9-foot oxygen-free cable with unbalanced 1/4" headphone plug
includes 3.5mm mini plug adapter
frequency response: 10-41,000 Hz (-10 dB)
sensitivity: 98 dB
impedance: 150 ohms
weight: 9.2 oz. (without cable)
warranty: 2 years
What's in the box
Over-ear headphones with 10' audio cable (1/4" plug)
9" Adapter (1/4"-to-3.5mm)
10' Balanced audio cable (4.4mm Pentaconn)
Hinged storage box
About this item
Written by Crutchfield's Jeff Miller
A classic revisited
Many of us here at Crutchfield credit Sennheiser's legendary "HD 600" series as our gateway into the world of truly high-end personal audio. These HD 660 S headphones keep the spirit of their stellar predecessors alive (and we recently ranked them one of our " Top 5 most comfortable headphones"). They feature a tweaked design and completely revamped driver system.
The HD 660 S headphones features velvet-soft ear pads and hold into place without squeezing too tightly.
The result is a smooth, timeless look and — more importantly — even greater musical detail. When paired with a high-performance headphone amp, you get great clarity with pinpoint imaging.
Our most comfortable audiophile headphones
In 2019, we did a deep dive on headphone comfort and asked 20 employees to test and score over 50 popular headphones. The HD 660 S was named our most comfortable set of audiophile headphones. This class of headphones is primarily geared toward sound, so they feature large, sophisticated drivers.
But while the open-back HD 660 S features larger earcups than most “general purpose” headphones, the weight is distributed nicely. And our testers said that they felt lighter than other large audiophile headphones. The velvety cloth ear pads press gently on the side of your head, and give your ears plenty of room to breathe.
Plus they stay in place really well. And we learned that security and stability were the most important comfort and fit traits to our testers.
Several ways to connect
These headphones includes two cables, one with 4.4mm balanced headphone plug. This is quickly becoming the new industry standard connection for balanced headphone operation, and I've seen more and more companies adopt it.
I've found that the compact, yet powerful iFi ZEN DAC pairs up really nicely with the HD 660 S 'phones. It's a natural combo. I heard the classic HD 600-series immediate, forward sound signature — but there was an extra level of depth I didn't notice when connecting directly to my phone.
(For more traditional headphone connections, Sennheiser includes another cable with an unbalanced 1/4" plug and a 3.5mm miniplug adapter.)