Headphone Reviews

Measurements Wired

Raw frequency response plots show the HD 4.40 BT fairly sensitive to movement on the ear below 200Hz. It's a little surprising as the pads are so plush; I think it may be because the space forward to back in the ear pad opening is a bit tight and the dummy ear was breaking the seal. On a normal sofer ear it's likely to seal quite a bit better; I did hear these as more on the high side of bass responses measured.

Response is generally along target lines, but can clearly be seen to be forward in two areas: a wide bass hump centered at 70Hz; and a wide midrange hump, tilted but centered around 800Hz-1kHz. I did hear these cans as mid-bass centric and forward in the upper-midrange.

There is a weird, deep notch at 4kHz; I have seen this type of thing before and it's usually to knock out something bad—though I don't know what that might be. I don't hear the notch, but I do hear these as a bit subdued in the low treble. Raw response above 6kHz is at about the right level, and the clean articulation saves these cans from sounding muffled. I heard the mid- and upper-treble as pretty good.

30Hz square wave has nice shape, though I don't feel it sounded as good as it measured. The shoulder is a bit abrupt and far back echoing that low treble deficit.

300Hz square wave is a little slow on the uptake but is pretty clean otherwise. Impulse response initial transient is really nice, and I did hear these cans as articulate. That second bump is not such a good thing...maybe an artifact from that notch at 4kHz?

THD+noise plots do show some distortion down low, but this is pretty common. Other wise distortion is very low in these cans. I heard them as warm, but quite clean. That notch at 4kHz plays a little havoc, but again, this feature is quite narrow band and not much noticeable.

Impedance plot shows a nominally 26 Ohm headphone. Here again you can see a small feature at 4kHz.

Isolation is quite good for a passive sealed headphone at -19dB. At 33mVrms to achieve 90dBspl at the ear, thes HD 4.40 BT will play at substanial level from a smartphone or tablet.

Measurements Bluetooth

Looking at the raw plots with Bluetooth, it seem I managed to get a more reliable seal and a more repeatable bass reading. I heard the bass as more accentuated here, but it's likely my attention was drawn due more bass error, likely due to phase shift through the coupling capacitors in the electronics somewhere. This can be seen in the 30Hz square wave sway-back shape.

The differences between the wired and BT response are subtle, and I don't think they add up on paper the same way they add up in your head while listening. The only meaningful feature I see is the response from 5-7kHz is a little more elevated, and the leading edge of the 300Hz square wave is a little quicker and more prominent. I do think I heard this as a snappier response in that area.

THD+noise is surprisingly low for wireless mode—likely indicating Sennheiser designing fairly low-noise circuits. Surprisingly, bass distortion seems to have measured lowered in wireless mode. Not sure what to think about that. Guess we'll leave this one with a mystery.