Subwoofer was made to get most of the closed enclosure. Expected effect was fast, energetic bass with not too much heavy booming.
It had to be in time with overall reaction of main speakers. Sub bases on polish speaker STX W.30.200.8.MC and an amplifier
also produced in Poland. Fully airtight sealed enclosure made off 25mm MDF planks. Quite heavy...
Closed speakers of monitor type, manufactured in Germany around 1979. Typical example of speakers from so called "Audio Golden Era". Relatively small, with big bass speaker, three way construction equipped with attenuators for mid and high frequencies allowing to decrease amount of mids and higs. Not so often used - fuses for each driver separately. Very rare box finish - made off a full wooden walnut planks. Below you can see original page from company leaflet.
Measurements made unveiled also their sensitivity at 1W/1m. It is around 89dB. Crossover is 2nd order reversed polarity.
As every single example of vintage audio they needed some treatment to start work and look good. Recent owner covered boxes with lacquer, which got old and changed colour to orange. Removing it was hard, but effect worth work. On the left original one, right - after lacquer remove. Nice!
Another problem is usually deteriorated foam ring around bass driver. Fortunately previous owner made a replacement. Unfortunately - with a wrong foams. They are too stiff and seriously restrict speaker cone movement, so they need to be replaced to correct ones. That is to be done soon.
Next thing to do with such old speakers is to recap the crossover, replace acoustic fill inside boxes and replace all seals under drivers. Quite common in 1970's was underdamping of closed boxes and complete lack of internal walls damping.
