[Glitch]

Philip,

IMHO, this is the coolest thing that has been posted here in quite a while! I’m undoubtedly biased since your project aligns with many of my interests and projects.

I have many questions about what you have done so far. I will be watching this thread closely to see the level of information detail that you are willing to share.

Would you elaborate on the connectivity to the non-B&O world? Which specific “use cases” are you currently supporting?

Glitch

p.s.  I fully understand how challenging it can be to find the female/board side connectors. I’ve run into a similar situation where a seemingly common connector is unobtainable new. In my case, I ended up salvaging the necessary connectors from used equipment.

 

[Glitch]

Did the previous owner give you any clues on the service history of the speakers?

Personally, I would just listen to them for a while and see if I liked them. You have plenty of time to make a decision. If you decide that you really like them and they will be a “forever speaker” for you, then invest the time and money in them.

Keep in mind that any time you open up vintage electronics it can be a can of worms. You can also negatively effect the value of an item if you are not careful (i.e. a scratch from the slip of a screwdriver or broken plastic clips). I would pay more for a untouched/unrestored piece of equipment than one with an amateurish repair. YMMV.

Glitch

[Glitch]

Could the previous owner have already replaced the foam? Are there any signs of work being done to the speakers?

Glitch

[Glitch]

Epic B and O wrote:

I will order new drivers off eBay. My only concern is the part numbers don’t exactly match. The one’s on eBay are 8480232, and mine is 8480239

If you can’t find drivers with the exact same part number, try to at least get a replacement with the same impedance. They probably will not sound the exactly that same as stock, but something with the same impedance has a much better chance at sounding OK than something with a different impedance.

Glitch

 

[Glitch]

Epic,

I suggest that you try to remove the old surrounds and glue before ordering replacement surrounds. You may end up fatally damaging the driver cones, depending on the glue used and your skill at removing the olds parts. This also opens up the possibility of ordering surrounds that will conceal any flaws left from the previous work.

I would also be very careful with using any solvents. They can have unintended consequences. When they work, they can work very well. When they don’t, it can be a real mess. Small test areas are the prudent way to proceed.

Glitch

[Glitch]

Can anyone provide an explanation for how the “beam width control” actually controls the beam width on the Beolab8? I understand what the feature is supposed to be. I understand how this feature is supposed to work on B&O speakers with mechanical baffles. It is not clear to me how B&O would accomplish this with a seemingly standard 3-way configuration.

Glitch

 

[Glitch]

… and here(?)

 

[Glitch]

klesolin wrote:

How can they get damaged from within the speaker?

I’ve always assumed that the damaged coils were a result of people pulling their crossovers to check if their coils were damaged. 😉

An alternative (more serious) explanation is that the coils break loose from a hard impact during shipping.

Glitch

 

[Glitch]

1. Remove amp
2. Remove bottom plate
3. Remove wires from crossover(s). Wires are color coded and labeled on the crossover.
4. Pull hard.  The boards are held in place by friction (even though it might feel like they are welded in place). The boards slide into slots in the housing. There might be tape on the board to keep it from rattling. Try not to pull on any of the crossover components.

Hopefully this makes sense. Good luck!

Glitch

[Glitch]

Tuning issues are usually caused by a bad U264B chip (IC8-Board2) or a broken wire on the coax cable between the FM board and the CPU board.

Replacement U264B chips can be hit or miss for working with a BM6000 (depending on the manufacturer). The ones sold at beoparts-shop.com work well. The cheap ones from China sometimes work, but you might need to try a handful of them before you find one that is compatible.

The broken coax wire is usually at the CPU end of the cable where the center wire connects to the connector pin. This can be repaired by soldering in a short piece of wire to reestablish the connection.

Glitch

 

[Glitch]

Evan wrote:

In my experience it seems our human listening isn’t mega sensitive to height, more so side to side. I’m thinking it shouldn’t be a huge issue to place the center relatively low. Not to invalidate your experience at all, Glitch. I have a colleague who has a pair of center channels, one above and one below and he has tuned the [acoustic] image between them.

Different people are sensitive to different things. What one person doesn’t notice, really bothers another. Room acoustics can be quite different also. I could see where the bottom-center location would work someone with a dead floor and a live ceiling. The stronger reflection from ceiling would move the apparent image upward.

I’ve considered the over-under setup. I just can’t figure out a way to make it look “right enough” to be a permanent solution.

Glitch

 

[Glitch]

Evan wrote:

I think for home theater it is best that there is a dedicated center channel physically centered below the screen. This will anchor the sound stage and center channel content to the image really well.

Yep, I understand why most people like the “centered below the screen” location. I like the center of my TV screen to be below eye level, which keeps the TV low. The center speaker is almost on the floor. Now the sound is coming from well below the actors faces (which are usually higher on the screen) and things like coffee tables are in the direct path to the speaker. The bigger the TV’s get, the worse this problem becomes. The “dual mono on the side” addresses some of these issues, but admittedly causes other issues.

