- Looking to take your first steps into the audiophile world? Then consider the Sennheiser HD 660S your ticket, as the sound they deliver is way beyond most mainstream headphones.
- Although you can use them with any device equipped with a 3.5mm headphone jack, they greatly benefit from a headphone amp or DAC. Yes, it will increase the overall entry price, but it’s worth it.
- If you’ve already got an amp or DAC and are looking for a new pair of headphones, there’s a very good reason the Sennheiser HD 660S are so revered: They sound amazing.
- The $500 retail price may seem expensive, but for the overall quality on offer, and compared to the thousands of dollars it’s possible to spend on audiophile headphones, they represent strong value.
Table of Contents: Masthead Sticky
After my first extended listen to the Sennheiser HD 660S headphones, I took a day to gather my thoughts. Surely they didn’t sound as good as I thought that first evening trying them, right? I listened for hours, so I didn’t think I was mistaken, but still, I went back to them with lowered expectations just in case.
The second time listening turned into a third, and a fourth, and so on. The Sennheiser HD 660S may be one of the best pairs of headphones I’ve ever listened to at home. But to get to this stage had taken some work and some extra equipment beyond the headphones and a basic music source.
Let's go into detail about why, and what you need to replicate the same stunning sound I've enjoyed from them.
Specifications
- Impedance: 150ohm
- Drivers: Open, dynamic
- Frequency response: 9 - 41,500 Hz
- Weight: 9.17 oz. (260 grams)
- Connection: 4.4mm balanced, 6.3mm unbalanced, XLR-4 balanced, 3.5mm jack
Design
The Sennheiser HD 660S are headphones to enjoy at home, not outside on the street or on public transport. For starters, they're wired headphones, and the thick cable extends down from both cups before becoming one, and terminating in a 6.35mm unbalanced jack plug. You use an adapter (included in the box) to convert it to 3.5mm, plus there's a 4.4mm balanced and an XLR-4 balanced cable in the box for use with an amp. Also, these are open-back headphones, meaning they don't block out sound from around you, or from others hearing what you're listening to.
The plastic body is lightweight, the padding on the hanger and the earcups is thick, soft, and springy, and there is plenty of flex to ensure they don't grip your head too much. These are very comfortable headphones that are perfect for relaxing on the couch while wearing. There's no creaks or groans from the chassis, and they have all the quality you expect from a pair of headphones that cost $500.
Simply put, I like the overall design. There's an air of "studio cans" about them with the oversized elliptical cups and black metal grill over the drivers, along with the Sennheiser branding running over the top of the hanger. The cups cover your ears completely and I like the handy three dot marking on the left cup, making it easier to identify which way to put them on without looking for the L or R mark. The cable is about 10 feet long, which is handy if you want to plug the headphones into an amp that's not right next to your favorite chair.
It's hard to say anything negative about the HD 660S' design and comfort. They have a mature style that's ideally suited to the home, and a classiness that will make you want to leave them placed on top of your turntable, rather than hiding them away in a drawer or back in the box. You'll want people to see them because anyone who knows the HD 660S' name and heritage - their predecessor, the HD 650 headphones, are revered in audiophile circles - will quickly understand you take your music very seriously.
Audio performance
Open-back headphones mean a massive, wide soundstage, right? Yes, but that's the first surprise with the HD 660S. They're so well balanced the sound is much more intimate and centered than I expected, but with the wonderful airiness that comes with an open-back design. There's a fabulous richness to the midrange backed by a bass thump that's controlled and punchy, and some bright and detailed treble. The sound is about as well-rounded, exciting, and engaging as headphones get.
High praise, but to get the best from the HD 660S you won't want to just plug them into your iPhone or music player. Just using an iPhone 11 Pro with the 3.5mm headphone adapter will not do for the HD 660S. If the headphones could physically react to receiving an unamped signal, it would be to sit there drumming their fingers on the table, waiting for a challenge.
The sound I described above just isn't possible from a standard source. The HD 660S laugh at the iPhone 11 Pro, snort in derision at the LG V60 ThinQ with its Quad DAC amp, and while they enjoy the hi-res sound from my Sony NW-A45 player, the amount of power on offer simply isn't enough. The solution comes in the shape of the iFi Nano iDSD Black Label portable DAC.
This makes the HD 660S sit up and take notice. Using the iPhone 11 Pro equipped with the camera connection kit (an OTG cable is required to connect the iFi Nano to a USB Type-C equipped device), the headphones suddenly have the power they need, and what a difference it makes. The necessity for external power is another reason these headphones need to stay at home. There's enough sound leakage through the open backs that no one will be thanking you for wearing them in Starbucks anyway.
My voyage of discovery wearing the HD 660S led me to understand how much they excel with electronic music. The mix of lazy synth, steady bass kick, and dreamy vocals in Kavinsky's "Nightcall" suits them perfectly. Move on to Micheal Jackson's "Billie Jean" to hear the headphones' wonderful soundstage, stereo separation, vocal detail, and precise control of the bass and mids.
The War on Drugs' "Strangest Thing" sounds sublime, and the temptation is always there to turn up the volume to become totally enveloped by the sparkling percussion, the detailed strum of the guitar, and the power of the lead singer's tortured tones. By three minutes, when the main riff kicks in, you won't want to take these headphones off ever again. They really are that involving and emotional.
Classical music, particularly live performances, also play to the HD 660S' strengths, as does complex instrumental music. Listen to any live performance of Holst's "Mars: The Bringer of War from The Planets Suite", or "Apache" by The Shadows for proof of the HD 660S' ability to adapt to just about anything and play it superbly. Provided, that is, they have enough power to do so.
Features and extras
Here's the part of the review where we talk about things like noise cancellation, the accompanying app, or what the touch controls are like - except the HD 660S have none of those things. They are headphones, and they play music. That's it. They don't have Bluetooth so there's no need for a battery or charging.
The Sennheiser HD 660S are often described as audiophile headphones, and you certainly do get amazing sound quality, but to reach that stage you may have to get a little "audiophiley," in that you should investigate headphone amps or a DAC. Don't expect your phone to do the job here, as it won't. It still can serve as the music source if you look at something like the $199 iFi Nano I used or the $499 Chord Mojo.
If you are already kitted out with a headphone amp at home, or are even looking at Sennheiser's own HDV 820 digital headphone amp (yours for $2,400), then you don't need anything else apart from lots of time and an eclectic music collection - with some preferably in hi-res - to enjoy the HD 660S.
The bottom line
The Sennheiser HD 660S headphones aren't made to go up against brands like Beats or Sony, and neither do they challenge a pair of good Bluetooth headphones for versatility. If you're thinking of these as everyday headphones for your commute, then it's better to go with a more mainstream set. If you're looking for headphones to explore your hi-res music collection at home, and you either own or don't mind buying a headphone amp of some kind, then you'll be floored by the sound produced by these stunning headphones.
If you want to move on from your Bluetooth headphones, no matter how good they are, and take a gentle first step into the audiophile world, the Sennheiser HD 660S are a relatively reasonably priced way of doing so, just remember that it's not the only cost you'll incur if you want to get the best out of them. In other words, they're not cheap, but they're absolutely worth it.
What are your alternatives?
For an alternative, take a look at the Audeze LCD-2 Classic. These $799 open-back headphones are well-regarded and noted for their rich, warm sound and wide soundstage. Like the HD660S they also have various wired connection types, and a neat design suited to the home.
Pros: Stunning sound, classy design, quality build, variety of wired connection types
Cons: To get the best from them you'll need an amplifier