• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

Woofer is stiff and scraping when pushed

D

DoctorBotany

New Member
I recently acquired a pair of Infinity CS-3007 speakers and was in the middle of a refoam job when I realized that 3/4 of the 8" woofers seem to be blown (I'm new). Since I wasted a bunch of time and money on them already I figured I'd make sure by posting here.

When I push down lightly on the "good" woofer's cone it is bouncy and doesn't make noise. When I do the same to the others it is stiff, and if I do move the cone there is a scraping noise (that's with any up and down movement whatsoever). I've researched it and seen that this could be a problem with the cone scraping the voice coil, or the voice coil itself, or the speaker is "blown" which I'm not exactly sure what that means. Anyway, the question is, is there anything I can do to fix these drivers short of re-coning (if that would even help)? If not I'm thinking I'll just have to part them out. Thanks.
 
Register to hide this ad
Your symptoms are characteristic of burned voice coils. What happens is, too much signal causes the voice coil to overheat and actually melt - leaving a little blob of copper between the VC and the magnet. "Blown" is not meaningless, that's exactly what it sounds like you have. The only repair would be reconing with a new VC. Good luck.

Cheers,
Larry B.
 
Another mode is overdriving the woofers so that the rear end of the cylindrical voice coil former (looks like a paper towel core coming off the back of the cone, and the voice coil is wound around the outside) slaps against the magnet when the cone is on its backward travel, thus crunching the former, which no longer fits into the narrow voice coil gap, so it scrapes. Academic which one it is really, because both require reconing.

You might inspect the spider carefully and make sure it's attached completely. That's the circular accordion thing at the base of the cone that attaches the cone to the basket. If it's come unglued the bottom end of the cone can get off center and the VC scrapes.

You might look for replacement woofers on the bay, it may be cheaper than reconing.
 
As for 'blown' being meaningless, it is certainly a vague term in many cases. Some (usually inexperienced) people will use it to describe anything from rotten surrounds to a driver that is just not playing, both of which can be fixed, and have nothing to do with burned voice coils or wrecked cones and formers, which can't be fixed as easily and isn't worth the cost except for expensive drivers.
 
Actually, the more common failure mode is over excursion in the forward direction(the result of woofers being wired in the correct polarity), the former extends forward beyond the front of the pole piece where it has already pushed the limits of the damper and suspension, the edge of the former gets hooked on the pole piece and crunched, same result as crashing the back of the gap. There are a few woofers notorious for extending past the pole piece and becoming "locked" in that full forward extension.
 
Don't know if its applicable in your case but i had a speaker that must have been dropped and it caused the magnet on the back to shift. It caused one side of the coil to rub on the magnet. It was obvious by looking at the speaker that the magnet was crooked.
 
toxcrusadr said:
As for 'blown' being meaningless, it is certainly a vague term in many cases. Some (usually inexperienced) people will use it to describe anything from rotten surrounds to a driver that is just not playing, both of which can be fixed, and have nothing to do with burned voice coils or wrecked cones and formers, which can't be fixed as easily and isn't worth the cost except for expensive drivers.
Click to expand...

Obviously, I have no control over other people misusing a term which has a fixed meaning. This isn't "Alice In Wonderland" - words do have actual meanings, despite widespread misuse.

"Blown", as far back as I can remember, described a failure in the continuity of a voice coil - nothing less, nothing more.

As always, just my opinion, YMMV.

Cheers,
Larry B.
 
If you have ever seen an Altec, JBL, or EV large format driver diaphragm fail from being over stressed to where the Aluminum centering the voice coil fails turing it to small flakes on the facet lines the word blown becomes quite appropriate. I've seen diaphragms where the dome as been torn loose from the voice coil and surround. Thats blown, too. Ever seen a voice coil separate with the former from a cone. I ve seen D130's and Altec 421's do that. Thats blown, too. ever heard a funny noise similar to some one rapidly striking a cone, where the voice coil has become partially unattached from a cone. That isn't, blown I guess torn would be better. But for most folks when a speaker fails physically its as if a small explosion took place separating the voice coil from the cone or diaphragm, that's blown. Now when the voice coil wire insulation fails and the coil shorts out and takes out a direct coupled SS amplifier and there's a smell and a small puff a smoke. The amp has failed, blown seems right and to a consumer mind and the speaker blew up to. The word means failed in this since, not that there was an explosion. Its like saying a sound system sounds sweet. Show me how a system tastes sweet. Remember when it comes to sound and its reproduction, there is nothing to see, or feel, or smell about the sound itself. So we use other terms that relate to our other senses to describe the phenomenon. Cut the guy some slack. We all know he means the speaker has failed some how.
 
