The procedure is complete. It required a bit of drill action (acting as a grinder) on the inside plastic to allow the huge magnets to fit, but it didn't compromise the enclosure.

At first the sound was more accurate but didn't have that "edge" the Penta's seem to be able to do.

Then I realised by removing the last part of the mid-range crossover I had shifted the phase 180 degrees. I reversed the polarity of the leads and ...

❓

I would love to pitch these against some 5's now. I actually reckon they'd win!

I ended up going for the FRS8M's instead of the less sensitive model. The other ones have a real flat response, less power handling and would have fitted straight in, and my Penta 1's use a 3.3ohm reduction (the 2 & 3's use 2.2ohm) so the M's looked the better bet.

Incidently, the original mount brackets for fitting the original mid-ranges fit perfectly without modifcation. A nice surprise.

I could definitely use those drivers, but I live in the USA.

snoopy wrote:

Can anyone explain the mid-range part of the crossover? It's very complex ...

In my judgement ??? :

L1, C1 does the basic filtering

R1 controls volume

L2, C2, gets rid of any minor left over signal

L3, C3, gets rid of any minor left over signal

C4, R2, L4, C5, matches impendence (zobel network)

 

Basically I'll be getting rid of the entire last part of the network for my new mid-range units. I'm wondering what else before the last part will colour the sound, that is, was stuck in to compensate for the original crap mid-range drivers.

Andrew

 

I know this is a year old...sorry.

Just a quick look at that crossover (and I'm by no means the best at reading schematics...) - looks like there's trap circuits and impedance compensation circuits in there.

Are you talking about getting rid of L5 and C8? Looks like some kind of bandpass filter.

My guess (without trying to figure the X-over out) is that the outer two units' response rolls off at a lower frequency than the inner two units. This is done to avoid comb-filtering artifacts in the response, when the wavelegths get to be smaller than the center-to-center spacing of the drive units.

That way you get the extra radiating area and, hence, efficiency in the lower range of the midrange's passband without the comb-filter cancellations higher in the response.

Jon

So this thread basically covers how Penta owners can get rid of

- The original amplifier
- The original drivers
- The original crossover design

But the Bang & Olufsen logo on them is pretty cool, huh ?

Martin

Dillen wrote:

So this thread basically covers how Penta owners can get rid of

- The original amplifier
- The original drivers
- The original crossover design

But the Bang & Olufsen logo on them is pretty cool, huh ?

Martin

😂That's pretty good Martin.

Yeah, it was really late when I replied to this thread (way past bedtime), and I was going to say that I think it would be a mistake to alter the X-over in any way. There's definitely some complex response shaping going on here, and by arbitrarily deleting part of that, you're only going to mess things up.

Jon

I agree.
There's some serious filtering going on there.
Bang & Olufsen didn't mount all those expensive components just because
they've accidentally ordered too many.
Put a Penta speaker through a monitored frequency sweep, change a driver or
a filter component and see if you can make them any better.
I think, you'll be surprised.

The amplifier is one of the best from B&O. Discretely built and still housed
in that little box. Even the transformer has been fitted in there.
Technically, there's very little to improve, even with modern components and
todays techniques.
The signal path capacitors and operational (pre-)amplifiers can be replaced
with better modern types but that's about it. Not much for such an old construction.

I respect the Penta speakers very highly.
B&O managed to put a speaker together that sounds great, packs a fair
party punch while providing an almost completely flat frequency response.
Even the design is timeless.
Mainting the Penta's as you would anything else you like, and you'll have
superb speakers for a long time.
Neglect them and you will have speakers with dead amplifiers, dried out cross-over
capacitors and drivers with foam rot.
This is often the case when people put them down these days. What they are judging
are the owners level of maintenance rather than the engineers creations.

I feel that many owners simply forgot what they bought, what they sounded
like when new.
They are wonderful speakers but as everything else of this nature, they do require
a bit of attention from time to time.
 
Martin