Cone sag

[jim henderson]

I just bought a 2226 off of eBay and noticed that the cone/spider has sagged as if the driver has been stored face up for a long time. The offset looks like quite a bit but measures only 0.170”. Is this going to be a problem? If I mounted the driver facing down would it eventually correct itself?

[boputnam]

Can you post pics that show what you see?

Any evidence of these having been previously worked on?

I don't believe you can "restore" a sagged spider. Recone...

[Thom]

I've seen this before and often wondered about it. Doesn't this have to come from the suspension shrinking up or a long time DC bias which I'm inclined to think would probably fry the coil. This was intended more as a question than the answer.

[boputnam]

Well the 2226 has a pleated surround and is "relatively" new - that's why I was hoping for some pics.

I don't own any, but the 2226H have a natural position where the surround descends slightly from the basket edge. I don't know if the spider is "flat" in rest position...

[boputnam]

This recent eBay is clearly a recone with non-OEM kit - note the:
- oversized dust cover
- four instead of three pleats
- lack of exposed leads (TOP pic)

... all as compared to the stock design (BOTTOM pic)...

[spwal]

Hi,

is this something to be concered about with the Model 19 speakers?

How would i know if the cones are sagging? I think these might have been sitting for a long time.

thanks

sean

[John]

Hi,

is this something to be concered about with the Model 19 speakers?

How would i know if the cones are sagging? I think these might have been sitting for a long time.

thanks

sean

I do not think you have any thing to worry about. My 19,s are 28 years old and there is no cone sag.

[subwoof]

One of the major contributors to this kind of offset is the actual waveform being presented to the speaker AND the box tunng relationship. A good tutorial on this is in the crown MA5002 operartion manual. Crown incorporated a switch on this high power amp to specificly correct this common cause of premature cone failure at *high* excursions.

When the "average" center position of the cone is negative, the cone will eventually develop a "sinking" cone. The same applies for the positive.

I have seen many of these over the years and the most common problem is when the speaker is used BELOW the actual tuning design of the cabinet ( or is in a homemade cab with incorrect tuning ) which causes the cone to "unload"

The only cure for this is a recone. A new cone will give you 2007 glues and materials that are superior to the ( possibly ) 1987 one you bought. A dead give away is the color of the lead wires. previous to 1992 they were copper and they had some issues.
sub

[Thom]

I'm not taking issue with that, just questioning it. Using speakers not properly loaded can certainly wear them out but, I believe, that this should be neutral position wise. The signal you normally feed them should push the cone away from and pull the cone towards the magnet equally to the best of my knowledge, barring DC offset. And, you don't get away with much DC offset without frying voice coils. Many a nam vet who brought home a Sansui 2000 can attest to that. I'm running on general knowledge and mechanical principle here not really specific expertise so if I'm full of shit straighten me out.

[jim henderson]

Here's a pic.

[boputnam]

By itself, that doesn't look "wrong". Since your post I checked all the pics I have of pleated surround woofs, and most/all look like that. My 2242's are buried deepest in the trailer so can't check them. But, here's a picture of the edge from the brochure - clearly looks like yours.

Why do you suspect there is a problem?

[speakerdave]

The signal you normally feed them should push the cone away from and pull the cone towards the magnet equally to the best of my knowledge, barring DC offset.

Not true. Music is not made of sine waves, sharp transients least of all. Initial half cycles of sounds are generally positive and generally stronger, the extent of that depending on what is making it.

If subwoof is correct, the sucked in cones result from long hard use with the total system reproductive chain 180 degrees out of absolute phase.

Speculating here: the back slant of surrounds, which I have also observed, may be created by design to absorb those positive transients without mechanical damage, and the voice coil is centered with that backslant.

David

[subwoof]

Look at the spider from the side when the speaker is sitting on a table face up..

The tops ALL should be even and parallel with the table. A *tiny* sag is sometimes seen with the foam surround models ( esp the 18" 2245 ) but the rolled cloth types should not.

The voice coil is MUCH deeper than the coil gap so the only real disadvantage of an offset is the limited Xmax and of course, the possibility the speaker will bottom out when driven hard.

sub

[BenB]

"If subwoof is correct, the sucked in cones result from long hard use with the total system reproductive chain 180 degrees out of absolute phase."

So, play them hard, in phase to correct the offset? And make sure the music you play has lots of transients with correct, natural, absolute phase.

[speakerdave]

I thought that question was already answered in post #8, but I suppose you could try it and let us know.

David

[boputnam]

...the voice coil is centered with that (surround) backslant.That is my grab, but we would benefit from some pics of the spider, as per my first post...


Look at the spider from the side when the speaker is sitting on a table face up..

The tops ALL (spider pleats) should be even and parallel with the table. Yup.

