refoaming question

[JKent]

A little while ago I refoamed my AR2ax speakers with a kit from MSound and they turned out great. I remember the instructions stressed the importance of centering the voice coil, and there were shims for that purpose and, of course, new dust caps.

Now I'm refoaming one Allison: Four woofer. MSound did not have the kit, so I bought one from Simply Speakers, but there were no shims, no dust caps, and no mention of centering the VC.

Any ideas/comments/suggestions?

thanks

Kent

[Guest Robert M]

No problem at all. I am not familiar with that exact speaker, but after you glue the inner edge and it dries, you can move the cone in and out and kind of center it by feel. Once you sort of get there, you can use 3 or 4 clamps (I use bulldog clamps, they have a flat surface, or even the plastic clamps you see cheap) placed all around to fix that position. Once fixed, push up and down to ensure no rubbing. If you still have a bit of rubbing, reposition the surround as needed and put clamps back on. Once you feel good about its location, then just go around gluing and lifting and placing clamps back down as you go around. I have never shimmed, don't intend to.

[Carlspeak]

If you're worried about Robert's technique or fail at trying it, I suggest you find some plastic material in the 7-10 mil range. 10 is probably the most common. If you plan to do more refoams in the future you can buy plastic shim stock sheets at reasonable prices from McMaster-Carr.

Dust caps are available from Parts Express.

Don't do business with whomever sent you that incomplete kit.

Remember, it's all about the music

Carl

Carl's Custom Loudspeakers

[JKent]

thanks Robert and Carl. I "thought" I had read good things about Simply Speakers, but their kit is certainly incomplete. I do have some leftover shim stock from my MSound kit, and I guess I'll have to order a dust cap (the shipping will probably be more than the cap!)

[frankmarsi]

12-11-06

My Two Cents Here, some 'purists' feel that it's not necessary to use shims if one is alert and mechanically minded to a degree. There are plus and minus aspects to either method. I prefer to use the 'non-shim' method because in terms of the AR 12 inch woofer I truly believe it's dust cover is an important part of its look and perhaps even its sound in my mind. Feel what you will,think what you think, but this is my method.

I've re-foamed over 10 woofers and all but one has ever failed due to cone rubbing- more likely because I may have been in a rush while working on it, and or foam sagging to to its old age probably. If I'm not mistaken, a couple of accomplished and well seasoned individuals who have had actual AR Corp. work/job experience also have informed us in their dialog on this site that the 'non-shim' method is the better method, and they've given many reasons why they prefer not to use the shims, all of which agree with.

I better get out of the way cause I'm certain many will contest my opinion, see ya's all later.

FM

[Carlspeak]

I started refoaming woofers professionally some years ago and got into trouble early on. During my OJT phase, I also did the push&feel technique. It worked about 50% of the time. But, it soon became evident I needed to shim the VC air gap. Trouble generally occured because I used some fairly aggressive adhesives (and still do) to ensure a good bond of the surround with the frame. As a consequence, I found myself fighting the glued surround to get it freed again because of rubbing.

Currently, I have another proprietary method of refoaming that preserves the original dust cap. It works about 75% of the time. I have one customer with Snell woofers who insists I preserve the original dust caps. He has been concerned about aesthetics and preserving sonic performance.

For those who, on their own, do very few refoams, I always recommend shimming. It's 100% effective. Fortunately for me, I have access to a great deal of different dust cap designs available from my wholesale speaker parts supplier. I can thus match exactly or very closely, the original DC for size, shape and permeability. The argument of preserving the original dust cap isn't valid because the surround is being replaced anyway. It serves a vastly more vital role in the woofer's final performance that the dustcap. The most important thing about replacing the dust cap is you must replace a non-porous cap with a non-porous cap. Conversely, replace a screen cap with a screen cap.

Now, just imagine a cross-section of a woofer. Normally, the cone is kept centered by both the spider and the surround. Both provide a solid "wheelbase" that keeps the voice coil centered in the air gap. Without the surround, it's only the spider that's left to do the centering. Unfortunately, the spider is located at the base of the cone. Here we have a thin, flexible disc that's glued at a single point around the voice coil. Some voice coils are quite small in diameter compared to the cone OD. This further exacerbates the potential for tilting the vc at an angle. Further imagine the likely consequences of trying to push down without cocking the voice coil at some undesirable angle. Sometimes the job feels good with the push technique. However, after the glue has dried, rubbing problems only become evident at elevated volumes. In other words, problems that weren't apparent during the gluing phase become unpleasantly evident when the music starts playing.

Remember, it's all about the music

Carl

Carl's Custom Loudspeakers

[JKent]

Thanks Frank and Carl. The first and only woofers I refoamed used kits from MSound and I followed their very complete instructions, shown here:

http://www.citlink.net/~msound/refoam/

There are 12 pages I think, and the necessity of shimming is urged. Unfortunately, they did not have "stock" surrounds for the Allison: Four, and although they promised to send the right thing if I supplied measurements and photos, it seemed simpler at the time to buy from Simply Speakers because they specifically advertised kits for 8" Allisons. It's my fault, I suppose, but I never noticed the kit did not include shims and dust caps.

Live and learn :-(

[JKent]

PS: Here's the terse reply I got from Simply Speakers when I asked for a dust cap and shims:

Hello,

We are sorry you feel that way. Happy refoaming!

