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Speaker Question

#21
Kevin1960 said:
Sometimes when the coil has overheated, the coatings on the coil will bubble up and expand. The speaker will continue to work but it will scrape the sides of the magnet or buzz. This can help indicate the overall condition of the driver and indicate a need for re-coning.
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But the issue of 'touching' the cone, what of that specifically?.. The voice coil/permanent magnet relationship I'm already familiar with. But, would very gently pushing back on the cone (using both hands, one on either side of the cone)reveal the damage on the voice coil by reproducing the motion of the cone's "throw?" I mean, wouldn't you feel/hear some resistive scrapping as you did this? I blew a 15" JBL bass speaker some decades back, but I knew it was gone just by the distortion.. Never did any secondary physical confirmation.. I just had it re-coned.
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#22
Kevin1960 said:
It all depends on why you would do this and what are you looking for? The construction of a speaker typically has a coil of coated wire that is suspended in a slot that moves inside the magnet. Sometimes when the coil has overheated, the coatings on the coil will bubble up and expand. The speaker will continue to work but it will scrape the sides of the magnet or buzz. This can help indicate the overall condition of the driver and indicate a need for reconing.
Click to expand...
After reading some earlier posts, I decided to check out the speakers themselves. I gently checked the in/ out movement. One of the speakers moves effortlessly with no resistance while the other moves but has a lot more resistance. So I believe that I have found the problem. So a re cone would include replacing the voice coil? Is it safe to say that a speaker should move freely in/ out with virtually no resistance. Thanks to all for your insight
 
#23
jsf729 said:
After reading some earlier posts, I decided to check out the speakers themselves. I gently checked the in/ out movement. One of the speakers moves effortlessly with no resistance while the other moves but has a lot more resistance. So I believe that I have found the problem. So a re cone would include replacing the voice coil? Is it safe to say that a speaker should move freely in/ out with virtually no resistance. Thanks to all for your insight
Click to expand...
A speaker should move smoothly and there should be no rubbing, scraping or clicking as it moves in or out. In my limited experience with speaker issues I would say that a difference in stiffness/compliance of the surround and spider could cause two speakers that are both good to feel slightly different. The speaker tech I worked with felt that smoothness AND silence when moving the cone was the key. If there was resistance you could both hear and feel (like something is binding/rubbing), that was the tell tale sign. The phrase I recall was that "you needed to listen for interference using both your ears and your fingertips". A dynamic frequency sweep especially at a low frequency would often highlight the interference detected as a rhythmic clicking.
 
#24
Rattman said:
But the issue of 'touching' the cone, what of that specifically?.. The voice coil/permanent magnet relationship I'm already familiar with. But, would very gently pushing back on the cone (using both hands, one on either side of the cone)reveal the damage on the voice coil by reproducing the motion of the cone's "throw?" I mean, wouldn't you feel/hear some resistive scrapping as you did this? I blew a 15" JBL bass speaker some decades back, but I knew it was gone just by the distortion.. Never did any secondary physical confirmation.. I just had it re-coned.
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Click to expand...
So long as the foam surround and spyder below the cone is visible and in good shape, this is the technique used to check for a damaged driver. however if the foam surround is damaged and is rotted away it is not recommended because both the spyder and foam surround provide the spacing and suspension necessary to keep the coil from scraping the sides of the slot in the magnet and possibly damaging the coating to the coil. This could prevent you from just doing a refoaming job and being done. The slot space and coil have a very tight tolerance. I should also mention that no signal applied, and this check should be made with the driver face up, Gravity can have an influence on this test.
At one time I did have a driver that distorted at only a certain frequency. I bypassed the crossover completely and eliminated that as my cause. I suspect it did have some coil coating damage or the glue that connected the spyder to the cone had come loose as I could never detect it rubbing or scrapping the gap in the magnet.
That driver was replaced. You can't always determine what kind of damage has occurred to a driver. If you have narrowed it down to the driver at fault , just have it reconed by a professional recone shop and move on. The tolerances needed to recone a driver requires a light and patient and experienced touch.
 
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#25
Al Kraft said:
A speaker should move smoothly and there should be no rubbing, scraping or clicking as it moves in or out. In my limited experience with speaker issues I would say that a difference in stiffness/compliance of the surround and spider could cause two speakers that are both good to feel slightly different. The speaker tech I worked with felt that smoothness AND silence when moving the cone was the key. If there was resistance you could both hear and feel (like something is binding/rubbing), that was the tell tale sign. The phrase I recall was that "you needed to listen for interference using both your ears and your fingertips". A dynamic frequency sweep especially at a low frequency would often highlight the interference detected as a rhythmic clicking.
Click to expand...
This is exactly right.
 
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#26
jsf729 said:
After reading some earlier posts, I decided to check out the speakers themselves. I gently checked the in/ out movement. One of the speakers moves effortlessly with no resistance while the other moves but has a lot more resistance. So I believe that I have found the problem. So a re cone would include replacing the voice coil? Is it safe to say that a speaker should move freely in/ out with virtually no resistance. Thanks to all for your insight
Click to expand...
Yes there should be no resistance. If you feel any friction it means the coil is rubbing and has most likely warped or gotten so hot that the coating has started to come off. A re cone kit will include the voice coil. I'm not sure if this link is the right kit for your speaker, just wanted to show you an example. You should be able to contact Eden for exact specs, especially if it's an older cab.

