Sennheiser makes a lot of headphone models, and it can be a bit confusing to make sense of the lineup. Some models are close cousins, and then it's even tougher to keep track of them all. Take the Sennheiser HD-25 Aluminum ($330), the 25th anniversary edition of the classic HD-25 headphone. Then again, the HD-25 Aluminum looks like a twin of the Sennheiser Amperior ($349), and to keep things interesting Sennheiser just introduced another very similar model, the HD 26 Pro ($320). I don't have an on-ear Sennheiser Momentum ($200) in house to compare, but I know it well enough to say the HD-25 Aluminum and HD-26 Pro both sound better. Sennheiser also offers a non-aluminum HD-25-1 II, which runs $250.
The HD-25 Aluminum weighs just 6.7 ounces, impedance is rated at 70 ohms, and it's designed in Germany but made in Ireland. The HD-26 Pro weighs 6.3 ounces, impedance is rated at 100 ohms, and it's designed and made in Germany. The HD 26 Pro features ActiveGard to protect your hearing from sudden, very loud audio peaks of 105 or more decibels. The ActiveGard function can be turned on and off with switches on each ear cup. Both headphones are closed-back designs that effectively hush environmental noise to a significant degree, and both come with user-replaceable 4.9-foot long cables terminated with 3.5mm plugs, with screw-on 6.3mm adapters. The cables lack mic and phone controls.
The HD-26 Pro's matte and high-gloss black finish looks understated next to the HD-25 Aluminum, and I was surprised by the difference in comfort; the HD 26's lower ear pad pressure and softer cushions make a big difference. The HD-25 Aluminum comes with a nicely padded travel case, while the HD-26 Pro doesn't include a case.
The HD-25 Aluminum has aluminum ear cups, but otherwise both headphones are mostly made of plastic. Even so, they feel ruggedly built and should stand up to some rough handling without falling apart. Both headphones come with two-year warranties -- that's double the length of coverage of most headphones.
Plugged into my iPod Classic, the HD-25 Aluminum's deep bass definition is phenomenal. Treble clarity is exceptional -- the detailing on percussion instruments and drums is awe-inspiring. There's an immediacy to the presentation I find irresistible. Comfort is good, though the ear pads' clamping pressure is a tad high, but these headphones will definitely stay in place if you move around a lot. At home, my Schiit Asgard 2 headphone amplifier ups the clarity a notch or two, and the soundstage width opens up. Vocals on the a href="http://www.amazon.com/XX/dp/B002N1AEN2/ref=sr_1_1?s=music&ie=UTF8&qid=1389364929&sr=1-1&keywords=XX" >XX's first album were upfront and present. Switching over to the V-Moda M80 on-ear headphones pushed bass fullness down, the midrange up, and the M80s lost some treble clarity. The HD-25 Aluminum was clearly better sounding in every regard.
Next up, I demoed the HD-26 Pro, and the sound was even more dynamically alive, spatially expansive, with a sweeter, more refined treble than the HD-25 Aluminum. And thanks to its lower ear pad pressure, it was more comfortable. The HD-25 Aluminum has a fuller, richer balance, but I think the HD-26 Pro is more accurate.
I also compared these two Sennheisers to Bowers & Wilkins' P5 on-ear headphones. First off, the Sennheisers' bass reaches deeper and its dynamic impact is more viscerally felt; the soundstage is bigger, more open and less inside my head. The P5 sounds closer and more immediate, which some buyers might prefer. I didn't, but the P5 scores a decisive win on comfort -- my ears didn't feel as tightly clamped with the P5s on my noggin as they did with either of the Sennheisers.