Complete Guide to Bose QuietComfort 20 (QC-20) Headphones

01
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Bose QuietComfort 20 Measurements

Bose Corporation

I measured the performance of the QC-20 using a G.R.A.S. 43AG ear/cheek simulator, a Clio FW audio analyzer, a laptop computer running TrueRTA software with an M-Audio MobilePre USB audio interface, and a Musical Fidelity V-Can headphone amplifier. (I don't usually use the full ear/cheek simulator to measure in-ear headphones, but due to the unusual shape of the QC-20's silicon tips, it didn't fit well into the G.R.A.S. RA0045 coupler I normally use for measurements of in-ears.)

Measurements were calibrated for ear entrance point (EEP), roughly the point in space dead center at the opening of your ear canal. I used the clamp mechanism of the 43AG to assure a good seal of the headphone on the simulator, and a consistent result overall. Note that beyond the calibration to EEP, I do not apply a diffuse-field or other compensation curve. ​​​Some research has questioned the validity of such compensation, and until the industry agrees on a good, research-supported standard, I prefer to show raw data.

Sensitivity of the QC-20, measured with a 1 mW signal at 32 ohms (my standard impedance calculation for internally amplified headphones like the QC-20) is 104.8 dB, high enough to get loud levels from probably any source device.

02
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QC-20 Frequency Response

Brent Butterworth

Frequency response of the QC-20 in left (blue) and right (red) channels, test level referenced to 94 dB @ 500 Hz. There is no standard for what constitutes a "good" frequency response in headphones, and because psychoacoustics is complicated and ear shapes vary, the correlation between objective response measurements and subjective listening impressions sometimes isn't clear. However, but this chart does let you compare models objectively. The QC-20 shows a little less bass response than most in-ears, which tend to have a bump in bass output around 100 Hz. It also shows a somewhat more prominent treble response, with a lot of energy between 2 and 10 kHz.

03
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QC-20 Frequency Response, noise cancelling on and off

Brent Butterworth

Frequency response of the QC-20, right channel, with noise cancelling on (red trace) and off (yellow trace). As you can see, the response is essentially identical in both modes. This is the best result I have ever measured on this test. Every other noise-cancelling headphone I have tested changes its response at least a little when NC is switched on; sometimes the change in sound is dramatic (and annoying).

04
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QC-20 Spectral Decay

Brent Butterworth

Spectral decay (waterfall) plot of the QC-20, right channel. Long blue streaks indicate resonances, which are generally undesirable. Not much to worry about here. Just a very, very narrow (and thus probably inaudible) resonance around 2.3 kHz.

05
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QC-20 Frequency Response, 5 vs. 75 ohms source impedance

Brent Butterworth

Frequency response of the MS 500, right channel, when fed by an amp (Musical Fidelity V-Can) with 5 ohms output impedance (red trace), and with 75 ohms output impedance (green trace). Ideally, the lines should overlap perfectly, and here they do -- which is usually the case with internally amplified headphones like the QC-20. Thus, the QC-20's frequency response and tonal balance won't change if you use a low-quality headphone amp, like those built into most laptops and cheap smartphones.

06
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QC-20 Distortion

Brent Butterworth

Total harmonic distortion (THD) of the QC-20, right channel, measured at a test level of 100 dBA. The lower this line is on the chart, the better. Ideally it would overlap the bottom border of the chart. Except for that strange little 4% distortion peak at 600 Hz, the QC-20's distortion is very low, especially in the bass.

07
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QC-20 Isolation

Brent Butterworth

Isolation of the QC-20, right channel, with NC off (green trace) and NC on (purple trace). Levels below 75 dB indicate attenuation of outside noise -- i.e., 65 dB on the chart means a -10 dB reduction in outside sounds at that sound frequency. The lower the line is on the chart, the better. At higher frequencies, the NC effect is good, about -20 to -25 dB. In the lower frequencies, where the noise from jet engines resides, the result is the best I can remember measuring, as good as -45 dB at 160 Hz. That's equivalent to a 96 percent reduction in sound level. Note that the purple trace hits the bottom of my chart.

08
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QC-20 Impedance

Brent Butterworth

Impedance of the QC-20, right channel. Generally, impedance that is consistent (i.e., flat) at all frequencies is better, but with the very high impedance of the QC-20's internal amplifier input, this is not a concern.