To quote Bobby Owsinksi from his book: The Mastering Engineer's Handbook, 4th Edition:
"The LEDR test is a substitute for about $30,000 to $40,000 worth of test equipment.
Stereophile also has an article about it, written in 1989 (!) by Bob Katz.
Luckily it's 2016 and we don't have to buy expensive CDs anymore, as there is an online version of this test here: http://www.audiocheck.net/audiotests_ledr.php
If the sound for the up image doesn’t go straight up from your loudspeaker,six feet in the air as you sit there in your position,then you’ve got a problem with your crossover or with reflections above the loudspeaker.
If the sound doesn’t travel from left to right evenly and smoothly with the left-to-right test,then you’ve got problems with objects between your loudspeakers.
And the same with the beyond signal, which is supposed to go from about one foot to the left of the left speaker, gradually over to one foot to the right of the right speaker, which detects reflections from the side wall."