Sennheiser HD 25-II Studio Headphone Review

The HD 25-II is right on the border between efficient and inefficient headphones. On smartphones and dinkier laptop headphone jacks, one might feel the lack of volume headroom, whilst with most modern audio interfaces the HD 25-II should do fine. The isolation provided by these headphones also means that SPL can be kept down because it doesn’t need to compete with the outside din. 70 Ohm impedance shouldn’t be a problem and allows the HD 25-II to be used with up to 9 Ohm output impedance headphone outputs.

Sennheiser has a long tradition of manufacturing headphones for professional applications and the HD 25-II embodies much of their material science and industrial design know-how. When you pick up the box the HD 25-II gets sold in, it might feel that they’ve forgotten to put the actual headphones in. At only 140 grams, the headphone feels almost like a toy, nearly everything is made of plastic, save for the screws and actual conductive surfaces. Only once you’ve used them for a while you realize that the plastic Sennheiser has used stands up to everyday abuse perfectly. This plastic is unbreakable, you can bend it obscenely and it will flex back. Having owned these headphones for 2 years, only two weak points presented themselves. The cable connections at the earcup can start losing contact, especially if the cable gets unplugged frequently, the fix is to bend back the contact surface with a needle. And the ratchet mechanism which holds the earcup to the headband can become loose in time. Other than that, the HD 25-II is indestructible.

The U-curve strikes again! Mids to upper mids are okay, but the enormous boost at 100 Hz will accentuate every bass instrument string, or synth. The 8 kHz peak might be useful to pick out a hiss, but for mixing or mastering it’s a no-go. The peak will overemphasize overtones, making the engineer attenuate them too much thus resulting in a dull sounding mix. What’s more – the treble response drops like a rock after 15 kHz, which might not be an issue for older folks, but people under 30 will certainly feel a loss of “air”. Generally, this frequency response isn’t drastically worse than that of other on-ears at this price segment, like the Audio-Technica ATH-M60x for example.

Channel balance on the HD 25-II is fine, which isn’t surprising for a Sennheiser headphone. What can mess up the channel balance is a problem that’s inherent in all on-ear headphones – the sound varies, depending on the headphone’s position on the listener’s ears. This is another strike against using the HD 25-II where sound quality is critical.

You don’t want to be wearing them for too long. The pads are covered in a nylon-like cover which provides superb outside noise isolation, however, it can get rather sweaty after a few hours. The headband itself isn’t too bad, but the HD25-II relies on a rather strong clamp to keep the earcups snug on your ears. The clamp can get especially brutal if the listener is wearing glasses because the legs will probably get pushed into the temples of one’s head. In other words – you’re not buying the HD 25-II for comfort.

This is tricky, as Sennheiser offers the HD 25-II in many different packages. The HD 25-II can be bought in the “HD 25” package for 150$, which is barebones with a single 1.5m straight cable. This is a great deal, as you get the most useful things cheaper than most alternatives like the Audio-Technica ATH-M60x. The more expensive “HD 25 Plus” package throws in an extra coiled cable, a pouch and a pair of plush ear pads which are more comfortable, but have less low end extension and let more sound in.