Beovox 3000 Type 6220

A 94 year old grandmother in Copenhagen, had put her Beovox 3000 speakers from 1969 up for sale. Grandma had only used the speakers to listen to the radio news, and she had not moved the speakers since they were purchased.

She was very kind. I bought the speakers because they were untouched in mint condition, and because I needed the Type 6220 for my project.

This “Peerless L100 WG” 10” bass that

Bang & Olufsen chose for the Beovox 3000 is very “rugged” and can withstand 50 Watt sinewave. To ensure that my project does not stall because of a lack of drivers, I have bought some spare units around Denmark, but also because the bass units shown need to be measured

Beovox 3000 Type 6220 modification DIY

The loudspeaker is the part of the playing chain in a hifi system, that has the greatest direct effect on reproduced sound. There are many good loudspeaker systems, but only very few that reach the exact sound signature or "sound mark" on the hifi scale we all strive for.

As a kind of control point for good well-resolved naturally reproduced hifi sound, Edgar Villchur's AR3a, AR10pi and AR11 from the seventies are among the best 3-way loudspeaker systems, where the AR3a in particular was a milestone. More about Acoustic Research in the AR3a "improved" thread.

On the domestic hifi scene, Bang & Olufsen's UNI-Phase development reached a decisive milestone in good loudspeaker sound, when, among other things, the acoustic suspension systems Beovox M70, M100, S45, S75 and others were introduced.

UNI-Phase speaker Beovox S75 with 10" Seas woofer, Philips AD5060 SQ4 5" midrange, Philips AD0211 SQ4 silkdome and Peerless DT115 4 Ohm

Already 7 years earlier, before the development of the UNI-Phase speaker, B&O's speaker series with the Beovox 1100, Beovox 3000 and Beovox 5000 set new limits for what can be described as excellent hi-fi sound.

Especially the Beovox 3000 where B&O with the simple two-way system managed to get a superbly fine interplay between the Peerless 10” L100 WG bass and the

Seas 2” dome.

Just hear what Kevin in London says about the Beovox 3000 and note the listening test at the end of the video:

www.youtube.com/watch?v=Yqt1H3wRwGk&list=PLrhnoIoVIDT3KCSUg6h1woEiM7cRQEn70&index=18

I already own a set of Beovox S75 UNI-Phase speakers and my opinion is they sound great, but I also bought two sets of vintage 1970 ~ Beovox 3000 rosewood in 2023.

Before anything else, I think that Jacob Jensen's design with the Beovox 3000 is the most beautiful speaker delivered from Bang & Olufsen. But the reason why I bought the speakers was because I wanted to change the speaker from 1969, so that the midrange frequencies would stand out more clearly in the stereo image. A stereo perspective in line with the development of the sound image from the 4-way system in the Beovox S75.

The UNI-Phase princip

For that purpose, I had studied the UNI-Phase principle with the "filler driver" that is used in the Beovox S45, for example. In the S45 (and S75 among others) B&O has used a fantastically fast 4” Seas midrange, where the sensitivity matches the 10” Peerless bass L100 WG, in addition to this lower midrange, I had purchased a set of Celestion MD500 2” midrange domes to handle the frequencies in the upper midrange. After several attempts in the 4-way setup with Celestion’s MF500, the choice fell on ITT’s LPKM 130/50 2” dome , which in this line-up fits better sonically.

As the top tweeter for this 4-way speaker, the choice was the fine tweeter from the D28AF from Dynaudio, which appealed to the listening panel more than Scanspeak’s D2905/950000 tweeter dome.

Will I destroy the UNI-Phase principle by changing the driver?

The concern was, that with my changes to the Beovox 3000 I would destroy the excellent work with the UNI-Phase principle where the midrange unit is “phase-reversed” and thereby provides less phase distortion and ultimately a better frequency response. Beovox UNI-Phase was developed by B&O engineers Erik Bækgaard and Espen Kokholm and the patent-pending principle was presented at the AES convention in 1975 (Audio Engineering Society).

It is not intended to be read in Danish, but the conclusion is that the UNI-Phase principle enables the loudspeaker to reproduce square waves with low distortion and good transient response. There is an English version of B&O's development work from back then at the AES convention in Rotterdam.

Luck followed me

Fortunately, it turned out that the calculations regarding phase linearity and reproduction of square curves still hold, even if the location of the driver units on the speaker’s front panel was changed. A so-called “Filler-driver” technique is used at the crossover frequency between the bass and midrange unit, which overall achieves better frequency linearity and frequency coherence between the units. For further information about the UNI-Phase principle, please refer to the AES article from 1975 by Erik Bækgaard and Espen Kokholm.

