The AR 12-inch Woofer "Collapsed-Spider" Syndrome

[tysontom]

The Collapsed Spider

We have discussed this in years past, but good advice is that when storing old Alnico #3700 12-inch or 200003-0 Ferrite 12-inch woofers, do no place it magnet-down (or magnet-up) for prolonged periods of time.  This is true also of the AR speaker cabinets themselves using this woofer; i.e., when storing (or mounting) the speaker, do not place or store the speaker cabinet face-up or face-down for long periods of time.  This can result in a condition known as "collapsed spider."  This sounds quite ominous, but the spider fabric is literally stretched somewhat, and the cone doesn't want to center properly, and the woofer will therefore not operate correctly.  This condition applies to other AR woofers, too, but to a lesser degree.

The suspension system used on these early AR woofers is extremely compliant—more so than about any other similar woofer.  Originally, AR designed the "classic" acoustic-suspension woofer to have approximately 85% acoustic restoring force and 15% mechanical restoring force, just enough to center the voice coil in the gap.  The result is the very low harmonic distortion exhibited by these woofers when mounted in the AR-3, AR-3a, AR-11, etc. cabinet.  For many years the AR woofer had the lowest distortion of any loudspeaker, and today there are precious-few speakers of comparable size and performance than can equal, let alone surpass this performance.  By contrast, most competitive and most contemporary drivers with similar parameters have significantly less compliance, probably on the order of 60/40 or even 50/50 acoustical/mechanical, but with other comparable parameters.  These stiffer suspensions work fine and are more robust, but these designs actually have higher distortion, all things remaining equal.

Insofar as the voice coil/cone assembly is relatively heavy, more than 80-100 gms or so, the compliant spider and surround (skiver) cannot hold the weight of the moving assembly and will tend to settle. 

Therefore, if you are preparing to re-foam some AR 12-inch woofers or just storing spares, do not store them magnet-down.

—Tom Tyson

[nefertem]

Tom that was very informative do you of any modern 12 in woofers that are close to specification for AR3 owners that might have no other options in restoration 

[Giorgio AR]

Hi Tom, the 12 "woofer spider argument is useful in keeping our beloved woofers in shape.
I am writing to ask you what you think about my idea, following a test of mine to reposition the spider in the right resting position (it was sunk about 5/6 mm downwards) I turned the voofer upside down by placing it on my pellet stove for about 20 ', slowly the cone went down to the stove floor; then I removed the speakers from the stove and tried positioning the correct spider alignment vertically, it was perfectly horizontal, then I repositioned the woofer again with the cone facing down and thickened the circumference until the spider was horizontal again, leaving it to cool the speakers for about 30 ', I checked: shape of the spider, rest of the cone in the 2 positions: in my opinion he found his original position and elasticity.
The stove when I did the experiment was at full speed, with a metal temperature of about 50 ° c, you can probably try (having an appropriate oven) with higher temperatures, I think up to 80 ° and you can probably add some thinner to soften and uniform the treatment of the spider.
If you have never tried and from what I know, you have many woofers, I hope you try this system to test what I detected.
Sorry Tom for my English, I use google translate, I hope I have written in a understandable way.

[Giorgio AR]

Hi Tom, another input:

I have to give you an input on the weight and mass of the 12 "ceramic woofers.
Pete b. And Luigifedele, weighed, measured the cone, coil etc. of the 12 "woofers. All is well, but the weight (and is missing in all the subsequent refoaming to the original) of the bead of thick glue around the inner ring of the foam, at the time, when I removed this material, the weight was a few grams, therefore in percentage on the high cone! Besides the fact that mechanically this "reinforcement" on the foam changes its response to oscillations.
All refoamed woofers, I think they need to be weighted on the periphery of the cone?
What do you think Tom, I am attaching a photo where you can see very well this ring on the foam of a 12 "woofer, ring that I found on all the original untouched AR 4", 8 ", 10" and 12 "?

 

[lakecat]

I have to ask as I am storing an alnico woofer, is how can it be stored? Just rotate the woofer occasionally?

[AR55]

Something else to keep in mind when storing drivers is moisture.  Excess moisture can be a big contributor to the deterioration of spiders, cones, surrounds, etc.  I live in North Florida where during much of the year the outside humidity is over 80%.  Even though I store my spare drivers in a conditioned room and have the HVAC system set to keep the inside humidity below 60%, I still place a small silica gel pack in the box.  

