Wharfedale SFB/3 Surround Replacement

[progducer]

Im new to the forum, and this is my first post. I have done some searching for previous threads but there still seems to be some vagueness regarding this issue.

Mine have the brown foam which is mostly rotted. In interest of keeping the driver performance close to original spec, should I search out custom foam? Something like this:

Charcoal foam - Open-cell foam for shipping, packaging, padding

Or modern roll-foam surrounds from Parts Express, etc?

I have been instructed to use felt for the SFB3 Tweeter. Again, would foam be a better choice?

Picture gallery: https://goo.gl/photos/pVoFQyPMVpZVQ7tZA

Thanks for the help!

 

[klipschorn]

I believe I replied to one of your posts on another system. Regarding that foam from the Foam factory, if it is soft it may just work. The thickness is right; I have some obtained from Joanne's Fabric Stores but it's 3/16" thick and has a thin cloth backing which is easily peeled off. However, 3/16" a tad too thick and tends to raise the cone about a half a millimeter although that may not be a serious problem with a 12 or 15 incher but with an 8 or 10 incher, it will. Absolutely not good for a super 3.

I've been on the Foam factory site a few years ago but decided to use the felt surround. I was glad to see this post of yours as I'm going to order some of that foam if for no other reason that to run some tests with some 8, 10, 12 and 15 inch red magnet Wharfedales.

I just called the Foam factory and was informed that if I were to hold a 6 inch diameter circle of that foam by the edge, it would droop towards the floor like a sheet of paper; it wouldn't stay parallel to the floor. Seems like the right stuff so I'll place an order.

If you are interested in the results, I'll keep you in the loop here and the results will be posted in my website.

I'm kind of excited about this and sincerely appreciate your making mention of this foam and rekindling an almost extinguished ember.

Robert

 

[klipschorn]

The foam from the Foam Factory of which you made mention is an exact replacement for the foam on older Whatfrdales, with exception of the colour. It is described as 1/8" Charcoal Regular Foam - 54" x Lineal Foot. It is 54" wide and the cost is $0.99 per foot. I just received my 10 feet and was elated to find it to be a better replacement in that it won't rot or deteriorate.

Robert.

 

[system7]

At a certain point, you must become a light unto yourself:

I hope you can help here because I have recently bought two 8" units, Super 8/FS/AL MODEL and North England M8; drivers from the Fifties I believe and both having foam surround and there is not the slightest sign of any polymer applied to the surrounds in order to make the acoustically sealed.
Super 8FSAL (large magnet, foam surround, aluminium coil) was the predecessor of Super 8RSDD. (large magnet, roll surround, double diaphragm).
Even in my time, foam surrounds were falling to bits. I think they went over to a cloth roll surround around this time. There was a recipe to seal this (liquid latex in special solvent I think) and it was always applied on the back so competitors could not tell we were sealing them. Peter Fryer started the laser holography and Doppler Velocimeter work around then so R&D was also trying various sealing and damping stuff for surrounds. But we were never given the secret recipe for Super 8 surrounds ... 8>D

Was the foam surrounds ever coated, e.g. the drivers used in the SFB?
I can't remember if the foam surrounds were sealed, only that they were all falling to bits including those in our museum.
I think GAB mentions sealing surrounds in one of his books. Every now & then, Service Dept would come to R&D with some foam material to try cos a customer needed to recone only 1 of an old foam surround pair but mostly, policy was to persuade the customer to accept "new" cloth roll surrounds.

The Wharfedale Super 8/

I'd think a modern foam roll surround will work better than some old piece of tat rustled up in the 1950's in England, a time of great material shortage and post-war rationing. The function of the surround is just to centre the cone. Cone tweeters usually use a fairly rigid surround, and have little need of excursion, so felt might be OK, but again, foam is used successfully in many later designs like peerless.

 

[klipschorn]

At a certain point, you must become a light unto yourself:


The Wharfedale Super 8/

I'd think a modern foam roll surround will work better than some old piece of tat rustled up in the 1950's in England, a time of great material shortage and post-war rationing. The function of the surround is just to centre the cone. Cone tweeters usually use a fairly rigid surround, and have little need of excursion, so felt might be OK, but again, foam is used successfully in many later designs like peerless.

Steve, I agree with you wholeheartedly. I've seen half roll foam surrounds and those that I have seen are all quite resistant to air leakage due to the ultra fine porosity of the foam not to exclude the possible addition of a latex sealant.

I found a Super 8 FS/AL that has the original tan foam and it's still compressible and returns to its original shape. There is no evidence of a sealant being applied to either side of the foam or impregnated therein. It can be seen here. http://www.ln271828.net/super8-2.html

The foam will give a slightly lower Fs than a cloth surround or a treated half roll. This, of course, assumes identical cone & coil mass.

That W15FS can be seen here. http://www.ln271828.net/W15FSCS.html
How much effect an open cell foam affects vent tuning is unknown to me but the system can be manually tuned. Assuming add drivers being made under high quality control standards, duplication of that tuning can be applied to subsequent cabinets on a production line with negligible differences.

