Its actually your speaker that consumes alot of electricity....LCD consume minimal electricity than the old TV set.

I'm assuming home theater system means you have LCD/plasma TV, AV, amp, DVD/bluray player, etc. Of all these, the AV component consume the most watt. Apart from that, the longer an electric device turns on, the more it will consume electricity due to the heat.

Most home appliances consume high electricity in the form of heat....such as, iron, toaster, rice cooker, fridge, air conditioner. Other than that, your washing machine is also a beast when consuming electricity. So in order to save on your electricity bill, you need to learn how to maximize the use of your appliances with minimal ON time.

Doing things like washing machine on MAX load, ironing all your weekly clothes in one go, turn off any switches/plugs you don't use, open your fridge only when necessary, etc will contribute to save more on your coming bill. There's lots of info on saving in the net...try look it up. Your home theater is only a slice of what your electricity bill is.