Display custom post types with custom date field value (before today) & order by custom date field

I prefer to use WP_Query (for more info read “When should you use WP_Query vs query_posts() vs get_posts()?“), try this way:

$args = array(
  'post_type'      => 'soiree',
  'post_status'    => 'publish',
  'posts_per_page' => -1,
  'orderby'        => 'date_de_concert',
  // you don't need 'meta_key' => 'date_de_concert' when using meta_query
  //'meta_key'     => 'date_de_concert',
  'order'          => 'DESC',
  'meta_query'     => array(
                        array(
                          'key'     => 'date_de_concert',
                          'value'   => strtotime( 'today' ),
                          'compare' => '<'
                        )
                      )
);

$concert_query = new WP_Query( $args );

if ( $concert_query->have_posts() ) : while ( $concert_query->have_posts() ) : $concert_query->the_post();