directly over the ox. I was feeding them from my Yamaha amp using low level outputs. to my GX3 that is rated for 450 watts at 4 ohms. The GX3 was set two notches down from full, roughly 90%. The Yamaha amp at the time of the smoke was around -5dbs. Not sure how that plays out with the low level output, but at -5dBs on the hi level outputs there would have slight audible signs of clipping. I am always careful to back the volume down if I hear the slightest bit of distortion or clipping.
    Something I just found out from my daughter, who was sitting in the sweet spot the hole time :eek: said she heard, what sounded like a driver bottoming out a couple times in the last few minutes. Thought it was ok since I didn't do anything about it. I was in and out on the deck several times cooking steaks so I didn't hear it. So obviously I was driving the whole system just a bit to hard. :o

    So I guess the real fix here would be a second set of Mini's and another amp. :D I'm sure my wife will agree. :rolleyes:

    Here is the foam that was on top of the XO.




    Dave

    Leave a comment:


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

    Keep in mind that in this particular case, the shunt resistor is taking in as much power as the midrange driver.
    Exactly.

    I'm not saying anything bad about the ministatements in particular, just about the power handling issues with three ways in general.

    I mean, think for a minute-you buy your emotiva xpa-2 and pump 500 watts into 4 ohms. The xpa-2 is massively heatsinked, with multiple output devices, to handle the heat generated. Now where is that 500 watts going? At most, drivers are 1-2% efficient at converting the electrical energy into acoustic energy. So 490 watts of your xpa-2's output has to be dissapated as heat. That can really only be in two places-the voice coil and the resistors. (ignoring the small contribution of other resistive elements, i.e. the R of the inductors etc...)

    Now you're not really putting 490 watts into your VC and resistors...but you get the drift. In a three way, especially a low impedance/4 ohm 3 way, if played loudly, care needs to be chosen in regards to heat dissapation.

    Active speakers do get around this limitation quite well. See john k's article on hybrid designs. You don't even need multichannel amplification to address this.



    You have to read the article to fully appreciate the graph. It would be even more pertinent for a three way (the graph is for a 2 way).

    I'm not against resistors and passive designs. But they can waste more heat than is commonly realized and this should be incorporated into the design (If part of the design target is higher average spl levels...)

    Leave a comment:


  • Dean1000
    replied
    Re: Just caught my speaker on fire!

    Please use extreme caution if you play Talking Heads "Burning Down the House" :D

    Leave a comment:


  • Pete Schumacher
    replied
    Re: Just caught my speaker on fire!

    Originally posted by markk View Post

    The average power in the midrange network can be 20-60% of the power dissapated. In a three way playing loudly, say 50 watts is being pumped into the unit(essentially all of it turned into heat), then a possible worst case would have 30 watts are going into the midrange leg. So it's pretty easy to imagine that 5-15 watts would dissapate as heat in the resistor. It would be operating close to maximum, and, heat transfer would be limited if the resistor is glued onto wood, with one side bonded closely to the wood, and the other sides covered a bit with hot glue.

    This is definitely an arguement in favor of an active setup in a 3 way or high power setup.
    Keep in mind that in this particular case, the shunt resistor is taking in as much power as the midrange driver.

    Leave a comment:


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

    Check the speaker drivers as well. See if they still have changed from factory specs. If you are cranking that much power you should consider exterior mounting for ventilation (and inspection?).


    Again, check that amp. A warm cap??? I have seen amps let DC pass when the volume goes up. Under rated xover parts typically don't just melt! The cone coil just blows.

    charles

    Leave a comment:


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

    im in the process of a 3-way build, and this problem had not accured to me. im glad you shared this with us. good tips curt. an aluminum heat sink is a very simple fix. i hope those with tatorials and this aspect.

    Leave a comment:


  • Pete00t
    replied
    Re: Just caught my speaker on fire!

    I love a mystery. Curt I dont think its your design. I do wonder if he went glue heavy on the the resister. Insulating it with the glue. Perhaps thats even silicon. If its exterior even worse. Causing a heat build up. My 2 cents . I dont have facts

    Leave a comment:


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

    Originally posted by markk View Post
    This is definitely an arguement in favor of an active setup in a 3 way or high power setup.
    I'm not sure its so much an argument in favor of active as it is an argument in favor of proper component sizing and implementation. -Not that I don't recognize the positive attributes of an active design.

    At the risk of being obtuse and redundant, I'll list some suggestions on getting the most power dissipation from a power resistor without becoming a fire hazard.

    *Resistors will be cooled by convection. Mount them where they will have plenty of airflow potential. -Near the port vent area is not a bad idea.

