Frequency Response. The 650’s go from 10Hz-39,500kHz, while the HE400i’s go from 20Hz-35,000kHz.
Sensitivity. 103dB for the 650 vs. 93dB for the 400i.
Impedance. 300 Ohms for the HD650 vs. 35 Ohms for the 400i. Though the 400i’s have low impedance, they will really need an amp to sound their best. What is Headphone Impedance?
Driver. The HE400i’s use planar magnetic drivers, while the HD650’s use your traditional dynamic driver. Essentially, both use a magnetic field around a conductor to drive the diaphragm, but a planar magnetic driver requires more magnets, and needs those magnets on both sides of the diaphragm. A dynamic driver only needs 1 magnet. This is why planar magnetic headphones are much heavier than dynamic headphones. Learn more about how both of these drivers work: What is a Headphone Driver? Because the magnets in a planar driver are situated in an even manner, the flow of force exerted onto the diaphragm is always constant, even though the position of the conductor changes. This is why planar magnetic headphones can generally be driven at higher volumes without much distortion, while a dynamic headphone will suffer at times in this regard. Find out more about How Planar Magnetic Drivers work!
Bass. The bass hits harder with the 650, while it’s more textured and runs deeper on the 400i.
Mid-range. Ah, the all important mids. The HD650’s more forward sounding mid-range is definitely superior, while the 400i’s are good but can sound “sucked out” at times.
Treble. The treble on the 650 is very relaxed, almost lulling you to sleep. A lot of people claim it’s darker and more veiled than a lot of headphones, and there is some truth to this, though I think by and large it’s an over-exaggeration. What is the Sennheiser Veil? The 400i’s have more treble energy, but may become sibilant at times. What does Sibilant mean?
Tonal Balance. The 650’s are more balanced overall across the spectrum, and also sound more realistic and true to life as far as instruments and vocals go. This is due to their superior mid-range, which is slightly forward (enough to make things really stand out).
Overall Sound. While the HD650’s are much warmer, lusher, and have a harder hitting bass, the 400i’s are more detailed, open, and airy by contrast. Their bass extends further, and it’s more textured. The 650’s may put you to sleep because of how relaxed they are, while the 400i’s kind of make you want to evaluate the sound and really dissect it. Because the instruments have more room to breathe, you’re really able to pick apart individuals and get a phenomenal sense of their Timbre. What is Timbre? They really take on a stunning sense of realism. This was especially apparent on Led Zeppelin’s Over the Hills and Far Away. Everything was so crystal clear that I had a hard time believing it was the same song! It’s as if I was listening to it for the first time, as it was meant to be heard. The electric guitar is really something to behold with these puppies. So in a nutshell: the 650 sounds more natural, while the 400i is more aggressive.
Weight. Because of the fact that Planar Magnetic headphones have more magnets, they are heavier than their dynamic counterparts. The HD650 weighs 9.2 oz. compared to the 13.05 of the 400i.
Cable. The cable of the 650’s feels like something you would see in a $20-40 pair of cans, but it isn’t a deal breaker by any means. The 400i’s cable by contrast is thicker and seems to be around the right size. Also, the HD650’s chord is 120″ while the 400i’s is 60″. Both also terminate in a 3.5mm jack and come with a 1/4″ adapter.
Warranty. The HD650’s come with a 2 year parts and labor warranty, while the 400i’s come with 1 year for each.
Overall, I would go with the HE400i over the HD650, because I prefer a more open sound as opposed to a warmer one.
My recommendation today is the HD600 however. Between the HD600 and 400i, it’s a really tough call, but I would give the very slight edge to the 600’s as they do most everything right. They are more tonally balanced, have a better mid-range, and sound snappier and crispier by contrast. They also have the best price to performance ratio, and serve as the benchmark Gold Standard that all headphones should strive towards. Interested in learning everything you need to know?
Stu is determined to provide the truth about all things audio, and strives to deliver excellent content to you the reader! In his spare time, he likes to fish, paint, play guitar, attend church, take photos, record videos, graphic design, and more. His attention to detail and perfectionist attitude are what allow him to excel, but it can be both a blessing and a hindrance at times.