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jwc

"stiff" woofer

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So a question for the group here.

 

I have a bass cabinet loaded with 4 woofers each with different chamber.  Bought used.

 

All 4 woofers have an impedance check with multimeter about 6.7 ohms.  All 4 woofers same model.

 

I can play music into all 4 separately with no distortion to my ear.

 

However, one of them lacks bass in 200Hz and below.  The music is there but lacks "bump or thump".  You can see it on a RTA.

 

I was inspecting the woofers up close and they are all tight sealed.  No cracks or visible flaws for that matter.

 

The one that lacks the low end is "stiff".  You know how you can tap on a woofer cone and it has that typical "thump" sound and the cone moves a little.  Well the one woofer makes no noise and the cone is rigid.  Almost like it got reconed or something and not broken in or a defective cone.

 

Any thoughts on this?  Should I run some low end material through it over night?  Or is there a way to check for some other defectiveness?  It would be a pain to uninstall the woofer; so I'm trying to see what I can do while installed.

 

jc  

 

 

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Sounds like the VC coil is frozen because the magnet shifted.

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I've heard of that.  So music will play without audible distortion?  I guess this is possible.  Good thought.

 

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Voice coil could also be warped and frozen in the gap from extreme heating if it had been overdriven or if an amplifier was bad at sometime in the past sending dc to the drivers voice coil before you owned them.

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The "no distortion" thing doesn't make sense to me. The cone isn't moving -- shouldn't it sound terrible?

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I haven't measured distortion.  Plays music clearly....just lacks punch.    Sounds like a 6" woofer.

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Maybe check for electrical continuity between the terminals and frame?

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Speculation, but I think the spider is broken. Voice coil / magnet interaction will still occur but motion will be restricted, which affects bandwidth.

Time to replace the woofer.

Just my 2 cents.

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I uninstalled it.  That cone wont move.  Looks intact.  

 

Thanks guys

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Our buddy Terry Cruse sent me a K-33 out of a Cornwall to see why it did not work many years ago.  He had just reached (I believe) 124 db and suddenly the woofer was just silent.  When I cut into it found the voice coil had come out of the magnet gap and then just impacted back into the top of the magnet assembly crushing it in the process.  Might be what happened to yours.

 

Bob Crites

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Travel limit exceeded... 😛

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28 minutes ago, codewritinfool said:

Tough to have a stiff woofer that you can’t use.

The night is young.

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I don't know if my buddy's woofer was having the same issue as yours.  But he didn't even know he had an issue until he played some bass heavy material at high volumes, heard a pop, turn the system off in a panic, waited a few minutes, looked around turn the system back on and had twice as more low frequency out put (ok maybe not twice as much) but he called me right away asking me my thought.  I just figured something was frozen and he knocked it loose with the bass heavy material and cranking the volume.  Maybe give it a try, what else do you have to lose?

 

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3 hours ago, The Dude said:

Maybe give it a try, what else do you have to lose

7 other woofers. 

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7 other woofers. 
oh yeah, there is that.

Sent from my SM-G955U using Tapatalk

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  1. Know I would hate it
  2. Just one of those things

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Hooking up a battery similar to how you would check multiple woofer phase probably would have shown the problem also.  Recone/Replace.

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