    *If you use the Aluminum housed Vishay/Dale or Arcol and you do not use a heat sink, be sure to derate their power capabilities accordingly. - About 30% of their rated power would be a good ballpark figure. More accurate derating specs can be found here:
    http://www.mouser.com/catalog/specsheets/rhnh.pdf Obviously mounting them on a heat sink is a wise choice, but heat sinks are expensive. As an alternative, surplus CPU heat sinks are available for $5 or so, and can be modified to mount the resistors. -A dab of heat sink grease or similar is mandatory for optimum heat transfer.

    *The ceramic sand cast resistors such as PE's are obviously not designed for heat sinking, but some transfer can be gained by rigidly mounting them to an aluminum plate or heat sink. Don't use glue or cable ties, but mechanically sandwich them between two plates of aluminum screwed together. -The overlap becomes the heat sink 'fins', so don't scrimp on the size too much. -Aluminum flat stock, channel, or square tubing are available at your local hardware store. The other concern here is to make sure the resistor leads are insulated from the aluminum.

    *Heated air rises. Mount the resistor or heat sink so that any fins are orientated vertically and are unobstructed by other materials.

    *As tempting as it looks, using the woofer magnet assembly or basket for a heat sink is probably not all that good of an idea. For one thing, magnet materials are not particularly good at transferring heat.

    *If the crossover is mounted in a small sealed area, such as a base, temperatures can become an issue as well. Add some ventilation holes, or use an aluminum plate to transfer the heat from the inside out...

    C

    Leave a comment:


  • Pete00t
    replied
    Re: Just caught my speaker on fire!

    Did the burn start on the positive side or the negative?

    Leave a comment:


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

    In a typical two way with a 7", the bulk of the power is dissapated in the woofer. Given that a 2 way based on a 7" woofer will likely over excurt at 10-20 watts, the 10-20% of power that is dissapated in in the tweeter network means that even if the tweeter network sees 5-10 watts, it's hard to imagine a scenario where a resistor in the tweeter leg of this two way dissapates more than 5 watts.

    Things might be different with a large two way or three way.



    Look halfway down on one of Art Ludwig's page

    http://www.silcom.com/~aludwig/EARS....nd_loud_sounds

    The average power in the midrange network can be 20-60% of the power dissapated. In a three way playing loudly, say 50 watts is being pumped into the unit(essentially all of it turned into heat), then a possible worst case would have 30 watts are going into the midrange leg. So it's pretty easy to imagine that 5-15 watts would dissapate as heat in the resistor. It would be operating close to maximum, and, heat transfer would be limited if the resistor is glued onto wood, with one side bonded closely to the wood, and the other sides covered a bit with hot glue.

    This is definitely an arguement in favor of an active setup in a 3 way or high power setup.

    Leave a comment:


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

    don't be cheap don't be stupid. 25w resistor is not right a pair of 10 watts is not right get these 50watters!



    http://www.newark.com/vishay-dale/rh...w-1/dp/41K9167


    I use 6 6ohm ones in parallel gives me a 300watt 1 ohm resistor I run a 500 watt sub amp into my dayton rss390 no matter how loud or how long or how deep the bass is my resistor circuit remains at room temp!

    Leave a comment:


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

    bump it up to a 25w resistor and mount if 1/2" off the board. Also mount the board with a 1/2" spacer.

    Leave a comment:


  • dthomas
    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
    Good idea to double up and spread the heat across 2 resistors. But it may be as simple that the problem was what he used to mount the crossover on. If that resistor is doing its job under heavy load the resistor will get hot. Hot enough to catch a piece of wood on fire? Obviously. I suspect the crossover mounting board was the first to go up and then the resistor

    Mounting 10W power resistors tight to a peice of masonite or mdf is not real good practice. The heat gets trapped between the resistor and the board and easily cause a heat issue. Mounting that resistor a 1/2 above the board might be all that is needed to give it proper ventilation and avoid an issue like that. Also using a fire rated PCB or perf board would go a long way also.

    I suspect the issue had more to do with how closely/tightly the resistor was mounted to the wood. The wood itself is the likely issue.

    Leave a comment:


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

    I had this happen to my woofer. The darn thing actually smoked up the room.

    There were plenty of suggestions reguarding the crossovers rated parts. In my situation it turned out to be the amp. It somehow started to shunt DC voltage into the speaker.

    Check out the amp as well. Test it on cheap "test" speakers or put a volt meter on it and make sure you don't have DC current coming off the terminals - Not good!! If so you need it repaired.

    charles

    Leave a comment:

Working...
X