DIY question: substitute material for standard speaker surround foam?

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byrdmk

Member
I posted this in the speaker forum but I think it fits well here, too. :D

I have a pair of Bang and Olufsen RL 60s. They have this "ABR" (auxillary bass radiator) and the foam that suspends the ABR has rotted away. I know that this has been discussed before, but my question is a little different. Does anyone who has experience re-foaming speakers have any recommendations for a substitute for speaker foam surrounds that I could get as a flat sheet? The prior threads kind of danced around this but I thought maybe someone would have an idea.

The original ABRs were suspended by foam, so I'd like to use a foam of sorts, but I don't have a lot of experience here and am wondering if anyone has any ideas for what I could buy as a flat sheet that would pretty much mimic speaker surround foam. Any guesses?

So far I have found neoprene foam "skin" but I am concerned that it might be a little too rubbery. The neoprene skin is 1/16" thick. Any thoughts?
 
I would not reccomend using a flat sheet. The foams are ribbed to help ensure the proper travel is availgood and have a large effect on the peramiters of the driver/radiator. If you need foams and a looking to do a flat sheet to save money, you can get good foam surrounds off ebay for $10 and a few $ shipping, or less even.

That said, I know a guy who runs a studio and did his old Altecs with that thin, white foam packing material and swears they still sound good.
 
Thanks folks. Again, this in no ordinary project, it's not a typical re-foam job. I kinda wish it was...this ABR is really odd. I definitely need a flat piece of foam. There is no driven speaker cone here, just have to suspend a flat thin rectangular piece of metal on a flat piece of foam. I would love to use authentic speaker foam, polyester urethane or otherwise.

One person has recommended getting some dish packing sleeves from my local uhaul shop. That is usually a thin piece of foam...

I am definitely not doing a flat sheet to save money. It's just the nature of this project.
 
That's a tough one. If it were me, I would try to find a spot to replace it with a long external port. After all, what are the odds of getting the tuning right when rebuilding this passive?
 
Can you not contact B&O and see if they have the correct replacements, or can rebuild the PR?

Seems unless you get the same stuff they had, you're probably not going to get the right stiffness, and could even run the risk of damaging the other drivers since the box wouldn't be tuned right...
 
similost said:
Can you not contact B&O and see if they have the correct replacements, or can rebuild the PR?

Seems unless you get the same stuff they had, you're probably not going to get the right stiffness, and could even run the risk of damaging the other drivers since the box wouldn't be tuned right...
Click to expand...

Was just about to post this!

It seems there was some interest here, and for that I thank you guys! I have a solution that is a little bit different than I expected, straight from an authorized B&O service provider. He knew about the problem immediately and how to fix it.

He said to get a thin piece of fiberboard and cut it to fit the size of the ABR opening. Then, you get 4-5 inches of 2" diameter PVC pipe and a 90degree connector piece of the same size and seal them together. Then you build a port in the board using the PVC pipe. The PVC pipe is glued to the back of the fiberboard cutout and the 90degree piece goes through a hole drilled into the board. He said to seal everything up really well with silicone and then put the fiberboard/port in place of where the foam used to be. Screw it on and seal with silicone. He also recommended adding a little bit of fiberglass insulation behind the board, especially near the port tube. He was clear that this is the way to go and said this really improves bass response.

JUST FYI, in case anyone else needs this info! I did see a similar fix to this elsewhere, but was not sure it would work. I think that this fix is substantially similar to what B&O did when they changed this design for the RL 60.2's.
 
Hi,

FWIW as long as the replacement surround is not too stiff the ABR
will keep its correct tuning, due to box air stiffness tuning the ABR,
not its surround.

rgds, sreten.
 
Last edited:
There is / was a guy in Japan who made custom surrounds where size and shape were unique.
He made a mould from expanded polystyrene foam (packing material hard foam), the covered it with jersey cloth, then painted it with a water-dispersed polyurethane.
I've done the latter, on a surround that was almost ready to collapse, yet still had enough strength to support a thin brushing of Syntegra (made by Dow). I put on several layers.
 
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