Released back in the 1988 (yes, 31 years ago!) the Sennheiser HD25 was aimed mainly at film-making and broadcast professionals. The main design goals at that time were sound isolation and an accurate tonal response, so that broadcasters could hear themselves clearly. Over time the HD25 has found itself useful for many applications. From official headsets of the Concorde supersonic airliner to covering a single ear of many DJ’s, the HD25 excels when reliability and isolation is paramount. But what about accuracy? Read on to find out whether a 31 year old headphone can be useful for the modern sound engineer on the go.

Pros
  • Superb isolation
  • Low THD
  • Field repairs possible without tools
  • Generally very durable
  • All parts available from Sennheiser

Pros list with Sonarworks Reference correction

  • Tonally neutral
Cons
  • U-shaped sound signature
  • Not exactly comfortable
  • The cable connection to the earcup is a known failure point
  • Treble rolls-off after 15kHz
Use cases Recommended music genres:
Anything bass-heavy
Best use case:
DJ-ing
Location sound
Tech specs Type
Closed back, On-ear
Impedance
70 Ohm
Distortion
<0.3%
Frequency response
16 Hz to 22 kHz
Connector
threaded 3.5mm angled jack
Adapter
Screw-on 6.3mm adapter
Weight
140 g (without cable)
Require headphone amp
No
Headphone amp

The HD25-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 HD25-II should do fine. Isolation provided by these headphones also means that SPL can be kept down, because it doesn’t need compete with the outside din. 70 Ohm impedance shouldn’t be a problem and allows the HD25-II to be used with up to 9 Ohm output impedance headphone outputs.

Build quality

Sennheiser have a long tradition of manufacturing headphones for professional applications and the HD25-II embodies much of their material science and industrial design know-how. When you pick up the box the HD25-II gets sold in, it might feel that they’ve forgot to put the actual headphones in. At only 140 grams, the headphone feels almost like a toy, almost 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 have 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 HD25-II is indestructible.

Sound

The U-curve strikes again! Mids to upper mids are okay, but the enormous boost at 100Hz will accentuate every bass instrument string or synthetic. The 8kHz peak might be useful to pick out 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 15kHz, 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 what can be found other on-ears at this price segment, like the ATH-M60x for example.

Channel balance

Channel balance on the HD25-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 HD25-II where sound quality is critical.

Comfort

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 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 in to the temples of one’s head. In other words – you’re not buying the HD25-II for the comfort.

Value

This is tricky, as Sennheiser offers the HD25-II in many different packages. The HD25-II can be bought in the “HD25” 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 ATH-M60x. The more expensive “HD25 Plus” package throws in an extra coiled cable, a pouch and a pair of plush earpads which are more comfortable, but have less low end extension and let more sound in.

Observations on how headphones perform after applying Sonarworks Reference correction Total Harmonic Distortion

Generally harmonic distortion is inaudible, which is commendable. The distortion peak at 6khz is narrow enough to not cause trouble, unless precision work is to be done around that area. Not bad for a 31 year old driver!

How accurate and consistent is the correction effect among different listeners?

Consistency is mainly hurt by the fact that the HD25-II is an on-ear headphone. Fit issues will change the sound, which is why one should stick to over-ear headphones when sound quality is paramount.

How much do they differ pair to pair in terms of frequency response?

Consistency in manufacturing is Sennheiser’s forte. The HD25-II is no different and shows very good consistency. Again, real-world consistency will depend on the fit.

Rating

Build 8
Sound 5
Comfort 5
Harmonic Distortion 8
Channel balance
8 /9
Accuracy and consistency
5 /9
Value 8
Out of the box
With Sonarworks Reference correction

Conclusion

After 31 years, the HD25-II has found happy users in its intended broadcast segment, however DJ’s and drummer adore it even more for it’s superb isolation. Ultimately mixing engineers should look elsewhere, unless forced to make do.

Final Rating

7.4
With Sonarworks Reference 4
Calibration Enabled
6.7
Without Sonarworks
Calibration

Remove coloration from your
headphones with Reference 4

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