[lostagain]

What is the general consensus on repairing these? foam or rubber.

[Glitch]

I don’t think that there is a consensus. The purists will say foam, since it has the best chance at delivering the same as stock performance. The rest will say rubber, presumably because they think it will last longer(?).

I’m firmly in the foam camp. My assumption is that modern foam formulations won’t have the degradation issues that the original ones did. Regardless of longevity, I’d rather listen to (possibly) higher performance than always be wondering what I gave up with the heavier rubber surrounds. YMMV.

Glitch

 

[Dillen]

Compare the T/S parameters of a driver restored with foam to one restored with rubber (both played in to losen up the stiff new surrounds), and you will no longer
have any doubts.

I did exactly that.
I was expecting a difference but… oh dear, was I surprised.

Foam!

Martin

[lostagain]

Thank You gents, foam it is then, any particular supplier although i did see one on the bay (not the Chinese one) or the Dutch one AF, will replace the sealing rings as well then perhaps the caps in the crossovers.

[Evan]

Dillen wrote:

Compare the T/S parameters of a driver restored with foam to one restored with rubber (both played in to losen up the stiff new surrounds), and you will no longer have any doubts. I did exactly that. I was expecting a difference but… oh dear, was I surprised. Foam! Martin

Cool idea, Martin. Are there measurements you can share?

Would be interesting to throw them on klippel to do a deep dive and show the measurements here.

Evan

[Dillen]

Sorry, I didn’t keep the numbers.
It was several years ago, but it should be easy to replicate for someone with time and means.

Martin

[Glitch]

Dillen wrote:

Compare the T/S parameters of a driver restored with foam to one restored with rubber (both played in to losen up the stiff new surrounds)

How close was the driver with the new foam to the original? All of the Penta midrange surrounds that I’ve dealt with were already too far gone to make meaningful measurements.

For anyone doing a surround replacement: Running T/S parameters, even if it is a crude DIY version, is helpful to verify your work. In this scenario, you are looking for any outliers (which can be caused by a variety of reasons). It is also helpful for sorting drivers if you are trying to make your speakers as balanced (left to right) as possible.

Glitch

 

[Dillen]

I looked through my notes, and I don’t have the measurements anylonger, but I
do remember my surprise experiencing the huge difference from foam to rubber, and
I also remember that the driver that was restored with foam was closer to the
(same) driver with original, old but intact surround than ones that were restored with rubber.

Another thing is, that the glue often supplied with new rubber surrounds usually won’t hold for very long.
It just doesn’t grip very well and, even after several weeks/months, you can often peel
the surrounds off again completely intact with no remains of glue sticking to them.
Most rubber surrounds are rubbish when it comes to finding a suitable glue (read: that is commercially available and not toxic).

Martin

[Evan]

I have a set of pentas to refoam yet, but likely wont be until mid-24 until I get around to it.

I will definitely be using foam surrounds on them and will toss one on the Klippel machine here to measure purely out of curiosity. If anyone has a rubber-surrounded mid they’ve made, I would be happy to measure it then return it.

[Author]

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