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Wharfedale Sand Filled Baffle SFB/3

I can't be sure but I think mine were done with conventional front roll surrounds ,they had done SFB3s at Wembley before when I asked.It was a few years ago ,the only issue I found was that two of the bolts on one of the drivers weren't quite long enough.
 
smithy said:
I can't be sure but I think mine were done with conventional front roll surrounds ,they had done SFB3s at Wembley before when I asked.It was a few years ago ,the only issue I found was that two of the bolts on one of the drivers weren't quite long enough.
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These speakers, or at least the woofer and mid, probably get all their cone control from the spider, and the surround is just there to hold it together.
 
smithy said:
I can't be sure but I think mine were done with conventional front roll surrounds ,they had done SFB3s at Wembley before when I asked.It was a few years ago ,the only issue I found was that two of the bolts on one of the drivers weren't quite long enough.
Click to expand...

That is interesting as it implies Wembley had to increase the baffle/basket spacing to get clearance for the roll surround as one would assume the bolts were long enough previously. I have a feeling there is more clearance behind the cone than in front, so the current plan it to go with the roll facing backwards.

Yank said:
These speakers, or at least the woofer and mid, probably get all their cone control from the spider, and the surround is just there to hold it together.
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There looks to be a little cone-sag on the 12” unit, which is to be expected I guess given it is 60 years old and has probably sat with a rotted surround for decades, so I’m hoping it is possible to re-centre it as part of the refoam process.
 
You're no doubt already aware but I believe the bass unit was designed to have an ultra floppy surround etc for very low free air resonance...
 
Yes, I’m aware of that, but sadly even finding the exact specification of the original has eluded me let alone the prospect of sourcing an identical replacement. As such the only option on the table is just to refoam as best as posible with what is available. I don’t think modern foam surrounds have much compliance so they should hopefully work ok if not exactly as it should be. I’m hoping it is possible to get the system resonance within a reasonable range of where it should be. The other variable is I have no clue if the spider has hardened at all, and I suspect that defines much of the driver behaviour.
 
Following the measure twice cut once rule the 12 and 10 driver dimensions I need are C, B and A where A is to the outside edge of the green felt and B is to the inside edge of the frame.

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10”:
A: 242mm
B: 225mm
C: 188-190mm (quite contaminated with rotted foam so hard to really nail it).

12”:
A: 300mm
B: 278mm
C: 246mm

PS When interpreting the earlier pictures the basket cut-out is the width of the green felt and no more, there is no ledge beyond that.
 
cooky1257 said:
Thanks Tony, that should really help nail down suitable candidates.
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Thanks Frank, I’ll also give you a ‘D’ measurement for the 12” as if you have a look back over the last page you’ll note there is a very defined edge contour to the cone, it bends through a right angle, i.e. a long flat overlap is not possible. My best guess is 237mm, say a 4mm surround attachment area on the rear. There is no such issue with the 10”.
 
Tony L said:
Thanks Frank, I’ll also give you a ‘D’ measurement for the 12” as if you have a look back over the last page you’ll note there is a very defined edge contour to the cone, it bends through a right angle, i.e. a long flat overlap is not possible. My best guess is 237mm, say a 4mm surround attachment area on the rear. There is no such issue with the 10”.
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OK I get the idea. We deffo need a flat attach for that one.
 
The original foam looks very much as if it was foam rubber rather than the closed cell foam surrounds are available in now. Would be extremely compliant in comparison to modern surrounds. But even less durable, probably, unless it was treated in some way, or an exotic formula.

Edit - ahh, just read this:
As Raymond Cooke of KEF remembered: “I read how much Gilbert Briggs had lowered the free air cone resonance of woofers by replacing their paper ‘accordion’ type surrounds by cloth “. Briggs called the cloth – a mixture of foam and felt – Plastic Foam Suspension.
 
It is very hard to establish what it was 60 years ago, but now it looks like a rotted open-cell foam more similar to a very thin layer of the stuff used for JR149, Isobarik etc grilles than anything else I can bring to mind. It has also perished in a similar way. I can’t see how it could ever have been air-tight and I imagine it was pretty flimsy. It looks fairly thick though, at least a mm.

I realise it is impossible to do this ‘right’ as even if I was prepared to pay to have surrounds manufactured (which I’m not as I just have a single speaker) there is no formal spec I can find to work from. I’m hoping the addition of a roll-surround in some ways makes up for a less compliant material. It also needs to be factored that I’m no volume freak so to be honest one could probably ‘hard-edge’ them for all the excursion they’ll be getting. I’ve never seen the cones of my 15” Tannoys move at all at the levels I play and the 10” and 12” working together in phase are likely a similar surface area.
 
Clive Sinclair sold some open baffle speakers that looked like a 1970s version of this idea, with similar dimensions, they were just a chipboard panel, covered in foam, with a wooden surround. I think they just had an elliptical driver, and maybe no tweeter. I heard a pair once - once was enough.
 
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Here’s another shot of the 12” unit, it is about thr best I can get with my iPhone in the dull grey light of today (it is snowing here). The foam certainly looks to be open-cell and is quite thick, I reckon 2mm or so, but whether that is part of the decaying process I have no idea. The picture also shows the sharply defined cone edge profile that might be of some use to Frank.
 
Quite surprisingly, an SFB/3 has just come up for sale here in Minneapolis. It has the "Windsor Deluxe" cabinet, and the seller is asking $350 USD.

8q6BT1x.jpg
 
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