gpspake on "posts_where filter doesn't work in a class."

I'm trying to get all of the posts with a custom post type that have been published in the past 5 days.

Although this is overly difficult, and it doesn't look like a better method will be available until 3.7, I've managed to get it working inside of a custom template by filtering adding a filter to posts_where.

The problem is, I need to do this inside of a class and I can't figure out what I'm doing wrong. I'm almost certain that it is my code that is the problem.

Here is the code that works:

function filter_where( $where = '' ) {    // posts in the last 5 days
  $where .= " AND post_date > '" . date('Y-m-d', strtotime('-5 days')) . "'";
  return $where;
}

add_filter( 'posts_where', 'filter_where' );

$args = array(
 'post_type' => 'listserv',
 'tax_query' => array(
   'relation' => 'AND',
   array(
     'taxonomy' => 'listserv',
     'field' => 'slug',
     'terms' => 'staff-listserv'
  )
 )
);

$query = new WP_Query( $args );
echo '<div id="content" style="">';
while( $query->have_posts() ) : $query->the_post();

echo '<a href="#">'. get_the_title() .'</a><br/>';

endwhile;
echo '</div>';

remove_filter( 'posts_where', 'filter_where' );
?>

The problem is, when I put everything in to a class and move the second part in to a method, it simply returns the 8 most recently published posts and pages.

Here's what that code looks like:

class Test_Range {

	private function filter_where( $where = '' ) {    // posts in the last 30 days
	    $where .= " AND post_date > '" . date('Y-m-d', strtotime('-40 days')) . "'";
	    return $where;
	}

	public function range_announcements() {

		$filter_where = $this->filter_where();

		add_filter( 'posts_where', $filter_where);

			$args = array(
							'post_type' => 'listserv',
							'suppress_filters' => false,
							'tax_query' => array(
								'relation' => 'AND',
								array(
									'taxonomy' => 'listserv',
									'field' => 'slug',
									'terms' => 'staff-listserv'
								)
							)
						);

		$query = new WP_Query( $args );
		$announcements = '<div id="content" style="">';
		while( $query->have_posts() ) : $query->the_post();

    $announcements .= '<a href="#">'. get_the_title() .'</a><br/>';

    endwhile;
    $announcements .= '</div>';

		echo $announcements;

		remove_filter( 'posts_where', $filter_where );
	}

}

$testing_the_range = New Test_Range();
$testing_the_range -> range_announcements();

I've been messing with this for hours and I'm not sure what to try next. Any suggestions?