Speaker Restoration

A while ago, my coworker buddy stood at my doorstep, hauling two -for lack of a better word- obscenely large speakers along with him. Turns out he bought two pairs of 30 year old Bang&Olufsen Pentas, one pair of them powered (Beolab), the other not (Beovox). For some reason, the passive ones ended up staying at my place. Yay!

Thank you one more time, André!

Most unfortunately, all of those speakers were in absolutely desolate shape, simply terrible: Smashed woofers, rotten foam on all of the midrange drivers, while two of them were completely shot. The front grilles all filthy and ugly, candle wax stuck on top of one of them and, boy, were they dirty in general. Needless to mention, they also sounded horribly screeching and flat; Outright dreadful.


Time had inexorably rendered them into worthless pieces of junk. Such a shame! Much Unjust! So Sad! I simply had to do something about this.

You see, the beauty of these speakers lies within the fact that the midranges are configured for line array operation, within certain frequencies. Phase correction of the outward driver pair is done by physically shifting them backwards by a few millimeters, so the sound from those drivers is delayed by a few nanoseconds. This produces a sound beam, emanating from the front, minimizing floor and ceiling reflections. It also gives the stereo image they produce an airy, wide open, yet deeply detailed and defined quality not usually found in your average $1000 run-off-the-mill speakers.

So naturally, the first thing was to check for replacement midranges. Refoaming was out of question, since two of them were totally dead and measured open on the voice coil. B&O still supplies them, but quoted a price of EUR 235 per unit. Bloody ouch!

Also considering that the original ITT/NOKIA drivers were always a tiny little bit on the crappy side perhaps, another solution had to be found.


After following up on countless posts in diverse message boards, I read about some drivers from Visaton (a quality manufacturer from Germany), for which others reported success with. However, the reported drivers were 8 Ohm types, while the original had 4 Ohms (3.4 Ohm DC). After browsing around some more, I found that there’s a 4 Ohm version and decided to give it a try. The drivers had to be mechanically modified to fit into the mounting holes on the B&O enclosure, but that -thanks to my coworker’s ingenuity- turned out to be not much of a problem after all.


I decided to replace the cheapo spade connectors on the speaker terminals by soldering the wires to the terminals and using a 6 pin automotive high current connector for the entire assembly. Those mechanically interlock when connected and are coded, so cannot be connected up the wrong way.


While at it, I also completely redid the wiring for all the bass drivers. Instead of the daisy chain style 0.75mm2 wiring put it place by B&O, Im using 2.5mm2 wiring arranged in a star topology. The wires are soldered to the terminals, at the driver side. Distance between PCB14 and Terminal Blocks is kept at a minimum.


Due to age, the crossovers were completely recapped with Audyn MKT caps. It was my choice to replace all electrolytics, not just those directly in the signal path. Different electrical parameters of the replacement drivers also necessitated  tuning a few resistor values. I used both simulation and lots of trial-and-error listening to do this (which is the reason for the yellow tape on the floor, marking the speaker positions).


Theoretically not entirely perfect, but I didn’t want to replace any of the inductors and have no facilities for taking any meaningful speaker measurements. Yet, outcome in terms of sound is extremely good: very clear and elucidated mids and heights, absolutely profound and dry bass response, always comfortable to listen to (even at stupidly high or idiotic low volumes) and quite well balanced overall. Also, many orders of magnitude  better than the pair of (quite good) Quart MB speakers I used before.

My thread on beoworld has more detailed information about the crossover modifications.

Next was redoing the front grilles with black fabric instead of the original grey one. All the originally grey plastic parts were also repainted  in maté black.

So here’s what they look like now:


Final step, I did a new paint job on the became-undefinable, once-must-have-been coppery-silvery-goldish deco stripes running around the grilles. My color of choice was a dark metallic red, matching the interior of my living room.



I think they sound (and look) absolutely stunning. The only thing I’ve ever heard that comes even close in terms of spatial resolution (stereo imaging and depth) are Martin Logan Sequel electrostatic speakers. My coworker was so impressed that he also had -after listening to my pair for a while- the same replacements and modifications (except paint job) done to his powered pair.


Old 80s Speakers in all new and shiny glory. Absolutely, totally gorgeous!


And in case you wonder: If you were to give me EUR 2000 and cover all expenses, then yes, I’d consider applying the very same procedures to your pair of Beovox Pentas. Yes, it was quite a bit of work that took me several moons of working on them in my spare time.


2 thoughts on “Speaker Restoration

  1. Hi Niston, Great job on the Pentas! I was just wondering how exactly you modified the Visaton drivers to fit into the cabinet. I think ill replace mine with these, and also ordered a couple of SEAS Prestige tweets as well.

    • Basically, it’s as simple as cutting off the mounting flanges. Remove all of the excess metal, so that the drivers can fit into the mounting holes (inserted into baffle from the front). Take great care however, it’s easy to cut away too much. Error will result in a small open space between driver and cabinet. Remove just enough of the metal, so as to have the driver’s edge sits firmly on the baffle (in the mounting hole). The original driver sealing rings and mounting hardware can be reused. Add some washers for spacing if a driver doesn’t rest tight enough – they should not move at all, once screws are fastened. All the drivers should be well aligned (not point slightly side- or upwards).

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