Penta II Midrange Refoams - worth the effort?

Hi all, looking for your advice, I have read some threads on how to do the job, not a problem, I've refoamed many woofers, admittedly, nothing this small. The question here is whether it's worth the time and effort....

Picked up a great original owner pair months ago, polished them up and they have been in daily use ever since, really like the sound quality. 

The original foams on all 8 mids are going, not gone, but they have deteriorated and need replacing at least cosmetically.  

I have run these at good volume levels and I never see the cones moving in and out, like a woofer, so I question the need to replace foams that may appear more cosmetic in nature than functional - please fill me in here, I'm sure I'm wrong, but I typically see the piston movement when you have a foam or butyl suspension around a cone driver like this. 

If I need to replace them, AudioFriends is where I'll go - they have either foam or butyl rubber versions available.  Butyl makes sense to never have to do them again, but not original (odd they chose butyl for the woofers).  Does anyone have experience with replacing both kinds?  Process should be the same, maybe some issues with dry time, otherwise, I believe I'll do the rubber once and for all. 

Thanks in advance for your opinions and advice - being locked down, makes a nice little project if it's really necessary, thanks! 

 

PS - haven't mastered posting pics here - click on the image to see them both. Temporary location for now....

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 video about replacing the foam surrounds, using a Penta midrange as an example. In the video, the new surround is simply put in place, without much visible centering (at least visible on the video). At 8:33 subtitle reads "Perfect centered by under laying spider". Is it really that easy? I have refoamed a pair of CX50s and the centering was the most annoying part of the whole ordeal!

lausvi:

 "Perfect centered by under laying spider". Is it really that easy?

I'd say no.
Of course, you can get lucky... or you could get unlucky.
I have seen several cases of both...

The spider only holds the cone (and with that the outer end of the voice coil) at one point.
The surround holds the other end - the end farthest from the voice coil.
The inner end of the voice coil is not supported.
The spider is rarely touched when doing a refoam job, leaving the placement of the surround responsible for a perfect axial movement of the voice coil in relation to the magnet pole piece.

Sellers of new surrounds often seem to play the replacement job down, refraining from showing the shim'ing process and/or telling/showing what to do when things don't work out right - thereby encouraging more DIY-buyers to try their luck.

Martin

Good HiFi in the Netherlands has a set of 8 foam surrounds for Beolab Penta. They cost 23€. I have bought several foam surrounds for CX50/CX100 at Good HiFi and been satisfied with the quality.

/riis

Ok, I went on and bought a replacement kit from GoodHifi. The surrounds seem to fit fine and while tedious, it wasn't too bad to do them (I have now done one of the two speakers, ie. 4 midranges, took me about two evenings to finish).

I found that the Penta midranges (mine were ITT branded, Made in Western Germany :)) actually didn't need much centering at all, they were pretty easy on that part. The new rings are perhaps a 0,5-1mm smaller, so there is room for adjusting. I glued to new foam first to the cone, and after it had dried, to the outside rim of the speaker. Simply pressing in the cone and listening for any scraping I figured they were centered good enough and used cloth-pegs to hold them in place while the glue hardened.

The old ones were looking pretty bad, all had cracks and they were all around sticky and spotty. Still holding in though, and still sounding very reasonable.

Here one can also see how the elements are in different levels, the tweeter is deep inside the mounting and the two outer mid-ranges re slightly higher than the inner ones that are flush with the mounting bracket.

 

And here is the after-shot:

I might have used a bit too much glue, but I'd say they look Ok, will do a final clean before re-install.

Now that I have done one speaker, it'll be interesting to listen if there is a notable difference.

Hi!

Thanks for the thread! I have recently refoamed my Penta mkIIs but for some reason one midrange produces an audible buzz. Its most easily heard while playing piano music. Do you think the buzz could be a result of a badly aligned foam surround? Should I re-do the foam fix or try to find a replacement driver?

 

Dillen:

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.

Has anyone confirmed the performance of the Audiofriends rubber surrounds? Like the OP I am hoping the rubber surrounds will last longer than the foam surrounds without a huge negative impact to the sound quality. I don’t want to have to change them again in 20 years, during my retirement.

One other thought I had was how the sound will shift over the years as the foam degrades. That must surely impact the sound quality as well, right? Or will there just be minimal change followed by a sharp drop off at the end of their operational life?

I have purchased both rubber and foam surrounds from them, and have just been waiting to complete the project. So anyone with personal experience to share? If not, I might just stick with foam as Dillen wisely suggests.