[warnerwh]

A friend in construction tells me the schools use rigid insulation around the music rooms to keep the sound in. I'm going to need to do some soundproofing in my new house and am looking for the most cost effective way out. Will the rigid insulation under an extra sheet of 5/8" sheetrock help much?  
I'm probably only going to need to do a ceiling or one wall but need to do a decent job as I like listening to fairly loud volume at times. Any help is appreciated

[JLM]

Cost effective options:  

Gauge metal "Z" furring strips that separate the wall/ceiling framing from the drywall.

Suspended ceiling, better yet add loose insulation on top.

Staggered offset double stud walls with loose insulation.  Use 2x6 top and bottom plates.  Frame one set of 2x4 studs along each face of the plates such that each set of studs are offset from the other.  

Replace sheet metal ductwork with lined flexible ductwork as far back towards the furnace as possible.

Replace typical interior doors with weather sealed, insulated exterior doors.

IMO anything "rigid" transmits vibrations more than something "loose".