JBL Spider Sag?

[scottosan]

JBL Spider Sunken?

Just got my speakers back from reconing (JBL 128H) and they mentioned the the spiders were sunken a bit which is not too uncommon for vintage speakers. I asked what the implications were and they said they i should be fine if i am not pushing these to their limits. I know that a recone would be ideal, but would also mean a non-JBL aftermarket cone and also no white cone anymore. What is your opinion? These are in a JBL L150.

Note: I editted it as I read there is a difference between sag and sunken. Sag being vertical while speaker is installed and sunken meaning that the voice coil would be symetrically closer to the magnet

 

[Copa1934]

Just got my speakers back from reconing (JBL 128H) and they mentioned the the spiders were sunken a bit which is not too uncommon for vintage speakers. I asked what the implications were and they said they i should be fine if i am not pushing these to their limits. I know that a recone would be ideal, but would also mean a non-JBL aftermarket cone and also no white cone anymore. What is your opinion? These are in a JBL L150.

Note: I editted it as I read there is a difference between sag and sunken. Sag being vertical while speaker is installed and sunken meaning that the voice coil would be symetrically closer to the magnet

Not sure I follow the distinction there, since to me they are (to me anyway) the same thing. Once the spider looses it's "elasticity" (it's ability to bring the cone back to neutral position) all matters of things can happen, sag, shifting, etc.

As for uncommon, BS. I have several JBL woofers with sagging spiders. Spiders, like anything else in a speaker "motor" will wear out. People have tried "wicking" the spider with Acetone or MEK (to restore the spider) with mixed results.

If you were told this by a "known" speaker repair place that would have me a tad concerned.

You'll get quite the mixed opinion on "original" vs "aftermarket". Some would even argue that a recone with factory kits is not original, but that's the extremist. Some of us are strictly about the sound. So bad motor assembly means recone, or at the very least replacing bad/defective parts. This will turn into quite the topic especially when purists chime in.

Personally I've reconed a couple JBL woofers and midranges. They were just too bad to reuse the cones, either due to tears, creases or other damage.

 

[scottosan]

Not sure I follow the distinction there, since to me they are (to me anyway) the same thing. Once the spider looses it's "elasticity" (it's ability to bring the cone back to neutral position) all matters of things can happen, sag, shifting, etc.

As for uncommon, BS. I have several JBL woofers with sagging spiders. Spiders, like anything else in a speaker "motor" will wear out. People have tried "wicking" the spider with Acetone or MEK (to restore the spider) with mixed results.

If you were told this by a "known" speaker repair place that would have me a tad concerned.

You'll get quite the mixed opinion on "original" vs "aftermarket". Some would even argue that a recone with factory kits is not original, but that's the extremist. Some of us are strictly about the sound. So bad motor assembly means recone, or at the very least replacing bad/defective parts. This will turn into quite the topic especially when purists chime in.

Personally I've reconed a couple JBL woofers and midranges. They were just too bad to reuse the cones, either due to tears, creases or other damage.

The said it is NOT uncommon for this to occur. I assume this in inline with what you are saying that it is commone, correct? With your JBL's with sunk spiders, are they without any audible issue?

Thanks,
Scott

 

[Chris Brown]

I rotate my woofers every few years or so, which I've always thought would help with any sag over time. Really though, on both my 128H and 128H-1 woofers, I've seen no evidence that there is any sag at all or that this is even an issue worth worrying about on these woofers. I certainly don't go easy on my speakers either, quite the opposite.

 

[scottosan]

I rotate my woofers every few years or so, which I've always thought would help with any sag over time. Really though, on both my 128H and 128H-1 woofers, I've seen no evidence that there is any sag at all or that this is even an issue worth worrying about on these woofers. I certainly don't go easy on my speakers either, quite the opposite.

