ITT Schaub-Lorenz D 250 SD Symmetric Drive [Scan-Speak 21W-3804 & Scan-Speak D-3804], 1970-1972, made in Denmark

Link: troelsgravesen | diyaudio

The bass driver cone is made from long-fibre paper pulp, today only found in the ScanSpeak 18W/8542-00 driver - and not to forget, the JA8008. To my ears, a cone material that can deliver excellent midrange quality. The voice coil is wound on a 38 mm aluminium former ensuring good power handling compared to coils wound on the usual paper former of that time. The driver display a nice smooth response only up to 800 Hz, from where a steadily decline is seen. Why this is so is a hard to tell, but the surround, a relatively weak magnet and lack of dust cap may all play a role. Mms should not necessarily count for an early roll-off.

The D3804 domes are quite sensitive displaying some 92-93 dB/2.8V/1m and with a little creativeness, a two-way system can be modelled with a decent flat response up to 16-18 kHz as can be seen below.

SD (meaning): Symmetric Drive
Woofer: Scan-Speak 21W-3804
Tweeter: Scan-Speak D-3804 38 mm 4 Ohm (Dynaco / Scandyna A-25)

Specifications to DIN 45.500
Frequency range: 40-20.000 Hz
Sensitivity: 2,5 W (96 dB/1 m)
Impedance: 40
Power rating: 50 W
Music power: 100 W

Impedance: 8 Ohm
Dimensions (HxWxD): 50x29х25 сm
Volume: 24 litres

Weight: 10 kg