[tysontom]

11 hours ago, lakecat said:

I have to ask as I am storing an alnico woofer, is how can it be stored? Just rotate the woofer occasionally?

What I've  done is to rotate (flip) the woofer from time-to-time, magnet-up or magnet-down, but this is probably not 100% satisfactory.  When you store the speaker, "magnet-up," with cone facing downward, always use shims or blocks to raise the basket up off the table to prevent the surround from touching the table.

Probably the best way to stabilize the cone is to get small foam or Styrofoam pieces to place under the cone between the  cone and each arm of the speaker frame, to hold the cone in the center position.  Note that the 200003 stamped-steel woofer cone naturally sits very slightly below the center position anyway, so just stabilizing the cone so that it does not sag is good.  It may be necessary to slit the nylon screen that is glued to most of the early woofers (to prevent fiberglass from entering the area under the cone) enough to place the foam under the cone.  A small slit about 2-inches or so will probably work.  Also, in lieu of foam or Styrofoam pieces, paper towels, cut into small sections and folded over several times to make a section about an inch thick, can be placed under the cone as well.

I watched a YouTube video recently where someone raised a sagging cone/spider to a level position with shims, then lightly sprayed the spider with water and quickly dried the spider with a heat gun or hair drier to quickly bring it back.  The material used for most spiders is linen, but it is treated with a preservative, so I'm not sure that the water would completely be absorbed by the spray (this is the old trick to make a sagging AR linen grill "tighten" up a bit; i.e., lightly spray water and then use a hair drier to make it bounce back).  Getting the moisture down in the voice-coil area is also not a great idea, but it might be worth a try in extreme cases. 

[tysontom]

AR also warned against storing speakers face-down:

 

[lakecat]

Thanks Tom....I do flip it occasionally but supporting it is a good idea and will do it.

[Pete B]

Thanks for the info Tom, do you know any more details about how spiders are made?

[tysontom]

22 hours ago, Pete B said:

Thanks for the info Tom, do you know any more details about how spiders are made?

Pete, I don't know the details of how spiders are made other than they are formed under heat and pressure in a mold.  I believe the majority of spiders are made from linen or similar materials, then coated for longevity and stability. 

I saw a YouTube video recently where some guy had a collapsed spider on a large subwoofer driver, and he sprayed water on the material while keeping the cone "centered" with spacers.  He used a shrinkable-tubing heat gun to quickly evaporate the water and to hopefully cause the spider to shrink and return to its original shape.  It looked to me like it partially worked, but there were definite sags in the spider that never went completely away; and if the surround material was treated, I don't know how the water could penetrate past the coating to get to the fibers.  AR once had a recommendation that to get the sags out of a linen grill cloth, the best way to do that was to use a fine mist spray of distilled water on the fabric and then hold a light bulb (back in the incandescent days) close to the fabric to allow it to shrink and thus draw up the slack and sagging.  Of course, that did work quite well, but the surround is a different deal altogether.  Once badly stretched, it's likely that there would be no fix other than to replace the spider.

--Tom

[tysontom]

Just now, tysontom said:

Pete, I don't know the details of how spiders are made other than they are formed under heat and pressure in a mold.  I believe the majority of spiders are made from linen or similar materials, then coated for longevity and stability. 

I saw a YouTube video recently where some guy had a collapsed spider on a large subwoofer driver, and he sprayed water on the material while keeping the cone "centered" with spacers.  He used a shrinkable-tubing heat gun to quickly evaporate the water and to hopefully cause the spider to shrink and return to its original shape.  It looked to me like it partially worked, but there were definite sags in the spider that never went completely away; and if the surround material was treated, I don't know how the water could penetrate past the coating to get to the fibers.  AR once had a recommendation that to get the sags out of a linen grill cloth, the best way to do that was to use a fine mist spray of distilled water on the fabric and then hold a light bulb (back in the incandescent days) close to the fabric to allow it to shrink and thus draw up the slack and sagging.  Of course, that did work quite well, but the surround is a different deal altogether.  Once badly stretched, it's likely that there would be no fix other than to replace the spider.

--Tom

I didn't mean to repeat the details of my first message!

