Reviewed on: SoundStage! Solo, August 2021
I measured the Sony WF-1000XM4 earphones using laboratory-grade equipment: a GRAS Model 43AG ear/cheek simulator with the RA0402 high-resolution ear simulator with KB5000/KB5001 simulated pinnae, and a Audiomatica Clio 12 QC audio analyzer. For isolation measurements, I used a laptop computer running TrueRTA software with an M-Audio MobilePre USB audio interface. A Reiyin WT-04 USB Bluetooth transmitter was used to send signals from the Clio 12 QC to the earphones. These are “flat” measurements; no diffuse-field or free-field compensation curve was employed. Note that my usual impedance and sensitivity measurements are irrelevant for wireless earphones, and impossible to do without disassembling them, and are thus not included here. If you’d like to learn more about what our measurements mean, click here.
The above chart shows the WF-1000XM4s’ frequency response measured with the RA0402 ear simulator, with noise canceling off. It’s fairly normal except the midrange is more prominent than usual—or the bass and the lower treble peak between 2 and 4kHz are less prominent than usual.
Here we can compare the frequency response with noise canceling on and off. There’s almost no difference. As it should be.
This chart shows the WF-1000XM4s’ right-channel response (again, with noise canceling off) compared with other true wireless earphones: the KEF Mu3s (which are the true wireless earphones I’ve found come closest to the Harman curve), the Technics EAH-AZ70s, and the AKG N5005s, which are the passive earphones said to come closest to the Harman curve. You can see how much flatter the Sonys measure than the others, but in headphone measurements, flat is not the norm.
I had a lot of artifacts in my spectral-decay (waterfall) measurement, probably related to a Bluetooth artifact or noise, so I had to smooth it to 1/6th octave to be able to make sense of it. You can see some small resonances around 4 and 5kHz, but they are well-damped and gone within a few milliseconds.
The WF-1000XM4s’ distortion is very low at 90dBA (measured with pink noise), which is a pretty loud listening level. At 100dBA, the distortion gets very high, but at 98dBA (not shown), it’s only a little higher than at 90dBA. So if you turn the earphones and your source device all the way up, with material that has a lot of peaks close to 0dBFS, you might hear a few notes break up—but listening at such an extremely loud level is very unwise.
This chart shows the WF-1000XM4s’ isolation in Ambient Sound mode, and with noise canceling on and off. I compared these results with the KEF Mu3 earphones (which have lousy noise canceling) and the Technics EAH-AZ70s (which have excellent noise canceling). The Sonys don’t offer the best noise canceling I’ve seen in this product category, but they’re well above-average.
Latency with the WF-1000XM4s connected to the Reiyin WT-04 Bluetooth transmitter typically measures about 233ms. That’s decent for true wireless earphones, although you’ll do better if you can use aptX Adaptive or aptX Low Latency—and probably with LDAC, too, but I don’t have a Bluetooth transmitter that includes LDAC.
Bottom line: The Sony WF-1000XM4 earphones combine very good noise canceling with a frequency response that’s a bit midrange-heavy (or bass- and treble-light), but still well within the range of normal.
. . . Brent Butterworth