The HPNC300s' noise-cancellation circuitry runs on a single AAA battery located above the right ear cup. The lengthy 5.5-foot cable is fitted with a 1/8-inch stereo miniplug, and RCA throws in an airline adapter as well. Three hinges built into the band let the headphones fold up for storage in the supplied carry pouch.
Aside from a few accessories and the folding design, low price is the sole upside to the HPNC300s. We found them uncomfortable to wear over the short or long term; the ear cups are nicely padded, but they exerted too much pressure on our outer ears. Furthermore, their sound quality was far below that of our $10 Sennheiser PX 30 headphones, and their noise-canceling effect was barely noticeable. All kinds of music we listened to over the RCA HPNC300s exhibited an annoying, canned quality; the tunes sounded stuck inside our heads. Moreover, bass response was lumpy and treble was dull.
The noise cancellation's most obvious effect was to raise the music's volume level. That's a good thing, because even with the boost, the HPNC300s wouldn't get terribly loud with our Jens of Sweden MP-110 MP3 player.
We didn't rave about Sony's MDR-NC5 noise-canceling headphones, but they were more comfortable and sounded a bit better than the HPNC300s. If you can spend a little more, consider moving up to Shure's E2c in-ear headphones. Their noise-isolation design works better than the RCA model's noise-cancellation electronics, and they offer better sound quality and performance.