Photos of units used in the modified Beovox 3000

as well as discarded drivers

Discarded units : Scanspeak D3804, Seas H087, Bose tweeters, Sinus silkdome tweeter, Philips 5" 5060 SQ midrange, Seas 10" woofer, Celestion MD500, Scanspeak D2905/95 tweeter, and more than one box type testet with no luck....

and many more..................

The photos shown cover a larger number of speaker units that have all been through several listening tests in order to find the best setup for this modification of the Beovox 3000 Type 6220.

I have listened to the original Type 6220 speakers intermittently for some years, and they have, with good CD and LP recordings, delivered a very natural musical reproduction that satisfies the listener. The Type 6220 has just reached the “mark” ... the “benchmark” that makes the listener happy.

But, and there is a “but” ... the Beovox 3000 Type 6220 does many things well as a hi-fi speaker (for example, I like the overall sound from the Type 6220 better than from the KEF units in the LS3/5a), but I think that the midrange could be defined a little better, and the UNI-Phase principle comes into play as an option.

My idea was to move two extra units into the Beovox 3000 box, and copy the coherent sound image from the Beovox M70 and S75 into the Type 6220. (I had 2 sets of Type 6220, so why not try?)

But first, suitable units had to be selected. As a 10” bass, the choice was simple, after many listening tests with drivers from Seas, Scanspeak, Vifa, Philips and Peerless.

PeerLess L100 WG

There are very few 10” woofer cones that, with acoustic suspension, are fast enough to reproduce and define fine bass tones from a double bass. In my opinion the best 10” vintage woofers come from Seas (25 F-EW, 25 F-EWX, 25 F-WB) and Peerless (M100 WG, P100 WF, L100 WG, L100 WF)....all with super light weight papercones!

The choice fell on the Peerless L100 WG, 4 Ohm, fo: 20Hz, 50W, which with the field strength from the alnico magnet and lightweight membrane plays bass tones into the room to a greater extent without “pumping” bass sound out, as the majority of modern woofers do. The vast majority of newer woofers are manufactured with a focus on high field strength and a membrane that, regardless of the size of the magnet motor, resists break-up. But the modern woofers do not sound natural and live-like, as is the case with the L100 WG from Peerless

"The quartet" plays in the open air... first time...

Next, choosing the deep midrange speaker. In the Beovox S75, B&O used a 5” Philips unit with no. AD 5061 SQ4 res. 60Hz. The Philips unit was tested together with Philips AD 5060 W4, Scanspeak 13M 3808 and Peerless KO-40MRF, but all were blown away by the speed of the Seas H084 10F-M with coated papercone. A lightning fast natural sounding lower midrange unit with ultra-light papercone that defines midrange tones perfect.

For the upper midrange, the choice was between Celestion MF/MD500, Dynaudio D54a or ITT’s 50mm dome with no. LPKM 130/50. In terms of durability, the choice should have been Dynaudio’s D54a, but ITT’s LPKM 130/50 fit better sonically in this 4-way system than the Celestion MD500. The choice was ITT’s 50mm dome.

As for the tweeter, many different types were tested. Bose papercone tweeter, Sinus silkdome tweeter, Scanspeak D3804, Seas H087, Seas H086, Scanspeak D2905/9500, Peerless TD115 1” and Dynaudio D28AF. The choice was the

Dynaudio D28AF....beautiful sound from D28AF.

Then work began on changing the Beovox 3000’s crossover filter, which only needed to be changed slightly compared to B&O’s filter for the Beovox M70. The Beovox M70 used the very good-sounding ITT LPKM 130/50 and the Dynaudio D28AF was a good fit in terms of impedance compared to the Seas H086, but the D28AF had a better sound...

The Seas H084 10F-M midrange was close in impedance to the Philips AD5061, but the Seas 10F-M had a faster response to frequency changes. So therefore the crossover values from the S75 could be used for the Seas 10F-M.

The Peerless woofer has an impedance curve that is reasonably close to the 10” woofer that B&O used in the M70. The woofer that B&O used in the M70 is produced and manufactured by B&O, and is not, as many assume, a Philips 10” Woofer. Regardless of who manufactured the woofer for the Beovox M70 (I have two sets), the Peerless L100 WG reproduces the bass tones better.

As the next step in the work process, I built a test stand that could accept several speaker units of different sizes and diameters. Speaker units where we in advance knew the sensitivity and how much dispersion the individual driver could perform. This knowledge of the drivers' properties made the work of adjusting the units to the rest of the speaker system easier. The following series of pictures shows how complex the work becomes when you want to build a hi-fi speaker.