Invalid Link Removed
 
#27
jsf729 said:
After reading some earlier posts, I decided to check out the speakers themselves. I gently checked the in/ out movement. One of the speakers moves effortlessly with no resistance while the other moves but has a lot more resistance. So I believe that I have found the problem. So a re cone would include replacing the voice coil? Is it safe to say that a speaker should move freely in/ out with virtually no resistance. Thanks to all for your insight
Click to expand...
Yes a/b comparisons can really help to narrow down where a problem is and can be a good tool in your troubleshooting tool box. I usually keep a good spare cheap driver to use as a sub when trouble shooting speakers to sub out a suspected driver.
 
#28
Reedt2000 said:
Yes there should be no resistance. If you feel any friction it means the coil is rubbing and has most likely warped or gotten so hot that the coating has started to come off. A re cone kit will include the voice coil. I'm not sure if this link is the right kit for your speaker, just wanted to show you an example. You should be able to contact Eden for exact specs, especially if it's an older cab.

Invalid Link Removed
Click to expand...
Thanks! Already emailed my local speaker shop for an appointment. Really informative thread. Thanks to all who contributed!
 
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#29
Al Kraft said:
The most common failure mode I've experienced with speakers and time relates to deterioration of the surround/spider/dust cover materials and/or adhesives. This was primarily in home audio gear (JBL specifically) that could not have been treated more gently.

I would imagine repeated over-powering a driver could result in premature fatigue and/or heat related failures. Storage and general exposure to high heat, UV rays (direct sunlight) and/or high humidity could also result in a shorter useful life.

All that said, I'm still using Peavey Scorpion loaded PA cabs that I bought new in 1984. They've been treated well and stored in ideal conditions. Those speakers (while not the highest-end products in the world) sound as good today as they did when I first bought them.
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Yeah, I have a pair of JBL L166's (successor to the famous L100's) that have foam surrounds. They disintegrated and I successfully replaced them myself. But not a good material selection for permanence.
 
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#34
There's a lot of really goofy suggestions in this thread that do not relate at all to the problems here. First of all, there are no foam surrounds being used, so this kind of "fix" makes no sense. Second, the testing that's used to determine the type of damage that the driver has incurred involves looking at the electro-mechanical parameters and comparing with the manufacturing standards for that driver. The quickest one to look at is Fs, generally it goes way down when the spider deteriorates. Another is Xmax (or displacement) distortion symmetry, which will vary greatly from standard with a damaged driver, in fact that's one way to determine Xmax and if it's possible to reach Xmax with less than the standard design test power, that's another giant indicator. It's almost impossible to see the kind of spider damage that is typically found in measurements with over-excursion damage.

The root problem is that there was serious over-excursion of the drivers. While the visible damage might be creasing of the paper at the cone edge where it bonds to the surround, there is almost certainly corresponding damage to the spider that has reduced it's spring constant, and thus every parameter involved with the driver's performance. The micro-tearing of the linen fibers within the spider can not be fixed, and the re-coning takes care of that because all of the soft parts are replaced in the process.

The damage to the cone edge is common to a suspension system that uses a flat accordion surround (also called a C-66 surround) that makes a transition to the cone that has a formed rim matching the surround. This is an area of very high stress, and as amp power has grown this has become a vulnerable area for damage. Most bass speakers use an M roll or double-half-roll surround which meets the cone edge at the angle of the cone which eliminates this weak spot, which is especially vulnerable on the lighter cones used to obtain nice mid voicings.
 
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#38
jsf729 said:
So basically is it overpower that causes the over excursion or a frequency (either low or high)
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In my experience, virtually all cases of speaker failures resulting from operation are a result of being overpowered for their rated capability. This results in thermal (heat) damage and/or mechanical damage such as over-excursion. Frequencies IME tend to be more related to which drivers are likely to be the most susceptible first to the type of overpower situation. Please note that it is entirely possible for a speaker to experience an overpower condition by an amplifier with a lower rated output than the speaker's rating.
 
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#39
jsf729 said:
So basically is it overpower that causes the over excursion or a frequency (either low or high)
Click to expand...
Mechanical damage is always caused by excessive low frequency power, which drives the speaker (well) beyond its mechanical capabilities. Power handling decreases as the frequency drops very quickly below the F10 point (-10dB response).
 
#40
agedhorse said:
Mechanical damage is always caused by excessive low frequency power, which drives the speaker (well) beyond its mechanical capabilities. Power handling decreases as the frequency drops very quickly below the F10 point (-10dB response).
Click to expand...
I have a quick question on that and I don't disagree with anything you said. However, isn't it also possible for a mid or high frequency driver to be mechanically damaged by receiving excessive power within their normal frequency range (no amp driven to distortion or weird harmonics) say in a bi-amped situation where there is an active crossover at the amp?

In this hypothetical case I wouldn't think the low frequency power would be a significant factor. I'm just trying to differentiate in my mind between mechanical failures in general and the typical failure mode of elements within a speaker cab which is being sent a single full range signal. Thanks in advance for being a patient teacher.
 

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