I am about to buy this movie (what contains the sensurround sound). Questions is: Do I need to have the AC-3 demodulator to get the ultrasonic bass out of my sub (my laserdisc player has the ac-3 rf output)? Or can I get it with normal composite setup?

If you want to hear the Sensurround mix, it is encoded on the AC3 track which means you need an AC3-RF Demodulator (or older Processors / AV Receivers that had them built in) to extract it.

Hooking up the left / right analog or optical output will give you the standard Dolby Surround mix that might be a fold down of the Sensurround mix but I have no idea if that was done.

More information here….

Alien (1979) [8760-85]

Yeah, you’ll need the AC-3 demodulator if you want to actually get the discrete bass channel out of that RF output. With just composite you’re only getting the analog stereo (or PCM if you use digital out), so no true 5.1/LFE. Without the demod you’ll miss the low-end rumble that Sensurround was known for.

Everything above is correct but FWIW even the PCM track on that disc is SUPER bass-heavy