Closed-back, over-the-ear (circumaural) headphones were the original noise-isolating headphones. Closed-back headphones seal your ears off from external sound, but the isolation is purely acoustic; noise-canceling headphones use electronics and do a slightly better job of blocking noise.
But there are a few downsides to that approach; noise-canceling headphones always use batteries, and on some models when the batteries run out of juice, the party's over. No more music. The noise-canceling signal puts a small amount of pressure on your eardrums, which some people find uncomfortable.
The other, bigger downside to noise-canceling headphones are their electronics, which can degrade the music's sound quality. Dollar for dollar, closed-back models block almost as much noise, and always sound better.
The closed-back Shure SRH940 is fairly light (11 ounces), and the thickly padded headband and plush velvet earpads make for headphones that are extremely comfortable to wear over long periods of time. The earcups' decorative covers appear to be metal, but there's lots of gray plastic in the design, which is why it feels so light and comfy.
Despite all the plastic, the SRH940's durability seems first-rate. It's a collapsible design with 90-degree swivel earcups for convenient storage and portability in the supplied semihard storage case.
The 42-ohm SRH940 headphones come with two detachable cables--a coiled 9.84-foot cable and a straight 8.2-foot one--and thanks to the bayonet clip mount, you never accidentally yank the cable out. The cables are terminated with 3.5mm plugs at each end, and there's a screw-on 6.3mm adapter for home use.
I did the bulk of my home listening with the Centrance DACport digital-to-analog converter/headphone amplifier (review in the works). These headphones deliver an extraordinary amount of detail and resolution, but it's easy to listen to for hours on end. There's no pumped-up bass or any other frequency range, the SRH940s just sound accurate. Well-recorded hand drums and percussion sound right, so you hear more of the tactile "feel" of hands on drums; the Sennehiser HD-650 full-size headphones sound more distant, and the drums' dynamics are restricted. On their new "Helplessness Blues" CD, the Fleet Foxes' vocals, bathed in reverberation and spread across the stereo soundstage, are a thing of beauty.
The SRH940s are much more open-sounding, and less stuck inside my head than the closed-back V-Moda Crossfade M-80 headphones. I found their sound superior in every way to the M-80s, and it's also more comfortable on my ears.
I watched some movies with the SRH940s, with a Woo Audio WA-6SE tube headphone amp hooked up to an Oppo BDP-95 Blu-ray player. "Idiots & Angels," a surrealist animated film by Bill Plympton has an especially well-mixed soundtrack, and the SRH940s somehow projected much of that sound well outside my head. I was so engrossed in the film, it was easy to forget I was wearing headphones.
Not all full-size headphones are compatible with iPods, but the SRH940 model is. Its big, open sound field was intact, and while the bass wasn't as deep and full, most of what I liked about the headphones' sound at home remained with my iPod Classic. Bowers & Wilkins' smaller P5 on-ear headphones had a thicker sound balance that emphasized the bass more than the SRH940 on's brilliant self-titled CD. I have no doubt some listeners will prefer the P5's rounder sound, but to my ears the SRH940 sounds more accurate. I could hear the band's rhythm section grooving more on the Shure set; the music was less engaging over the P5s.
MSRP for the SRH940 headphones is $375 and MAP is $299.