Thursday, July 18, 2024

Sennheiser HD 660 S Open Back Headphone Review

Affiliate disclosure: As an Amazon Associate I earn from qualifying purchases. All opinions remain my own. You can learn more about our editorial policies here.

Today we take a look at the Sennheiser HD 660 S Open Back Headphone Review. Sennheiser is a company that knows a thing or two about audio. They have been in the business of making some of the best headphones on the market for over 50 years. In their lineup, there are many different models for various needs and budgets. But what sets them apart from other companies? What makes them so special? Well, we’ll tell you why Sennheiser HD 660 open-back headphones are worth checking out!

The Sennheiser HD660 S has been around for quite some time now. It’s become almost a classic headphone that you can’t help but love. They offer so many great advantages they are hard not to add to any headphone shopping list. The Sennheiser HD660 S features sound quality that is amazing, while the build quality is excellent. If you’re looking for a headphone with great sound and an affordable price tag, then this might be the perfect choice for you.

Sennheiser HD660 S Specs

  • Reference class open back, dynamic headphone employing new and improved transducers delivering low harmonic distortion (learn about Open Back vs Closed Back Headphones)
  • New and improved transducers, combined with a dynamically configured T400 base that opens up back, soft-seal design, make for an open-back dynamic headphone with low harmonic distortion.
  • Transducers are hand selected for precise (1 dB) left / right matching tolerance insure exceptional accuracy and presentation of stereo spatial characteristics

SENNHEISER HD 660 S - Audiophile Open Back Headphone
as of July 17, 2024 7:38 am
  • The impedance, which is measured in ohms, is 150 nominal. It may be connected directly to home and mobile Hires audio devices with minimal degradation of sound quality. Contact pressure was measured at 6.0 N – 1 N
  • Detachable cables with aramid reinforcement and high conductive OFC copper for signal integrity with little handling noise are available.
  • Two connection cables are included: one with a 6.35 millimeter stereo plug and the other with a 4.4 millimeter Pentaconn balanced stereo plug. A 6.35 millimeter to 3.5 millimeter adaptor is also supplied. Wired Connectivity
  • Frequency response 10 to 41,000 Hz ( 10 dB), Impedance 150 ohm

What’s in the Box?

The box that comes with the Sennheiser headphones contains:

1 x Sennheiser Headphone

2 x MMCX connectors

1 x 3.5mm Audio Cable

1 x User Manual

Sennheiser HD 660 Cable
View on Amazon

Sennheiser HD660S Headphone Design Build Quality and Comfort

It looks like an updated version of the popular HD 650 series with an all matte black finish. Except for the outer grill panels, and inner headband; the HD660S’ body is made up almost exclusively from plastic.

Even though the body is mostly plastic, they are still one of the most durable headphones on the market. They’re sturdy enough for daily use, comfortable, and sound great. I’ve owned several pairs of these Sennheisers over the years, and they never fail to impress with the build quality.

Only one part needs replacement—the headphones’ earpads. They tend to wear down quite fast. It may be necessary to replace them once a year or so if you want to keep using them for an extended period of time.

Take your sound to the next level, see our Topping DX3 Pro+ Amp / DAC Review

Similar to the build quality, the comfort of the HD 660 S is top notch. Due to the plastic construction they are lightweight (around 260 grams). The ear cups feature dense foam that is wrapped in velour. Our one complaint is the headphone pads wear out pretty quickly but more about that later.

We did find the force of the clamp to be a little excessive out of the box. As we started to break in the open-back headphone we found it to be more tolerable. We did do a few long listening sessions during the text of 3 hours and did not experience any discomfort after they were broke in. I also rank these as the best headphones for glasses due to the design and comfort.

Sennheiser HD 660 Front
Amazon Detail

Sennheiser HD 660 S Sound Quality

When listening to music through these headphones, you’ll notice how well-balanced the sound is. You will hear every instrument clearly, and the highs and lows are crisp and clear. When listening to vocals, you’ll find yourself singing along to the lyrics as if you were standing next to the singer.

The bass response was god and offered lots of punchy bass. The speed and pacing of the bass was excellent but it defiantly starts to roll off around 80hz. We liked the HD 660 S for almost all the musical genres we tested but the bass roll off will be a consideration if you mostly listen to sub-bass focused music.

The mids are the highlight for me. They are smooth and natural sounding and would say they are defiantly an upgrade to previous models. We found the warm mids perfect for critical listening for these headphones with such a reasonable price.

The highs are bright but not fatiguing. I will note that although I enjoyed the sound it is not a totally neutral sound signature. Overall they sound great for the price range. Sure you can find better pro-style monitors but from a pure enjoyment listening perspective these are hard to beat at the price.

Music Soundstage

We found the soundstage very impressive during our Sennheiser HD 660 S Open Back Headphone Review. When listening to music through these Sennheiser headphones, you get a wide soundstage. The sound seems to come from everywhere. They offer exceptional stereo imaging for this price point and you can easily tell where each instrument is located in the song. Comparing these to the AKG Q701 we found they produced a larger and more coherent soundstage. We also did a compare with the HIFIMAN Ananda, which is a planar magnetic at a higher price point. We found the HIFIMAN Ananda to present a larger and more defined soundstage but did not enjoy listening nearly as much.