Jim - any way you can get some shots of the surround, with the basket laying on the motor, cone up? Try some different rear lighting angles...

[edgewound]

I agree with Subwoof on this one.

The spider is the key to the fatigue issue, and where the voice coil lies in in its static position.

There is no way to correct a sagging spider by playing it hard it the opposite polarity....the spider is a resin impregnated fabric...once it's stretched, it's stretched....and the the only way to correct it is to recone it.

[4313B]

Spider fatigue is such an issue that JBL has taken steps to reduce it significantly in their latest designs.

[Thom]

Not true. Music is not made of sine waves, sharp transients least of all. Initial half cycles of sounds are generally positive and generally stronger, the extent of that depending on what is making it.

If subwoof is correct, the sucked in cones result from long hard use with the total system reproductive chain 180 degrees out of absolute phase.

Speculating here: the back slant of surrounds, which I have also observed, may be created by design to absorb those positive transients without mechanical damage, and the voice coil is centered with that backslant.

David

I'm not calling you wrong here but I do question it, For sure music isn't sine waves but I believe (could be wrong) that over a period of time you should have as many attacks one direction as the other. Phasing speakers is only relative. JBL's marking of pos and neg was not backwards until the whole industry except them accepted a standard that was reversed. It is not important to hook the black wire to the neg term and the red wire to the pos term it is only important that all use the same standard not because you may damage the drivers but because you will have cancellation. Otherwise it would probably be recommended that you rotate at certain intervals and someone as sophisticated as JBL would not have gotten it wrong. They didn't get it wrong. The standard, which I never new existed( all these years years and I always tested) didn't exist when they made red pos bk neg cone pulls in.

[speakerdave]

Absolute phase is a widely debated issue. There is no industry standard regarding it. Recordings are not consistently done either way, and some are said to change in the middle. Many manufacturers do not indicate whether their amps are inverting or non-inverting. In fact Conrad-Johnson even has in the past produced one preamp that is non-inverting on line inputs and inverting on phono inputs.

JBL's choice of terminal color for forward cone motion has nothing to do with absolute phase. I don't know why they did it.


. . . . I believe (could be wrong) that over a period of time you should have as many attacks one direction as the other. . . .

What difference does it make what you believe? Do you have any factual information to support this?


. . . . Phasing speakers is only relative. . . .

Not true. There is relative phase or polarity of channels and passbands. There is absolute phase as regards a recording's original sound source and the reconversion to sound.

David

[Thom]

The I believe was the caveat because I will not state something as an absolute if there is some chance I could be wrong. Obviously the "I believe" makes it a weaker statement. You seam pretty convinced that you are right on this and I'm not prepared to state absolutely with no uncertainty you are wrong. You could be right. I fail to understand the attitude that seems to be there behind "who cares what you believe" hopefully I just read that into it. If you feel I attacked it was not meant that way.

[speakerdave]

The I believe was the caveat because I will not state something as an absolute if there is some chance I could be wrong. Obviously the "I believe" makes it a weaker statement. You seam pretty convinced that you are right on this and I'm not prepared to state absolutely with no uncertainty you are wrong. You could be right. I fail to understand the attitude that seems to be there behind "who cares what you believe" hopefully I just read that into it. If you feel I attacked it was not meant that way.

I actually haven't taken a position about absolute phase in this or any other thread. Looking into it is new for me. I've just been posting to try and clarify confusions in terminology.

David

[subwoof]

Just where did the 180 degrees come from??
And who assumes that all music is comprised of sinewaves??
And that they are symetrical??

Audio waveforms are very complex summations of odd and even harmonics of various waveforms and and when they are divided up into bands ( as in a PA system ), and are sent to high power amplifiers and then to speakers in specific ( NON CHANGING DESIGN ) cabinets, the possibility of an offset force on the cone is higher and *will* result in spider ( and surround ) fatigue over time.

Unequal air mass loading on the front of a speaker VS the rear will put an unequal dynamic force on the cones and this is a consequence of cabinet type and tuning. Ever look at a fender twin guitar cabinet?? A rear loaded folder horn?? A JBL 4560 type bass reflex / front load combination??

This is basic physics and is unchanged by salesman's hype or manufacturers "breakthrough" claims.

And remember the speaker cone asembly is like a car tire. It WILL and DOES wear out over time by various means and has to be changed often over a cars lifetime for proper performance. Vintage means nothing on a old mustang when driving on a rainy twisting road at night.

Large PA companies usd to recone speakers every 6 months, needed or not.

And like a speaker, putting a NEW cone in it wil give improved performance over the original.

sub

[speakerdave]

"left field??"
Yes, actually. I shouldn't have taken the thread off topic.

