custom posts type with custom taxonomy wp_query

I having some difficulty figuring out how to query a custom post type in a specific (custom) category..

So far I have the following code in my functions.php

function post_type_discog() {

 register_post_type('discography',
  array(
    'labels' => array(
    'name' => __( 'Discography' ),
    'singular_name' => __( 'Discography' ),
    'add_new' => __( 'Add New' ),
    'add_new_item' => __( 'Add New Discography' ),
    'edit' => __( 'Edit' ),
    'edit_item' => __( 'Edit Discography' ),
    'new_item' => __( 'New Discography' ),
    'view' => __( 'View Discography' ),
    'view_item' => __( 'View Discography' ),
    'search_items' => __( 'Search Discographys' ),
    'not_found' => __( 'No Discographys found' ),
    'not_found_in_trash' => __( 'No Discographys found in Trash' ),
    'parent' => __( 'Parent Discography' ),
   ),
      'public' => true,
      'show_ui' => true,
   'exclude_from_search' => true,
   'hierarchical' => true,
   'supports' => array( 'title', 'editor', 'thumbnail' ),
   'query_var' => true
   )
   );
 }
 add_action('init', 'post_type_discog');

 add_action( 'init', 'create_discog_taxonomies', 0 );

 function create_discog_taxonomies()
 {
   // Add new taxonomy, make it hierarchical (like categories)
   $labels = array(
     'name' => _x( 'Recordings', 'taxonomy general name' ),
     'singular_name' => _x( 'Recording', 'taxonomy singular name' ),
     'search_items' =>  __( 'Search Recordings' ),
     'popular_items' => __( 'Popular Recordings' ),
     'all_items' => __( 'All Recordings' ),
     'parent_item' => __( 'Parent Recording' ),
     'parent_item_colon' => __( 'Parent Recording:' ),
     'edit_item' => __( 'Edit Recording' ),
     'update_item' => __( 'Update Recording' ),
     'add_new_item' => __( 'Add New Recording' ),
     'new_item_name' => __( 'New Recording Name' ),
   );
   register_taxonomy('recordings',array('discography'), array(
     'hierarchical' => true,
     'labels' => $labels,
     'show_ui' => true,
     'query_var' => true,
     'rewrite' => array( 'slug' => 'recordings' ),
   ));
 }

Which works great (on the surface at least!). I can create a custom post type (which I can retrieve with WP_Query like so:

<?php
    $new = new WP_Query('post_type=discography');
    while ($new->have_posts()) : $new->the_post();
     the_content();
    endwhile;
?>

But if I add a category I can’t seem to filter my results as I normally would, by adding:

category_name=”my-category”

to the WP_Query

$new = new WP_Query('post_type=discography&category_name=my-category');

This won’t display anything! I’ve tried renaming ‘category_name’ to ‘recordings_name’, but then it just displays all the entries in that custom post type.

Help!