Woofer only turns on when music is loud

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dwarfed centipede

Woofer only turns on when music is loud
« on: 6 Jan 2015, 08:54 pm »
Hey everyone it's been awhile!  I literally haven't even touched a speaker wire since the last time I posted here.  Been busy with bicycle racing and other hobbies and sadly neglected this one. 

This is the first place I turned to for some expert advice from all you hifi guru's.  So my issue is I have a car amp running a speaker pair consisting of a crossover with a tweeter and woofer.  Awhile ago I noticed the left speakers would take awhile to start working after I turned on my car.  After some fumbling around, I found if I fiddled with the high pass/ low pass toggle on my amp, all the speakers would eventually turn on.  But now even fiddling with this button, I still can't get the left woofer to come on.  The tweeter is working great.  This also only seems to happen when it gets cold outside and sometimes if I turn the music up real loud it will kick on and then I can lower the volume and everything is fine until I start the car up the next time.  I didn't notice any issues in the summer other than the occasional needing to mess with the button issue.  Is my amp toast?  It's not a real hifi amp (concept) and a tad underpowered for my speakers, so I was temped just to buy a new one.  But if there's a way to save myself the $500+ on a decent upgrade and get this one working again, I'm open to ideas or suggestions.  Thanks!

Wayner

Re: Woofer only turns on when music is loud
« Reply #1 on: 6 Jan 2015, 09:01 pm »
Sounds like a warped voice coil in the woofer. New woofer may be required.

Wayner

thunderbrick

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Re: Woofer only turns on when music is loud
« Reply #2 on: 6 Jan 2015, 09:26 pm »
Tap off of the woofer leads and see if another speaker is getting the signal when the woofer isn't performing.

mcgsxr

Re: Woofer only turns on when music is loud
« Reply #3 on: 6 Jan 2015, 09:27 pm »
Potential ground issue?  Could be either the driver, or the amp.  Agree that tapping another woofer off it will prove insightful.

DaveC113

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Re: Woofer only turns on when music is loud
« Reply #4 on: 6 Jan 2015, 09:30 pm »
Could also be an xo cap going bad.

dwarfed centipede

Re: Woofer only turns on when music is loud
« Reply #5 on: 7 Jan 2015, 02:56 pm »
So what I'm gathering is you suspect it may be a woofer problem and not necessarily the amp.  I hadn't thought of tapping the woofer.  That's going to be a good troubleshooting step for sure.  I was also going to try to swap the L and R channels too and see if the problem follows.  Thanks everyone.

thunderbrick

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Re: Woofer only turns on when music is loud
« Reply #6 on: 7 Jan 2015, 03:33 pm »
Could also be an xo cap going bad.

+1!

KenSeger

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Re: Woofer only turns on when music is loud
« Reply #7 on: 7 Jan 2015, 03:44 pm »
Feeding the woofer with the other channel's signal is a good idea for trouble shooting.  First grab some wire so you can change *just* the woofer driver, i.e. feed the woofer with the output from the other channel's crossover.  Otherwise just swapping amp output only tests whether it is in A. speaker/crossover or B. amp.
Then change the amp output.  That way you'll know where the problem is.

If it is the woofer, if the construction of the woofer allows it, take a close look at the flexible wire between the voicecoil and the terminals.  Sometimes just a touch up on these delicate soldering joints is all that is needed if there is a cold solder joint(sometimes the solder has a crystalline rather than smooth appearance).  Usually if a voice coil is warped, there will be distortion at all playing levels and you can feel/hear the scraping if you gently move the cone by hand.
Ken

Wayner

Re: Woofer only turns on when music is loud
« Reply #8 on: 7 Jan 2015, 05:18 pm »
If it's a 12db per octave slope on the woofer, then only a coil is in series with the woofer's voice coil. The cap would be across the coils.

I've have seen voice coils so warped that it took lots of power to make them move. Of course none of us know what the real problem is here, but we can play the odds. I worked on a Dynaco A25 in which the woofer's voice coil was actually on fire at some point, as the entire assembly looked like a fire scene.

Just sayin'.

Also, if the speaker is blown, there are many resources available to re-cone it, so it's not like its the end of the world......

Wayner

dwarfed centipede

Re: Woofer only turns on when music is loud
« Reply #9 on: 20 Jan 2016, 03:39 pm »
I finally got around to taking the door apart and found the issue with the woofer.  It turns out the mounting bracket was made of MDF and had gotten wet so it disintegrated and the woofer was laying against the door.  I made a new bracket out of marine board and all is working again.