Instruct: Classify Amazon reviews into positive or negative sentiment
Query: MDR-NC20's are great. MDR-NC50's are LOUSY

The SONY-NC20 Noise cancelling headphones are great. Unfortunately, they have been discontinued.I was able to find them listed on Amazon.com, and ordered them. However, the vendor sent MDR-NC50's, evidently the replacement model, and far inferior from an audio standpoint.The vendor agreed to return them, but I was responsible for shipping them back.Wearing the MDR-NC50 headphones yeilds an unpleasant "negative pressure" sensation on the eardrums. The sound, when using NC feature, also suffers, and is very "canned".