Members agedhorse Posted April 20, 2012 Members Share Posted April 20, 2012 Today I replaced a sub driver in a customer's cabinet with a brand new OEM replacement (couldn't recone due to some mechanical damage) and it didn't work. Read the proper DC resistance on the VC, double-checked the wiring and had the correct DCR at the input to the cabinet. Put a scope on the speaker input and had proper signal (~voltage and ~current), but no sound. Really scratched my head on this for a while and then it occured to me... The manufacturer forgot to magnetize the magnet. This is the first time in over 30 years that I have seen this, and I have reconed maybe a thousand speakers (factory certified for some of the largest manufacturers) so I'm no noobie virgin. Not going to name the manufacturer since it was not in a finished product so may have undergone a less than complete QC (obviously). Link to comment Share on other sites More sharing options...
Members drumstix Posted April 20, 2012 Members Share Posted April 20, 2012 Great story! Link to comment Share on other sites More sharing options...
Members Dogoth Posted April 20, 2012 Members Share Posted April 20, 2012 That IS a first. I know I've never heard of it happening. I'm not sure I'd have figured it out in under a week (I'd still be scratching my head). Amazing what we assume after umpeen thousand repatitive actions. Thanks great story to share :-) Link to comment Share on other sites More sharing options...
Members ey86798 Posted April 20, 2012 Members Share Posted April 20, 2012 That is literally the LAST thing I would have thought of, faced with that scenario! Link to comment Share on other sites More sharing options...
Members Just Mike Posted April 20, 2012 Members Share Posted April 20, 2012 Inconceivable! But seriously, I just can't see how this could happen. When the magnets are magnetized, you would think there would be a test at that point. Then after the speaker was put together, you'd think there'd be another QC check point. I've been to the Peavey factory and seen this procedure in operation. BTW, the magnetization process is quite noisy! Link to comment Share on other sites More sharing options...
Members lonotes Posted April 20, 2012 Members Share Posted April 20, 2012 How far up the suppliers chain did you have to go before you found someone willing to believe you, and then issue a RMA? Link to comment Share on other sites More sharing options...
Members dedmeet Posted April 20, 2012 Members Share Posted April 20, 2012 Is it possible, albeit unlikely, that something de-magnetized the driver en route. Old ferrite magnets would lose strength quickly if subjected to sharp impact. Link to comment Share on other sites More sharing options...
Members RoadRanger Posted April 20, 2012 Members Share Posted April 20, 2012 The manufacturer forgot to magnetize the magnet.So, do you think you've finally seen everything? LOLNot going to name the manufacturer since it was not in a finished product so may have undergone a less than complete QC (obviously).So, if you buy a raw driver it's never been tested to see if it has any output or vc rub or ? Link to comment Share on other sites More sharing options...
Members dennis a Posted April 20, 2012 Members Share Posted April 20, 2012 if you buy a raw driver it's never been tested to see if it has any output or vc rub or ? Not if it rolled off the assembly line after 4PM Friday Link to comment Share on other sites More sharing options...
Members Two of Seven Posted April 20, 2012 Members Share Posted April 20, 2012 I encountered a bizarre speaker malfunction - just last night as it happens. Old dual 15 + horn cab with late 80s BW 1505s. Noticed one 15 was putting out reduced volume and no bass. Felt the cone and it was free, no rubbing but moved like molasses. ??? Popped it out, removed the basket and saw the remains of what used to be a foam dust cover for the pole vent. That foam had rotted and migrated to the gap and coated the inside of the vc - and cooked to a nice roofing tar consistency! Carefully used some carb cleaner and acetone to get all the gunk out - put her back together and good as new ! I have seen foam surrounds melt like that before - never noticed that little foam cover on the pole pieces though. Now I'll have to go and pre-empt the other three 1505s. Link to comment Share on other sites More sharing options...
Members dboomer Posted April 20, 2012 Members Share Posted April 20, 2012 This is the first time in over 30 years that I have seen this. You just haven't looked hard enough ... you just have to go through a few hundred thousand I've also seen magnets that were only half-charged as well as magnets who's polarity was reversed. Link to comment Share on other sites More sharing options...