I recall seeing some Electro-Voice speakers with the vent designed in the outer ring of the speaker basket. Simply make the cabinet the recommended size, front load the speaker and away ya go. It may have been more of a marketing gimmick than science. If memory serves me well, it was short lived.

 

[odcics2]

Any update to this thread?

I found a pair of SFB/3 "Deluxe" speakers in Blonde. Tweeter foam and 10" 'foam' need work. The 12" has felt and appears ok. I haven't taken them out of the cabinet yet.

There are a lot of different opinions on the correct replacement for the surrounds.
Were the drivers any different electrically when they used different surround methods?

 

[klipschorn]

Greg,
That foam from the Foam factory should work very well. I bought 3 yards of it myself. (see my messages # 2 & #3. I suggest you remove the dust cap and shim the coil so the spider is flat. This will also stabilize the cone.
For the tweeter, felt will work well, about 1/16" to 3/32 inch in thickness, or thinness. Joann's fabric Stores have it in various colours. Depending on the tweeter, the duct can may be an integral part of the cone but in such an old cabinet, that may not be the case.

If you need any help, suggestions and the like, PM me. I have a website with info on old Whafedales that you may fine interesting or even helpful. I'll take the liberty of providing a link to those pages here.

The Wharfedale Pages

Robert

 

[odcics2]

I read ALL of the Wharfedale section. Very informative!
I feel lucky to have run across these speakers. It took some looking to figure out what they were and how well respected they are! Thanks for the PM and this reply.
Greg

 

[klipschorn]

Hello again, Greg.
If the felt on the 12" is charcoal grey, in all probability is original. Also, if the glue seam affixing the cone to the felt looks neat, that's also a sign of originality as many who replace the surrounds tend to do other than a clean, neat professional job, not that it matters much regarding performance but more to appearance.
If the label on the back of the 12", assuming there is one, is labeled 12CS or W12CS, then again, it's probably original as the CS stands for cloth surround.
A couple of years ago, I actually considered building a pair of SFB's but decided against it as they'd not be original so what's the point?
I have a W12CS and a pair of W15CS's all 3 being original and working; the only issue with one of the 15's was a dust cap coming off.

 

[odcics2]

Here's a few pics of one speakers drivers.
Tweeter dust cap was loose on the top of the cone.
Not much left of the tweeter foam at all!

Woofer and mid were wired in series.

Is that yellow mid foam original?
Other speaker has felt on the woofer,no mid foam at all and
crumbling foam on the tweeter.

 

[klipschorn]

The yellow (tan) foam sure looks original but looking at the glue on the underside of the cone makes me think of Elmer's white glue. Also, if it is original, it's in remarkably good condition considering a comparison to the tweeter foam, not to mention that that speaker is wired in series with the 12" and the excursion due to the bass notes would surely have caused separation and rupture. Look at the tweeter and it's only handling the highs above 3000hz or 5000hz. I might add here that the capacitor for the tweeter is, in all probability still good as it's the oil filled type. However, if you feel better about it, change it as replacement polypropylenes are quite inexpensive.

Regarding the tweeter, the centering device. I hope my web page on that was clear enough. If not, PM me and I'll add to that page. When I wrote that page, I tried to make it easy for a novice to understand but some of that may have slipped through the infamous cracks. Once the centering device is removed, you could desolder the braided wires from the connecting strip. Use a small alligator clip as a heat sink between the terminal and the cone; you don't want to damage the solder joint at the cone. Besides, the coil wire is aluminum and can't be soldered by conventional means. Sma alligator clips, about an inch long are light weight. This will allow complete removal of the cone and application of the annulus will be much easier. When replacing the assembly, shim the coil before replacing the centering device. This will stabilise the cone and make it easier to affix the annulus to the basket.

Once the cone is removed, use a compressed air can to clean the gap; hold the speaker upside down and away from your eyes (use goggles). The foam disk has fragmented and the pieces, small as they are, will be all over the inside of the gap and inner magnet assembly.

If the 10" unit works ok, it might be better to leave well enough alone; it's up to you. If you do replace the foam, remove the dust cap and shim the coil with the spider flat. Oh, does it or the 12" have a corrugated cloth spider or the older phenolic type? If the phenolic type and if the coil isn't rubbing, then the screws holding the spider haven't been tampered with. Shimming should still be done to prevent the coil from touching the pole piece or the inner edge of the top plate which could damage it as the cone will tilt as you apply the foam. Plus, it will stabilize the cone while the foam is applied. Oh, if you have to remove the cone and if it has a phenolic spider, DON'T lose the screw and/or nuts. They look like SAE (Society of Automotive Engineers) but are BSW, (British Standard Whitworth) and are not easily found. In fact, I doubt the Brits are still using BSW. the same applies to the screw in the center of the tweeter pole piece.

The cloth surround on the 12" looks ok and probably is. If you would, take some front view piccies of the speakers also as well as the spiders on the two larger units.

Gee, I know that so much of this detail isn't in my web pages. Gonna have to fix that. Your questions have inspired me. Thank You.

Robert