Color organs are cheap to build , and to buy . But , if you REALLY want to get the BEST "bang" for your buck , and for a truly GREAT effect , this is a case where speakers play the most important role . You need to have speakers that have good bass to them , and not some cheap tinny sounding el cheapo speakers that you picked up at a flea market , or yard sale . And , they need to be able to crank out some power . The more "rumbly" they are ( without distortion ) , the better they will do .
Myself , I bought some ADVENT 5:1 speaker set with a sub that I use JUST for my thunder storm soundtrack ( yes , they are hidden/protected from the elements ). I use two , floods , one in the front , and one on the side . Both are NOT directly visible from a direct line of sight , which also makes them more realistic .
There is a website that a fellow goes into , in great detail explaining how important of a role , lighting has ( lighting , not lightening ) .
I'll see if I can dig it up . has some EXCELLENT ideas , and believe me .. there IS a major difference in appearance/scare factor , when your lighting is setup properly . And this goes for the fake lightening as well . If they can't see the floods , then the realism is even greater.
Again , cheap speakers for this will not do . The better the speakers , the more realistic the effect will be .