I've had the 840s for about week now. Here's what I think I know so far:
The first hour out of the box is pretty scary. Mechanical, congested - not a pretty picture. I think they start breaking in pretty fast, but they went in a picnic cooler with a bath towel for a while.
After about 48 hours in the cooler, they sounded like different cans. Quite punchy, a little rise in the mid treble and engaging but discombobulated bass. Bass sounded like it was from a different pair of 'phones. Very disconnected from the rest of the spectrum. Back in the cooler.
After 72 hours, things had smoothed out a lot. Now there was a bump in the bass that imparted a "one-note" effect, but it was obvious that things were still a-changin'. They had become enjoyable cans. (They sounded much better through my Woo 6 SE's high impedance outputs than through the low impedance jacks, BTW. I guess when Jack says the low jacks are for 32 Ohms or less he means 32, not 44) Midrange resolution and timbre were good, but sometimes the midrange seemed recessed. I didn't buy them to use on my home rig though. It's not fair to expect them to be reference-level phones and they're not likely going to be.
I bought them to use with my portable rig. So, they went there next. On my iPod and RSA Tomahawk they sound right at home. In this context, they are immediately engaging. Resolution across the band is very good, there's lots of bass, reasonably tight and with good impact, and the midrange generally sounds about right. Mid treble is a bit hot sometimes, but upper treble seems a bit rolled off. I do not find them bright, though. I can't abide bright and these cans present no problem in that area.
On some material, the rising top and bottom still make the mids sound recessed. But most of the time, it makes for a "fun" listen, good for most blues and rock, and for me anyway, small group jazz came off very nicely.
Shure says these cans are intended for the home studio pro/semi-pro market (although I would certainly look at the flatter 440 instead of the consumer-oriented 840 for that use.) Some features caught my eye as being right on point for pro use - the headband that's padded on all sides, for example. These cans are quite comfy when pulled down around your neck. And the top of them won't tear stuff up.
The coiled cord would be great plugged into a board or computer or camera at work. But at home or on the portable rig, it's a pain in the neck. So shortly after it snapped back and hit a sensitive part of my body (Thumbnail.
What were you thinking?) I made up a straight cable from some Mogami Mini-Quad that I had on hand. Much easier to live with. (And thanks to Shure for using a more-or less standard plug on the cord!)
With the Mogani cable, both bass and treble smoothed out some more. Midrange is now just about right on and rarely sounds recessed at all. But the bass is huge. Probably too huge. Giveth with one hand and taketh away with the other. So I guess the hunt will be on to find wire that really does the deed. And while we're in Tweak Land, the more neutral 440s with 840 ear pads might very well be worth investigation.
The cliche "spouse test": My wife stopped on her way out of the room for a few-seconds listen. About twenty minutes later, she handed the portable rig back and declared the 840's "pretty sweet". So, I guess overdone bass possibly not withstanding, they're keepers.
-Carl
