Friday, September 22, 2017

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I measured the Libratone Q Adapts using a G.R.A.S. Model 43AG ear/cheek simulator, a Clio 10 FW audio analyzer, a laptop computer running TrueRTA software with an M-Audio MobilePre USB audio interface, a Musical Fidelity V-Can headphone amplifier, an Audio-gd NFB-1AMP amplifier for distortion measurements, and a Sony HWS-BTA2W Bluetooth transmitter/receiver. In some cases, the inherent latency of Bluetooth necessitated a change in measurement technique, to using pink noise as a stimulus rather than the swept logarithmic “chirp” tone I normally use. This is a “flat” measurement; no diffuse-field or free-field compensation curve was employed.

Frequency response

The response curve seen here, measured with the Q Adapts in Bluetooth mode with noise canceling on, isn’t quite as anomalous as it might seem at first glance. The large peak in the 2.5kHz frequency is fairly typical of most of the headphones and earphones I measure. There are a few dB more bass relative to that peak than I’m used to measuring, and a little less energy between 3 and 10kHz. There does seem to be a bit of a mismatch in the bass response between the left and right channels, probably due to different internal acoustics in the two earpieces (which is fairly common in active headphones), but it’s unlikely to be audible.

Frequency response Bluetooth vs. passive

This chart shows the response in Bluetooth mode with NC set to Level 4, compared with a passive connection using the included cable. It’s not a huge difference compared with what I’ve measured in some other active headphones, but it indicates that the sound will be a bit different: more bass kick in Bluetooth, more upper bass (and perhaps a bit of a bloated sound) in wired mode.

Frequency response

This chart shows the response in Bluetooth mode with NC off (Level 2) and on (Level 4). This is a subtler difference than I usually measure in this test; many headphones sound completely different with NC on, but the Q Adapts will sound pretty much the same either way. The measured response with Level 1 (open mike mode) was essentially the same as with Level 2, and the response with Level 3 was essentially the same as with Level 4.

Frequency response

This chart shows the Q Adapts’ measured right-channel frequency response compared with Bluetooth NC headphones (Bose QC35s), wired NC ’phones (AKG N60 NCs), and conventional closed-back ’phones (NAD Viso HP50). The Q Adapts have a more pronounced response in both the bass and treble, which suggests that they’ll sound fairly balanced yet rather vivid, with perhaps some deemphasis of the midrange.

Waterfall

The spectral-decay (waterfall) chart shows a little bit more resonance below 500Hz than I’m used to seeing, but all the resonances are extremely well damped and die out within a few milliseconds.

THD

The total harmonic distortion (THD) of the Q Adapts (which I had to measure using a wired connection because of Bluetooth’s latency) is low for compact headphones such as these, hitting about 1% at 20Hz at 90dBA, and 3% at the extremely loud listening level of 100dBA.

Isolation

In this chart, the external noise level is 75dB SPL; the numbers below that indicate the degree of attenuation of outside sounds. For comparison, I’ve included the isolation plots of two other noise-canceling headphones: the Bose QC25s and AKG N60 NCs (which, like the Q Adapts, are both on-ear headphones, which in my experience can’t match the isolation of comparable over-ear models). The Q Adapts beat out the N60 NCs in the midrange around 1kHz, but don’t cancel bass frequencies as well. They might do a little better at rejecting the noise of conversations or an airliner’s air-circulation system, but probably not quite as well at reducing the noise of jet engines.

Impedance

Using a wired connection, the electrical impedance of the Q Adapts is basically flat at 25 ohms, and the electrical phase is similarly flat.

The Q Adapts’ sensitivity, measured between 300Hz and 3kHz with a 1mW signal, and calculated for 32 ohms impedance (my “unless otherwise specified” test impedance for active models with passive input), is 100.2dB. That means that, unlike some active headphones, the Q Adapts will play plenty loud enough when connected with a cable to the average smartphone.

. . . Brent Butterworth
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