Members agedhorse Posted April 20, 2012 Author Members Share Posted April 20, 2012 I encountered a bizarre speaker malfunction - just last night as it happens. Old dual 15 + horn cab with late 80s BW 1505s. Noticed one 15 was putting out reduced volume and no bass. Felt the cone and it was free, no rubbing but moved like molasses. ??? Popped it out, removed the basket and saw the remains of what used to be a foam dust cover for the pole vent. That foam had rotted and migrated to the gap and coated the inside of the vc - and cooked to a nice roofing tar consistency! Carefully used some carb cleaner and acetone to get all the gunk out - put her back together and good as new !I have seen foam surrounds melt like that before - never noticed that little foam cover on the pole pieces though. Now I'll have to go and pre-empt the other three 1505s. Classic problem with Peavey BW's, the foam vent filter disintegrates. Link to comment Share on other sites More sharing options...
Members agedhorse Posted April 20, 2012 Author Members Share Posted April 20, 2012 Is it possible, albeit unlikely, that something de-magnetized the driver en route. Old ferrite magnets would lose strength quickly if subjected to sharp impact. Nope, zero magnetism. Link to comment Share on other sites More sharing options...
Members agedhorse Posted April 20, 2012 Author Members Share Posted April 20, 2012 You just haven't looked hard enough ... you just have to go through a few hundred thousand I've also seen magnets that were only half-charged as well as magnets who's polarity was reversed. I'm familiar with polarization issues, and the corresponding change in winding direction, something that I often check when reconing a product that I am not familiar with. Half-charged I haven't seen but with Alnico I have experienced weakening. I have no desire to become experienced with a few hundred thousand speakers Link to comment Share on other sites More sharing options...
Members soul-x Posted April 20, 2012 Members Share Posted April 20, 2012 I saw that on an OEM motorcycle stator once. Took me a fair amount of time and a lot of cussing to figure that one out. Link to comment Share on other sites More sharing options...
Members RoadRanger Posted April 20, 2012 Members Share Posted April 20, 2012 Anybody here old enough to ever have to polarize an automobile generator? Link to comment Share on other sites More sharing options...
Members agedhorse Posted April 21, 2012 Author Members Share Posted April 21, 2012 Anybody here old enough to ever have to polarize an automobile generator? Yes, and just a flash of the field too. Link to comment Share on other sites More sharing options...
Members W. M. Hellinger Posted April 21, 2012 Members Share Posted April 21, 2012 Anybody here old enough to ever have to polarize an automobile generator? Yes... sort of. My first scooter, which was a 1959 shovel-pan w/generator and magneto ignition. I "converted" the lighting to sans battery operation with an adapto-kit, and I remember reading "something" in the adapto-kit instructions about polarizing the generator... but beings as there were no pictures and a lot of text involved with this particular detail... like the male gender that I am... I blew through that, cut to the chase scene... hooked things up and expected results. Everything worked fine... the lights came on when the motor ran. Either I got lucky or lights didn't much care what the polarity was. Link to comment Share on other sites More sharing options...
Members RoadRanger Posted April 21, 2012 Members Share Posted April 21, 2012 Stepping motors are interesting in that they are magnetized after assembly and if you disassemble and reassemble one you lose about 1/2 it's torque . Link to comment Share on other sites More sharing options...
Members Dogoth Posted April 21, 2012 Members Share Posted April 21, 2012 Anybody here old enough to ever have to polarize an automobile generator? Although I've only seen a couple. There used to be SPEAKERS with field coils rather than permanent magnets. Now THAT'S old technology. Link to comment Share on other sites More sharing options...
Members agedhorse Posted April 21, 2012 Author Members Share Posted April 21, 2012 Speakers are generally magnetized after assembly (except for the dust cap) too, or at least used to be. Magnetizing makes a big bang! Link to comment Share on other sites More sharing options...
Members RoadRanger Posted April 21, 2012 Members Share Posted April 21, 2012 Although I've only seen a couple. There used to be SPEAKERS with field coils rather than permanent magnets. Now THAT'S old technology.Alnico was invented in 1931 but wasn't used in consumer products until after WWII. I think field coils were still around in the 50's? Link to comment Share on other sites More sharing options...
Members Don Davis Posted April 21, 2012 Members Share Posted April 21, 2012 Don't they run a tone signal test on all speakers before they ship? How did that one get by QC. Link to comment Share on other sites More sharing options...
Members Coaster Posted April 21, 2012 Members Share Posted April 21, 2012 Don't they run a tone signal test on all speakers before they ship? How did that one get by QC. they forgot to put the magnet plug in so all the magnetite leaked out during shipping. as always it is a shipping problem. Link to comment Share on other sites More sharing options...
Members IsildursBane Posted April 21, 2012 Members Share Posted April 21, 2012 they forgot to put the magnet plug in You must be a boat owner. -Dan. Link to comment Share on other sites More sharing options...
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