Here's a link to a web page that may help you:

http://www.customaudiodesigns.co.uk/...g/underlay.htm





In article ,
says...
Hi Folks,

I'm the proud dad of 11-year-old twin boys. Unfortunately, their
bedroom is right above the dining room and when they jump from their
bunks the whole ceiling shakes and booms.

As part of a renovation project I will have the DR ceiling open and
will have access to the joists. What could I do to stiffen the floor
above and silence some of the noise? (I'm thinking ahead to the
boombox days coming soon, too.)

The DR is 12x16 with 2x10 joists running the long way, 16" o.c. Would
adding more blocking or sistering the joists with 2x?s work, and which
would be better? What about insulation? I'd like to do this as cheaply
as possible (of course!)

Thx,
Mitch