Description

The HDC 451 NoiseGard mobile set are open stereo headphones with active noise compensation for mobile applications. Powered by two AA batteries, these headphones reduce ambient noise by up to 10 decibels. This functionality protects hearing and reduces stress. The headphones terminate in a standard 0.125-inch miniplug for portable audio systems, plus a 0.25-inch adapter is provided for connecting to home stereo systems and a 2x-mono adapter for airline audio and some other devices.
Technical Details
- Open, supra-aural headphones with NoiseGard technology
- Reduces ambient noise by up to 10 dB
- Improves audio quality in noisy environments
- Compatible with nearly any portable or home system with included adapters
- Requires 2 AA batteries to power noise reduction

Users reviews:
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Amazon reviews:
I put on the headphones, hit the switch, turn on the music, and I can't hear certain distant but extremely annoying coworker phone calls. The sound of the copier fades into nothing. I can't hear my computer's LOUD fan. And best of all, I'm unaware of my loud coworker's ninetieth retelling of the features of his car to the entire universe. It's just me and my Bollywood, and that's all I need :-)
The headphones are wonderful on the commuter train. I can hear the loud, obnoxious cell phone callers, but the phones make them seem like a dull background drone. I'm only faintly aware of the Crazy Frog cell phone rings and the loud conversations of people around me. Give me a magazine, and I'm on my own planet. The train noise itself fades to virtually nothing, and I'm shocked by its loudness if I have to adjust the headphones for a moment.
These headphones have not just spared me some annoyance, but they've lowered my stress level considerably and saved my sanity. Considering that I paid full retail for these, and not the nice discount price you see above, I'm still thrilled at the purchase, and would purchase them again for a higher price in a heartbeat.
They also do a good job against co-workers who are under the mistaken impression that nobody can hear their phone conversations through cloth cubicle walls. And they're worth their weight in gold in a hyper-ventilated datacenter!
(I say several pairs because the original wiring design caused a break at the battery pack in pair #1, after 2 years of daily use in commuting. Pair#2 fell victim to a drop after 18 months and the plastic holding the earpiece to the headband snapped. Still a good value at Amazon's price.)
I *would* feel more comfortable schlepping these daily if they folded or had a hard case.
As far as noise reduction, there is a slight improvement. It seems to block out a lot of the residual noises (typing, hum of the AC, conversations across the room, traffic passing, etc.). But I still hear people talking closer to me, phones ringing...more direct sounds. The open-ear design probably makes some difference. But I tend to find the over-ear design hot and uncomfortable with extended use. I think the trade off is worth it.
The cord could stand to be a little longer. On a plane with it sitting in your lap or on a tray table, it's perfect. But plugging it into my computer (even with the jack on the front of my G5) the battery pack becomes awkward and usually gives in to gravity (pulling the headphones off my head).
A little pricey at $99, though. Get 'um down to the $70-80 range and it's a no-brainer. But even at $99 they're plenty comfortable, good sound quality and a solid brand name with a good reputation.
I cannot think of travelling without these headphones. I can clearly listen to the words in a movie and enjoy on-flight music .. as bad as it usually is.
There is a slight pressure on the ear due to the interaction between the low-frequency sound and reverse phase LF emitted my the headphones, so do not leave them on for more than a few hours.
Ive used it with my CD, Minidisk and MP3 players. The batteries easily last for 100 hours. I clip the battery compartment to the seat pocket.
The headphones intentionally let high-frequency sounds through so that you can hear announcements. I wish I could modify the circuit to block out HF sounds as well!