M8a woes...

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  • Andrew Pratt
    Moderator Emeritus
    • Aug 2000
    • 16507

    M8a woes...

    So tonight of all nights I decide to host a HT demo night for the local guys so before they arrive I start up the system and make sure all is well. At first things looked good until I smelt a burning smell that I couldn't place...then my cousin who's staying with us tells me when he was listening to the system this afternoon the protection lights on the Rotel power amp came on which has never happened before. So after some further investigation it turns out I've got two blown tweeters So with people starting to arrive I pulled out the M8a drivers to get access to the XO's in vain hope that all that was wrong was that the wires to the tweeters had come loose when I moved them around yesterday...no such luck. I did find the source of the burning smell though as the resistor on the woofer XO must have got so hot it started to burn the wood board it was mounted to 8O Strangely enough the woofers are all ok but the left and centre speakers tweeters are not working at all. I still don't really know what happened to cause this as my cousin insists he wasn't listening that loud but I'm wondering if the new IB sub caused to much undo stress on the rotel amp causing it to clip or something.




  • ThomasW
    Moderator Emeritus
    • Aug 2000
    • 10934

    #2
    Big bummer...........

    The IB is limited by the excursion limits of the drivers, your old ported boxes were limited by the power handling of the VC's. As a result I don't think the IB creates anything specific that would cause this to happen except it's very low distortion.

    Most people use distorted sound as their indicator of when speakers are being over driven, they then turn it down. When the system has high output with low distortion there's much less of an 'indicator' for the system being over driven. So it gets turned up and up and up until poof...... :#

    The smell means that the system was playing high levels and the result was toasted parts. Also the charred wood means that the system was being played very loud for a prolonged period of time. The toasted power resistor is probably what saved the woofers.

    Yes the amp was clipping but he didn't have enough common sense to know how loud the system was playing.

    Your cousin owes you some new tweeters and replacement parts for the XO. :smackbutt:

    My policy is that no one operates the big HT system unless I'm present!




    theAudioWorx
    Klone-Audio

    IB subwoofer FAQ page


    "Complicated equipment and light reflectors and various other items of hardware are enough, to my mind, to prevent the birdie from coming out." ...... Henri Cartier-Bresson

    Comment

    • Pat
      Super Senior Member
      • Aug 2000
      • 1637

      #3
      Andrew, that really sucks, sorry to hear about the toasty tweeters




      Pat's Page
      Pat's Page

      Comment

      • Hank
        Super Senior Member
        • Jul 2002
        • 1345

        #4
        Andrew: sorry to hear about your crispy tweets. I thought I blew a tweet once, but on investigation, a right angle bend on a power resistor had succumed to heat concentration at that point and the lead melted in two. The tweet was fine.
        Your cousin: how old is he? Therein lies the answer to his insisting he didn't have the system too loud. If he's young and is used to a car system cranked up to thumping-down-the-street levels (which is 40% distortion anyway), then he probably cranked it up, and not hearing distortion, had it too loud for too long. I agree that he owes you new tweets.

        Comment

        • Andrew Pratt
          Moderator Emeritus
          • Aug 2000
          • 16507

          #5
          Maybe I should put a fuse on those tweeters for future idiot proofing my speakers :roll: I trested the tweeters by connecting the speaker cables directly to the tweeters so yes I know they're both :#

          As for my cousin he's old enough to know better but I sometimes wonder just how common, common sense really is with some people :evil:




          Comment

          • ThomasW
            Moderator Emeritus
            • Aug 2000
            • 10934

            #6
            I don't know if XT25's can be fixed with replacement elements like a dome tweeter can. For some reason I think this isn't how they are built.

            I think we should think about changing the burned woofer resistor to a cluster of resistors with to raise the overall power handling.

            And yes a good way to 'idiot proof' a speaker is to put fast blow fuses in-line with the inputs. Doing that doesn't guarantee they won't be killed by an overdriven amp, but they go a long way in preventing problems. The penalty for using fuses is a slight decrease in sound qualtiy.




            theAudioWorx
            Klone-Audio

            IB subwoofer FAQ page


            "Complicated equipment and light reflectors and various other items of hardware are enough, to my mind, to prevent the birdie from coming out." ...... Henri Cartier-Bresson

            Comment

            • Andrew Pratt
              Moderator Emeritus
              • Aug 2000
              • 16507

              #7
              If I were to put in an inline fuse how big should it be?




              Comment

              • Andrew Pratt
                Moderator Emeritus
                • Aug 2000
                • 16507

                #8
                I just got off the phone with Solen and the XT25's are now only $60cdn each so they've dropped quite a bit since I last purchased some. I also got another resistor to replace that one that got toasty...i can still measure resistance across it but for $1 it might as well get replaced as well while I'm at it.




                Comment

                • ThomasW
                  Moderator Emeritus
                  • Aug 2000
                  • 10934

                  #9
                  I suggest buying 8 resistors and making a cluster of 4 in a series/parallel array (same value as single resistor) to bump up the power handling.

                  Use a 2 or 3 amp fast 'blow-fuse' for the tweeters.




                  theAudioWorx
                  Klone-Audio

                  IB subwoofer FAQ page


                  "Complicated equipment and light reflectors and various other items of hardware are enough, to my mind, to prevent the birdie from coming out." ...... Henri Cartier-Bresson

                  Comment

                  • Andrew Pratt
                    Moderator Emeritus
                    • Aug 2000
                    • 16507

                    #10
                    Ok I'll do that too.




                    Comment

                    • Bent
                      Super Senior Member
                      • Sep 2003
                      • 1570

                      #11
                      Are regular carbon-type resistors suitable in this league, or should one look for a ceramic wire-wound type?

                      Or is the wire-wound type going to introduce unwanted inductive reactance?

                      Comment

                      • Andrew Pratt
                        Moderator Emeritus
                        • Aug 2000
                        • 16507

                        #12
                        Bent these are the ones I use Solen I changed my order so that I'm now getting enough to do a cluster of four in each of the 4 speakers.




                        Comment

                        • Bent
                          Super Senior Member
                          • Sep 2003
                          • 1570

                          #13
                          I see.

                          They look to be of excellent quality.

                          Comment

                          • Andrew Pratt
                            Moderator Emeritus
                            • Aug 2000
                            • 16507

                            #14
                            Solen tends to carry high quality XO parts and for the most part their prices are very reasonable...esp considering they're in Canada (well Quebec anyway :roll: )




                            Comment

                            • Andrew Pratt
                              Moderator Emeritus
                              • Aug 2000
                              • 16507

                              #15
                              The new tweeters and resistors arrived tonight so I went to work redoing the lowpass XO's and installing the replacement tweeters. So far everything's back to normal...well other then my finger that I managed to drip hot glue onto....burned pretty badly too :roll:




                              Comment

                              • ThomasW
                                Moderator Emeritus
                                • Aug 2000
                                • 10934

                                #16
                                Geee's Andrew,

                                I think it's time to get adult supervision for activities that take place at your house




                                theAudioWorx
                                Klone-Audio

                                IB subwoofer FAQ page


                                "Complicated equipment and light reflectors and various other items of hardware are enough, to my mind, to prevent the birdie from coming out." ...... Henri Cartier-Bresson

                                Comment

                                • Andrew Pratt
                                  Moderator Emeritus
                                  • Aug 2000
                                  • 16507

                                  #17
                                  :LOL:




                                  Comment

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