Announcement

Collapse
No announcement yet.

Just caught my speaker on fire!

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

  • #31
    Re: Just caught my speaker on fire!

    Originally posted by billcurrier View Post
    Your cabinets look very nice from the little I could see of them.
    Here is the build pics on them if you are interested.
    Dave
    http://www.pellegreneacoustics.com/

    Trench Seam Method for MDF
    https://picasaweb.google.com/101632266659473725850

    Comment


    • #32
      Re: Just caught my speaker on fire!

      I'm sorry it had to happen to you but usually some good can come out of a bad experience. I will definitely test my passive crossovers outside the box for a long period of time to see how hot the resistors get and will double any that I feel are too warm for my liking.

      I'm just glad you guys are safe, especially the speakers. :p

      Comment


      • #33
        Re: Just caught my speaker on fire!

        I'm becoming a fan of outboard XOs!!!

        Better ventilation.
        Been doing that awhile. Safer and easier to tweak.

        Comment


        • #34
          Re: Just caught my speaker on fire!

          I try to avoid resistors if I can but I'm currently working on a 3-way that uses the DC200 woofer, ND28F tweeter and DC130BS-8 midrange. The mid needs an L-pad. I started with a 5 ohm 20 watt series and an 8 ohm 10 watt parallel resistor. They got quite hot to the touch so I used an infrared thermometer and got a reading of 180 F. I increase the series to 40 watts and parallel to 20 watts and the series was still pretty warm so I am now at 5 ohm 50 watt (2-25 watt in parallel) series and one 8 ohm 20 watt in parallel. Readings now get up to 120 F at 70% of full power on a 120 watt/channel amp. SPL readings at 2 meters was over 100 dB so I figure I should be ok.

          I've actually blistered my fingers on another system in the past while grabbing a resistor during the high power test of the xover and speaker system.

          My speakers are torn apart now for painting but with this warning, I plan to do some more testing. The crossovers are glued down. Now I wonder if the glue will melt. I put the resistors on top of some 1/8" brazing rods so that the rods look like railroad ties and the resistors look like railroad rails. One rod on each end of the resistors. That should give some some distance between the resistor and the hardboard and some ventilation.

          I keep trying to figure out some kind of external "box" to house the xovers in. Whenever a resistor is involved, external mounting should provide some safety. I've never found any other components getting hot. I even tried a 50 watt variable L-pad and it got quite hot.

          I did the testing with the amp in mono mode so both channels were being routed to one speaker. After I felt safe with the 50 watt series resistor, I ran the speakers in stereo and they didn't get as warm. The amp has a power meter for each channel and it seemed to hover around 25 watts with peaks of 120+ watts.

          Comment


          • #35
            Re: Just caught my speaker on fire!

            Active crossovers.



            Whaaaaat....? :D

            Comment


            • #36
              Re: Just caught my speaker on fire!

              This is exactly why hot glue doesn't belong on resistors. I'm glad the damage wasn't worse.
              "He who fights with monsters should look to it that he himself does not become a monster. And when you gaze long into an abyss the abyss also gazes into you." Friedrich Nietzsche

              http://www.diy-ny.com/

              Comment


              • #37
                Re: Just caught my speaker on fire!

                Taking the 4th of July to the next level, Dave?
                Oh well you've got some cleanup and repairing to do. Great lesson for all of us too. Thanks for the pics.

                Comment


                • #38
                  Re: Just caught my speaker on fire!

                  Dave, You definitely need to open the other Mini and address this issue there as well. I don't think the tweeter resistors will need to be replaced, but let me know if they look like they show any signs of overheating.

                  Keep in mind that the power ratings on the Arcol and Vishay resistors assume they are mounted on a properly sized heat sink, but it sounds like if we double up with the sandcast resistors, raise them up off the board, and get them out into free air, that Freddie won't be able to cause any more damage.

                  C
                  Curt's Speaker Design Works

                  "It is the mark of an educated mind to be able to entertain a thought without accepting it."
                  - Aristotle

                  Comment


                  • #39
                    Re: Just caught my speaker on fire!

                    Wow... glad it didn't do more damage, like melt/short a cap and cause a blown driver or something worse.

                    Fire of course would also be bad. I would think that inside the box, you likely would have a limited enough supply of oxygen that a small fire might limit itself and choke out... but burning thru a cone and letting fresh air in could be another story...

                    Strange that I was just thinking about this a few days back, not the fire part, but how much power various crossover parts might end up dissipating. Started mocking up a few XO's in a SPICE program to see what kinds of peak currents were flowing. Now, I want to model up a Mini Statement XO and see what that resistor will see with various power levels in. I'll report back when I do...

                    Comment


                    • #40
                      Re: Just caught my speaker on fire!

                      If you can smoke a shunt resistor you can smoke a voice coil.

                      It's another benefit of active crossover . . . you can size the individual amps to their respective drivers, and avoid all the excitement . . .
                      "It suggests that there is something that is happening in the real system that is not quite captured in the models."

                      Comment


                      • #41
                        Re: Just caught my speaker on fire!

                        Originally posted by curt_c View Post
                        Dave, You definitely need to open the other Mini and address this issue there as well. I don't think the tweeter resistors will need to be replaced, but let me know if they look like they show any signs of overheating.

                        Keep in mind that the power ratings on the Arcol and Vishay resistors assume they are mounted on a properly sized heat sink, but it sounds like if we double up with the sandcast resistors, raise them up off the board, and get them out into free air, that Freddie won't be able to cause any more damage.

                        C
                        I got the other one opened up yesterday. Here is a pic of the mid xo. It appears it was on its way as well. The hot glue melted off the resistor and there is a burn mark on it. Probably from the foam that was covering them.



                        I think I may just replace them with the same resistors paralleled as you suggest. I already have the resistors. Along with the proper installation techniques they should be fine. All the other ox boards look fine. I should also mention when I pulled the first one out the night it happened the large cap was warm as well. I assume that should be expected.

                        Thanks Dave
                        http://www.pellegreneacoustics.com/

                        Trench Seam Method for MDF
                        https://picasaweb.google.com/101632266659473725850

                        Comment


                        • #42
                          Re: Just caught my speaker on fire!

                          Originally posted by davepellegrene View Post
                          I should also mention when I pulled the first one out the night it happened the large cap was warm as well. I assume that should be expected.

                          Thanks Dave
                          I've never seemed to heat up any caps in my stuff. Could be just that it was an adjacent heat source?

                          Later,
                          Wolf
                          "Wolf, you shall now be known as "King of the Zip ties." -Pete00t
                          "Wolf and speakers equivalent to Picasso and 'Blue'" -dantheman
                          "He is a true ambassador for this forum and speaker DIY in general." -Ed Froste
                          "We're all in this together, so keep your stick on the ice!" - Red Green aka Steve Smith

                          *InDIYana event website*

                          Photobucket pages:
                          https://app.photobucket.com/u/wolf_teeth_speaker

                          My blog/writeups/thoughts here at PE:
                          http://techtalk.parts-express.com/blog.php?u=4102

                          Comment


                          • #43
                            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

                            Comment


                            • #44
                              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.
                              Dave

                              If you can read this, thank a teacher.
                              If you are reading it in English thank a Veteran
                              .

                              Comment


                              • #45
                                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.

                                Comment

                                Working...
                                X