The Surprisingly Good Logitech UE6000 and UE9000 Measurements
As you can see from the charts above, both headphones measure quite similarly. I suspect both headphones share a lot of design effort in common, and the small differences between the two are likely caused by small differences in the capsule geometries due to the changes in electronics and battery compartment. I heard very little difference between cans in listening tests. Only that the UE6000 sounded slightly cleaner than the UE9000.
In raw frequency response measurements, neither can was particularly sensitive to positional changes on the head. I found the foam in the ear cushions and protein leather coverings to be quite effective in forming a good seal to the head.
Compensated frequency response measures show a broad and mildly elevated bass boost, and a slight presence hump at around 1kHz. I've seen this shape before, and typically find it quite satisfying, delivering both a warmth to the sound and a nice sense of vocal presence. Thereafter, the headphones fall about 10dB to 3kHz; I feel this is about right. The UE6000 remains fairly constant at this level until it reaches 10kHz, and then drops off about 8dB. Although measurements at these frequencies are often somewhat unreliable, I do like the overall shape of the curve here with the UE6000, though the top octave could be about 3dB higher. The UE9000 does exhibit a clear peak at 10kHz, which I'd rather not see, but I don't think it was particularly audible in this case.
30Hz square wave response is indicative of a nicely controlled, warm sounding headphone. The low distortion in the lowest octaves of these cans also indicate tight bass and decent power handling.
300Hz square wave response shows a mild and about right overshoot on the leading edge. The UE6000 shows a slight missmatch between channels, which is not really evident on the frequency response plot. The UE9000 shows a slightly noisier waveform top, which can also be seen in the impulse response of these cans. I'm thinking the additional complexity of the enclosure of the UE9000 to accomodate the additional Bluetooth electronics and microphones may contribute here.
The passive isolation of these headphones is quite good, among the best I've seen.
Impedance and phase plots show these these headphones to be nicely behaved. Nominal impedance of the UE6000 is about 52 Ohms, with the UE9000 about 5 Ohms higher. Voltage required to achieve 90dBspl at the ear for both headphones was about 50mVrms, which makes them fairly easy to achieve solid listening levels with portable devices. The isolation and efficiency (not to mention the great sound quality) of these headphones makes them ideal for portable applications.
Raw frequency response measurements show the UE9000 somewhat more sensitive to positional changes both in the lowest frequencies and in a bump at about 800Hz. The UE6000 had somewhat mismatched channels between 400Hz and 1000Hz. Not sure what's going on here, but noise canceling headphones have microphones inside the ear chamber, and it's possible that slight mismatches due to positioning may be amplified by the noise canceling circuit.
Compensated frequency response shows a clear, and fairly peaked, elevated bass response. Both cans also exhibit a broad, strong dip centered at about 400Hz prior to rising again to the presence peak at 1kHz. Obviously the noise canceling electronics are also providing some EQ changes to these cans. Above 1kHz the response of both headphones are nearly identical to the passive measurements.
In listening tests I did hear the bass as somewhat to strong and loose. The level increase is evident in the frequency response, but the looseness of the sound is clear in the 30Hz square wave top descending below the zero line. Because this is likely a function of phase shift through the electronic EQ and not losses through the earpads, no increase in THD+noise is evident in the lows. THD+noise is only slightly higher in the noise canceling mode when compared to the passive mode.
300Hz square wave shape is somewhat poorer on both cans, but is substantially better than many noise cancelers I've previously measured. In fact, only the Polk Ultrafocus 8000 appears to have better measurements to my eyes.
Impulse response measurements indicate the electronic circuit does invert the signal. The UE6000 continues to ring slightly less than the UE9000, as with the passive measurements.
Isolation measurements show the noise canceling circuit is not particularly effective, generally lowering the noise about 10dB under 500Hz when compared to passive measurements. I think this is an area where Logitech UE will have to make improvements if they want to compete with Bose for a slot in the noise canceling market. Fortunately, they've got a great sounding start on the process.
I think the UE9000 had some sort of glitch in the efficiency measures. Both cans can be easily driven to solid listening levels with portable devices.