I was not sure if this should be a separete thread or if it should be in one of the other threads about modifing Pentas. Moderators will hopfully help me place it in the right place

My Pentas were a bit of a dissapointment in the beginnig, they sounded better after a while of (a)buse but not at all as they should. Thanks to the experience from all helpfull people here on Beoworld I modified the OP-amps and replaced the capacitors in the filters, and there was significant improvement to the details in the sound. The commonly used expression with "lifting a carpet from the speakers" was certanly a suitable description here.

I was not happy with the midrange though, it has a some what nasal sound to it that is very obvious when comparing with other high quality speakers. The modifications/restoration made it better but not good enough. Several people here and on other places seem to share my opinion here. The midranges in my Pentas are from Nokia and probably not as bad as the speakers in their telephones but they are for sure not good.

An "easy" way of dealing with this is of course to order new ones from B&O, if they are still available. But I have always been interested in changing things in to something else than what was originally intended. Most of the time it is just stupid, but it is always more interesting and sometimes really awarding. I will describe here what I did and how.

To be continued...

First of all my mid ranges were on the verge of foam rot, and I only discovered that after putting my butter fingers on them. The foam fell apart when I touched them. So the need for replacement in some way was absolutely necesarry.

My choice for the new elements were Peerless 830986, not so expensive but almost the same physical size and when you need 8 of them the price is some what interesting...

They were not a straight fit, the corners on the square shaped frame had to be grinded down a bit to fit the holes in the Penta baffel.

The Nokia originals:

The New Peerless elements:

A comparasion between old and new:

As seen on the last picture the old mid range fell apart totaly. You can also see the grinded corners on the frame. The grinding I did in my kitchen with a quite powerfull machine wich made the work easy and fast but it also made my kitchen look like sh-t. Picture of the sink after only two elements done, walls, floor and ceiling looked the same:

Of course all work was done while drinking beer, -work in progress:

I started with changing the elements in one speaker just to feel the difference. i discovered directly that it was not at all so good. The problem was that the midrange level now was a bit to low, hard to say so much about the quality of the sound.

To make sure it was not due to the fact that the elements were new, i left the speakes on for a few days to give them about 100 hours of music to get setteld. That made a difference but still not okay. The elements are in series 2 by 2 so I re arranged the wiring to the elements so they were connected in parallel in stead. Now the balance between the ellements felt better. I am aware of the filters being designed for the specific impedance of the original ellements and that altering the impedance also alters the frequency that the filters work with. The filters are also a bit different between the two pairs of ellements. But this modification made it more correct in my oppinion.

How sound is experienced is very difficult to put in to words, and as always it is a matter of taste, and placebo effects is very hard to avoid. It is not easy to admit that an investment/modification has made the opposite of what was expected. But I am a quite experienced listner and I am very hardened when it comes to experiments and testing and all the things that might affect the results since I am working with testing and evaluation proffesionally. Disappoining results is not something strange for me :-)

Both speakers are now converted but the second one still need some time to be run in before I give my final verdict on this. I am not at all afraid to admit that it was a failure if it turns out to be that way. So give me a couple of days to evalute this properly.

Interesting indeed.
The change from four 4ohm drivers to four 8ohm drivers will certainly change something soundwise, no
matter what way they are coupled it will be very different from the original setup.
Furthermore, the use of "full range" drivers rather than dedicated midranges will also do something.
Hard to believe it will provide a better sound reproduction altogether but when it comes to
speakers one can often be surprised. Do let us know the results.

Martin

Hi Turbo,

It's indeed very difficult to find matching drivers for B&O speakers. Especially if the original ones are no longer available (I don't know if the midranges drivers are still available by B&O but I think they prob are.)

I suggest , in order to get as good a sound as possible, to consider refoaming the original ones. I have refoamed many,many speakers now and the results are very satisfactory. If you can do it yourself (not that difficult, but a bit of a learning curve needed) it's a cheap solution that often gives very very good results and probably closest to original specs. The foam rings are available and cheap and the biggest factor is your time of cleanup and reglueing. 

Anyways, I look forward reading your update in a couple of days.

Dillen:

The change from four 4ohm drivers to four 8ohm drivers will certainly change something soundwise, no
matter what way they are coupled it will be very different from the original setup.
Furthermore, the use of "full range" drivers rather than dedicated midranges will also do something.
Hard to believe it will provide a better sound reproduction altogether but when it comes to
speakers one can often be surprised. Do let us know the results.

