This is a review and detailed measurements of the Sennheiser HD660 S open-back headphone. It is on kind loan from a member and costs US $400.
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You would be hard pressed telling it apart from the similarly numbered Sennheiser headphones which is not a bad thing.
Note: The measurements you are about to see are made using a standardized Gras 45C. Headphone measurements by definition are approximate and variable so don't be surprised if other measurements even if performed with the same fixtures as mine, differ in end results. Protocols vary such as headband pressure and averaging (which I don't do). As you will see, I confirm the approximate accuracy of the measurements using Equalization and listening tests. Ultimately headphone measurements are less exact than speakers mostly in bass and above a few kilohertz so keep that in mind as you read these tests. If you think you have an exact idea of a headphone performance, you are likely wrong!
Fitment on the fixture was easy.
Sennheiser HD660 S Headphone Measurements
As usual we start with the headphone frequency response as comparison to our preference curve:
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We have our typical loss of bass response and deficiency in lower treble which likely quashes its spatial qualities. Not sure what is up with that peak resonance above 5 kHz. EQ is mandatory and here is the graph to build from:
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Distortion is similar to other Sennheisers being dominant in bass:
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The redesign from HD650 seems to have been to lower the impedance:
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This is half as much, reducing the dependency on high output voltage from the amp (i.e. making it more mobile friendly). Sensitivity is average:
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Group delay is messy:
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Sennheiser HD660S Listening Tests and Equalization
Out of the box sound was very good, proving that you need to EQ (or compare to another neutral headphone) to know what you are missing. After inserting three filters, I was shocked how much the tonality and overall fidelity improved:
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The bass boost is self explanatory. The middle filter made a substantial improvement to its spatial qualities which was a delight to listen to now. The last filter doesn't make a tonal difference but seems to have the effect of lowering distortion.
I had an easy time driving the HD660S with my RME ADI-2 DAC. It sounded superb (with EQ) up to reasonably loud levels. Above that I thought the bass became less distinct but that was not safe or long term listening level.
With the EQ I sat back and enjoyed the sound with track after track. Turn it off and sound collapses with a more mundane but not annoying tonality.
Comfort was great compared to my much heavier everyday headphone. But after half hour the tips of my ears were starting to become uncomfortable a bit.
The core DNA of this line of headphones from Sennheiser seems to be maintained in this revision. Response is a bit more rough than HD650 but both need EQ anyway. And with it, you have a very top performing headphone.
I am going to put the Sennheiser HD660S on my recommended list.
As always, questions, comments, recommendations, etc. are welcome.
are much appreciated using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/