Just for clarification, the spiders are not level to the plane of the frame (with the speaker laying on its back with the cone facing up) the center appears to be symmetrically sunken. Does that make sense? I cant get a pic now

 

[Chris Brown]

Just for clarification, the spiders are not level to the plane of the frame (with the speaker laying on its back with the cone facing up) the center appears to be symmetrically sunken. Does that make sense? I cant get a pic now

The main question I would be concerned with is if the cone is returning to the neutral position or not while the woofer is installed in the cabinet. I wouldn't worry much about how it acts while laying back on the magnet, where gravity is a factor.

 

[scottosan]

The main question I would be concerned with is if the cone is returning to the neutral position or not while the woofer is installed in the cabinet. I wouldn't worry much about how it acts while laying back on the magnet, where gravity is a factor.

Holding it vertically, it still appears sunk in the center. The cone seems firm without alot of play. These have been sitting for many years. I will eventually recone, but would like to enjoy them and make sure that I like them before dropping anymore money on them.

 

[scottosan]

I also imagining that alot of functional vintage speakers may be suffering from this, but not noticed until the speaker is removed from the cab. I don't want to over worry about this if its a known phenomenon.

 

[Copa1934]

I also imagining that alot of functional vintage speakers may be suffering from this, but not noticed until the speaker is removed from the cab. I don't want to over worry about this if its a known phenomenon.

I think one would have to be fairly naive to assume that a "weak" spider is not an issue or minor issue. The whole point of the spider returning the cone to neutral is based on the mass of the cone, cap and VC. With Air (acoustic) Suspension this is not as critical due to the air trapped in the cabinet serving as the "return spring" so to speak. With Bass (ported) Reflex design speakers the spider plays role of centering AND the return spring. With the spider in a "weak" state you can have over excursion, and likely a change in acoustical behavior, i.e. poor performance.

Over time a person will not even notice this. Exception might be a long period of time between "familiar" recordings, in which one notices that at "same" volumes the speakers clearly sound different.

If you think it's no big deal, wait till that VC comes out of the gap and smashes against the pole piece. I'm not playing "chicken little" here. There are other factors at play, so many (most) people may never have this happen, but when it's visible it's time to take things seriously.

When the cone is on it's back, cone facing up, sag is NOT supposed to occur right away. In fact I've had many speakers sit for days with NO sag to speak of. But the ones with bad spiders sag as soon as they are turned over.

Some drivers, like the 122a, have a metal ring where the cone attaches to the VC. This adds mass and may cause the spider to sag quicker, but not right away. One of my 122a drivers sags pretty bad, the other not. They each read (T/S) differently when tested with DATS.

And my error as I misread your first post, so yes it is common or NOT uncommon. Sorry about that.

Should you panic? No. But you should consider replacing the spider (and surround), which I've done without having to replace everything else.

 

[scottosan]

I think one would have to be fairly naive to assume that a "weak" spider is not an issue or minor issue. The whole point of the spider returning the cone to neutral is based on the mass of the cone, cap and VC. With Air (acoustic) Suspension this is not as critical due to the air trapped in the cabinet serving as the "return spring" so to speak. With Bass (ported) Reflex design speakers the spider plays role of centering AND the return spring. With the spider in a "weak" state you can have over excursion, and likely a change in acoustical behavior, i.e. poor performance.

Over time a person will not even notice this. Exception might be a long period of time between "familiar" recordings, in which one notices that at "same" volumes the speakers clearly sound different.

If you think it's no big deal, wait till that VC comes out of the gap and smashes against the pole piece. I'm not playing "chicken little" here. There are other factors at play, so many (most) people may never have this happen, but when it's visible it's time to take things seriously.

When the cone is on it's back, cone facing up, sag is NOT supposed to occur right away. In fact I've had many speakers sit for days with NO sag to speak of. But the ones with bad spiders sag as soon as they are turned over.

Some drivers, like the 122a, have a metal ring where the cone attaches to the VC. This adds mass and may cause the spider to sag quicker, but not right away. One of my 122a drivers sags pretty bad, the other not. They each read (T/S) differently when tested with DATS.

And my error as I misread your first post, so yes it is common or NOT uncommon. Sorry about that.