Martin

Martin, I agree with you totally here, if we are just looking att the electrical perspective of this conversion, the difference in impedance will not only affect the frequency of the filters and the obvious difference in load on the amplifier. The lower impedance will make a higher power output from the amplifier, as long as it is capable of the lower load. That is not a problem here really because of the total load of the amplifier will not be that big. And the power on these frequencies is not that big.

But the load on the amplifier also makes a difference in it self, by that I mean that the amplifier sounds different depending on the load it is being presented to in means of impedance, resistance and capacitance. By that I mean that even if the elements vere identical in every perspective expect one single paramater of the mentioned it would still sound different because of the amplifier would behave differantly.

As seen in the data sheet on these elements they are called "full range" but that is not really true, I have been reading a lot about these elements and they do not preform well on the lower and higher frequencies that they are supposed to work with. There is one special thing that is apparently not so good about them, around 10 000Hz they obviously sound really bad. That is not a problem in this application since the filters starts to cut them of at 7000Hz.

The positive thing here is that the element is not forced to work in its lowest or highest frequency range and that makes it a pretty "easy" work to deliver music without unusual distortion.

double post

cooldude:

Hi Turbo,

It's indeed very difficult to find matching drivers for B&O speakers. Especially if the original ones are no longer available (I don't know if the midranges drivers are still available by B&O but I think they prob are.)

I suggest , in order to get as good a sound as possible, to consider refoaming the original ones. I have refoamed many,many speakers now and the results are very satisfactory. If you can do it yourself (not that difficult, but a bit of a learning curve needed) it's a cheap solution that often gives very very good results and probably closest to original specs. The foam rings are available and cheap and the biggest factor is your time of cleanup and reglueing. 

Anyways, I look forward reading your update in a couple of days.

I never really tried to find original replacements. Refoaming is one way to go, and I am for sure capable of doing it myself, but from the prices I have found on Ebay etc, it would be quite expensive.

I am not going that way because I am sure that the mid ranges on the Penats never were especially great from the beginning! No use on fixing something that could be replaced for something better. The original specs is not what I want, there are improvements to be done to this old construction. And to be honest even B&O cut corners in quality in components. Nothing proves that better than all the modification tips you can find here. Besides the agening of components that happends to all old electronics.

I could be wrong on choosing theese elements, but then i will let you now so no one else do the same misstake.

Hi Jens

I think a few of us will be very interested in your results, and as you say, you can never tell with speakers, all strange things are possible

Yes, I too am following this thread with interest.
I have a pair of Beovox Pentas with midranges that are in the early stages of foamrot.

Andy T.

Jandyt:

Yes, I too am following this thread with interest.
I have a pair of Beovox Pentas with midranges that are in the early stages of foamrot.

Of course you already know this Andy, but it gives me the chance to grumble anyway - don't ever touch the foam stuff!  It is the nastiest, stickiest, most adhesive gunk known to man - like an excretion of the devil's bottom! (I went through a whole can of WD40 cleaning up behind that stuff when I refoamed a pair of CXs, and also belts on a 7700 cassette deck that had gone the same way...)

Now that's over with, I can ask if anyone else has noticed that speaker foams/belts in stuff that was in a smokey atmosphere seem to turn into that sticky tar-like mess far faster than stuff that has never been subjected to smoke?  Must be some science behind this....

The causes of foamrot!
This has been discussed so many times, and always with no satisfactory answer.
Sunlight?  I don't think so, as I have repaired Beo4s with rotten foam behind the display. Sunlight has never been there.
Tobacco? Don't think so, but may excaserbate (sp) the problem. I have seen remotes riddled with filthy brown nicotine, but still with good foam.
Humidity? Possibly.
Lack of humidity? Possibly.
Chemical reaction with air? Then why can one speaker be fine, and another goosed?
My new theory is -----

-----lack of movement!

I have a pair of Beolab Pentas that have been in use for 16 hours a day, since they were new in 1993. Perhaps switched off for around three weeks each year. That is a lot of hours (do the sum)!
One stands in a corner where the sun never reaches, the other has direct sunlight on it.
Neither is subjected to nicotine, as I smokes figs outside, or in the garage.
I have central heating.

All 8 midranges are like new. Not even tacky to the touch!

Andy T.

Gooey molten belt residue can be shifted fairly easily using IPA.
I agree, it can make the worst mess and is very hard to get off fingers and clothes.

