Sony MDR-NC500D Digital Noise-Canceling Headphone

I bought these headphones after trying them out at Narita airport in Tokyo earlier this year. I didn't have time to charge the internal battery before the flight, so I used AA batteries in the included adapter cable. That was the only time that I used the external battery. I've logged about 75,000 air miles using these headphones without a single problem.

The noise reduction is excellent, and the headphones are quite comfortable. The digital technology allows the user to adapt the noise reduction curve to the ambient conditions.

Yesterday I swapped headphones with a friend while riding in the back of a Canadair regional jet between San Francisco and Albuquerque. Those of you who have ridden in that section of this aircraft know that it's one of the noisiest rides around. I found that I could barely hear my iPod with his noise-canceling phones, while listening was easy and enjoyable with the Sony digitals.

Since they're digital, the phones are thicker than other brands. That's not a big problem for me. However, the huge case is a problem and doesn't fit easily in my briefcase, so I've started carrying the headphones in a stuff sack with another sack for the charger and other accessories. Everything now fits fine in my briefcase and carry-on.

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The headphone has 3 modes of operation for different noise environments: Office, Bus & Airplane.

The noise cancelling is great when working, mainly for Office mode; for Bus & Airplane modes, the headphone easily gets into very low frequency (~3Hz) pumping (oscillation) depending on how it's worn, and the pumping is very strong and it hurts! This problem is repeatable with two brand new sets on four 13+ hour international flights.

When worn tightly with no air leakage (better for noise isolation you would think), it easily get into low frequency pumping, for both Bus mode & Airplane mode; office mode is OK, but the noise cancelling is not as good as the other two modes for airplane noise.

When worn loosely, it works great. It appears that the headphone needs high noise leakage to the internal noise pickup microphone to function properly, but not everyone likes to leave big gap when wearing the headphone, and sometimes it's not the comfortable position.

Office usage is good, haven't used it on bus ride, so no comment for bus ride usage.

For $400, this is not acceptable at all! Once this problem is fixed, it'll be a 5 stars product.