The sound distribution for a big project as the famous «Exposition Universelle de Bruxelles» in the year 1958 - the mythic «Expo 58» ! - was a famous challenge for the engineers and technicians of this era.

First, the size of the place : more than 200 hectares, and more than 2 kilometer total lenght !

Also the different music program zones and the amount of sound points...

And then, the wish of a optimum quality.

Informations of this page are coming from a text of R. Deschepper in the magasine «Toute La Radio» (belgian edition) , september 1958. About pics and documents...

The exhibition plan made by the Exhibition technical department creates zones like this : (see the numbers ont hte drawing) :

• Green Zones : Program A (belgian zone)
• Gray zones : Program B (foreign zone)
• ⊕ : Bird singing program
• - - - : wires connections
• 1 : Broadcasting central
• 2 : Grande esplanade
• 3 : Jardin des Quatre Saisons
• 4 : Grand auditorium
• 5 : Pavillon de l'Elegance
• 6 : Pavillon de la Françe
• 9 : Silent zone (park)
• 10: Playground (with independant program)
• 11: Belgique Joyeuse (avec diffusion indépendante)

When making the project, the team has seen wired junctions were impossible, beacause of the exhibition size and land configuration. Mister François Landrain, technical adviser of the «Commisariat Général», has suggest radio broadcasting links.

Because of the high level of sound quality asked, the choice of FM modulation with metric waves has been made.

All of this has been decided in march 1957, meaning the company who make the installation had only less than one year to design, build and test all the system! The exhibition start April 17, 1958.

The SBR company make the senders and receivers. The loudspeakers, Goodmans brand, were supplied by the Ivens company.

Broadcast room. (clic on pic to enlarge)

We can see three of the five senders, the tape players and control panels.

The sound central was installed in the Grand Palace.

The central has a few rooms: Sender room (see pic), one studio, one mixing room, two speakerines rooms, tape recording rooms, spare parts.

The central has broadcast all the time three musical programs. Two by radio broadcast, (one for the belgian zone and one for forreign zone), and one by wires to the «Jardin des Quatre Saisons» (garden of four seasons).

A fourth program was composed only by bird songs, and was for the sound points inside the nature parts of the exhibition.

There was three senders always broadcasting (2 musical programs and the birds song), the two others were for spare.

One of the five SBR transmitters. The left panel has all the modulation controls, the right panel has all the high-frequency stages controls.

Every transmitter was 250W output power, and the broadcast frequencies (quartz stabilized) were : 76,60 ; 76,95 ; 77,65 ; 78,00 and 78,35 MHz. This was a choice, being out of the FM radio range, to avoid problems with the existing stations. The system has been received over 100 kms away from Bruxelles...

Antennas were simple di-poles, placed on the roof.

All programs were recorded on magnetic tapes (38cm/sec), but it was also possible to broadcast on the plant live radio stations. Of course it was also possible to make calls and announcment with microphones.

Only one operator was enough to maintain the system. He just has to take care of the magnetic tapes, change this ones and check the equipments.

Large part of the magnetic tapes comes already recorded from a music company, others were recorded on place from discs or radio stations. One music specialist was part of the staff, to compose good music programs and content every visitor. There was almost no claims about that.

The bird songs were recorded by an english specialist, Mr. L. Kosch.

A sound point used in gardens.

Every point included the loudspeakers, the 10 watt amplifier (EL84 push-pull), the receiver. A simple power mains plug was enough to start one sound point !

The advantage of this system was obvious. If a supplemental point was needed, only bring one and plug it on mains, without amplifier output impedance problem (like in wired systems)

Every point was adjustable on every broadcast frequency, and the sound power was adjustable.

Another sound point, designed to be a support for flower decoration.

Wall-type sound point.

All of this sound points were designed to be used outside, even with the belgian waether !

Then tropicalized material has been used (to be moist-resistant) and the boxes were metallic water-proof designed.

Metallic external decoration with holes gives the final look...

General use sound point.

All the sound system has been unplugged from mains during the exhibition. This for two reasons : during the tests, engineers discovered that power up and down every day had a negative effect on the equipement life ; but also by staying powered, it was possible to make general calls on the complete site during night and day.

All of these sound points were realized industrially, and used the printed-circuit technique. This was new at this era...

Every sound point was fitted with four 20cm-diameter loudspeakers, but also with a squelch system, to avoid noise production when there was ne reception of signal from emitters.

All in all, there was more than 450 sound points (every model) for the whole exhibition.

Some links were wired, because wery close to the central system.

In the «Grande Esplanade», it was needed to use local loudspeakers for some fairs. It was the same for the «Grand Auditorium» and for the «Palais de l'Elégance».

The «Jardin des Quatre Saisons» was wired also, but with a special quality sound-system. It was really open air Hi-Fi. It uses three 60W Williamson amplifiers, one of the 3 sypplied 120 high frequencies loudspeakers, and the two others supplied 40 big low frequencies loudspeakers. All of these loudspeakers were installed in special cabinets, all independant from each other and placed everywhere in the garden. Frequency separation was made by a preamp with filter, before the amplifiers (active system).

The music program was high quality 18th century music.