I am using documents sent to me by Violet of Passion Elipson and Patrick Pennetier from Hifi-Antique. So thanks to both for their help.
This little known family of speakers from Elipson seems to be an attempt to capitalise on the success of the 1303, the first product designed under the new ownership of Mr Bonnet de la Tour and a departure from the plaster cabinets to more conventional MDF, in an attempt to conquer the traditional hifi client (and the dealers...).
It was a successful strategy, specially because the 1303 was a very good product keeping all the same design principles as the original spheres, i-e time alignment, and resonators to provide exceptional transient response and excellent midrange.
The 1800 series seems to be an attempt to simplify manufacture and get rid of the resonator(s), at least in the entry level model, the 1801 Prelude.
From the review below, published by Stereoplay, a French magazine of some fame at the time, you can see that it is quite a good bookshelf speaker, equipped with a popular 17cm driver from Focal, the 7C02 and the famous TWM from Siare, which equipped the top of the range 4050. The filter is 12db/oct electrically, and very well made, but certainly not over the top - no impedance compensation for example.
It was sold for under 3500 francs at the time, a month salary of a electronic technician at the time.
The third harmonic distortion is less than 0.3% past 100Hz, a great achievement. It would certainly sound pretty good, and it is exactly what Yves Dupre says in his review.
ELIPSON 1800 SERIES
MODEL TYPE DRIVER POWER IMPEDANCE FREQ RESP ±4dB/Hz EFFICIENCY DIMENSIONS in CMS WEIGHT FINISH
1801/11 2 170/19 50W 8 Ohms 60/20000 86dB 41x20x20 8KG WALNUT
1802/12 3 170/110/19 75W 8 Ohms 50/20000 88dB 80x23x25 12KG WALNUT
1803/13 3 170/80/25 100W 8 Ohms 45/20000 87dB 89x23x29 17KG WALNUT
1804/14 3 210/170/25 100W 8 Ohms 40/20000 86dB 102x28x36 25KG WALNUT
1815 3 250/210/50x20 130W 8 Ohms 32/20000 88dB 116x33x40 35KG WALNUT
1805/06 4 2x250/250/130/50x20 150W 8 Ohms 30/20000 88dB 101x45x50 45KG WALNUT/OAK