The good thing about the lack of a perfect solution is that it opens the door for experimentation.

Have you thought about mocking up your original concept? Possibly something like pulling the tweeter/mid module and pairing it with a couple of conventional speakers as surrogates for the woofers?

Glitch

 

[Glitch]

Evan wrote:

The problem with putting the same signal through both speakers is that you only serve a listener exactly in-between them.

This is only true if the radial dispersion is constant, which is not the case for the higher frequencies.  This explanation isn’t quite correct. What I meant to say is something more along the lines of… This does not have to be the case if the system was designed to not have a small, narrow sweet spot.

Consider the sound system in your car. The driver is much closer to the driver’s side speaker than the passenger side speaker, and vice versa for the passenger. Despite this, both driver and passenger can simultaneously experience a (mostly) centered image. The car audio engineers achieve this by carefully manipulating the dispersion fields of the higher frequency drivers. An overly simplified explanation is that a speaker is louder on-axis than off-axis. The speakers are arranged such the the far speaker is on-axis and the closer on is off-axis by the exact amount that it needs to be to get an equal sound level at the listener’s position. Look up some of the papers from Dr. Bose for a detailed explanation of the theory behind this.

It would be awesome of Geoff Martin could chime in and provide the dispersion data for the Pentas. I have to believe that B&O has this, but is likely wishful thinking on my part that they would make it available.

Glitch

 

[Glitch]

Evan wrote:

et me know what you guys think.

From a general sound perspective, I don’t see any reason why it wouldn’t work. As long as you keep the cabinet volume and reflex tube length/diameter the same you will, in general, have a similar frequency response. Even if you mess up the very low frequency response, this won’t be critical for voices since they don’t contain those frequencies.

Would you actually be happy with the form factor? I’m having a hard time imagining what this would look like under a TV.

Did you plan to have the bottom-most mid-range close to the floor? Not having the tweeter and mids at ear level may mess with the vertical dispersion. I don’t know if this is a better or worse trade-off versus having the mid-range array horizontal.

Have you considered using a (well matched) pair of Pentas (in the original configuration) placed tight to sides of the TV? The mono pair would provide the a solid centered image and the apparent sweet spot could be roughly controlled by the angle. The other “surround” speakers could also be Pentas for the full overkill effect. 😉

Glitch

 

[Glitch]

It has been long enough where I’ve forgotten most of the finer details of recovering these grills. Hopefully you can see what you need from the picture.

Taking the grill off reminded me of how precarious the procedure feels. No matter how many times I’ve done it, it always seems like something is about to break. 😉

Glitch

 

[Glitch]

I used iCraft Supertape based on several recommendations in another forum. It has been seven years since I changed the grill cloth and it is still holding strong.

Glitch

 

[Glitch]

It is good to hear that you have made progress.

One tip related to changing the grill cloth is to use two sided tape to attach the new material. This makes it much easier to get the tension just right versus using glue.

There are a many other tips that people can provide for Pentas. You probably have already figured out that B&O enthusiasts are pretty passionate when it comes to Pentas ;-).

Glitch

 

[Glitch]

thomash wrote:

Meantime I sliced the front off this cartridge where the cantilever had broken off.

Pictures please.  I, and likely many others, find it very interesting to see the inner workings of things that people normally don’t cut apart.

It also might be worth a search of the forum history to see if anyone has tried this before. One of the more recent similar threads is here.

Glitch

 

[Glitch]

Audionerd87 wrote:

These decks can be made functional (although longevity is not a guarantee) with a parts machine as a donor

This has never worked for me… Eventually, I always fix the donor machine and it becomes a spare/backup machine ;-).

thomash wrote:

It would be nice to find a OK lower end cartridge with intact needle for this at a cheap price out of dead broken machine.

This is possible, but you will need to be very, very patient while waiting for something to become available. I think that many of the old B&O turntables get taken out of service when something happens to the cartridge. For the rest of the broken machines, people seem to remove the cartridge before they sell the rest for parts.

Additionally, when something does come up for sale, you have to quickly buy it before one of the other zealots from this forum snaps it up from under you.  😉

Glitch

[Glitch]

NickNS wrote:

First I checked polarisation with voltmeter, it was correct on two drivers and incorrect on other two.

I’m not quite sure what you mean by this… Did you mean to say continuity or resistance?

It looks like your the polarity of the drivers are marked with the “+” stickers. Check the wiring against the schematic.

NickNS wrote:

If you have any further suggestions on my next step, I’m here to listen

There are spade connectors at the crossover boards. One (or more) of these may be either disconnected or misconnected. Also, many possible crossover issues could be identified if you provide pictures.

All of the drivers look to be original, which is a good start.

Glitch

 

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