Hi Snoopy.  Thanks for this post.  I personally think the actual driver and crossover arrangement is severely holding back the speakers, and I don't know if investing in the amps is worth the effort before the driver and crossover setup is corrected.  I was writing a post on an audio website to someone who had just acquired a set of penta 2's, so I'll copy and past some of what I wrote:

"As you can see, you have 3 sets of drivers. It is technically a 3.5-way arrangement since the 4 midrange speakers have slightly shifted crossovers. The inner two are shifted slightly higher, while the outer two are shifted slightly lower in the frequency range. Unfortunately, in the case of the pentas, the drivers weren't matched all too perfectly, in either frequency range or quality. The tweeter you'll be happy to hear is a high quality SEAS 19mm ferrofluid unit. I don't remember the model number off the top of my head (you can look at the back of it). The model is discontinued but you can still see the info in the discontinued section of the SEAS website. An equivalent SEAS tweeter is about $30 to $40. Now, the standard SEAS version was a 6-ohm nominal impedance driver. If you look at the back of your tweeter though, you'll see "BO" at the end of the SEAS model number, and underneath it will says "8 ohms". The tweeter is an 8-ohm version made for B&O. We'll get to why later.

Now you're midranges I'm sorry to report are junk. They're made by Haes, a German oem manufacturer for german car speakers, such as those found in your standard bmw. I actually found the same speakers on partsexpress.com a couple years ago for $5 each. They're very low quality. Furthermore, B&O has arranged the crossover to drive these speakers outside of their intended frequency range. This explains the fuzzy mid range you're hearing.

The crossover design isn't anything to celebrate about. I've forgotten most of what I learned about crossovers several years ago when I was trying to design one, but I still remember one of the major issues I saw with the penta design. The crossover was first used in the Penta 1 in the 80's, and only changed slightly all the way to the Penta 3 in the 90's. A good crossover impedance matches drivers. You can use a 6-ohm driver with an 8-ohm driver without an issue. Those numbers are fairly deceiving anyway though, as the impedance actually changes across the frequency range. The Penta crossover doesn't impedance match the drivers. Instead, they just tried to match the nominal impedances of the drivers themselves, which as I said aren't very meaningful numbers anyway. The main woofers are 8 ohms. So, they had SEAS modify their 6 ohm tweeter to be an 8 ohm tweeter. The midranges are 4 ohms each, so what did they do with those? They put each pair in series. The two center midranges are in series, and so are the two outer, yielding 8 ohms total they thought. Unfortunately this reasoning works fine with resistors, but with speakers you don't just mix and match so that their nominal impedances add up to the same number and call it a day."

About 2 years ago I spent tons of time studying crossover designs on sites like diyaudio.com and www.zaphaudio.com.  Those are two I remember off the top of my head, but can pull up others from my bookmarks if you're interested.  I learned that a good 3-way crossover is incredibly difficult to design, and that the penta crossover was far from a shining example.  Someday when I have time I plan on replacing the midrange units and perhaps woofers with higher quality SEAS or Peerless units, and then attempting to use driver and acoustic chamber modeling software to pull together some semblance of a suitable crossover design.

Austin

While B&O may sometimes seem like they design to a budget I think that implying they didn't appreciate the significance of connecting the drivers in series a little unlikely. They would have also tested the resulting speaker extensively (their speaker test facilities are among the best in the world).

If the Penta's do have limitations then I believe it was with the full knowledge of B&O, the chances of them not understanding are, IMO, zero.

Interesting thread Snoopy - I wait eagerly to see how you get on with this project!

I think that Bulgarien attempted something similar a year or so ago, and was very pleased with the results. I have an easier way of driving my Beovox Pentas to my satisfaction though - it's called a Beomastger 8000 :)

Of course these speakers can be driven by anything (Beo 8000) but I'm after the glorious sound that comes from a proper Class D. In a nutshell I'm upgrading the speakers to B&O's latest technology but shifting the active filtering to passive filtering.

Regarding the Pentas, I believe the reason they sound so good is to do with the phasing introduced by the crossover, and because of reduced harmonics between the drivers given they are all doing a different job. At the end of the day they sound stunning at mod to high volumes - my mid-range certainly doesn't sound "fuzzy". It's easy to say B&O cut corners but in reality they never do - and especially not on a flagship product.

I'm collecting most the bits this week and the IcePower's are on the way!

Andrew

j0hnbarker wrote:

I think that Bulgarien attempted something similar a year or so ago, and was very pleased with the results.

Yes, here it is.

Hi Puncher!

I know several crossover experts have said that the 3-way crossovers are still ridiculously hard to design even today, and also that crossover designs have definitely changed in the past couple decades.  I wasn't really implying that b&o alone didn't know what they were doing; I'm saying I think there was an overall lack of knowledge in good 3-way xo design in the speaker industry 20 years ago.

Edit: I just noticed something Peter had said in a PM about the Pentas.  He said that they are amazing because they sound far better than would have been expected of their constituent parts.  This I totally agree with.  For the given set of parts in the Penta, we may have close to the best configuration.  What I'm wondering though is 20 years later whether the design can be tweeked with new parts.  Of course, at some level I suppose it's not really worth arguing until I actually get up off my seat, try it, and then test it with a calibrated microphone.

Austin

Oh yes, Bulgarien's page was very good.  If replacing the capicitors with polypropylene ones, the actual brand or quality doesn't really matter though.  The only problem with cheaper made in China polypropylene caps is that sometimes they aren't truely polypropylene.  Using inexpensive ones is fine as long as you buy them from a reputable supplier.

Austin

You're never going to hear the difference unless they are on the input side, it's the same old snakeoil argument for speaker wire. His capacitors were blown, and how his drivers looked like that I don't know (mine are perfect and been playing since 1989). The original capacitors and crossover must be fine if the Pentas sound this good. Yeah I thought of active amps but there is no need to destroy a crossover network that appears to be brilliantly designed.

A big argument for active amps is using surplus capacity to enhance the bass on smaller diameter cones and smaller volume cabinets. The 6000 shows the limitations of this, the Beolab 1 needed 400w to do 125w and the Penta doesn't need any of this because it's a true sized cabinet based on mathmatical formulas.

That's my argument for keeping the Pentas.

LED's have arrived. Stage 1 shall be up shortly. :)

Snoopy, I certainly don't believe in speaker wire snake oil (as my signature says - 'skeptic').  Electrolytic capacitors can certainly degrade enough over 20 years to create an audible difference.  It's a somewhat random degredation though, and it's very likely that electrolytic caps from 30 years ago are still working fine.  If you only plan on keeping the speakers for a couple years it won't matter, but if you plan on holding onto them there's no reason not use the polypropylenes.  Plus they're pretty cheap anyway as long as you don't buy a boutique brand.

Which crossover are you saying was brilliantly designed?  The crossovers changed across the different pentas.  At one point even the zobel filters were removed, I think when going to the penta 3.  I only know what my penta 3's sound like though, so I've never been able to listen to the different versions.  By the way, I found the main site I stuck to when studying crossovers.

http://sound.westhost.com/lr-passive.htm

Also, I think producing active crossovers would be too much of an undertaking without having the frequency response plots of the drivers.  As I said, I've only been able to source the graph for the tweeter.

Austin