[fedeleluigi]

On 4/26/2019 at 7:47 AM, Pete B said:

Thanks for the info Tom, do you know any more details about how spiders are made?

Hi Pete,

There is a lot of information on AR Drawings about the spider of the 200003 ferrite woofer . Examining  these documents carefully it comes to light that the first drawing of the AR 200003 spider dates back to 22 Jul 1969. So, most likely around this date the production of first 200003 ferrite woofer started. 

Revision B  dates  1 Jul 1974 and apparently there was no change in spider manufacturing from 22 Jul 1969 to 1 Jul 1974 because Revision B only reports “drawing no. change" but a previous revision (O) dated 12 Sep 1972 reports "Revised Notes, DWG No. was X-3705" and something could have been changed on that occasion.

Revision C (ISS. C) dates  5 Jul 1978 and apparently there is no variation about dimensions, material, treatment, supplier in comparison with Rev. B.  As regards supplier, it was LCC (Loudspeaker Components Corporation, Lancaster Wisconsin). I think that the same company is still operating nowdays and  they could still have the original molds/dies for the 200003 spider www.loudspeakercomponents.com .

Differently from the previous drawing, on this last revision it is also reported something about the spider compliance (maybe there was some compliance variation in comparison with the previous spiders) but it's difficult to understand the standard used (where and how must the 50 grams be exactly employed? How/where do you have to measure the deflection?).

You can find images of higher resolution on AR Drawings. The drawings are the 422th and the 423th but unfortunately there is no numeration. The last drawing is the 492th.

 

 

[fedeleluigi]

Differently from what is reported on some other pages of this forum (for example), the 200003 woofer spider has 7 corrugations (7 crests and 7 troughs ), not 6.

Actually the 7th crest and the 7th trough seem to be a little smaller than the other ones and become almost "invisible" after the gluing between spider and cone. In other words the 7th spider groove hosts the paper cone as shown in the drawing I've made.

 

[Pete B]

Great info, thanks very much!  How about that they are still in business.

[tysontom]

7 hours ago, fedeleluigi said:

Hi Pete,

There is a lot of information on AR Drawings about the spider of the 200003 ferrite woofer . Examining  these documents carefully it comes to light that the first drawing of the AR 200003 spider dates back to 22 Jul 1969. So, most likely around this date the production of first 200003 ferrite woofer started. 

Revision B  dates  1 Jul 1974 and apparently there was no change in spider manufacturing from 22 Jul 1969 to 1 Jul 1974 because Revision B only reports “drawing no. change" but a previous revision (O) dated 12 Sep 1972 reports "Revised Notes, DWG No. was X-3705" and something could have been changed on that occasion.

Revision C (ISS. C) dates  5 Jul 1978 and apparently there is no variation about dimensions, material, treatment, supplier (LCC, Loudspeaker Components Corporation, Lancaster Wisconsin. I think that the same company is still operating nowdays and  they could still have the original molds for the 200003 spider www.loudspeakercomponents.com ) in comparison with Rev. B.  Differently from the previous drawing, on this last revision it is also reported something about the spider compliance (maybe there was some compliance variation in comparison with the previous spiders) but it's difficult to understand the standard used (where and how must the 50 grams be exactly employed? where do you have to measure the deflection?).

You can find images of higher resolution on AR Drawings. The drawings are the 422th and the 423th but unfortunately there is no numeration. The last drawing is the 492th.

 

Great message!  Thanks for this further clarification.

One note: after the initial 200003 woofer, AR did change the compliance slightly to prevent the often-occurring back-plate voice-coil incursions.  This early 1969-1970 ferrite woofer (Roy and I can't determine precisely when the new ferrite woofer appeared in the AR-3a) was extremely compliant and prone to striking the bottom plate of the magnetic structure under very hard low-frequency input power.  This took an excursion of a little over an inch, peak-to-peak.  Sometime after AR moved to Norwood (1973), AR did revise this woofer to (1) eliminate the butyl-rubber coating on the surround, (2) change the dust cap and (3) slightly stiffen the spider to control excursion beyond the .5-inch linear travel.  Perhaps this corresponds to the drawing changes.  I did notice that the AR-11 woofer, for example, was slightly stiffer at extremes than the AR-3a ferrite woofer.  This did not materially affect the driver resonance or harmonic distortion, but it limited the excursion a bit more at extremes than the first edition in an effort to prevent flattening the voice coils under duress since the woofer did not have an extended back plate ("bumped").  AR also went to the aluminum bobbin for this woofer in the mid-1970s, and most of the later ones were aluminum rather than the earlier DuPont Nomex-treated-paper formers, even though the latter probably dissipated heat better into the magnet structure.