The three drivers just taken out of the test stand where the Philips 5” unit had been replaced with Seas 10F-M 084. We all knew at this point that we had hit on something right....a sound image emerged that was so coherent from the three units which, without a baffle, lay on the table and played absolutely superbly.

What a day for the speaker test!

The modified Beovox M70 crossover to support the 4 way system:

Peerless L100 WG, Seas 10F-M, ITT 130/50 LPKM 120TT and Dynaudio D28AF

Note : The extern D28AF tweeter has a 12 Ohm / 7W MOX-resistor across the terminals in order to balance output and impedance to the rest of the speaker system

Wood working on the Beovox 3000

speaker cabinet

Then work began on changing the front plate for the new speaker units, which became a bit difficult when ITT's dome is mounted from the back. But it was successful.

The back of the Beovox 3000 was changed to two input terminals, where previously there was only a 0.5 square wire out of the speaker. The previous outlet for external tweeter was reused with an XLR connector for the “loose tweeter” which is now placed on top of the speaker.

The original DIN terminal for external tweeter replaced with XLR male connector mounted in existing output hole.

A speaker stand made of wood

Here, finally, a set of speaker feet is made for the Beovox 3000 (DIY.. can also be used for the Beovox 1500) that raises the speaker about 14-15 cm from floor level.

Since the Peerless bass in the Beovox 3000 is placed about 6 cm measured from the bottom surface of the speaker box, the 10” bass is now raised about 20 cm from the floor level.

The feet were made of two rectangular MDF boards measuring 25 x 28 cm, where the bottom board is 16mm thick and the top board is 10mm thick.

The bottom board has first been glued with a 16mm triangular wooden strip all the way around and then veneered with about 0.7mm Rio rosewood on both the top surface and the beveled edges.

The 10mm MFD board is veneered with the same Rio rosewood on the top surface and the straight edges.

To keep the same “retro look” as the Beovox 3000, the idea was to veneer the edges of the top board, as it would just be visible. Luckily, there was a piece of African “Wengè” in stock. A glass-hard wood with a hardness above medium.

Below a series of photos that better describe the idea of a floor stand made of wood for this Beovox 3000 retro speaker.

My favorite wood veneer is rosewood. A veneer that I have saved for more than 30 years because Rio rosewood is no longer allowed to be cut down.

The speaker feet are designed so that the 4 solid 23 x 23 mm carved wooden blocks of dark solid African "Wenge" hardwood can be varied in height.

The wooden blocks are not glued to the base plate, but screwed in with screws in millimeter threads. As the photos show, threads have been cut into the solid hardwood blocks, so the height can be adjusted using the 5mm through-bolt screws shown. The top plate, however, is glued and doweled together with the wooden blocks.

The African wooden blocks are extremely hard and easily withstand fairly heavy clamping.

The 4 metal feet shown placed on the base plate are provided with an internal hard rubber insert (from Bauhaus) and can be adjusted in the same way and adjusted in height.

Using the two adjustment options, the speaker can be tilted a few degrees backwards if desired.

The two floor stands for the Beovox 3000 are finished. Now only two tweeter stands remain on top of the Beovox 3000 for the Dynaudio D28AF

Both stands under construction.....

The tweeter stands for Dynaudio D28AF that should give the Beovox 3000 the desired look of a complete speaker are ready.

Omega is the 24th letter in the Greek alphabet, and also has a symbolic meaning, as the Omega letter is used in connection with defining and indicating the value of a resistance in an electrically conductive material.

As the son of a watchmaker specializing in watches from Switzerland, you are well acquainted with the watch brand "Omega" founded in 1848 by Louis Brandt.

In addition to the well-known company, "Omega" stands for perfection and performance.

So for the watchmaker's son.....what was more obvious than to produce two "Omega" stands for the Dynaudio tweeters. And so it was.......

First: to mill out 4 MDF rings in 19 mm thickness diameter 11.5 cm (inside approx. 9.0cm), and to cut out 2 rectangular feet in 12.5 cm x 4 cm thickness 10 mm.

Second: to glue the rings together approx. 38 mm as the tweeter measures approx. 36 mm in height

First laser cut 2 round plates in 3 mm hardwood board diameter 11.0 cm

Then cut a chord of the rings with a circle height of approx. 10 mm

last glue veneer on both feet and MDF rings

Then drill holes for banana bushings intended for wooden chassis plate

After that a lot of sanding work plus surface treatment with Shellac intermediate sanding + Shellac + intermediate sanding + wax treatment

The "Omega" tweeter stands were a difficult solution, but the finished result looks nice in my opinion.

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