Accepting a friend's challenge, I've started a DT770 mod.
The DT770 is legendary as the original bass monster in full-size headphone land, and you can hear versions of it going up the beyerdynamic product line - in the DT880, the DT990 and the revolutionary T1.
For true bassaholics, this is a wonderful headphone, though there are costs to every set of design choices. In the case of the DT770, there's that closed-can sound just screaming to be opened up. My friend and I both wondered if this could be done without sacrificing the one quality for which the DT770 is the stuff of legend: thumping, pounding bass.
Two features of the DT770 are the rounded, semicircular backs and the velour pads. My assumption, going in, was that the closed-back add slam to the bass while the velour pads are not only comfortable and stylish but their semi-porous nature lets the drivers breathe without losing the bass.
These velour pads are basically velour-covered cushions glued to vinyl mounts which fit on and over the attachment rings on the sides of each cup. Notice how the vinyl has holes in it to allow transmission of sound into the pads. Some may argue that this co-opts the pads as partial filters.
Speaking of filters, each driver is lightly filtered by a thin circular pad that sits over the driver and baffle. Each filter is anchored by a plastic outer ring.
Removing the ring is fairly easy once you apply the right force. I slid a butter knife between the pad and the lip of each ring and leveraged it up.
Once the ring is gone, removing the pad is just a matter of grabbing it. Nothing else is holding it on.
Behind each pad is the glowing heart of Iron Man, or maybe it's just what happens when my flash attempts a photo-op with an all-white baffle.
Without the flash, you can see the baffle, which is just thin paper covering the driver grill. The idea behind such a contraption is to make it possible for hard-hitting bass to turn the paper into a ring of passive radiators. The back wave, as it bounces into action, adds volume to the bass.
Removing this paper baffle was as simple as getting a butter knife behind it and applying some leverage. To get "behind" the baffle, you have to find a slight opening between its outer ridges and the inner walls of each cup.
Flipped around, the baffle reveals a Grado-style shell, albeit one made of plastic and semi-open, a kind of circular comb.
I wondered what the theory was behind this curious contraption, a Grado-style air chamber with a porous comb-formation clothed in a cotton ring. I suspect it's an attempt to control standing waves. There's no question the paper baffle is meant to provide bass extension of the back wave but this cotton ring slows things down a little, damping unwanted resonances off of a plastic back.
The cotton ring is made of material reminiscent of the cloth in a Christmas display or on a Santa-ready chimney stocking.
This satellite-looking back gives you an idea of the aim behind the comb shell and cotton ring. The DT770 was designed to target that sweet spot between hard-driving bass and boomy, resonating bass.
Grado owners may be shocked to find plastic back here and no metal backplate.
The "comb ring" comes off easily revealing a plastic-backed driver that looks like it belongs in a Lego box.
Here is the driver. This picture doesn't quite do justice to the metal grill covering it but when all is said and done, the driver on the DT770 is the same size as that of any Grado. Could it be that these drivers are more related than people think? On it, you'll see a ring of eight uncovered holes that allow the driver to vent into the rear chamber.
I didn't get this driver wet. What you see is driver doping at its most basic and most blunt. Each driver is covered with a rubbery add-on that provides additional mass and suppresses cone breakup.
Discovering this gooey (though not sticky) rubbery face was something of a surprise. What may or may not be a surprise is the size of the magnet, which is right about the size of a Grado magnet.
One issue I wanted to explore was the degree to which these headphones employ good wiring to give them solid bass response.
Without directly criticizing the design, let me just say that I was surprised at the diameter of these wires in what is essentially a three-connector operation. To its credit, beyerdynamic gets a lot of play out of wire this thin.
Here's a better picture, providing a better perspective on the relative size of these wires.
One thing that struck me, as I was looking at the back of this driver, was how the T1 driver seems to employ a metal version of this plastic basket. Giving the T1 its due, and noting how its "Tesla" driver employs a ring magnet and achieves "values of over one Tesla (a unit of measurement for magnetic flux density)," I still can't help but see a family resemblance between the DT770 and its "revolutionary" big brother.
Having pulled it all apart, the next question was whether anything could be done to capture all that bass while also opening things up a bit. To this end, I brought in a cocobolo ring I made.
Well, okay, I brought in two cocobolo rings - an innie and and outee. The smaller innee was just about the right size (maybe a little tight) for a Grado-like first-stage shell. One issue is that beyerdynamic, much like Sennheiser, attaches the terminals to angle straight out from the driver, rather than tucking behind it.
As you can see here, the terminals poke out, making further insertion into the cup impossible, though it's a problem easily remedied. If one wanted to use the smaller shell, one would need to make some holes or carve out some space for these pesky terminals. An alternative solution - bending the metal - may be too risky.
Here's a quick and dirty version of the DT770 driver shelled like a Grado.
An alternative, one I liked better, was to go back to the baffle disc and apply the larger shell. To my ears, this provided better, deeper bass. Part of that is the disc, which provides a remedy for the infamous baffle effect (where bass slips around the back of the speaker enclosure - which is why you may get complaints from your neighbor behind the wall when you thought your bass was hardly "cranked up"). Grado doesn't use such a baffle because it wants to anchor its cushions to a ring that extends just past the edge of the forward shell.
I'm not suggesting that this is the final answer to the question of how the DT770 can be more open without losing bass, but in my A/Bing the original design with this tentative solution, I was impressed at how much better the DT770 sounded, at least to my ears. The bass was still there but the canniness was gone.