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The man behind A.O.S. looks back on his life with loudspeaker design.

Axel Oberhage

Foto: A.O.S. founder Axel Oberhage on the HighLake

I decided to get my first set of loudspeakers while I was still at school. Although I listened to music
each day right up until I went to bed, no amount of desire to get reasonably good-sounding speakers
would overcome my small budget. The first speakers I bought based upon the technical data I read
in the catalogue. What a mistake! The shabby little boxes sneezed and coughed acoustically; the
sound was truly awful. I opened them up and founda cheap oval bass driver, something resembling
a tweeter, a depressing little condensor and a tiny bit of fiberglass.

I decided there and then that Iwould build any speaker I owned, not buy a poor-sounding box of
inferior parts.

As lofty as this decision was, the technical literature of the early 70's provided very little help. The only
solution open to me was to "learn by doing," which is exactly what I did. During this time it was possible
to design a speaker with fairly accurate and musical midrange driver and tweeter. The bass section was
more difficult. I found some very expensive ScanSpeak 21 cm woofer with Alnico magnet and I must
admit that I had finally done it: built the first loudspeakers with which I was really happy.

The next advance in my loudspeaker design career came with the introduction of the first kits offered
by the legendary British manufacturer KEF. The legendary B139 bi-radial driver with its polystyrene
diaphragm made every other low frequency driver obsolete. The typical soft paper woofers at that time
sound absolutely flat. KEF's Bextrene midrange drivers brought even more precision to my designs.
At this time, many fine British Hi-Fi magazines found their way to hobbyists in whole Europe, published
a great number of interesting DIY speaker systems. This was the beginning of the DIY hi-fi scene in
Germany and maybe in UK and USA.

In 1983 I wrote a first article about a small speaker with double voice coil, the Focal 250DB. Even though
this kit becamea considerable success, I had little interest personally in the French sound of speaker kits.
The general philosophy did not fit my understanding of how music should be reproduced. I still remained
committed to British design philosophy.

At that point I heard one of John Wright's IMF transmission line loudspeakers.That was a key experience!
I had never heard such bass. I spent nearly $ 2000,- to buy my own pair of these expensive IMFTLS 80
speakers. Then I disassembled them and made construction drawings. I copied the crossovers and had
a British supplier, Falcon Acoustics, who built them for us. We started with the old version using the
KEF B 139 and the KEF B 110 and CELESTION tweeters. Having all the components at our disposal,
we offered IMF transmission line kits. The result? All over Germany many hi-fi hobbyists built a great
number of TL speakers!

Not more than a few years later, IMF disappeared from the market. John Wright began a new company:
TDL Electronics. We immediately became agents for TDL and for ten years we were the largest selling
TDL dealer for kits all over the world.
The Monitor TL e.g. had world wide many positive reviews. We built
a little bit smaller 3-way kit called Monitor Compact, had a very successfull review in the German
"Stereoplay" magazine and selled over a thousand sets to music lovers throughout Europe.

Nevertheless, we persistently continued to improve and refine our design. 1992 marked a radical advance
in midrange reproduction. Radical, because we stopped to use polypropylene and started with stiffer
materials based on a mixture with stiff paper (back to the roots).

By 1996 we were able to introduce yet another quantum leap in accurate musical reproduction when we
adopted the astounding ScanSpeak 18W 16545 K, with its rigid, resonance free papercarbon diaphragms.
This superb device is large enough for a natural uncolored sound down to the lowest midrange regions and
so unstressed as to evidence perfect impulse behavior far bejond 2 kHz.

Also in 1996, in our quest for continual improvement we abandoned the metal dome high frequency drivers
which we used for over ten years. They were replaced by the world standard of audiophile tweeters, the
fantastic ScanSpeak D2905 / 9700, a remarkable silk dome tweeter who provides improved definition
and accurate high frequency reproduction. The magnificent result of this neverending quest for sonic
perfection is our top design speaker: the Studio 90 TL.

Today, in September 2002 we introduce a new and improved version, the Studio 100 TL. The bi-radial bass
unit, despite of some changes more than 20 years old, will be replaced by a new and special Scan Speak
25 W 8565-AOS. The acoustical and technical aspects are perfect (typically Scan Speak). Distortions are
remarkably lower, higher power handling is possible and most of all, the bass section is more quick more
powerful, more dry. Only reason to mourn: the cabinet is 20 mm wider.

John Wright died after a short illness on June 1, 1999. It is a loss for all lovers of transmision line speakers.
John and I were friends for many years. I learned a great deal from him. I am committed to continuing John's
ideas and ideas using the best knowledge and preserve and maintain the
transmission line techniques.

Starnberg, March 2001 (revised Sept. 2002)

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