Somewhere out there, perhaps there's an on-ear headphone that beats the overall audio quality, design, comfort, and looks of the Beyerdynamic T51, but I've yet to run across it. Of course, with a manufacturer's suggested retail price of $299, this is a product for dedicated audiophiles.
Let's get the most important thing out of the way first. How good do they sound? One word: great — there's excellent sound across the entire frequency range. The headphones offer pumping, deep bass, lifelike vocals and wide clarity in an immersive soundstage. The mids have clean detail, with small boosts around 95dB and 113dB. The highs are crisp and efficient. I've had all five members of our family test drive the sound — and all found the T51i's audio near-perfect.
The TF1i is also the best-designed on-ear headphone I've used. It avoids the "stuffed" feeling of in-ear earpods, but lacks the propensity for falling off your head or sliding around while you're in motion. This is due to the adjustable headband and swiveling earcups. The earcups fold up compactly when not in use, so you can pack them in the nylon carry case they come with.
Designed for compatibility with the iPod, iPad, and iPhone, the TF1i boasts a convenient three-button remote control and microphone for phone calls and media playback. The headphones also come with a 6.35 mm adapter for use with hi-fi equipment or headphones amplifers, as well as an airplane adapter.
The ear pads themselves are made of soft synthetic leather and sit comfortably over your ears thanks to the memory foam filling. This filling also blocks out most external noise (so use with care if you use 'em while walking). The TF1i also looks great with their "light champagne tone," brushed metal ear-cup surfaces.
If you only occasionally use headphones, there are less expensive alternatives. However, if you use headphones or earbuds constantly and can handle the price tag, the TF1i offers superb sound in a design that couldn't be more comfortable.