1tumbleweed said:
"Blown", as far back as I can remember, described a failure in the continuity of a voice coil - nothing less, nothing more.
Click to expand...

Totally agree with you. I was only trying to say that when someone doesn't know any of this, they may use 'blown' to describe any driver that doesn't work, and that could be due to a number of causes.

bowtie427ss said:
Actually, the more common failure mode is over excursion in the forward direction(the result of woofers being wired in the correct polarity), the former extends forward beyond the front of the pole piece where it has already pushed the limits of the damper and suspension, the edge of the former gets hooked on the pole piece and crunched, same result as crashing the back of the gap. There are a few woofers notorious for extending past the pole piece and becoming "locked" in that full forward extension.
Click to expand...

Ah, good to know.

I had a pair of Mission 737's with 8" woofers come through my hands. Dust caps were completely gone, and voice coil wires were sticking out of the gap, waving in various directions. Definitely 'blown'. :eek:

What made me describe it as hitting on the back side instead of overexcursion to the front was the time I was driving 15" 4 ohm woofers with a Denon integrated that was not rated for 4 ohms. It ran out of gas without even cranking them up, and I was hearing distortion and a slapping noise on bass notes. Needless to say I shut that down quick. About the only time I've come close to abusing a speaker. I assumed the slapping noise was the former hitting the magnet in the back. Proud to say that my experience in overdriving woofers is extremely limited. :thumbsup:
 
Atv023 said:
Don't know if its applicable in your case but i had a speaker that must have been dropped and it caused the magnet on the back to shift. It caused one side of the coil to rub on the magnet. It was obvious by looking at the speaker that the magnet was crooked.
Click to expand...

I was wondering about magnet shift, too. Are Infinity magnets glued in place? Seems odd that three woofs out of four would have met a calamitous end.

GeeDeeEmm
 
Lets start over from the begining...
DoctorBotany said:
I recently acquired a pair of Infinity CS-3007 speakers and was in the middle of a refoam job when I realized that 3/4 of the 8" woofers seem to be blown (I'm new). Since I wasted a bunch of time and money on them already I figured I'd make sure by posting here.
Click to expand...
Now,do tell us about the refoaming job.
How were the voice coils centered ?
Were the dust caps removed and then shims used ??
Or did you use the test tone method to center the voice coils ???

Were the voice coils even centered during the refoam job ?

If the voice coils were'nt properly centered,then you get what you have here,voice coil rub.
You've made it clear that you're new to this,so it's not a stretch at all that what you have here is simply a botched refoam job.

And if they have'nt been completely refoamed yet...
Well then you need to understand that the tension from the foam surrounds is pretty much what centers the voice coils.
And if the old surrounds were/are compromised then they wont center the voice coils properly.

Also,if the foams were "shot" for a long while and they were still played that way,it's entirely possible that the voice coils were damaged from such.
(ie: from rubbing over time)

So we probably are gonna need more specific details to give solid useable advice here.

Bret P.
 
Last edited:
xero-D-hero said:
Lets start over from the begining...

Now,do tell us about the refoaming job.
How were the voice coils centered ?
Were the dust caps removed and then shims used ??
Or did you use the test tone method to center the voice coils ???

Were the voice coils even centered during the refoam job ?

If the voice coils were'nt properly centered,then you get what you have here,voice coil rub.
You've made it clear that your new to this,so it's not a stretch at all that what you have here is simply a botched refoam job.

And if they have'nt been completely refoamed yet...
Well then you need to understand that the tension from the foam surrounds is pretty much what centers the voice coils.
And if the old surrounds were/are compromised then they wont center the voice coils properly.