Sennheiser HD 660 Close-up
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Sennheiser HD 660S Power Requirements

Its input impedance is 150 ohms and its sensitivity is 104 decibels. Most devices were able to provide enough sound so that I could listen comfortably at normal volumes. I thought that they were even better sounding through my dedicated headphone amplifier. On the Sennheiser HD 660 S headphones without a discrete amplifier, I found that they were slightly less open than when run through a dedicated headphone amp (which was not surprising). So if you want to hear them at their most natural sound, then you may need to invest in a headphone amplifier. Even so, they’re extremely efficient, so there isn’t any need for them to be very strong amplifiers either. With amplifiers such as the Liquid Spark and JDLs Atom, you’ll get plenty of power for these very cleanly.

Monolith 133304 Liquid Spark Headphone Amplifier - by Alex Cavalli
as of July 17, 2024 7:38 am

Comparable To Other Headphones

There are a few other dynamic driver open back headphones you may want to check out if you are considering the Sennheiser HD660 S. These also offer great sound quality and comfort and it will really come down to your personal preference.

Beyerdynamic DT 990 PRO

These Beyerdynamics are very similar to the Sennheiser HD 660 S and probably the top competitor. Like the HD 660 S, they are extremely comfortable but offer a different sound signature. We find them to be brighter with a deeper bass than you get with the 660 S. Defiantly a pair of dynamic driver headphones with a different sound signature to check out for comparison.

Beyerdynamic DT 990 Pro Over-Ear Studio Headphones For Mixing, Mastering, and Editing
as of July 17, 2024 7:38 am

Sennheiser HD 560S

We find the HD 560 S another great pair of headphones to compare with the HD 660 S. Although both are made by Sennheiser, the HD 560 S has a slightly more neutral sound signature. For pure listening enjoyment, we prefer the HD 660 S but if you are considering a budget pair of studio monitors to get into mixing and mastering audio, the HD 560 S may be the better choice.

Sennheiser HD 560 S Over-The-Ear Audiophile Headphones
as of July 17, 2024 7:38 am

Sennheiser HD660 S Pros and Cons Summary

The Sennheiser HD 660 S headphones are a great choice for anyone looking for a comfortable pair of headphones that offer great sound quality. They are dynamic and involving, making them perfect for listening to music or watching movies. Their soundstage is large and coherent, making it easy to locate each instrument in a song.

The few drawbacks we found is they do not have the flattest EQ so would want a different pair of headphones for mixing. They also have a dropoff around 80hz so may not be the best bet if you are focused on music with lots of sub-bass.


The final outcome of our Sennheiser HD 660 S Open Back Headphone Review concludes they are comfortable, have a great soundstage and a non-fatiguing combination of clarity and rich tone. We found they work great for a variety of music genres but you may want to check out other options if you are mainly focused on music with lots of sub-bass. If you are looking in the market for these headphones you may also want to compare them to the Byerdynamic DT 990 for a comparison of a brighter sound signature a deeper bass.

Overall these are one of our top picks if you are looking for dynamic drivers in an open back headphone form in the sub $500 range. If you are looking for budget friendly headphones, make sure to checkout our Best Headphones under $200.


When did the Sennheiser HD 660S come out?

  • The Sennheiser HD 660 S headphones were first available for purchase in the United States on November 16 2017.

How many ohms are the 660S?

  • The Sennheiser HD 660 S headphones are open-back headphones and are the impedance is 150 ohms and its sensitivity is 104 decibels. We found the headphones will work being powered by most devices but for best sound quality a headphone amp is recommended. An amp allowed the headphones to open up and provided fuller bass and a wider soundstage.

Where are the Sennheiser HD 660 S headphones made?

  • The HD 660 S open back headphones are designed and engineered by Sennheiser in Germany. Once design has completed, they are manufactured at the Tulamore, Ireland plant ran by Sennheiser 

Are Sennheiser HD 660 S worth it?

  • Absolutely, they provide one of the best listening experiences in this price range and are durable and comfortable.

Which one would you prefer the Sennheiser HD 660 S or AKG Pro Audio K712 for recording and mixing?

  • Although we love the Sennheiser HD 660 S sound from a pure listening enjoyment perspective they are not the most neutral headphones on the market for mixing. When mixing, you will want a set of headphones (typically open-back) that are as close to natural as possible. This allows you to hear the recording without the sound signature of the headphones interfering. The AKG K712 would be our pick in this situation as they have a more neutral tone than the HD 660 S. For recording we would recommend a closed-back headphone to avoid sound leakage and to provide some noise isolation during the recording session. For a recording headphone in this price range, check out the Byerdymanic DT 770.

Which is better Sennheiser HD 660 S vs Sennheiser HD 560 S?

  • Although both headphones are made by Sennheiser they have two different purposes. From a listening enjoyment and build quality the HD 660 S is the better headphone. On the other hand, if you are looking for a pair of open back headphones with a flatter sound signature for starting out in mixing and mastering audio, the HD 560 S would be one of your top picks.
  • Sennheiser is a company that knows a thing or two about audio. They have been in the business of making some of the best headphones on the market for over 50 years. Through market research and testing they are able to provide high quality, affordable headphones that meet the needs of professionals and consumers alike.
Hi, I am Quinn. I am an experienced audio engineer who has worked in the audio field for the past 20 years. I enjoy most genres of music and enjoy home recording and learning about new recording techniques. In my free time I enjoy reviewing the latest audio gear and gaming.

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