B&C 18SW115 visible arcing of voice coil through v

Message Topic Search Topic Options Post Reply Create New Topic Printable Version Translate Topic

   Hey!I'm running a b&c 18sw115 8 ohm driver in a paraflex c2e cabinet,
Recently we had to leave our behind our set with the local authorities, after playing ar a party abroad..
Finally we retrieved all of our gear a couple of weeks ago and last week we were eager to get our babies playing again!
But strangely one of the subs was making some strange rattling sounds from the moment I turned it on.. I started with maybe 25% power..
So i quickly turned off this specific cabinet, and heard it was still making  weird noises just from the cone resonating with the other speakers.

I was curious what was going on so I gave it just a tiny bit of power, and went to inspect the driver again. (In this cabinet design the driver is mounted with the magnet facing the opening, so easily visible/reachable)
I stuck my head in the cabinet and to my surprise noticed through the rear vent hole that some blue sparks were visible inside the voice coil.. i have never heard or read about something like this happening. 
Is it time for a recone? Or is it salvagable...

Either way just curious what might be going on

Thanks 

Author	Message Topic Search Topic Options Post Reply Create New Topic Printable Version Translate Topic
Mattbass23 Members Profile Send Private Message Find Members Posts Add to Buddy List New Member Joined: 09 July 2017 Location: Holland Status: Offline Points: 4	Post Options Post Reply Quote Mattbass23 Report Post Thanks(0) Quote Reply Topic: B&C 18SW115 visible arcing of voice coil through v Posted: 20 April 2023 at 11:00pm
	Hey! I'm running a b&c 18sw115 8 ohm driver in a paraflex c2e cabinet, Recently we had to leave our behind our set with the local authorities, after playing ar a party abroad.. Finally we retrieved all of our gear a couple of weeks ago and last week we were eager to get our babies playing again! But strangely one of the subs was making some strange rattling sounds from the moment I turned it on.. I started with maybe 25% power.. So i quickly turned off this specific cabinet, and heard it was still making weird noises just from the cone resonating with the other speakers. I was curious what was going on so I gave it just a tiny bit of power, and went to inspect the driver again. (In this cabinet design the driver is mounted with the magnet facing the opening, so easily visible/reachable) I stuck my head in the cabinet and to my surprise noticed through the rear vent hole that some blue sparks were visible inside the voice coil.. i have never heard or read about something like this happening. Is it time for a recone? Or is it salvagable... Either way just curious what might be going on Thanks

Conanski Members Profile Send Private Message Find Members Posts Add to Buddy List Old Croc Joined: 26 January 2006 Location: Ottawa, Canada Status: Offline Points: 2757	Post Options Post Reply Quote Conanski Report Post Thanks(0) Quote Reply Posted: 22 April 2023 at 5:26am
	Sounds like that driver is blown.. the coil come unglued and is now rubbing in the gap. That means they were all pushed to and in at least one case beyond it's thermal limits, the only reason all drivers didn't die may just come down to production tolerances... that was the weakest one in the batch you have.

studio45 Members Profile Send Private Message Find Members Posts Add to Buddy List Old Croc Joined: 16 October 2007 Location: United Kingdom Status: Offline Points: 3881	Post Options Post Reply Quote studio45 Report Post Thanks(1) Quote Reply Posted: 25 April 2023 at 2:51pm
	Well, that driver is definitely blown. Sounds like its voice coil has damage causing shorts between turns, but still has some intact turns. These are acting as a generator when they are moved in the magnetic gap by the vibrations from the other subs. The voltage produced is arcing across some tiny gap, this then produces a back-EMF and tries to move the cone with opposing force. This causes the rattling sound. You can exploit this phenomenon to test a driver's coil without any signal or voltage source. Gently press the cone while the terminals are disconnected, there should be no sound. Now take a piece of wire or metal and lightly touch/brush both terminals while moving the cone. You should get a scratching sound when the circuit completes and breaks. This indicates an intact coil. If there is still no sound, the coil is open circuit.
	Studio45 - Repairs & Building Commotion Soundsystem -Mobile PA