How many buttkickers do I need for a sectional

I am looking to have a media room in my basement and thinking about putting an L shaped sectional (probably one of the palliser models). If I do this and want to install buttkicker LFEs, is there some rule of thumb for how many I need?) Do I need one per piece of the sectional or if they are all connected will they rumble together.

Also, If I install the buttkicker on convertible bed part of sectional will this cause metallic rattling from the folded bedframe (not sure if anyone has done this but figured it's worth a shot).

Thanks!