Regards,

Sean Ryan, Tom Ryan, and the crew at Simply Speakers

I already left positive feedback on ebay. Oh well.

[Carlspeak]

>PS: Here's the terse reply I got from Simply Speakers when I

>asked for a dust cap and shims:

>

>Hello,

>We are sorry you feel that way. Happy refoaming!

>Regards,

>Sean Ryan, Tom Ryan, and the crew at Simply Speakers

>

>I already left positive feedback on ebay. Oh well.

>

Thanks for the heads up kent.

Looks like you got 'Simply' screwed

Remember, it's all about the music

Carl

Carl's Custom Loudspeakers

[dynaco_dan]

Hi Kent;

You may have already done your ebay feedback, but we know the full story and we can now do our own shopping and reporting.

Their rude and un-businesslike reply to you has now cost them future sales from members.

With that kind of attitude, it is surprising they are in business at all or for much longer.

Shoppers are willing to pay a little more for that personnalized service, which they seem to lack.

Thank you for telling us all of your SIMPLY SPEAKERS experience here.

[pmsummer]

Sorry to hear about your rude response from Simply Speakers. Shame.

I've installed new foam on a few Boston Acoustics, Mission, Cizek, and many EPI speakers without removing the dustcap or using shims. I glue the surround to the cone first. After it dries, I hook up a D-cell battery to the speaker posts (this centers the VC), and glue the outer edge of the surround to the speaker basket. I use about 32 wooden clothes-pins to clamp the surround to the baskets.

No problems yet, but YMMV.

Keep watch for the season.

[JKent]

Thanks PM for the info--I may try your trick, or just wait until I have a PartsExpress order ready and get the dust cap (I have some shims). And thanks Vern & Carl for the sympathy!

Kent

[dynaco_dan]

>Thanks PM for the info--I may try your trick, or just wait

>until I have a PartsExpress order ready and get the dust cap

>(I have some shims). And thanks Vern & Carl for the

>sympathy!

>Kent

Hi Kent;

My first experience was about 10+ years ago with a kit by mailorder.

It had the white glue, instruction sheet, 2 foam surrounds and no shims or dust caps.

I was needing to re-do 2 - AR-3A woofers, which need an unusual size surround.

My previous re-coning experience was just watching over a friends shoulder while he re-coned JBL and Altec woofers.

Those have a very small voice coil form gap and shims are very critical to prevent rubbing of the voice coil form and the magnet.

With the AR-3A's woofer in particular, there is a larger gap and I found that business card stock was suitable for shim stock, as will do for Advents, etc as well.

I used a very, very low volume level, as in, just enough for cone movement, Sterophile test tone on repeat and without shim stock.

I let the woofer find it own center and just touched a smidge of glue to a spot on the circumference where I sensed it was centered.

By moving the entire cone ever so slightly off center there would be a buzz as the voice coil form would start rubbing the magnet.

This was not very scientific, but there has been no problems since.

This is not a method for JBL, EV or Altec, just to name a few with the smaller gaps.

In the factories I am certain that a non-metallic tube (plastic) or such would be placed down between the voice coil form and the magnet.

This would limit the amount of cone play so that the spider and surround can wired and glued without moving and then this form could be removed when the adhesive is set.

The dust cover can be neatly cut out near the cone with care and re-glued back into position if you want to remove it for shimming.

Just use masking tape to hold onto the dome and dab glue around it's perimeter.

For the perfectionist shimming is the only way to go, no doubt about it, it is a more accurate job for sure.

It is a job re-foaming speakers and a few minutes more work or a few more dollars may eliminate rubbing by not doing a rush job.

Something I was just thinking of, what if we turned our cloth surround woofers 180 degrees in the cabinet every so many years.

[KlausDK]

Hi

I have succesfully refoamed about 12 AR woofers (2x8", 2x10" and 8x12"), and I have never used shims. Like Frank I want to preserve my original dustcaps. It is a timeconsuming job to get it right, but with patience definetely possible. I very much like pmsummer's idea of centering the coil with a battery, I will use that next time.

BR Klaus

[Guest Americain]

Just for posterity, when I refoam I cut up a business card and use it for my shims. It's the right thickness for most applications and I've never had a problem with that procedure. I agree with one poster here who said that he always shims. I'd do it every time too.

[Carlspeak]

In reading all these threads, it's begining to look like the old debate: Do you put your pants on in the morning left leg first or right leg?

For the occasional refoamer who choses to shim, the business card idea seems a good one. I have one additional thought on the subject.

In some cases, shimming has a clear benefit. Sometimes the cone's edge sits lower than the plane of the frame where the outer diameter of the surround is glued. In that case, it's pretty tough to get the inner diameter of the surround glued to the cone's edge first. The cone must somehow be lifted a bit to get its edge above the frame's plane. Without shimming this can be a challenge. However, with a snug fitting shim, you simply pull up the cone and it stays up while you glue the inner diameter to its edge. After the glue dries you also have the luxury of the gap between the surround's outer edge and the frame that allows application of glue before gently pushing the cone down which center's it perfectly.

Remember, it's all about the music

Carl

Carl's Custom Loudspeakers

[dynaco_dan]

Hi there;

One little service trick I remember seeing at a service shop.

This is more than we would do with re-foaming only.

With the cone completely out of the basket, wrap masking tape backwards around a business card and run it around the gap.

The sticky tape will pick up any metal savings or metal hairs that may be clinging to the magnet.

To shim or not to shim, that is the question.