Martin

Dillen:

Gooey molten belt residue can be shifted fairly easily using IPA.
I agree, it can make the worst mess and is very hard to get off fingers and clothes.

Martin

Let me see if this sounds familiar to you Martin, though your workspace is most certainly more organised than mine...

Take apart tape deck. Stick fingers into previously un-noticed belt residue.  Say naughty word. Walk to get stuff to clean hands, treading into the bit of sticky belt that dropped to the floor unseen.  Don't notice you are now leaving sticky black marks on the wooden floor until it is too late.  Say more naughty words. etc etc.

Some old belts go powdery, some stay pretty much the same.  B&O ones (so far) turn into something like Marmite....

Jandyt:

The causes of foamrot!
<snip>
My new theory is -----

-----lack of movement!

Well, constant movement would prevent stuff settling on the speaker, as the air would constantly be blowing it away. Plus the constant air movement would lead to pollutants being more diluted.

It is definitely true for drivebelts. Left static they stick to the drivetrain (small metal pulleys like motor pulleys first..) So I always advised customers to use cassette decks/turntables occasionally. 

Someone I know had their Pioneer TT spinning constantly for well over a year.  Not what I had in mind, but the drivebelt is fine....

rayfenwick:

Take apart tape deck. Stick fingers into previously un-noticed belt residue.  Say naughty word. Walk to get stuff to clean hands, treading into the bit of sticky belt that dropped to the floor unseen.  Don't notice you are now leaving sticky black marks on the wooden floor until it is too late.  Say more naughty words. etc etc.

Some old belts go powdery, some stay pretty much the same.  B&O ones (so far) turn into something like Marmite....

 

Ah! - but it wouldn't be as much fun or nearly as satisfying if it was easy Ray

I like the Marmite analogy though - you either love it or hate it!

Chris.

You mean anything worth appreciating is worth suffering for - that kinda thing?  No pain, no gain?

I actually like Marmite, but this stuff is nowhere near as tasty.... (as I found out when I ate a biscuit whilst having some un-noticed goo on my fingers.... )

Did I mention I *really* hate that stuff?  

Ray, I 've been there, except I picked my nose rather than eat a bisquit. 

Martin

Dillen:

Ray, I 've been there, except I picked my nose rather than eat a bisquit. 

Martin

Thanks for that Martin - it is the only way my electronics capabilities  will ever be compared to yours 

I think I forgot to mention one thing about the installation of the new elements. The original way they are mounted can not be used with these elements. I used a simple solution, thick glue. Simular to silicone but made for making engine gaskets, it is black so it is not visible and the only problem could be if I want to change the elements again. This stuff is extremely strong and I guess that serious violence is needed if I want to replace the elemntes.

One thing that would be really interesting would be to compare this modification to new/old (but in nice condition) B&O-elements and refoamed elements. I am thinking of refoaming my old ones just for this. But it will always be so many issues to if I got it right and quality of the new foam etc, that this would not prove anything.

New elements would be more interesting, but it would be quite expensive to do this. If I knew anyone with Pentas it would be easier, but most of my friends think that I am an idiot putting money and time in to this. No one I know is interested in this and they think that their systems sounds perfect, systems they have bought from the supermarket or inherited from some relative...

Very interesting discusion, by the way.  Many issuses could be covered here, and I hope this could be to interest or use to the Penta owners. 

So far, with no deeper analysis, it seems to be a very good modification. I have mostly been using the speakers for radio background listening and some playing while drunk Sounds as always very good for this, they are really impressive when played loud with a good quality CD.

I will do some more serious listening this week.

After listening to the speakers for a while now, I have this conclussion: -I do not really know what I have acomplished

To be honest, the difference is not that big when listening to music with good sound quality. I have experienced greater improvements with the capacitor replacement, and changing the OP-amps in the amplifiers. However there seems to be a bigger difference when listening of lower quality of music, that is MP3 and such. The anoying mid range has become "softer" I find myself listening to the same tracks without being anoyed with the sharp penetrating guitars and other sounds in that frequency range.

I am quite sure that this is not due to the level of the elements being lower. When listening to very familiar tracks like Brothers in arms and some Ulf Lundell tracks it really sonds good and the voices and guitars sounds very good as they did before. So far the improvements are, as I said in the listening to MP3 oflower quality, and I really try to avoid these.

I will get back with some more findings!