--Tom Tyson

--Tom

[fedeleluigi]

On 4/27/2019 at 6:58 PM, tysontom said:

This early 1969-1970 ferrite woofer (Roy and I can't determine precisely when the new ferrite woofer appeared in the AR-3a)

Hi Tom,

Unfortunately, nowdays  it’s very hard to accurately reconstruct the history of all that AR did and made. Unfortunately,  many witnesses are no longer available (or the available ones do not remember the events exactly) and many important historical documents are lost.

As regards the introduction of the 12” ferrite woofer,  the dates of some AR drawings  (magnet, cone-skiver and the spider in my previous post)  would suggest that its production probably started in 1969 (please, see the attached pictures with highlighted dates).  Obviously, the dates of these drawings do not prove with absolute certainty that the production of the 12” ferrite woofer definitely started in 1969.

If the L.C.C., Loudspeaker Components Corporation, Lancaster Wisconsin  (mentioned in some  AR drawings) and today’s Loudspeaker Components, L.L.C., Lancaster Wisconsin  are the same company,   there might be a chance that it can still have some important documents (receipts, part orders  etc.) that could be very userful for trying to establish the exact production date for some of the drivers made by AR.

Luigi

 

this drawing is the 4th in "AR Drawings"

 

 

 

this drawing is the 316th in "AR Drawings"

[Giorgio AR]

9 hours ago, fedeleluigi said:

Hi Tom,

Unfortunately, nowdays  it’s very hard to accurately reconstruct the history of all that AR did and made. Unfortunately,  many witnesses are no longer available (or the available ones do not remember the events exactly) and many important historical documents are lost.

As regards the introduction of the 12” ferrite woofer,  the dates of some AR drawings  (magnet, cone-skiver and the spider in my previous post)  would suggest that its production probably started in 1969 (please, see the attached pictures with highlighted dates).  Obviously, the dates of these drawings do not prove with absolute certainty that the production of the 12” ferrite woofer definitely started in 1969.

If the L.C.C., Loudspeaker Components Corporation, Lancaster Wisconsin  (mentioned in some  AR drawings) and today’s Loudspeaker Components, L.L.C., Lancaster Wisconsin  are the same company,   there might be a chance that it can still have some important documents (receipts, part orders  etc.) that could be very userful for trying to establish the exact production date for some of the drivers made by AR.

Luigi

 

this drawing is the 4th in "AR Drawings"

 

 

 

this drawing is the 316th in "AR Drawings"

Tom, with your post you gave a great input ...
Luigi your report seems like a great investigator's job, a lot of observation and detail, historical research, good reasoning and finally re-ordering of all the acquired data!
I think that little by little, with the contribution of many other competent and passionate people, we will be able to recreate the two most delicate parts and those most subject to deterioration: Spiders and coils (the failure of one of these two particular causes the inactivity of our precious objects) .
Being able to recreate these components in accordance with the original will be almost like winning a million dollar lottery for AR fans!

[RoyC]

On 5/22/2019 at 5:20 AM, fedeleluigi said:

As regards the introduction of the 12” ferrite woofer,  the dates of some AR drawings  (magnet, cone-skiver and the spider in my previous post)  would suggest that its production probably started in 1969 (please, see the attached pictures with highlighted dates).  Obviously, the dates of these drawings do not prove with absolute certainty that the production of the 12” ferrite woofer definitely started in 1969.

Luigi

this drawing is the 4th in "AR Drawings"

Hi Luigi,

Thanks for posting the drawings. They are consistent with my experience.

I have never seen an alnico magnet/cloth surround woofer in any AR-3 or 3a with date stamps showing manufacture dates after 1969. On the other hand, I have seen many of the notched ferrite magnet/foam surround woofers shown in the drawing in 3a's with manufacture dates from very early 1970 into 1972 (when the notches were removed). I have only seen a few post-1970 AR-3's, and they were also equipped with the notched magnet woofer...along with the AR-3a style mid. It makes sense to me that the ferrite magnet woofer would have been ready to go by 1970.

