How to hide header on certain pages?

This is useful. How to hide the nav bar that is just under the header that contains the logo, menu, search field and who is logged in?
I am able to use the following to remove most of the items, but, the bar is still there:

$xt->assign("menu", "");

$xt->assign("logo", "");

$xt->assign("username", "");

$xt->assign("navbar-header", "");