[HipoFutura]

Can storing speakers cone up/down for extended periods cause sag? I have a pair of 3345H drivers zip tied cones together in storage waiting for me to build the enclosures. Is this a safe practice? How long can they safely stay this way? I've seen forumlas used to determine if a woofer can be used in a down-firing enclosure and not sag.

This reminds me of the pro/con arguement about storing car engine cylinder heads. They should be stored standing on end, not flat. Over time they can sag; despite the fact that they are made from slabs of iron. Don

[4313B]

Can storing speakers cone up/down for extended periods cause sag?Absolutely.

[moldyoldy]

I've seen several instances where everything returned to normal after a few hours of use in the intended orientation, particularly in drivers with heavy cones and high-compliance suspensions.

[HipoFutura]

Once the anxiety attack passed, I re-packed the drivers vertical. Don't know when I'll find the time to build the enclosures - hopefully by summer 07. Don

[Thom]

There's been no disagreement here as to whether speaker suspensions wear out or not. What was being discussed was whether being hooked one polarity or another could cause the suspension to sag one direction or the other. I know on another sight it is stated that Mac chose not to use a down firing woofer as gravity over time would effect it. I should think woofers might last longer these days when most of them are not subjected to warped vinyl, with loudness contour with bass boost.

[moldyoldy]

......What was being discussed was whether being hooked one polarity or another could cause the suspension to sag one direction or the other. I know on another sight it is stated that Mac chose not to use a down firing woofer as gravity over time would effect it.......

That's what the thread evolved to, the initial question from the author was much simpler.

As far as gravity and downfiring goes;

Below is a formula that takes into consideration the effects gravity will have on the "sag" of the cone structure of any woofer. You will need the Fs, Vas, Sd (surface area of the cone), and the Xmax to determine the relative long term usefulness of a particular driver in up or downfiring apps.

You can calculate the sag of a driver from;

Percentage of Sag = 24,849 / ( Xmax * Fs²) , where;

24,849 is a constant value based on the relationship of acceleration due to gravity and Pi.

The following is the same formula, including the relationship of acceleration and Pi;

Percentage of Sag = 981,000 / (Xmax * (2 * Pi * Fs)²), where;

981,000 is acceleration due to gravity (mm/S²) * 100 (for the percentage).

As a general rule of thumb, any time the sag exceeds 5% of the driver's Xmax, it's not recommended for a down-firing application.

Applicability of this info regarding the author's situation is minimal, and only provided to show that out-of-position storage will affect different drivers to different degrees, as opposed to many of the broad generalities previously posted.

[4313B]

And irrespective of those formulas, JBL does not advocate using the SUB1500 or W1500H in a downward firing position. ;)

[Thom]

If you decide to put brake fluid on the surround of a 135A (I don't wish to get into whether this a good practice or not, chances are that everbody agrees) you do not want to store it magnet down for at least a day or so. This is not theoretical.

[edgewound]

If you decide to put brake fluid on the surround of a 135A (I don't wish to get into whether this a good practice or not, chances are that everbody agrees) you do not want to store it magnet down for at least a day or so. This is not theoretical.

Thom...

Would you agree that bears defecate in the woods?

And that the Pope is, in fact, Catholic?

Or...are the above two statements open to interpretation?

I too, have painfully read many of your posts, and you seem to question everything here that has been answered with empirical, proveable, documented, repeated, archived answers...that are most likely 100% correct....and you still want clarification....and proof.

And then....you have the need to psychoanalyze the motives behind the poster of the answer.

Do you have an issue with good, accurate information?

There is collectively...I'd guesstimate... a few centuries worth of audio related experience held within these forums, with the majority of it devoted to the history, preservation and upkeep of products born from the mind and hands of James B. Lansing...and those that came after him.

So....just enjoy it and learn.
I know I have.

[Thom]

I feel it's my quest for good accurate information that some seam to have a problem with. I don't believe the bear is catholic but I have no idea if the pope has ever shit in the woods or not. Hey I noticed the 135A has a heavy cone and the night you doctor it if you leave it face down on the floor the cone can only move so far. If on the other hand you park it face up, there is nothing to stop it and it will sag a lot. Now wasn't that a lot of time to waste on a practice that really isn't all that desirable anyway. But, you can see that my earlier statement was correct although I suppose you could build a support for it. At least mine got very loose fore a couple of days and then became usable again. That's why it surprised me so much that when it comes to govt. you believe in shortcuts. You suggest That I not question and then you suggest that I learn. I suggest that these are mutually exclusive. I'm not going to waste any more time on brake fluid but I guarantee if you do it to that speaker and put it away for a week when you come back the suspension will have taken a set you will not like. If you don't believe me look it up in the factory book under brake fluid.

[edgewound]

I feel it's my quest for good accurate information that some seam to have a problem with..... You suggest That I not question and then you suggest that I learn. I suggest that these are mutually exclusive.

I suggest you try the search function....it works good.