This becomes important when replacing woofers in earlier AR-3a's originally equipped with the alnico magnet/cloth surround version. AR changed the woofer inductor coil in the crossover for the ferrite magnet/foam surround woofer from #7 (1.88mh) to #9 (2.85mh). When replacing woofers in earlier AR-3a cabinets it is therefore necessary to increase the woofer crossover inductor's value to 2.85mh when the replacement woofer is the later ferrite magnet version. This will have a much greater impact on achieving the correct sound than the usual, typically discussed repair items such as level control and capacitor types.

Roy

[Markpilk]

I suspect a collapsed spider may be what I’m dealing with on my AR3a’s. Mine are the Alnico cloth woofers and when pushing in on the pair, one is responding as it should. The other center seems to be rubbing and looks to be cocked a bit to the left and maybe hitting voice coil. I’ve not pulled the woofer and after reading through “Repairing AR3a” pdf, there doesn’t seem to be instructions to fix voice coil problems. Is there options to fix, if this is the case?

[Aadams]

I remember this Tysontom thread.  Unless your woofers have been placed face down or face up for a long time you probably don't have a collapsed spider from prolonged sag.  If the woofer voice coil has not been damaged in operation it is more likely that the spider glue bond has broken from the metal frame.  There are a few threads here with discussion and images of the problem on that era woofer but no repair instructions.  Once the woofer is removed, diagnosis is pretty simple but you will only get one easy shot at repairing it correctly.  If  you are not experienced at this I would not practice on this woofer.  It will not be easy to replace.

In order of preference, Contact member @RoyC, Vintage AR on ebay,  or Millersound.  http://www.millersound.net/

[Markpilk]

1 hour ago, Aadams said:

I remember this Tysontom thread.  Unless your woofers have been placed face down or face up for a long time you probably don't have a collapsed spider from prolonged sag.  If the woofer voice coil has not been damaged in operation it is more likely that the spider glue bond has broken from the metal frame.  There are a few threads here with discussion and images of the problem on that era woofer but no repair instructions.  Once the woofer is removed, diagnosis is pretty simple but you will only get one easy shot at repairing it correctly.  If  you are not experienced at this I would not practice on this woofer.  It will not be easy to replace.

In order of preference, Contact member @RoyC, Vintage AR on ebay,  or Millersound.  http://www.millersound.net/

Thanks Aadams. I purchased these about 3 years ago and have just now decided to see what it takes to get them up and working. They have been stored horizontally since I’ve had them, but not sure about previous owner. I’ll check the links you provided. Thanks again!

[giovanni56]

If it is helpful, I have weighed some mobile crews (cone+spider+coil and cone+spider+coil+foam), and the weights averaged 68 g without the foam and 80 g. However, when the whole moving assembly is installed, the foam and spider, in my opinion, add less mass than their weight, because the part of the two that is attached to the basket is not influential on the value of the total weight, to hazard a guess, perhaps the installed cone including the spider the coil and foam, will have a moving mass of about 72/74 grams, however, in T&S measurements, the Mms takes higher values, above 100gr, because of the contribution of the radiation impedance of the air mass that must move the cone and the mechanical impedance of the suspension (spider + foam).

[Pete B]

The air load for a 12" woofer cone is nowhere near 20g, rather it is probably one quarter of that.

What do you use to release the glue holding the spider.

[Pete B]

I've been looking closer at woofers with spider sag and have found something interesting.

If you look at this diagram of the spider, note that the wave is formed and is flat when the spider is made, but

it must stretch when the cone moves forward or back.  If it sits with the cone up or down for a long period of time

the spider becomes permanently stretched so it is longer than as manufactured.  Now the spider holds this length,

and since it is longer the cone now has two rest positions, one above the normal rest and one below, each requiring

the new length of the spider:   I hope this makes sense and I've seen it on quite a few different woofers.  It would be

excellent if we could find a way to shrink the spider back to the correct position.

https://community.classicspeakerpages.net/topic/10608-the-ar-12-inch-woofer-collapsed-spider-syndrome/?do=findComment&comment=124611