Also,if the foams were "shot" for a long while and they were still played that way,it's entirely possible that the voice coils were damaged from such.
(ie: from rubbing over time)

So we probably are gonna need more specific details to give solid useable advice here.

Bret P.
Click to expand...

That's what I was thinking, too. Could be as simple as the voice coil rubbing due to "unintended consequences" of learning to refoam, or rotting surrounds. That's best case scenario, but ... could be. Optimism rarely hurts. :)

To the poster: In the absence of any surround on the driver if you can find a sweet spot where the voice coil doesn't rub, you might have a shot at saving the driver.
 
I should let the OP answer this but it seemed to me that 'in the middle of a refoam job' meant maybe the one good woofer got refoamed, the second was froze up upon inspection, which caused him to check the others and found two more were trashed as well. The way I read it was that they were stiff and he couldn't find a spot where the VC didn't rub, and that was not caused by the refoaming but discovered before refoaming.
 
It's entirely possible that I messed it up during refoam but I'm pretty sure I didn't. It was when I went to center the voice coils that I discovered the issue. I forget what the technique was called but the refoam kit I had said to center the voice coil I should lightly push on the cone and find where it had the least resistance and most "bounce". But as soon as I touched one of the bad driver's cones I felt that it wasn't moving and would scrape if I forced it to move. One thing that may have been wrong is that I had already glued the new surrounds to the cone but not the outer ring of the basket. I was very careful of the cone while doing everything up until that point though, they were barely moved during the cleaning and gluing. So let me know if that could be the cause of my problem.

The old surrounds were practically non-existent when I saw them the first time, so from the comments I'm guessing they were just blasted for many years and burned out. I'll chalk it up to a lesson for me and try to sell the good drivers to get some money back. Thanks everyone for the responses so far.
 
Yeah it sounds like they were hinky when you got em. If you had completely glued down the surround and then found they were scraping, there would be no way to know, but if you can't center them before the gluing there's a problem. Most if not all woofers I've done moved free and clear from the start even if the old surrounds were pretty much gone. Possible the previous owner played them with weak/destroyed surrounds which could have made them sag and scrape. Or they overdrove them as discussed earlier. Too bad about this.

You might check around (ebay etc.) and see if you can find some. I seem to recall the CS series were not Infinity's top of the line so at least it's not a great loss to speakerdom if you can't get them going for a reasonable cost.
 
toxcrusadr said:
Another mode is overdriving the woofers so that the rear end of the cylindrical voice coil former (looks like a paper towel core coming off the back of the cone, and the voice coil is wound around the outside) slaps against the magnet when the cone is on its backward travel, thus crunching the former, which no longer fits into the narrow voice coil gap, so it scrapes. Academic which one it is really, because both require reconing.

You might inspect the spider carefully and make sure it's attached completely. That's the circular accordion thing at the base of the cone that attaches the cone to the basket. If it's come unglued the bottom end of the cone can get off center and the VC scrapes.

You might look for replacement woofers on the bay, it may be cheaper than reconing.
Click to expand...
I purchased a pair of KLH Five's a few years ago. Beautiful condition. Lightly pushed the cones in to test for rubs and all seemed fine. Had them for several months and then cranked them up for a friend. There was a snapping sound in both woofers. Took the woofers out and lifted the cone from underneath with my fingers. it was stopped half way. It should have kept moving until the spider could not stretch any further. Turns out, the aluminum former was driven DOWN and hit the lower pole piece, probably by pulling out or pushing in a cable on the power amp while live. I'm sure there was a loud snap when that happened. The bottom of the aluminum former was bent outward (flared) and would hit the inner edge of the upper pole piece on a large positive (outward) excursion. I had one repaired for $50 by a local expert and bought a second woofer for $50 off ebay. A finger pushing test would never find this problem. The service guy had to remove the entire cone/VC assembly and bend the former back in shape. Luckily, the bent section did not lit the VC wires.
 
tubed said:
Unless they produce no sound, my guess is the refoams need refoaming.
Click to expand...
I would tend to agree; pay special attention to the spider; you may need to shim the voice coils, especially if they had sagged in a previous life.
 
You must log in or register to reply here.
Back
Top Bottom