$ruum_like = "%{$ruum}%";
$stmt->bind_param("sss", $end, $start, $ruum_like);
$stmt = $db->prepare("SELECT ... WHERE field = ? AND field2 LIKE ?");
$stmt->bind_param("ss", $val1, $val2);
$stmt->execute();
$result = $stmt->get_result();
while ($mytable = $result->fetch_assoc()) {}