Wow, nothing, thanks guys......

Without a flexible surround, the cone would be unable to move and unable to produce vibrations in the air (no sound).

The midrange cones movements are much smaller (and much faster, hence the smaller size) than the woofers. You can't always see them moving, but touch them (carefully) and you can feel it.

With punctured surrounds drivers won't say a lot, as they will be sonically shortcircuited.
Any positive air pressure in front of the cones will equal out with the vaccum behind the cone through the punctures and vice versa.

At some point, the remains of the surround will start flapping around, vibrate and cause noise,
and when very little is left of the surround, the cone will no longer be supported. It will sag down and the voicecoil former will start rubbing on the magnet pole piece.
I can tell you, this you will be able to hear, and the chances of a repair will fade away fast. 

The surrounds also have a huge influence on the sound.
If you replace foam with rubber the drivers T/S parameters will move far away from what they were originally (the result is often a harsh and "struggled" sound).
Foam was chosen for a reason.

Don't consider rubber a once-and-for-all choice. It isn't. Just like foam it won't last forever. I have replaced many.
Consider foam and rubber surrounds two different things - like screws and nails. One is not necessarily better than the other and they can't always perform the same task equally good.

Martin 

Thanks Martin for the most helpful reply! As usual, you are a great souce of knowledge here

Interesting the rubber insight - I have yet to replace any butyl rubber surrounds, ie: several sets of KEFs, some Polks in the past, and even this set of Pentas, the woofer rubber is soft and pliable. 

I would have thought the T/S parameters to be the same or awfully close if this specialty vendor, Audio Friends, reproduced them just for this application?  I thought I'd asked him before and he said they were proper.....

You definitely have me leaning toward the foams and replacing them for the reasons you've noted.  

Thanks again and let me know about this final question about the specs, thanks! 

I actually read out the T/S parameters and compared.
I don't remember the exact readings but I remember that I was quite surprised. I also remember the sonical difference.
Not sure if the rubber rings in question was from Audiofriends as I wasn't the one who fitted them - I only replaced them with foam.

Martin

Thanks Martin - foam it is! Gonna make my order and have another lockdown project! 

LOL - now that I am ready to order the foams, I see on Ebay that AudioFriends has a message they are away until 12/31/20! I realize COVID is impacting business, but how can this be? I have reached out to Fred, no reply yet. Anyone have any info on them? thanks 

Audiofriends have closed their Ebay shop. Just like many others.
Ebay has become a both expensive and troubled place for sellers.
Look up the website instead.

Martin

Thanks again Martin, very helpful, I will go to his site and place an order directly

Fred hasn't actually closed his Ebay site, it's still active with listings and has conflicting info about his shipping. He should shut it down and remove his ads.

I emailed him there on Ebay and directly from his website about ordering, no reply to either one.  

But thanks again! 

Interesting discussion.

I have been considering re-foaming my Beolab Pentas. Currently only one of the mid-ranges has a slight slit, but I am sure they all would fall apart if touched.

AudioFriends have a YouTube