Should you panic? No. But you should consider replacing the spider (and surround), which I've done without having to replace everything else.

I just had the surrounds professionally replaced and that when they brought it up during the inspections. There does not seem to be any play, meaning that regardless how I hold the speaker, the spider stays put, meaning not effected by gravity. Its just recessed in the center regardless of how I hold it. Also, I have passive radiators instead of being ported.


Bottom line, what would you do? I listen at lower levels and doubt I would ever approach pushing these even close to max excursion. Ideally, I would like to enjoy them for a few months then once I know they are keeper, invest in a recone.

 

[Copa1934]

I just had the surrounds professionally replaced and that when they brought it up during the inspections. There does not seem to be any play, meaning that regardless how I hold the speaker, the spider stays put, meaning not effected by gravity. Its just recessed in the center regardless of how I hold it. Also, I have passive radiators instead of being ported.


Bottom line, what would you do? I listen at lower levels and doubt I would ever approach pushing these even close to max excursion. Ideally, I would like to enjoy them for a few months then once I know they are keeper, invest in a recone.

Speakers with passives have more in common with ported speakers, though personally I would argue that I like passives better than ported. I like air suspension best.

Are you saying the spiders are more "cupped". Sagging is quite obvious as it "sinks" in the middle (where the VC is). Cupped would be midway between the frame attach and the VC attach points. Mine were clearly sagging.

 

[scottosan]

Dumb question here. When the woofer energizes, does it move toward or away from the magnet before returning to neutral?

 

[Copa1934]

Dumb question here. When the woofer energizes, does it move toward or away from the magnet before returning to neutral?

Actually in and out. Speakers are not actually DC but AC. The DC (red+, Neg-) are for phase so that both speaker "drivers" are moving in the same direction, otherwise there would be a form of cancellation (audible difference in sound).

I can't honestly say that the drivers are "always" moving in the same direction since that is a function of the signal and stereo separation, etc. For mono playback I would assume they always move in the same direction at the same time, i.e. in synch.

 

[scottosan]

Here is 1

 

[Copa1934]

Here is 1

That is definitely "sag". Period. Mine are worse.

I don't know that I'd be terribly concerned, but at some point it would be good to replace. The surround "aids" in the centering of the cone, but as the surround loses it's "firmness" the cone will want to tilt, so to speak. And with many JBL (higher end) drivers, their gaps are really tight and you don't want the VC at an angle in the gap. Or rocking, for that matter.

Yes it's true that a magnetic field will "want" to center itself, but this is NOT 100%, otherwise why bother with a surround and spider? Oh, and yes I realize you don't want to "launch" a cone (for those inclined to remind me of this fact).

 

[Superampman]

I would take this query to the Lansing Heritage forum. Lots of extremely knowledgeable people there. In any case, a new after market spider can't help but be an improvement over a basically non-functional one. But before I went forward with replacement I would just dope them and stiffen them up first with a very thin dilution. That way you can continue with multiple coats till you achieve a tensile action and experiment a little. Keeping the vc centered in the magnetic field is obviously the goal. Best way imo is face down on a table so you can support the spider on either side of the cone with a couple of 6" rulers, wax paper, and tape while it dries.

 

[jdurbin1]

I keep my spare 128H stored face down to let gravity help that sag, but I do rotate the boxes every 6 months or so to prevent it going the other direction.

John

 

[scottosan]

Just an update. The L150 sound fantastic sag and all. These are in a league al their own compares to the 4311a and 4312a. I will be getting them reconed in the not so distant future.

 

[BMWCCA]

I just had the surrounds professionally replaced and that when they brought it up during the inspections. There does not seem to be any play, meaning that regardless how I hold the speaker, the spider stays put, meaning not effected by gravity. Its just recessed in the center regardless of how I hold it.

Do you know for sure they used correct surrounds? Happen to have any photos of the spiders before the re-surround work?

 

[scottosan]

They had no surrounds prior to this. They had been sitting in a spare bedroom for 15 years and there was literally no foam left, so the spider had nothing to counter the tension.